liu.seSearch for publications in DiVA
Change search
Refine search result
1 - 49 of 49
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Arnqvist, Göran
    et al.
    Department of Ecology and Environmental Science, Animal Ecology, University of Umeå, Umeå, Sweden.
    Edvardsson, Martin
    Department of Ecology and Environmental Science, Animal Ecology, University of Umeå, Umeå, Sweden.
    Friberg, Urban
    Department of Ecology and Environmental Science, Animal Ecology, University of Umeå, Umeå, Sweden.
    Nilsson, Tina
    Department of Ecology and Environmental Science, Animal Ecology, University of Umeå, Umeå, Sweden.
    Sexual conflict promotes speciation in insects.2000In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 97, no 19, p. 10460-10464Article in journal (Refereed)
    Abstract [en]

    Speciation rates among extant lineages of organisms vary extensively, but our understanding of the causes of this variation and, therefore, the processes of speciation is still remarkably incomplete. Both theoretical and empirical studies have indicated that sexual selection is important in speciation, but earlier discussions have focused almost exclusively on the potential role of female mate choice. Recent findings of postmating reproductive conflicts of interest between the sexes suggest a quite different route to speciation. Such conflicts may lead to perpetual antagonistic coevolution between males and females and may thus generate rapid evolutionary divergence of traits involved in reproduction. Here, we assess this hypothesis by contrasting pairs of related groups of insect species differing in the opportunity for postmating sexual conflict. Groups where females mate with many males exhibited speciation rates four times as high as in related groups where females mate only once. Our results not only highlight the general importance of postmating sexual selection in speciation, but also support the recent suggestion that sexual conflict is a key engine of speciation.

  • 2.
    Bailey, Richard I.
    et al.
    Department of Ecology and Genetics, Evolutionary Biology Centre (EBC), Uppsala University, Uppsala, Sweden .
    Innocenti, Paolo
    Department of Ecology and Genetics, Evolutionary Biology Centre (EBC), Uppsala University, Uppsala, Sweden .
    Morrow, Edward H.
    Department of Ecology and Genetics, Evolutionary Biology Centre (EBC), Uppsala University, Uppsala, Sweden .
    Friberg, Urban
    Department of Ecology and Genetics, Evolutionary Biology Centre (EBC), Uppsala University, Uppsala, Sweden .
    Qvarnström, Anna
    Department of Ecology and Genetics, Evolutionary Biology Centre (EBC), Uppsala University, Uppsala, Sweden .
    Female Drosophila melanogaster Gene Expression and Mate Choice: The X Chromosome Harbours Candidate Genes Underlying Sexual Isolation2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 2, article id e17358Article in journal (Refereed)
    Abstract [en]

    Background: The evolution of female choice mechanisms favouring males of their own kind is considered a crucial step during the early stages of speciation. However, although the genomics of mate choice may influence both the likelihood and speed of speciation, the identity and location of genes underlying assortative mating remain largely unknown. Methods and Findings: We used mate choice experiments and gene expression analysis of female Drosophila melanogaster to examine three key components influencing speciation. We show that the 1,498 genes in Zimbabwean female D. melanogaster whose expression levels differ when mating with more (Zimbabwean) versus less (Cosmopolitan strain) preferred males include many with high expression in the central nervous system and ovaries, are disproportionately X-linked and form a number of clusters with low recombination distance. Significant involvement of the brain and ovaries is consistent with the action of a combination of pre- and postcopulatory female choice mechanisms, while sex linkage and clustering of genes lead to high potential evolutionary rate and sheltering against the homogenizing effects of gene exchange between populations. Conclusion: Taken together our results imply favourable genomic conditions for the evolution of reproductive isolation through mate choice in Zimbabwean D. melanogaster and suggest that mate choice may, in general, act as an even more important engine of speciation than previously realized.

  • 3.
    Bilde, T.
    et al.
    Animal Ecology/Department of Ecology and Evolution, Evolutiona ry Biology Centre, University of Uppsala, Uppsala, Sweden / Department of Biological Sciences, Ecology and Genetics, University of Aarhus, Denmark.
    Friberg, Urban
    Animal Ecology/Department of Ecology and Evolution, Evolutiona ry Biology Centre, University of Uppsala, Uppsala Sweden / Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CaliforniaUSA.
    Maklakov, A. A.
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, University of Uppsala, Uppsala, Sweden / School of Biological, Earth and Environmental Sciences, The University of New South Wales, Kensington, Australia.
    Fry, J. D.
    University of Rochester, Department of Biology, Rochester, New York, USA.
    Arnqvist, Göran
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, University of Uppsala, Uppsala, Sweden.
    The genetic architecture of fitness in a seed beetle: assessing the potential for indirect genetic benefits of female choice2008In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 8, no 295, p. 95-Article in journal (Refereed)
    Abstract [en]

    Background

    Quantifying the amount of standing genetic variation in fitness represents an empirical challenge. Unfortunately, the shortage of detailed studies of the genetic architecture of fitness has hampered progress in several domains of evolutionary biology. One such area is the study of sexual selection. In particular, the evolution of adaptive female choice by indirect genetic benefits relies on the presence of genetic variation for fitness. Female choice by genetic benefits fall broadly into good genes (additive) models and compatibility (non-additive) models where the strength of selection is dictated by the genetic architecture of fitness. To characterize the genetic architecture of fitness, we employed a quantitative genetic design (the diallel cross) in a population of the seed beetle Callosobruchus maculatus, which is known to exhibit post-copulatory female choice. From reciprocal crosses of inbred lines, we assayed egg production, egg-to-adult survival, and lifetime offspring production of the outbred F1 daughters (F1 productivity).

    Results

    We used the bio model to estimate six components of genetic and environmental variance in fitness. We found sizeable additive and non-additive genetic variance in F1 productivity, but lower genetic variance in egg-to-adult survival, which was strongly influenced by maternal and paternal effects.

    Conclusion

    Our results show that, in order to gain a relevant understanding of the genetic architecture of fitness, measures of offspring fitness should be inclusive and should include quantifications of offspring reproductive success. We note that our estimate of additive genetic variance in F1 productivity (CV A = 14%) is sufficient to generate indirect selection on female choice. However, our results also show that the major determinant of offspring fitness is the genetic interaction between parental genomes, as indicated by large amounts of non-additive genetic variance (dominance and/or epistasis) for F1 productivity. We discuss the processes that may maintain additive and non-additive genetic variance for fitness and how these relate to indirect selection for female choice.

  • 4.
    Bilde, Trine
    et al.
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biol ogy Centre, Uppsala University , Uppsala Sweden / Department of Biological Sciences, Univer sity of Aarhus, Denmark.
    Maklakov, Alexei A
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala Sweden / School of Biological, Earth an d Environmental Sciences, The University of New South Wales, Kensington, Sydney, Australia.
    Meisner, Katrine
    Department of Biological Sciences, University of Aarhus, Denmark.
    la Guardia, Lucia
    Department of Biological Sciences, University of Aarhus, Denmark.
    Friberg, Urban
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala Sweden / Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California USA.
    Sex differences in the genetic architecture of lifespan in a seed beetle: extreme inbreeding extends male lifespan.2009In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 9, no 33Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Sex differences in lifespan are ubiquitous throughout the animal kingdom but the causes underlying this phenomenon remain poorly understood. Several explanations based on asymmetrical inheritance patterns (sex chromosomes or mitochondrial DNA) have been proposed, but these ideas have rarely been tested experimentally. Alternatively, sexual dimorphism in lifespan could result from sex-specific selection, caused by fundamental differences in how males and females optimize their fitness by allocating resources into current and future reproduction.

    RESULTS: Here we used sex-specific responses to inbreeding to study the genetic architecture of lifespan and mortality rates in Callosobruchus maculatus, a seed beetle that shows sexual dimorphism in lifespan. Two independent assays revealed opposing sex-specific responses to inbreeding. The combined data set showed that inbred males live longer than outbred males, while females show the opposite pattern. Both sexes suffered reduced fitness measured as lifetime reproductive success as a result of inbreeding.

    CONCLUSION: No model based on asymmetrical inheritance can explain increased male lifespan in response to inbreeding. Our results are however compatible with models based on sex-specific selection on reproductive strategies. We therefore suggest that sex-specific differences in lifespan in this species primarily result from sexually divergent selection.

  • 5.
    Brengdahl, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Kimber, Christopher
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Maguire-Baxter, Jack
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis2018In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 72, no 3, p. 568-577Article in journal (Refereed)
    Abstract [en]

    Life span differs between the sexes in many species. Three hypotheses to explain this interesting pattern have been proposed, involving different drivers: sexual selection, asymmetrical inheritance of cytoplasmic genomes, and hemizygosity of the X(Z) chromosome (the unguarded X hypothesis). Of these, the unguarded X has received the least experimental attention. This hypothesis suggests that the heterogametic sex suffers a shortened life span because recessive deleterious alleles on its single X(Z) chromosome are expressed unconditionally. In Drosophila melanogaster, the X chromosome is unusually large (approximate to 20% of the genome), providing a powerful model for evaluating theories involving the X. Here, we test the unguarded X hypothesis by forcing D. melanogaster females from a laboratory population to express recessive X-linked alleles to the same degree as males, using females exclusively made homozygous for the X chromosome. We find no evidence for reduced life span or egg-to-adult viability due to X homozygozity. In contrast, males and females homozygous for an autosome both suffer similar, significant reductions in those traits. The logic of the unguarded X hypothesis is indisputable, but our results suggest that the degree to which recessive deleterious X-linked alleles depress performance in the heterogametic sex appears too small to explain general sex differences in life span.

