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  • 1.
    Iinatti 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.
    Naresh, Vinesh Shenoi
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Dumea, Miruna
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Mital, Avani
    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.
    Age-specific effects of deletions: implications for aging theories2023In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 77, no 1, p. 254-263Article in journal (Refereed)
    Abstract [en]

    The evolution of aging requires mutations with late-life deleterious effects. Classic theories assume these mutations either have neutral (mutation accumulation) or beneficial (antagonistic pleiotropy) effects early in life, but it is also possible that they start out as mildly harmful and gradually become more deleterious with age. Despite a wealth of studies on the genetics of aging, we still have a poor understanding of how common mutations with age-specific effects are and what aging theory they support. To advance our knowledge on this topic, we measure a set of genomic deletions for their heterozygous effects on juvenile performance, fecundity at 3 ages, and adult survival. Most deletions have age-specific effects, and these are commonly harmful late in life. Many of the deletions assayed here would thus contribute to aging if present in a population. Taking only age-specific fecundity into account, some deletions support antagonistic pleiotropy, but the majority of them better fit a scenario where their negative effects on fecundity become progressively worse with age. Most deletions have a negative effect on juvenile performance, a fact that strengthens the conclusion that deletions primarily contribute to aging through negative effects that amplify with age.

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  • 2.
    Naresh, Vinesh Shenoi
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering. Indian Inst Sci Educ & Res Berhampur, India.
    Mital, Avani
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Iinatti Brengdahl, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Abson, Katie
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Henderson, Gina
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Maxwell, Melody
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Berger, David
    Uppsala Univ, Sweden.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    On aging and age-specific effects of spontaneous mutations2023In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 77, no 8, p. 1780-1790Article in journal (Refereed)
    Abstract [en]

    Evolutionary theory assumes that mutations that cause aging either have beneficial early-life effects that gradually become deleterious with advancing age (antagonistic pleiotropy [AP]) or that they only have deleterious effects at old age (mutation accumulation [MA]). Mechanistically, aging is predicted to result from damage accumulating in the soma. While this scenario is compatible with AP, it is not immediately obvious how damage would accumulate under MA. In a modified version of the MA theory, it has been suggested that mutations with weakly deleterious effects at young age can also contribute to aging, if they generate damage that gradually accumulates with age. Mutations with increasing deleterious effects have recently gained support from theoretical work and studies of large-effect mutations. Here we address if spontaneous mutations also have negative effects that increase with age. We accumulate mutations with early-life effects in Drosophila melanogaster across 27 generations and compare their relative effects on fecundity early and late in life. Our mutation accumulation lines on average have substantially lower early-life fecundity compared to controls. These effects were further maintained throughout life, but they did not increase with age. Our results suggest that most spontaneous mutations do not contribute to damage accumulation and aging.

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  • 3.
    Naresh, Vinesh Shenoi
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Iinatti Brengdahl, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Grace, Jaime L.
    Loyola Univ, IL 60660 USA.
    Eriksson, Björn
    Swedish Univ Agr Sci, Sweden.
    Rydén, Patrik
    Umea Univ, Sweden; Umea Univ, Sweden.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    A genome-wide test for paternal indirect genetic effects on lifespan in Drosophila melanogaster2022In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 289, no 1974, article id 20212707Article in journal (Refereed)
    Abstract [en]

    Exposing sires to various environmental manipulations has demonstrated that paternal effects can be non-trivial also in species where male investment in offspring is almost exclusively limited to sperm. Whether paternal effects also have a genetic component (i.e. paternal indirect genetic effects (PIGEs)) in such species is however largely unknown, primarily because of methodological difficulties separating indirect from direct effects of genes. PIGEs may nevertheless be important since they have the capacity to contribute to evolutionary change. Here we use Drosophila genetics to construct a breeding design that allows testing nearly complete haploid genomes (more than 99%) for PIGEs. Using this technique, we estimate the variance in male lifespan due to PIGEs among four populations and compare this to the total paternal genetic variance (the sum of paternal indirect and direct genetic effects). Our results indicate that a substantial part of the total paternal genetic variance results from PIGEs. A screen of 38 haploid genomes, randomly sampled from a single population, suggests that PIGEs also influence variation in lifespan within populations. Collectively, our results demonstrate that PIGEs may constitute an underappreciated source of phenotypic variation.