  • 6.
    Brengdahl, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Kimber, Christopher
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Maguire-Baxter, Jack
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Malacrinò, Antonino
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Genetic Quality Affects the Rate of Male and Female Reproductive Aging Differently in Drosophila melanogaster2018In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 192, no 6, p. 761-772Article in journal (Refereed)
    Abstract [en]

    Males and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive aging. Here we investigate whether reproductive aging and life span respond to condition differently in male and female Drosophila melanogaster, as predicted if sexual selection has shaped male and female resource-allocation patterns. We manipulate condition through genetic quality by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male reproductive output than on female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive aging between the sexes in low condition, but in high condition reproductive aging is relatively faster in males. No corresponding sex-specific change was found for life span. The sex difference in reproductive aging appearing in high condition was specifically due to a decreased aging rate in females rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more toward somatic maintenance than males.

  • 7.
    Burgevin, Lorraine
    et al.
    Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Maklakov, Alexei A.
    Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Intersexual correlation for same-sex sexual behaviour in an insect2013In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 85, no 4, p. 759-762Article in journal (Refereed)
    Abstract [en]

    Same-sex sexual behaviour is widespread across taxa and is particularly common in insects, in which up to 50% of copulation attempts by males are directed towards other males in some species. Research effort has focused on male-male same-sex behaviour and the prevailing theory is that benefits of high mating rate combined with poor sex discrimination explain the high incidence of male-male mounting. However, the evolution of female-female mounting is more enigmatic, since females typically do not mount males in order to mate. Using a full-sib design, we found an intersexual correlation for same-sex mounting in the beetle Callosobruchus maculatus. Variation in male-male mounting across families explained over 20% of variation in female-female mounting. Moreover, we found no evidence that same-sex behaviour was related to general activity level in either sex or carried a fitness cost to females. Taken together, our results suggest that female-female mounting is a relatively low-cost behaviour that may be maintained in the population via selection on males.

  • 8.
    Dowling, D K
    et al.
    Centre for Evolutionary Biology, School of Animal Biology (M092), University of Western Australia, Crawley, WA, Australia.
    Maklakov, A A
    Animal Ecology ⁄ Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden / School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia.
    Friberg, Urban
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, USA.
    Hailer, F
    Center for Conservation and Evolutionary Genetics, National Zoological Park and National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
    Applying the genetic theories of ageing to the cytoplasm: cytoplasmic genetic covariation for fitness and lifespan.2009In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 22, no 4, p. 818-27Article in journal (Refereed)
    Abstract [en]

    Two genetic models exist to explain the evolution of ageing - mutation accumulation (MA) and antagonistic pleiotropy (AP). Under MA, a reduced intensity of selection with age results in accumulation of late-acting deleterious mutations. Under AP, late-acting deleterious mutations accumulate because they confer beneficial effects early in life. Recent studies suggest that the mitochondrial genome is a major player in ageing. It therefore seems plausible that the MA and AP models will be relevant to genomes within the cytoplasm. This possibility has not been considered previously. We explore whether patterns of covariation between fitness and ageing across 25 cytoplasmic lines, sampled from a population of Drosophila melanogaster, are consistent with the genetic associations predicted under MA or AP. We find negative covariation for fitness and the rate of ageing, and positive covariation for fitness and lifespan. Notably, the direction of these associations is opposite to that typically predicted under AP.

  • 9.
    Dowling, Damian K.
    et al.
    Animal Ecology ⁄ Department of Ecology and Evolution, Evolut ionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Department of Ecology and Environmental Science, Umea ˚ University, Umeå , Sweden / Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, USA.
    Arnqvist, Göran
    Animal Ecology ⁄ Department of Ecology and Evolution, Evolut ionary Biology Centre, Uppsala University, Uppsala, Sweden.
    A comparison of nuclear and cytoplasmic genetic effects on sperm competitiveness and female remating in a seed beetle2007In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 20, no 6, p. 2113-2125Article in journal (Refereed)
    Abstract [en]

    It is widely assumed that male sperm competitiveness evolves adaptively. However, recent studies have found a cytoplasmic genetic component to phenotypic variation in some sperm traits presumed important in sperm competition. As cytoplasmic genes are maternally transmitted, they cannot respond to selection on sperm and this constraint may affect the scope in which sperm competitiveness can evolve adaptively. We examined nuclear and cytoplasmic genetic contributions to sperm competitiveness, using populations of Callosobruchus maculatus carrying orthogonal combinations of nuclear and cytoplasmic lineages. Our design also enabled us to examine genetic contributions to female remating. We found that sperm competitiveness and remating are primarily encoded by nuclear genes. In particular, a male's sperm competitiveness phenotype was contingent on an interaction between the competing male genotypes. Furthermore, cytoplasmic effects were detected on remating but not sperm competitiveness, suggesting that cytoplasmic genes do not generally play a profound evolutionary role in sperm competition.

  • 10.
    Dowling, Damian K
    et al.
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå , Sweden.
    Hailer, Frank
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Arnqvist, Göran
    Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Intergenomic epistasis for fitness: within-population interactions between cytoplasmic and nuclear genes in Drosophila melanogaster.2007In: Genetics, ISSN 0016-6731, E-ISSN 1943-2631, Vol. 175, no 1, p. 235-44Article in journal (Refereed)
    Abstract [en]

    The symbiotic relationship between the mitochondrial and nuclear genomes coordinates metabolic energy production and is fundamental to life among eukaryotes. Consequently, there is potential for strong selection to shape interactions between these two genomes. Substantial research attention has focused on the possibility that within-population sequence polymorphism in mitochondrial DNA (mtDNA) is maintained by mitonuclear fitness interactions. Early theory predicted that selection will often eliminate mitochondrial polymorphisms. However, recent models demonstrate that intergenomic interactions can promote the maintenance of polymorphism, especially if the nuclear genes involved are linked to the X chromosome. Most empirical studies to date that have assessed cytonuclear fitness interactions have studied variation across populations and it is still unclear how general and strong such interactions are within populations. We experimentally tested for cytonuclear interactions within a laboratory population of Drosophila melanogaster using 25 randomly sampled cytoplasmic genomes, expressed in three different haploid nuclear genetic backgrounds, while eliminating confounding effects of intracellular bacteria (e.g., Wolbachia). We found sizable cytonuclear fitness interactions within this population and present limited evidence suggesting that these effects were sex specific. Moreover, the relative fitness of cytonuclear genotypes was environment specific. Sequencing of mtDNA (2752 bp) revealed polymorphism within the population, suggesting that the observed cytoplasmic genetic effects may be mitochondrial in origin.

  • 11.
    Dowling, Damian K.
    et al.
    Centre for Evolutionary Biology, School of Animal Biology (M092), The University of Western Australia, Crawley, WA, Australia / Animal Ecology/Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, USA.
    Lindell, Johan
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Evolutionary implications of non-neutral mitochondrial genetic variation2008In: Trends in Ecology & Evolution, ISSN 0169-5347, E-ISSN 1872-8383, Vol. 23, no 10, p. 546-554Article, review/survey (Refereed)
    Abstract [en]

    Sequence variation in mitochondrial DNA (mtDNA) was traditionally considered to be selectively neutral. However, an accumulating body of evidence indicates that this assumption is invalid. Furthermore, recent advances indicate that mtDNA polymorphism can be maintained within populations via selection on the joint mitochondrial-nuclear genotype. Here, we review the latest findings that show mitochondrial and cytoplasmic genetic variation for life-history traits and fitness. We highlight the key importance of the mitochondrial-nuclear interaction as a unit of selection and discuss the consequences of mitochondrially encoded fitness effects on several key evolutionary processes. Our goal is to draw attention to the profound, yet neglected, influence of the mitochondrial genome on the fields of ecology and evolution.

  • 12.
    Erkosar, Berra
    et al.
    Univ Lausanne, Switzerland.
    Yashiro, Erika
    Univ Lausanne, Switzerland.
    Zajitschek, Felix
    Uppsala Univ, Sweden; Univ New South Wales, Australia.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Maklakov, Alexei A.
    Uppsala Univ, Sweden.
    van der Meer, Jan R.
    Univ Lausanne, Switzerland.
    Kawecki, Tadeusz J.
    Univ Lausanne, Switzerland.
    Host diet mediates a negative relationship between abundance and diversity of Drosophila gut microbiota2018In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 8, no 18, p. 9491-9502Article in journal (Refereed)
    Abstract [en]

    Nutrient supply to ecosystems has major effects on ecological diversity, but it is unclear to what degree the shape of this relationship is general versus dependent on the specific environment or community. Although the diet composition in terms of the source or proportions of different nutrient types is known to affect gut microbiota composition, the relationship between the quantity of nutrients supplied and the abundance and diversity of the intestinal microbial community remains to be elucidated. Here, we address this relationship using replicate populations of Drosophila melanogaster maintained over multiple generations on three diets differing in the concentration of yeast (the only source of most nutrients). While a 6.5-fold increase in yeast concentration led to a 100-fold increase in the total abundance of gut microbes, it caused a major decrease in their alpha diversity (by 45-60% depending on the diversity measure). This was accompanied by only minor shifts in the taxonomic affiliation of the most common operational taxonomic units (OTUs). Thus, nutrient concentration in host diet mediates a strong negative relationship between the nutrient abundance and microbial diversity in the Drosophila gut ecosystem.

  • 13.
    Friberg, Urban
    Department of Ecology and Environmental Science, Section of Animal Ecology, Umeå University, Umeå , Sweden.
    Genetic variation in male and female reproductive characters associated with sexual conflict in Drosophila melanogaster2005In: Behavior Genetics, ISSN 0001-8244, E-ISSN 1573-3297, Vol. 35, no 4, p. 455-462Article in journal (Refereed)
    Abstract [en]

    Recent studies have shown that elevated mating, courtship and seminal substances affect female fitness negatively in Drosophila melanogaster. It has also been shown that males vary with respect to these characters and that male harm to females correlates positively with components of male fitness. These results suggest that there is sexual conflict over the effect of such male characters. An important component of this scenario is that females have evolved counteradaptations to male harm, but so far there is limited evidence for this. Here I define female resistance as the ability to withstand an increased exposure to males. Across 10 genetically differentiated lines of D. melanogaster, I found genetic variation among females in the reduction of lifespan that followed from exposure to males of different durations. There was also genetic variation among males with regards to the degree to which they decrease the lifespan of their mates. These results suggest that genetic variation for female ability to endure male sexually antagonistic adaptations exists and may play an important role in male–female coevolution.

  • 14.
    Friberg, Urban
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University / Department of Ecology and Environmental Science, Section of Animal Ecology, Umeå University, Sweden.
    Male perception of female mating status: its effect on copulation duration and male and female fitness in Drosophila melanogaster2006In: Animal Behaviour, ISSN 0003-3472, E-ISSN 1095-8282, Vol. 72, no 6, p. 1259-1268Article in journal (Refereed)
    Abstract [en]

    When females mate with multiple partners, the risk of sperm competition depends on female mating history. To maximize fitness, males should adjust their copulatory investments according to this risk. In the fruit fly, Drosophila melanogaster, the female cuticular hydrocarbon (CH) profile changes when females mate, and males use this to assess female mating status. I tested whether this cue influenced the time males spent copulating with females and if this affected male fertilization success and female fitness. I manipulated female mating status by transferring CHs from either virgin or mated females to virgin females. Males copulated significantly longer with virgin females that had been coated with CHs from mated females (experimental group) than with virgin females coated with CHs from other virgin females (control group). Copulation duration did not differ between females from the experimental group and females that had already mated. To test whether differential investment in copulation affected male sperm defence and female fitness, experimental and control females were mated once to wild-type males and then either housed with males carrying a genetic marker (experiment 1) or alone (experiment 2). In experiment 1 male sperm defence was elevated when males perceived their partner as mated, and this was mainly due to females remating less. Increased male investment in copulation duration also affected female fitness, although this was reversed between experiments 1 and 2. Finally, these results also indicate that copulations are costly to males, since manipulated males copulated for longer with virgin females than they normally would, resulting in higher fertilization success.

  • 15.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Två kön och många organ: men bara en arvsmassa2016In: Tidskriften för svensk psykiatri, ISSN 1653-8579, no 4, p. 28-29Article in journal (Other academic)
    Abstract [sv]

    Hos många arter uppvisar könen en rad skillnader.Dessa omfattar vanligtvis deras utseende så väl som beteende. Vad är det egentligen som orsakar evolution av könsskillnader, hur är den möjlig då könen har i princip samma gener, och kan detta tänkas ha konsekvenser för hur vi människor fungerar?

  • 16.
    Friberg, Urban
    et al.
    Department of Ecology and Environmental Science, Section of Animal Ecology, Umeå University, Sweden.
    Arnqvist, Göran
    Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Sweden.
    Fitness effects of female mate choice: preferred males are detrimental for Drosophila melanogaster females2003In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 16, no 5, p. 797-811Article in journal (Refereed)
    Abstract [en]

    The evolution of female mate choice, broadly defined to include any female behaviour or morphology which biases matings towards certain male phenotypes, is traditionally thought to result from direct or indirect benefits which females acquire when mating with preferred males. In contrast, new models have shown that female mate choice can be generated by sexual conflict, where preferred males may cause a fitness depression in females. Several studies have shown that female Drosophila melanogaster bias matings towards large males. Here, we use male size as a proxy for male attractiveness and test how female fitness is affected by reproducing with large or small males, under two different male densities. Females housed with large males had reduced lifespan and aged at an accelerated rate compared with females housed with small males, and increased male density depressed female fitness further. These fitness differences were due to effects on several different fitness components. Female fitness covaried negatively with male courtship rate, which suggests a cost of courtship. Mating rate increased with male size, whereas female fitness peaked at an intermediate mating rate. Our results suggest that female mate choice in D. melanogaster is, at least in part, a by-product of sexual conflict over the mating rate.

  • 17.
    Friberg, Urban
    et al.
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden / Department of Ecology and Environmental Science, Umeå University, Umeå , Sweden /Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, USA.
    Dowling, D.K.
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    No evidence of mitochondrial genetic variation for sperm competition within a population of Drosophila melanogaster2008In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 21, no 6, p. 1798-1807Article in journal (Refereed)
    Abstract [en]

    Recent studies have advocated a role for mitochondrial DNA (mtDNA) in sperm competition. This is controversial because earlier theory and empirical work suggested that mitochondrial genetic variation for fitness is low. Yet, such studies dealt only with females and did not consider that variation that is neutral when expressed in females, might be non-neutral in males as, in most species, mtDNA is never selected in males. We measured male ability to compete for fertilizations, at young and late ages, across 25 cytoplasms expressed in three different nuclear genetic backgrounds, within a population of Drosophila melanogaster. We found no cytoplasmic (thus no mtDNA) genetic variation for either male offence or offensive sperm competitiveness. This contrasts with previous findings demonstrating cytoplasmic genetic variation for female fitness and female ageing across these same lines. Taken together, this suggests that mitochondrial genes do not contribute to variation in sperm competition at the within-population level.

  • 18.
    Friberg, Urban
    et al.
    Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden / Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA.
    Lew, Timothy
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA.
    Byrne, Pillip
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA / School of Botany and Zoology, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
    Rice, William
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA.
    Assessing the potential for an ongoing arms race within and between the sexes: selection and heritable variation2005In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 59, no 7, p. 1540-1551Article in journal (Refereed)
    Abstract [en]

    In promiscuous species, sexual selection generates two opposing male traits: offense (acquiring new mates and supplanting stored sperm) and defense (enforcing fidelity on one's mates and preventing sperm displacement when this fails). Coevolution between these traits requires both additive genetic variation and associated natural selection. Previous work with Drosophila melanogaster found autosomal genetic variation for these traits among inbred lines from a mixture of populations, but only nonheritable genetic variation was found within a single outbred population. These results do not support ongoing antagonistic coevolution between offense and defense, nor between either of these male traits and female reproductive characters. Here we use a new method (hemiclonal analysis) to study genomewide genetic variation in a large outbred laboratory population of D. melanogaster. Hemiclonal analysis estimates the additive genetic variation among random, genomewide haplotypes taken from a large, outbred, locally adapted laboratory population and determines the direction of the selection gradient on this variation. In contrast to earlier studies, we found low but biologically significant heritable variation for defensive and offensive offspring production as well as all their components (P1, fidelity, P2, and remating). Genetic correlations between these traits were substantially different from those reported for inbred lines. A positive genetic correlation was found between defense and offense, demonstrating that some shared genes influence both traits. In addition to this common variation, evidence for unique genetic variation for each trait was also found, supporting an ongoing coevolutionary arms race between defense and offense. Reproductive conflict between males can strongly influence female fitness. Correspondingly, we found genetic variation in both defense and offense that affected female fitness. No evidence was found for intersexual conflict in the context of male defense, but we found substantial intersexual conflict in the context of male offensive sperm competitive ability. These results indicate that conflict between competing males also promotes an associated arms race between the sexes.