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  • 4.
    Malacrino, Antonino
    et al.
    Westfal Wilhelms Univ Munster, Germany; Univ Mediterranea Reggio Calabria, Italy.
    Iinatti Brengdahl, Martin
    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.
    Mital, Avani
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Naresh, Vinesh Shenoi
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Mirabello, Claudio
    Linköping University, Department of Physics, Chemistry and Biology, Bioinformatics. Linköping University, Faculty of Science & Engineering.
    Friberg, Urban
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Ageing desexualizes the Drosophila brain transcriptome2022In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 289, no 1980, article id 20221115Article in journal (Refereed)
    Abstract [en]

    General evolutionary theory predicts that individuals in low condition should invest less in sexual traits compared to individuals in high condition. Whether this positive association between condition and investment also holds between young (high condition) and senesced (low condition) individuals is however less clear, since elevated investment into reproduction may be beneficial when individuals approach the end of their life. To address how investment into sexual traits changes with age, we study genes with sex-biased expression in the brain, the tissue from which sexual behaviours are directed. Across two distinct populations of Drosophila melanogaster, we find that old brains display fewer sex-biased genes, and that expression of both male-biased and female-biased genes converges towards a sexually intermediate phenotype owing to changes in both sexes with age. We further find that sex-biased genes in general show heightened age-dependent expression in comparison to unbiased genes and that age-related changes in the sexual brain transcriptome are commonly larger in males than females. Our results hence show that ageing causes a desexualization of the fruit fly brain transcriptome and that this change mirrors the general prediction that low condition individuals should invest less in sexual phenotypes.

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  • 5. Order onlineBuy this publication >>
    Iinatti Brengdahl, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    The effects of deleterious mutations on ageing2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Ageing is defined as the deterioration of an individual's physiological performance with advancing age, which leads to a decrease in reproduction and/or survival. The question why most organisms age has preoccupied humans for millennia and, over the last decades, resulted in an ever-increasing research effort to understand this phenomenon. The full explanation for why we age has, however, remained elusive. Evolutionary theories of ageing are based on two assumptions, which together inevitably result in organismal ageing, that the strength of selection declines with age and that mutations have age-specific effects. While a declining strength of selection with age naturally follows from external sources of death, the age-specific properties of mutations is a topic we only have a rudimentary understanding of. Established theories of ageing predict that mutations either have a beneficial or neutral effect early in life, and a deleterious effect later in life. New theory suggests that mutations with a small negative effect already early in life can also contribute to the evolution of ageing, a possibility that potentially explains empirical results that have been difficult to reconcile with current theories. Deleterious mutations may also directly or indirectly explain the sex differences in ageing and lifespan that are observed in many species.

    In this thesis, I investigate the age-specificity of deleterious mutations and test if they contribute to sex differences in ageing and lifespan. In paper I and II, I investigate the age-specificity of a set of supposedly deleterious mutations, by estimating their effect on fecundity in young, middle-aged and moderately old Drosophila melanogaster females. The majority of tested mutations show age-specific effects, with a detrimental effect that gradually increases with advancing age. These results thus support that mutations expressing a small negative effect already at an early age also can contribute to the evolution of ageing.

    In paper III, I manipulate the expression of autosomal deleterious mutations in D. melanogaster through inbreeding, and test if this has different effects on male and female ageing as predicted if sexual selection has shaped sex differences in ageing through condition-dependent investment in current reproduction. I find a sex difference in ageing in high condition, but not in low condition flies, suggesting that sexual selection indeed has shaped how resources are allocated between reproduction and somatic maintenance in relation to condition. I did not find a corresponding response for lifespan.

    In paper IV, I investigate if sex differences in lifespan are partly explained by the unconditional expression of recessive deleterious mutations on the single X-chromosome in males (the Unguarded X hypothesis). I test this hypothesis by forcing D. melanogaster females to express recessive mutations on the X-chromosome to the same extent as males do and assess their effect on female lifespan. This direct test did not show the expected reduction in female lifespan and thus fails to support the Unguarded X hypothesis as a major explanation of sex differences in lifespan.