  • 19.
    Friberg, Urban
    et al.
    Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden / Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA .
    Miller, Paige M.
    Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Stewart, Andrew D.
    Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Rice, William R.
    Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Mechanisms Promoting the Long-Term Persistence of a Wolbachia Infection in a Laboratory-Adapted Population of Drosophila melanogaster2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 1, article id e16448Article in journal (Refereed)
    Abstract [en]

    Intracellular bacteria of the genus Wolbachia are widespread endosymbionts across diverse insect taxa. Despite this prevalence, our understanding of how Wolbachia persists within populations is not well understood. Cytoplasmic incompatibility (CI) appears to be an important phenotype maintaining Wolbachia in many insects, but it is believed to be too weak to maintain Wolbachia in Drosophila melanogaster, suggesting that Wolbachia must also have other effects on this species. Here we estimate the net selective effect of Wolbachia on its host in a laboratory-adapted population of D. melanogaster, to determine the mechanisms leading to its persistence in the laboratory environment. We found i) no significant effects of Wolbachia infection on female egg-to-adult survival or adult fitness, ii) no reduced juvenile survival in males, iii) substantial levels of CI, and iv) a vertical transmission rate of Wolbachia higher than 99%. The fitness of cured females was, however, severely reduced (a decline of 37%) due to CI in offspring. Taken together these findings indicate that Wolbachia is maintained in our laboratory environment due to a combination of a nearly perfect transmission rate and substantial CI. Our results show that there would be strong selection against females losing their infection and producing progeny free from Wolbachia.

  • 20.
    Friberg, Urban
    et al.
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA.
    Rice, William R
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California, USA.
    Cut thy neighbor: cyclic birth and death of recombination hotspots via genetic conflict.2008In: Genetics, ISSN 0016-6731, E-ISSN 1943-2631, Vol. 179, no 4, p. 2229-2238Article in journal (Refereed)
    Abstract [en]

    Most recombination takes place in numerous, localized regions called hotspots. However, empirical evidence indicates that nascent hotspots are susceptible to removal due to biased gene conversion, so it is paradoxical that they should be so widespread. Previous modeling work has shown that hotspots can evolve due to genetic drift overpowering their intrinsic disadvantage. Here we synthesize recent theoretical and empirical results to show how natural selection can favor hotspots. We propose that hotspots are part of a cycle of antagonistic coevolution between two tightly linked chromosomal regions: an inducer region that initiates recombination during meiosis by cutting within a nearby region of DNA and the cut region itself, which can evolve to be resistant to cutting. Antagonistic coevolution between inducers and their cut sites is driven by recurrent episodes of Hill-Robertson interference, genetic hitchhiking, and biased gene conversion.

  • 21.
    Friberg, Urban
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology. Uppsala University, Sweden.
    Rice, William R.
    University of Calif Santa Barbara, CA 93111 USA.
    Sexually Antagonistic Zygotic Drive: A New Form of Genetic Conflict between the Sex Chromosomes2015In: Cold Spring Harbor Perspectives in Biology, ISSN 1943-0264, E-ISSN 1943-0264, Vol. 7, no 3, p. a017608-Article in journal (Refereed)
    Abstract [en]

    Sisters and brothers are completely unrelated with respect to the sex chromosomes they inherit from their heterogametic parent. This has the potential to result in a previously unappreciated form of genetic conflict between the sex chromosomes, called sexually antagonistic zygotic drive (SA-ZD). SA-ZD can arise whenever brothers and sisters compete over limited resources or there is brother-sister mating coupled with inbreeding depression. Although theory predicts that SA-ZD should be common and influence important evolutionary processes, there is little empirical evidence for its existence. Here we discuss the current understanding of SA-ZD, why it would be expected to elude empirical detection when present, and how it relates to other forms of genetic conflict.

  • 22.
    Friberg, Urban
    et al.
    Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Rice, Willliam R.
    Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, USA / Department of Mathematics, University of Tennessee, Knoxville, Tennessee, USA.
    Gavrilets, Sergey
    Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Sexually Antagonistic “Zygotic Drive” of the Sex Chromosomes2008In: PLOS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 4, no 12, article id 1000313Article in journal (Refereed)
    Abstract [en]

    Genomic conflict is perplexing because it causes the fitness of a species to decline rather than improve. Many diverse forms of genomic conflict have been identified, but this extant tally may be incomplete. Here, we show that the unusual characteristics of the sex chromosomes can, in principle, lead to a previously unappreciated form of sexual genomic conflict. The phenomenon occurs because there is selection in the heterogametic sex for sex-linked mutations that harm the sex of offspring that does not carry them, whenever there is competition among siblings. This harmful phenotype can be expressed as an antagonistic green-beard effect that is mediated by epigenetic parental effects, parental investment, and/or interactions among siblings. We call this form of genomic conflict sexually antagonistic “zygotic drive”, because it is functionally equivalent to meiotic drive, except that it operates during the zygotic and postzygotic stages of the life cycle rather than the meiotic and gametic stages. A combination of mathematical modeling and a survey of empirical studies is used to show that sexually antagonistic zygotic drive is feasible, likely to be widespread in nature, and that it can promote a genetic “arms race” between the homo- and heteromorphic sex chromosomes. This new category of genomic conflict has the potential to strongly influence other fundamental evolutionary processes, such as speciation and the degeneration of the Y and W sex chromosomes. It also fosters a new genetic hypothesis for the evolution of enigmatic fitness-reducing traits like the high frequency of spontaneous abortion, sterility, and homosexuality observed in humans.

  • 23.
    Friberg, Urban
    et al.
    Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, United States of America / Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden .
    Stewart, Andrew D.
    Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Rice, William R.
    Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, California, USA.
    Empirical Evidence for Son-Killing X Chromosomes and the Operation of SA-Zygotic Drive2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 8, article id e23508Article in journal (Refereed)
    Abstract [en]

    Background: Diploid organisms have two copies of all genes, but only one is carried by each haploid gamete and diploid offspring. This causes a fundamental genetic conflict over transmission rate between alternative alleles. Single genes, or gene clusters, only rarely code for the complex phenotypes needed to give them a transmission advantage (drive phenotype). However, all genes on a male's X and Y chromosomes co-segregate, allowing different sex-linked genes to code for different parts of the drive phenotype. Correspondingly, the well-characterized phenomenon of male gametic drive, occurring during haploid gametogenesis, is especially common on sex chromosomes. The new theory of sexually antagonistic zygotic drive of the sex chromosomes (SA-zygotic drive) extends the logic of gametic drive into the diploid phase of the lifecycle, whenever there is competition among siblings or harmful sib-sib mating. The X and Y are predicted to gain a transmission advantage by harming offspring of the sex that does not carry them. Results: Here we analyzed a mutant X-chromosome in Drosophila simulans that produced an excess of daughters when transmitted from males. We developed a series of tests to differentiate between gametic and SA-zygotic drive, and provide multiple lines of evidence that SA-zygotic drive is responsible for the sex ratio bias. Driving sires produce about 50% more surviving daughters than sons. Conclusion: Sex-ratio distortion due to genetic conflict has evolved via gametic drive and maternally transmitted endosymbionts. Our data indicate that sex chromosomes can also drive by harming the non-carrier sex of offspring.

  • 24.
    Friberg, Urban
    et al.
    Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Stewart, Andrew D.
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, USA.
    Rice, William R.
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, USA.
    X- and Y-chromosome linked paternal effects on a life-history trait2012In: Biology Letters, ISSN 1744-9561, E-ISSN 1744-957X, Vol. 8, no 1, p. 71-73Article in journal (Refereed)
    Abstract [en]

    Males and females usually invest asymmetrically in offspring. In species lacking parental care, females influence offspring in many ways, while males only contribute genetic material via their sperm. For this reason, maternal effects have long been considered an important source of phenotypic variation, while paternal effects have been presumed to be absent or negligible. The recent surge of studies showing trans-generational epigenetic effects questions this assumption, and indicates that paternal effects may be far more important than previously appreciated. Here, we test for sex-linked paternal effects in Drosophila melanogaster on a life-history trait, and find substantial support for both X- and Y-linked effects.

  • 25.
    Gavrilets, Sergey
    et al.
    Departments of Ecology and Evolutionary Biology and Mathematics, University of Tennessee, Knoxville,USA.
    Arnqvist, Göran
    Department of Ecology and Environmental Science, University of Umeå, Sweden.
    Friberg, Urban
    Department of Ecology and Environmental Science, University of Umeå, Sweden.
    The evolution of female mate choice by sexual conflict2001In: Proceedings of the Royal Society of London Series B, ISSN 0080-4649, Vol. 268, no 1466, p. 531-539Article in journal (Refereed)
    Abstract [en]

    Although empirical evidence has shown that many male traits have evolved via sexual selection by female mate choice, our understanding of the adaptive value of female mating preferences is still very incomplete. It has recently been suggested that female mate choice may result from females evolving resistance rather than attraction to males, but this has been disputed. Here, we develop a quantitative genetic model showing that sexual conflict over mating indeed results in the joint evolution of costly female mate choice and exaggerated male traits under a wide range of circumstances. In contrast to traditional explanations of costly female mate choice, which rely on indirect genetic benefits, our model shows that mate choice can be generated as a side–effect of females evolving to reduce the direct costs of mating.

  • 26.
    Gavrilets, Sergey
    et al.
    University of Tennessee, TN 37996 USA; University of Tennessee, TN 37996 USA; University of Tennessee, TN 37996 USA.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Rice, William R.
    University of Calif Santa Barbara, CA 93106 USA.
    Understanding Homosexuality: Moving on from Patterns to Mechanisms2018In: Archives of Sexual Behavior, ISSN 0004-0002, E-ISSN 1573-2800, Vol. 47, no 1, p. 27-31Article in journal (Other academic)
    Abstract [en]

    n/a

  • 27.
    Griffin, R. M.
    et al.
    Uppsala University, Sweden.
    Le Gall, D.
    Uppsala University, Sweden; Ecole Normale Super, France.
    Schielzeth, H.
    University of Bielefeld, Germany.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering. Uppsala University, Sweden.
    Within-population Y-linked genetic variation for lifespan in Drosophila melanogaster2015In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 28, no 11, p. 1940-1947Article in journal (Refereed)
    Abstract [en]

    The view that the Y chromosome is of little importance for phenotypic evolution stems from early studies of Drosophila melanogaster. This species Y chromosome contains only 13 protein-coding genes, is almost entirely heterochromatic and is not necessary for male viability. Population genetic theory further suggests that non-neutral variation can only be maintained at the Y chromosome under special circumstances. Yet, recent studies suggest that the D.melanogaster Y chromosome trans-regulates hundreds to thousands of X and autosomal genes. This finding suggests that the Y chromosome may play a far more active role in adaptive evolution than has previously been assumed. To evaluate the potential for the Y chromosome to contribute to phenotypic evolution from standing genetic variation, we test for Y-linked variation in lifespan within a population of D.melanogaster. Assessing variation for lifespan provides a powerful test because lifespan (i) shows sexual dimorphism, which the Y is primarily predicted to contribute to, (ii) is influenced by many genes, which provides the Y with many potential regulatory targets and (iii) is sensitive to heterochromatin remodelling, a mechanism through which the Y chromosome is believed to regulate gene expression. Our results show a small but significant effect of the Y chromosome and thus suggest that the Y chromosome has the potential to respond to selection from standing genetic variation. Despite its small effect size, Y-linked variation may still be important, in particular when evolution of sexual dimorphism is genetically constrained elsewhere in the genome.

  • 28.
    Griffin, Robert M
    et al.
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    Dean, Rebecca
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    Grace, Jaime L
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    Rydén, Patrik
    Department of Mathematics and Mathematical Statistics, Umeå University, Umeå ,Sweden / Computational Life Science Cluster (CLiC), Umeå University, Umeå , Sweden.
    Friberg, Urban
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    The shared genome is a pervasive constraint on the evolution of sex-biased gene expression.2013In: Molecular biology and evolution, ISSN 0737-4038, E-ISSN 1537-1719, Vol. 30, no 9, p. 2168-76Article in journal (Refereed)
    Abstract [en]

    Males and females share most of their genomes, and differences between the sexes can therefore not evolve through sequence divergence in protein coding genes. Sexual dimorphism is instead restricted to occur through sex-specific expression and splicing of gene products. Evolution of sexual dimorphism through these mechanisms should, however, also be constrained when the sexes share the genetic architecture for regulation of gene expression. Despite these obstacles, sexual dimorphism is prevalent in the animal kingdom and commonly evolves rapidly. Here, we ask whether the genetic architecture of gene expression is plastic and easily molded by sex-specific selection, or if sexual dimorphism evolves rapidly despite pervasive genetic constraint. To address this question, we explore the relationship between the intersexual genetic correlation for gene expression (rMF), which captures how independently genes are regulated in the sexes, and the evolution of sex-biased gene expression. Using transcriptome data from Drosophila melanogaster, we find that most genes have a high rMF and that genes currently exposed to sexually antagonistic selection have a higher average rMF than other genes. We further show that genes with a high rMF have less pronounced sex-biased gene expression than genes with a low rMF within D. melanogaster and that the strength of the rMF in D. melanogaster predicts the degree to which the sex bias of a gene's expression has changed between D. melanogaster and six other species in the Drosophila genus. In sum, our results show that a shared genome constrains both short- and long-term evolution of sexual dimorphism.

  • 29.
    Griffin, Robert M.
    et al.
    Uppsala University, Sweden; University of Turku, Finland.
    Schielzeth, Holger
    University of Bielefeld, Germany; Friedrich Schiller University of Jena, Germany.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Autosomal and X-Linked Additive Genetic Variation for Lifespan and Aging: Comparisons Within and Between the Sexes in Drosophila melanogaster2016In: G3-GENES GENOMES GENETICS, ISSN 2160-1836, Vol. 6, no 12, p. 3903-3911Article in journal (Refereed)
    Abstract [en]

    Theory makes several predictions concerning differences in genetic variation between the X chromosome and the autosomes due to male X hemizygosity. The X chromosome should: (i) typically show relatively less standing genetic variation than the autosomes, (ii) exhibit more variation in males compared to females because of dosage compensation, and (iii) potentially be enriched with sex-specific genetic variation. Here, we address each of these predictions for lifespan and aging in Drosophila melanogaster. To achieve unbiased estimates of X and autosomal additive genetic variance, we use 80 chromosome substitution lines; 40 for the X chromosome and 40 combining the two major autosomes, which we assay for sex-specific and cross-sex genetic (co)variation. We find significant X and autosomal additive genetic variance for both traits in both sexes (with reservation for X-linked variation of aging in females), but no conclusive evidence for depletion of X-linked variation (measured through females). Males display more X-linked variation for lifespan than females, but it is unclear if this is due to dosage compensation since also autosomal variation is larger in males. Finally, our results suggest that the X chromosome is enriched for sex-specific genetic variation in lifespan but results were less conclusive for aging overall. Collectively, these results suggest that the X chromosome has reduced capacity to respond to sexually concordant selection on lifespan from standing genetic variation, while its ability to respond to sexually antagonistic selection may be augmented.

  • 30.
    Johnsson, Martin
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Gering, Eben
    Department of Zoology, Michigan University, Michigan, USA.
    Willis, Pamela
    Department of Biology, University of Victoria, Victoria, British Columbia, Canada.
    Lopez, Saioa
    UCL Genetics Institute, University College London, London, UK.
    Van Dorp, Lucy
    UCL Genetics Institute, University College London, London, UK.
    Hellenthal, Garrett
    UCL Genetics Institute, University College London, London, UK.
    Henriksen, Rie
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Wright, Dominic
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Feralisation targets different genomic loci to domestication in the chicken.2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 12950Article in journal (Refereed)
    Abstract [en]

    Feralisation occurs when a domestic population recolonizes the wild, escaping its previous restricted environment, and has been considered as the reverse of domestication. We have previously shown that Kauai Island's feral chickens are a highly variable and admixed population. Here we map selective sweeps in feral Kauai chickens using whole-genome sequencing. The detected sweeps were mostly unique to feralisation and distinct to those selected for during domestication. To ascribe potential phenotypic functions to these genes we utilize a laboratory-controlled equivalent to the Kauai population-an advanced intercross between Red Junglefowl and domestic layer birds that has been used previously for both QTL and expression QTL studies. Certain sweep genes exhibit significant correlations with comb mass, maternal brooding behaviour and fecundity. Our analyses indicate that adaptations to feral and domestic environments involve different genomic regions and feral chickens show some evidence of adaptation at genes associated with sexual selection and reproduction.

  • 31.
    Lehtovaara, Anne
    et al.
    Ageing Research Group, Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Schielzeth, Holger
    Ageing Research Group, Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden, Department of Evolutionary Biology, Bielefeld University, Bielefeld, Germany.
    Flis, Ilona
    Ageing Research Group, Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Ageing Research Group, Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Heritability of life span is largely sex limited in Drosophila.2013In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 182, no 5, p. 653-65Article in journal (Refereed)
    Abstract [en]

    Males and females differ with respect to life span and rate of aging in most animal species. Such sexual dimorphism can be associated with a complex genetic architecture, where only part of the genetic variation is shared between the sexes. However, the extent to which this is true for life span and aging is not known, because studies of life span have given contradictory results and aging has not been studied from this perspective. Here we investigate the additive genetic architecture of life span and aging in Drosophila melanogaster. We find substantial amounts of additive genetic variation for both traits, with more than three-quarters of this variation available for sex-specific evolutionary change. This result shows that the sexes have a profoundly different additive genetic basis for these traits, which has several implications. First, it translates into an, on average, three-times-higher heritability of life span within, compared to between, the sexes. Second, it implies that the sexes are relatively free to evolve with respect to these traits. And third, as life span and aging are traits that integrate over all genetic factors that contribute to mortal disease, it also implies that the genetics of heritable disease differs vastly between the sexes.

  • 32.
    Maklakov, Alexei A.
    et al.
    Uppsala University, Sweden.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Ageing: Why Males Curtail the Longevity of Their Mates2016In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 26, no 20, p. R929-R932Article in journal (Other academic)
    Abstract [en]

    Male nematodes secrete pheromones that accelerate the somatic senescence of potential mates. A new study shows that this harm most likely is an unintended by-product of the males aim to speed up sexual maturation and delay reproductive senescence of future partners.