    List of papers
    1. Deleterious mutations show increasing negative effects with age in Drosophila melanogaster
    Open this publication in new window or tab >>Deleterious mutations show increasing negative effects with age in Drosophila melanogaster
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    2020 (English)In: BMC Biology, E-ISSN 1741-7007, Vol. 18, no 1, article id 128Article in journal (Refereed) Published
    Abstract [en]

    Background In order for aging to evolve in response to a declining strength of selection with age, a genetic architecture that allows for mutations with age-specific effects on organismal performance is required. Our understanding of how selective effects of individual mutations are distributed across ages is however poor. Established evolutionary theories assume that mutations causing aging have negative late-life effects, coupled to either positive or neutral effects early in life. New theory now suggests evolution of aging may also result from deleterious mutations with increasing negative effects with age, a possibility that has not yet been empirically explored. Results To directly test how the effects of deleterious mutations are distributed across ages, we separately measure age-specific effects on fecundity for each of 20 mutations inDrosophila melanogaster. We find that deleterious mutations in general have a negative effect that increases with age and that the rate of increase depends on how deleterious a mutation is early in life. Conclusions Our findings suggest that aging does not exclusively depend on genetic variants assumed by the established evolutionary theories of aging. Instead, aging can result from deleterious mutations with negative effects that amplify with age. If increasing negative effect with age is a general property of deleterious mutations, the proportion of mutations with the capacity to contribute towards aging may be considerably larger than previously believed.

    Place, publisher, year, edition, pages
    BMC, 2020
    Keywords
    Aging; Deleterious mutations; Drosophila melanogaster
    National Category
    Evolutionary Biology
    Identifiers
    urn:nbn:se:liu:diva-170986 (URN)10.1186/s12915-020-00858-5 (DOI)000576921200001 ()32993647 (PubMedID)
    Note

    Funding Agencies|Lars Hierta Memorial Foundation; Royal Physiographic Society in Lund; Olle Engkvist Stiftelse; Swedish Research CouncilSwedish Research Council; Linkoping University

    Available from: 2020-11-01 Created: 2020-11-01 Last updated: 2024-01-17
    2. Age-specific effects of deletions: implications for aging theories
    Open this publication in new window or tab >>Age-specific effects of deletions: implications for aging theories
    Show others...
    2023 (English)In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 77, no 1, p. 254-263Article in journal (Refereed) Published
    Abstract [en]

    The evolution of aging requires mutations with late-life deleterious effects. Classic theories assume these mutations either have neutral (mutation accumulation) or beneficial (antagonistic pleiotropy) effects early in life, but it is also possible that they start out as mildly harmful and gradually become more deleterious with age. Despite a wealth of studies on the genetics of aging, we still have a poor understanding of how common mutations with age-specific effects are and what aging theory they support. To advance our knowledge on this topic, we measure a set of genomic deletions for their heterozygous effects on juvenile performance, fecundity at 3 ages, and adult survival. Most deletions have age-specific effects, and these are commonly harmful late in life. Many of the deletions assayed here would thus contribute to aging if present in a population. Taking only age-specific fecundity into account, some deletions support antagonistic pleiotropy, but the majority of them better fit a scenario where their negative effects on fecundity become progressively worse with age. Most deletions have a negative effect on juvenile performance, a fact that strengthens the conclusion that deletions primarily contribute to aging through negative effects that amplify with age.

    Place, publisher, year, edition, pages
    OXFORD UNIV PRESS, 2023
    Keywords
    aging; age-specific effects; deletions; Drosophila melanogaster; mutations; positive pleiotropy
    National Category
    Evolutionary Biology
    Identifiers
    urn:nbn:se:liu:diva-196937 (URN)10.1093/evolut/qpac027 (DOI)001021686300019 ()36622771 (PubMedID)
    Available from: 2023-08-29 Created: 2023-08-29 Last updated: 2024-01-22
    3. Genetic Quality Affects the Rate of Male and Female Reproductive Aging Differently in Drosophila melanogaster
    Open this publication in new window or tab >>Genetic Quality Affects the Rate of Male and Female Reproductive Aging Differently in Drosophila melanogaster
    Show others...
    2018 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 192, no 6, p. 761-772Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    University of Chicago Press, 2018
    Keywords
    aging; condition; Drosophila melanogaster; genetic quality; sex differences; sexual selection
    National Category
    Evolutionary Biology
    Identifiers
    urn:nbn:se:liu:diva-153151 (URN)10.1086/700117 (DOI)000450454800010 ()30444654 (PubMedID)2-s2.0-85055256416 (Scopus ID)
    Note

    Funding Agencies|Helge Ax:son Johnsons stiftelse; Royal Physiographic Society in Lund; Swedish Research Council; Lawski Foundation

    Available from: 2018-12-01 Created: 2018-12-01 Last updated: 2023-10-25Bibliographically approved
    4. Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis
    Open this publication in new window or tab >>Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis
    2018 (English)In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 72, no 3, p. 568-577Article in journal (Refereed) Published
    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.

    Place, publisher, year, edition, pages
    WILEY, 2018
    Keywords
    Ageing; Drosophila; life span; sex differences; unguarded X