  • 33.
    Maklakov, Alexei A
    et al.
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden / Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
    Dowling, Damian K
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Arnqvist, Göran
    Animal Ecology, Department of Ecology and Evolution, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Within-population variation in cytoplasmic genes affects female life span and aging in Drosophila melanogaster2006In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 60, no 10, p. 2081-2086Article in journal (Refereed)
    Abstract [en]

    It has been suggested that mitochondrial DNA (mtDNA) may play an important role in aging. Yet, few empirical studies have tested this hypothesis, partly because the degree of sequence polymorphism in mtDNA is assumed to be low. However, low sequence variation may not necessarily translate into low phenotypic variation. Here, we report an experiment that tests whether there is within-population variation in cytoplasmic genes for female longevity and senescence. To achieve this, we randomly selected 25 "mitochondrial founders" from a single, panmictic population of Drosophila melanogaster and used these founders to generate distinct "mt" lines in which we controlled for the nuclear background by successive backcrossing. Potential confounding effects of cytoplasmically transmitted bacteria were eliminated by tetracycline treatment. The mt lines were then assayed for differences in longevity, Gompertz intercept (frailty), and demographic rate of change in mortality with age (rate-of-senescence) in females. We found significant cytoplasmic effects on all three variables. This provides evidence that genetic variation in cytoplasmic genes, presumably mtDNA, contributes to variation in female mortality and aging.

  • 34.
    Maklakov, Alexei A
    et al.
    Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Sweden.
    Immler, Simone
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    Løvlie, Hanne
    Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Sweden.
    Flis, Ilona
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    Friberg, Urban
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala, Sweden.
    The effect of sexual harassment on lethal mutation rate in female Drosophila melanogaster2013In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 280, no 1750Article in journal (Refereed)
    Abstract [en]

    The rate by which new mutations are introduced into a population may have far-reaching implications for processes at the population level. Theory assumes that all individuals within a population have the same mutation rate, but this assumption may not be true. Compared with individuals in high condition, those in poor condition may have fewer resources available to invest in DNA repair, resulting in elevated mutation rates. Alternatively, environmentally induced stress can result in increased investment in DNA repair at the expense of reproduction. Here, we directly test whether sexual harassment by males, known to reduce female condition, affects female capacity to alleviate DNA damage in Drosophila melanogaster fruitflies. Female gametes can repair double-strand DNA breaks in sperm, which allows manipulating mutation rate independently from female condition. We show that male harassment strongly not only reduces female fecundity, but also reduces the yield of dominant lethal mutations, supporting the hypothesis that stressed organisms invest relatively more in repair mechanisms. We discuss our results in the light of previous research and suggest that social effects such as density and courtship can play an important and underappreciated role in mediating condition-dependent mutation rate.

  • 35.
    Maklakov, Alexei A.
    et al.
    Uppsala University, Uppsala, Sweden.
    Rowe, Locke
    University of Toronto, Toronto, ON, Canada.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology.
    Why organisms age: Evolution of senescence under positive pleiotropy?2015In: Bioessays, ISSN 0265-9247, E-ISSN 1521-1878, Vol. 37, no 7, p. 802-807Article in journal (Refereed)
    Abstract [en]

    Two classic theories maintain that aging evolves eitherbecause of alleles whose deleterious effects are confinedto late life or because of alleles with broad pleiotropiceffects that increase early-life fitness at the expense oflate-life fitness. However, empirical studies often revealpositive pleiotropy for fitness across age classes, andrecent evidence suggests that selection on early-lifefitness can decelerate aging and increase lifespan, therebycasting doubt on the current consensus. Here, we brieflyreview these data and promote the simple argument thataging can evolve under positive pleiotropy between earlyandlate-life fitness when the deleterious effect ofmutations increases with age. We argue that thishypothesis makes testable predictions and is supportedby existing evidence.

  • 36.
    Malacrinò, Antonino
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering. Ohio State Univ, OH 43210 USA.
    Kimber, Christopher
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Brengdahl, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Heightened condition-dependence of the sexual transcriptome as a function of genetic quality in Drosophila melanogaster head tissue2019In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 286, no 1906, article id 20190819Article in journal (Refereed)
    Abstract [en]

    Theory suggests sexual traits should show heightened condition-dependent expression. This prediction has been tested extensively in experiments where condition has been manipulated through environmental quality. Condition-dependence as a function of genetic quality has, however, only rarely been addressed, despite its central importance in evolutionary theory. To address the effect of genetic quality on expression of sexual and non-sexual traits, we here compare gene expression in Drosophila melanogaster head tissue between flies with intact genomes (high condition) and flies carrying a major deleterious mutation (low condition). We find that sex-biased genes show heightened condition-dependent expression in both sexes, and that expression in low condition males and females regresses towards a more similar expression profile. As predicted, sex-biased expression was more sensitive to condition in males compared to females, but surprisingly female-biased, rather than male-biased, genes show higher sensitivity to condition in both sexes. Our results thus support the fundamental predictions of the theory of condition-dependence when condition is a function of genetic quality.

  • 37.
    Pischedda, Alison
    et al.
    University of Calif Santa Barbara, CA 93106 USA.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Stewart, Andrew D.
    Canisius Coll, NY 14208 USA.
    Miller, Paige M.
    University of Calif Santa Barbara, CA 93106 USA.
    Rice, William R.
    University of Calif Santa Barbara, CA 93106 USA.
    Sexual selection has minimal impact on effective population sizes in species with high rates of random offspring mortality: An empirical demonstration using fitness distributions2015In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 69, no 10, p. 2638-2647Article in journal (Refereed)
    Abstract [en]

    The effective population size (N-e) is a fundamental parameter in population genetics that influences the rate of loss of genetic diversity. Sexual selection has the potential to reduce N-e by causing the sex-specific distributions of individuals that successfully reproduce to diverge. To empirically estimate the effect of sexual selection on N-e, we obtained fitness distributions for males and females from an outbred, laboratory-adapted population of Drosophila melanogaster. We observed strong sexual selection in this population (the variance in male reproductive success was approximate to 14 times higher than that for females), but found that sexual selection had only a modest effect on N-e, which was 75% of the census size. This occurs because the substantial random offspring mortality in this population diminishes the effects of sexual selection on N-e, a result that necessarily applies to other high fecundity species. The inclusion of this random offspring mortality creates a scaling effect that reduces the variance/mean ratios for male and female reproductive success and causes them to converge. Our results demonstrate that measuring reproductive success without considering offspring mortality can underestimate N-e and overestimate the genetic consequences of sexual selection. Similarly, comparing genetic diversity among different genomic components may fail to detect strong sexual selection.

  • 38.
    Rice, William
    et al.
    Department of Ecology, Evolution & Marine Biology, University of California, Santa Barbara, CA, USA.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Gavrilets, Sergey
    Department of Ecology and Evolutionary Biology and Department of Mathematics, National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN, USA.
    Sexually antagonistic epigenetic marks that canalize sexually dimorphic development2016In: Molecular Ecology, ISSN 0962-1083, E-ISSN 1365-294X, Vol. 25, no 8, p. 1812-1822Article in journal (Refereed)
    Abstract [en]

    The sexes share the same autosomal genomes, yet sexual dimorphism is common due to sex-specific gene expression. When present, XX and XY karyotypes trigger alternate regulatory cascades that determine sex-specific gene expression profiles. In mammals, secretion of testosterone (T) by the testes during foetal development is the master switch influencing the gene expression pathways (male vs. female) that will be followed, but many genes have sex-specific expression prior to T secretion. Environmental factors, like endocrine disruptors and mimics, can interfere with sexual development. However, sex-specific ontogeny can be canalized by the production of epigenetic marks (epimarks) generated during early ontogeny that increase sensitivity of XY embryos to T and decrease sensitivity of XX embryos. Here, we integrate and synthesize the evidence indicating that canalizing epimarks are produced during early ontogeny. We will also describe the evidence that such epimarks sometimes carry over across generations and produce mosaicism in which some traits are discordant with the gonad. Such carryover epimarks are sexually antagonistic because they benefit the individual in which they were formed (via canalization) but harm opposite-sex offspring when they fail to erase across generations and produce gonad-trait discordances. SA-epimarks have the potential to: i) magnify phenotypic variation for many sexually selected traits, ii) generate overlap along many dimensions of the masculinity/femininity spectrum, and iii) influence medically important gonad-trait discordances like cryptorchidism, hypospadias and idiopathic hirsutism.

  • 39.
    Rice, William
    et al.
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, USA.
    Gavrilets, Sergey
    Department of Ecology and Evolutionary Biology / Department of Mathematics and the National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, USA.
    Friberg, Urban
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, USA / Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    The evolution of sex-specific grandparental harm2010In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 277, no 1694, p. 2727-2735Article in journal (Refereed)
    Abstract [en]

    Recent empirical studies indicate that grandparents favour some categories of grandchildren over others. Here, we expand the previous theoretical foundation for this finding and show that grandchild-harming phenotypes are predicted to evolve by 'sexually antagonistic zygotic drive (SA-zygotic drive) of the sex chromosomes'. We use the logic of Hamilton's rule to develop a new 'no-cost-to-self nepotism rule' that greatly simplifies the determination of the invasion criteria for mutations that cause grandparents to harm grandchildren. We use this theory to generate predictions that distinguish SA-zygotic drive from theory based solely on paternity assurance. The major diagnostic prediction is that grandmothers, and to a lesser degree grandfathers, will evolve grandson-harming phenotypes that reduce the level of sib competition experienced by their more closely related granddaughters, especially in their sons' families. This prediction is supported by data from recent studies showing (i) grandmothers invest more in granddaughters than grandsons, and counterintuitively, (ii) paternal grandmothers reduce the survival of their grandsons. We conclude that SA-zygotic drive is plausibly operating in humans via sexually antagonistic grandparental care.

  • 40.
    Rice, William
    et al.
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara.
    Linder, Jodell
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara.
    Friberg, Urban
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Lew, Timothy
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara.
    Morrow, Edward
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara.
    Stewart, Andrew
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara.
    Inter-locus antagonistic coevolution as an engine of speciation: assessment with hemiclonal analysis2005In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 102, no Suppl. 1, p. 6527-6534Article in journal (Refereed)
    Abstract [en]

    One of Ernst Mayr's legacies is the consensus that the allopatry model is the predominant mode of speciation in most sexually reproducing lineages. In this model, reproductive isolation develops as a pleiotropic byproduct of the genetic divergence that develops among physically isolated populations. Presently, there is no consensus concerning which, if any, evolutionary process is primarily responsible for driving the specific genetic divergence that leads to reproductive isolation. Here, we focus on the hypothesis that inter-locus antagonistic coevolution drives rapid genetic divergence among allopatric populations and thereby acts as an important “engine” of speciation. We assert that only data from studies of experimental evolution, rather than descriptive patterns of molecular evolution, can provide definitive evidence for this hypothesis. We describe and use an experimental approach, called hemiclonal analysis, that can be used in theDrosophila melanogaster laboratory model system to simultaneously screen nearly the entire genome for both standing genetic variation within a population and the net-selection gradient acting on the variation. Hemiclonal analysis has four stages: (i) creation of a laboratory “island population”; (ii) cytogenetic cloning of nearly genome-wide haplotypes to construct hemiclones; (iii) measurement of additive genetic variation among hemiclones; and (iv) measurement of the selection gradient acting on phenotypic variation among hemiclones. We apply hemiclonal analysis to test the hypothesis that there is ongoing antagonistic coevolution between the sexes in the D. melanogaster laboratory model system and then discuss the relevance of this analysis to natural systems.

  • 41.
    Rice, William R.
    et al.
    Department of Ecology, Evolution and Marine Biology, University of California, 93106-9610, Santa Barbara, CA, USA.
    Friberg, Urban
    Department of Ecology, Evolution and Marine Biology, University of California, 93106-9610, Santa Barbara, CA, USA.
    A Graphical Approach to Lineage Selection Between Clonals and Sexuals2009In: Lost Sex: The Evolutionary Biology of Parthenogenesis / [ed] Isa Schön, Koen Martens and Peter Dijk, Springer Netherlands, 2009, p. 75-97Chapter in book (Refereed)
    Abstract [en]

    Theories for the evolutionary advantages and disadvantages of sex address two fundamentally different questions: (i) Why does the genome of sexual lineages not “congeal,” (i.e., move toward a lowered recombination rate)?, and (ii) When there is a mixture of reproductively isolated clonal and sexual lineages, why do the clonals not accumulate and lead to a predominance of asexual reproduction within a clade? Here, we focus on the latter question. The relevant theory in this case is necessarily based on a special form of “lineage” selection between sexuals and clonals that do not share a common gene pool. We first briefly review the major genetic costs and benefits of clonal reproduction and conclude that the extant assemblage of theories provides an essentially complete description of the phenomenon. We next set out to combine and simplify these seemingly disparate theories by graphically representing the frameworks previously developed by Felsenstein (Genetics 78: 737–756, 1974) and Kimura and Maruyama (Genetics 54: 1337–1351, 1966) to show that the all of the proposed disadvantages to clonal reproduction can be expressed by a single factor: a decreased efficiency of natural selection in non-recombining lineages. This reduced efficiency derives from two distinct processes that only operate in clonal lineages: (i) background-trapping and (ii) the compensatory linkage disequilibrium that accrues in response to epistatic selection.

  • 42.
    Rice, William R
    et al.
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
    Friberg, Urban
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
    Genetics. Functionally degenerate--Y not so?2008In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 319, no 5859, p. 42-43Article in journal (Refereed)
    Abstract [en]

    The Y chromosome of the common fruit fly has few functional genes but regulates the expression of hundreds of autosomal and X-linked genes.

  • 43.
    Rice, William R
    et al.
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
    Friberg, Urban
    Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
    Genomic clues to an ancient asexual scandal.2007In: Genome Biology, ISSN 1465-6906, E-ISSN 1474-760X, Vol. 8, no 12, article id 232Article in journal (Refereed)
    Abstract [en]

    Despite abandoning meiosis, the bdelloid rotifers have persisted for millions of years and given rise to hundreds of species. Several mechanisms - allelic variants with different functions, high effective population size, and resistance to radiation - may contribute to their success.

    Bdelloid rotifers are diploid aquatic microinvertebrates that live in fresh or brackish water, especially in ephemeral habitats prone to periodic desiccation. They are the only well documented lineage that has eliminated meiosis yet has persisted for many millions of years (more than 35 million years [1]) and undergone an adaptive radiation - nearly 400 species in three families. Maynard Smith [2] referred to them as an "evolutionary scandal" because they are the exception to the usual pattern that asexual lineages die out before undergoing extensive speciation.

    The fact that asexuals are composed entirely of offspring-producing females gives them an intrinsic demographic advantage over sexual competitors whenever males do not help to produce offspring (referred to as the 'two-fold cost of sex' or the 'cost of producing males'). Evolutionary theory predicts, however, that obligate asexuals have a long-term evolutionary disadvantage, compared with sexuals, owing to a more pronounced 'Hill-Robertson effect', a reduction in the efficacy of natural selection that occurs because finite populations accumulate associations of linked genes (haplotypes) that interfere with selection [3, 4] (Figure 1).

    Figure 1

    The effect of genetic linkage on the effectiveness of selection. Consider two closely linked single nucleotide polymorphisms (SNPs A and B) with one of the 'alleles' at each site favored by selection (denoted by a superscript +). Selection acts more weakly on the 'interfering' haplotypes (A+B- and A-B+), where positive selection on one SNP is counterbalanced by negative selection on the other, compared with the 'reinforcing' haplotypes (A+B+ and A-B-), where selection on the two SNPs is complementary. This disparity causes interfering haplotypes to persist longer after they have accumulated by chance in finite populations. See Box 1 for further details.

    The Hill-Robertson effect arises when selection acts simultaneously at multiple linked sites (Figure 1). In this case, the fate of a mutation depends not only on its own selective value but also on that of its genetic backgrounds. Selection on genetic backgrounds introduces 'noise', which makes selection on a mutation less efficient. A similar interaction occurs between selection and random genetic drift, with smaller population sizes increasing the noise generated by drift. The cost of the Hill-Robertson effect in asexuals can be expressed as a reduced effective population size (N e , the size of an idealized, random-mating population with only chance fluctuations in family sizes) compared with the actual population size (census size, N; see Box 1 for further details). Because the strength of the Hill-Robertson effect increases with tighter linkage, non-meiotic species like bdelloid rotifers, in which 'interfering' haplotypes cannot be routinely broken up, should have a much reduced N e compared with their sexual competitors with similar census sizes, and should hence experience less effective selection. All else being equal, the bdelloids' ability to compete with sexuals should erode over time, leading to their eventual extinction. This has not happened, so the bdelloids must have one or more compensating advantages. Several recent studies indicate how bdelloids may have achieved their "scandalous" status.

  • 44.
    Rice, William R.
    et al.
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106, USA.
    Friberg, Urban
    Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Gavrilets, Sergey
    Department of Ecology and Evolutionary Biology and Department of Mathematics, National Institute for Mathematical and Biological Synthesis, University of Tennessee Knoxville, USA.
    Homosexuality as a Consequence of Epigenetically Canalized Sexual Development2012In: The Quarterly review of biology, ISSN 0033-5770, E-ISSN 1539-7718, Vol. 87, no 4, p. 343-368Article, review/survey (Refereed)
    Abstract [en]

    Male and female homosexuality have substantial prevalence in humans. Pedigree and twin studies indicate that homosexuality has substantial heritability in both sexes, yet concordance between identical twins is low and molecular studies have failed to find associated DNA markers. This paradoxical pattern calls for an explanation. We use published data on fetal androgen signaling and gene regulation via nongenetic changes in DNA packaging (epigenetics) to develop a new model for homosexuality. It is well established that fetal androgen signaling strongly influences sexual development. We show that an unappreciated feature of this process is reduced androgen sensitivity in XX fetuses and enhanced sensitivity in XY fetuses, and that this difference is most feasibly caused by numerous sex-specific epigenetic modifications ("epi-marks") originating in embryonic stem cells. These epi-marks buffer XX fetuses from masculinization due to excess fetal androgen exposure and similarly buffer XY fetuses from androgen underexposure. Extant data indicates that individual epi-marks influence some but not other sexually dimorphic traits, vary in strength across individuals, and are produced during ontogeny and erased between generations. Those that escape erasure will steer development of the sexual phenotypes they influence in a gonad-discordant direction in opposite sex offspring, mosaically feminizing XY offspring and masculinizing XX offspring. Such sex-specific epi-marks are sexually antagonistic (SA-epi-marks) because they canalize sexual development in the parent that produced them, but contribute to gonad-trait discordances in opposite-sex offspring when unerased. In this model, homosexuality occurs when stronger-than-average SA-epi-marks (influencing sexual preference) from an opposite-sex parent escape erasure and are then paired with a weaker-than-average de novo sex-specific epi-marks produced in opposite-sex offspring. Our model predicts that homosexuality is part of a wider phenomenon in which recently evolved androgen-influenced traits commonly display gonad-trait discordances at substantial frequency, and that the molecular feature underlying most homosexuality is not DNA polymorphism(s), but epi-marks that evolved to canalize sexual dimorphic development that sometimes carryover across generations and contribute to gonad-trait discordances in opposite-sex descendants.

  • 45.
    Rice, William R.
    et al.
    Department of Ecology, Evolution & Marine Biology, University of California, Santa Barbara, CA, USA.
    Friberg, Urban
    Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Gavrilets, Sergey
    Department of Ecology and Evolutionary Biology, Department of Mathematics, National Institute for Mathematical and Biological Synthesis (NIMBioS), University of Tennessee, Knoxville, TN, USA.
    Homosexuality via canalized sexual development: A testing protocol for a new epigenetic model2013In: Bioessays, ISSN 0265-9247, E-ISSN 1521-1878, Vol. 35, no 9, p. 764-770Article in journal (Refereed)
    Abstract [en]

    We recently synthesized and reinterpreted published studies to advance an epigenetic model for the development of homosexuality (HS). The model is based on epigenetic marks laid down in response to the XX vs. XY karyotype in embryonic stem cells. These marks boost sensitivity to testosterone in XY fetuses and lower it in XX fetuses, thereby canalizing sexual development. Our model predicts that a subset of these canalizing epigenetic marks stochastically carry over across generations and lead to mosaicism for sexual development in opposite-sex offspring - the homosexual phenotype being one such outcome. Here, we begin by outlining why HS has been under-appreciated as a commonplace phenomenon in nature, and how this trend is currently being reversed in the field of neurobiology. We next briefly describe our epigenetic model of HS, develop a set of predictions, and describe how epigenetic profiles of human stem cells can provide for a strong test of the model.

  • 46.
    Rice, William R
    et al.
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, USA.
    Gavrilets, Sergey
    Department of Ecology and Evolutionary Biology / Department of Mathematics, University of Tennessee, Knoxville, USA.
    Friberg, Urban
    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, USA.
    Sexually antagonistic chromosomal cuckoos.2009In: Biology Letters, ISSN 1744-9561, E-ISSN 1744-957X, Vol. 5, no 5, p. 686-688Article in journal (Refereed)
    Abstract [en]

    The two kinds of sex chromosomes in the heterogametic parent are transmitted to offspring with different sexes, causing opposite-sex siblings to be completely unrelated for genes located on these chromosomes. Just as the nest-parasitic cuckoo chick is selected to harm its unrelated nest-mates in order to garner more shared resources, sibling competition causes the sex chromosomes to be selected to harm siblings that do not carry them. Here we quantify and contrast this selection on the X and Y, or Z and W, sex chromosomes. We also develop a hypothesis for how this selection can contribute to the decay of the non-recombining sex chromosome.

  • 47.
    Stocks, Michael
    et al.
    University of Sheffield, Sheffield, United Kingdom; Department of Plant Ecology and Evolution, Uppsala University, Uppsala, Sweden.
    Dean, Rebecca
    Uppsala University, Uppsala, Sweden; Department of Genetics, Evolution and Environment, University College London, London, United Kingdom.
    Rogell, Björn
    Department of Animal Ecology, Uppsala University, Uppsala, Sweden; Department of Zoology, Stockholm University, Stockholm, Sweden.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, The Institute of Technology. Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.
    Sex-specific Trans-regulatory Variation on the Drosophila melanogaster X Chromosome2015In: PLoS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 11, no 2, p. 1-19, article id e1005015Article in journal (Refereed)
    Abstract [en]

    The X chromosome constitutes a unique genomic environment because it is present in onecopy in males, but two copies in females. This simple fact has motivated several theoreticalpredictions with respect to how standing genetic variation on the X chromosome should differfrom the autosomes. Unmasked expression of deleterious mutations in males and alower census size are expected to reduce variation, while allelic variants with sexually antagonisticeffects, and potentially those with a sex-specific effect, could accumulate on theX chromosome and contribute to increased genetic variation. In addition, incomplete dosagecompensation of the X chromosome could potentially dampen the male-specific effectsof random mutations, and promote the accumulation of X-linked alleles with sexually dimorphicphenotypic effects. Here we test both the amount and the type of genetic variation onthe X chromosome within a population of Drosophila melanogaster, by comparing the proportionof X linked and autosomal trans-regulatory SNPs with a sexually concordant anddiscordant effect on gene expression. We find that the X chromosome is depleted for SNPswith a sexually concordant effect, but hosts comparatively more SNPs with a sexually discordanteffect. Interestingly, the contrasting results for SNPs with sexually concordant anddiscordant effects are driven by SNPs with a larger influence on expression in females thanexpression in males. Furthermore, the distribution of these SNPs is shifted towards regionswhere dosage compensation is predicted to be less complete. These results suggest thatintrinsic properties of dosage compensation influence either the accumulation of differenttypes of trans-factors and/or their propensity to accumulate mutations. Our findings documenta potential mechanistic basis for sex-specific genetic variation, and identify the X as areservoir for sexually dimorphic phenotypic variation. These results have general implicationsfor X chromosome evolution, as well as the genetic basis of sex-specificevolutionary change.

  • 48.
    Zajitschek, Felix
    et al.
    Monash University, Australia; Uppsala University, Sweden.
    Zajitschek, Susanne R. K.
    Uppsala University, Sweden; Spanish Research Council CSIC, Spain.
    Canton, Cindy
    Uppsala University, Sweden.
    Georgolopoulos, Grigorios
    Uppsala University, Sweden.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering. Uppsala University, Sweden.
    Maklakov, Alexei A.
    Uppsala University, Sweden.
    Evolution under dietary restriction increases male reproductive performance without survival cost2016In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 283, no 1825, p. 20152726-Article in journal (Refereed)
    Abstract [en]

    Dietary restriction (DR), a reduction in nutrient intake without malnutrition, is the most reproducible way to extend lifespan in a wide range of organisms across the tree of life, yet the evolutionary underpinnings of the DR effect on lifespan are still widely debated. The leading theory suggests that this effect is adaptive and results from reallocation of resources from reproduction to somatic maintenance, in order to survive periods of famine in nature. However, such response would cease to be adaptive when DR is chronic and animals are selected to allocate more resources to reproduction. Nevertheless, chronic DR can also increase the strength of selection resulting in the evolution of more robust genotypes. We evolved Drosophila melanogaster fruit flies on DR, standard and high adult diets in replicate populations with overlapping generations. After approximately 25 generations of experimental evolution, male DR flies had higher fitness than males from standard and high populations. Strikingly, this increase in reproductive success did not come at a cost to survival. Our results suggest that sustained DR selects for more robust male genotypes that are overall better in converting resources into energy, which they allocate mostly to reproduction.

  • 49.
    Zajitschek, Felix
    et al.
    Department of Animal Ecology, Ageing Research Group, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Zajitschek, Susanne R. K.
    Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Friberg, Urban
    Department of Evolutionary Biology, Ageing Research Group, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Maklakov, Alexei A.
    Department of Animal Ecology, Ageing Research Group, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden.
    Interactive effects of sex, social environment, dietary restriction, and methionine on survival and reproduction in fruit flies2013In: Age (Omaha), ISSN 0161-9152, E-ISSN 1574-4647, Vol. 35, no 4, p. 1193-1204Article in journal (Refereed)
    Abstract [en]

    For the evolution of life histories, the trade-off between survival and reproduction is fundamental. Because sexes optimize fitness in different ways, this trade-off is expected to be resolved differently by males and females. Consequently, the sexes are predicted to respond differently to changes in resource availability. In fruit flies, research on dietary restriction has focused largely on females maintained in the absence of males, thereby neglecting sexual interactions that affect reproductive behavior of both sexes under more natural conditions. Here, we tested for the interactive effects of diet (40, 60, 100, and 300 % of standard yeast concentrations) and social environment (separate-sex vs. mixed-sex groups) on male and female Drosophila melanogaster life histories. Additionally, we evaluated the essential amino acid methionine as an agent that can uncouple the survival-reproduction trade-off. We show sex differences in the effect of social environment on survival patterns, but not on reproductive fitness. In females, yeast had a positive effect on reproduction and a negative effect on survival. In males, yeast had a negative effect on reproduction and the effect on survival depended on the social environment. Methionine reduced survival, but had no effect on reproduction. Our findings highlight the need to include both sexes and to vary social environments in research programs aimed at lifespan extension and call for further evaluation of the fecundity-restoring effect of methionine.

1 - 49 of 49
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf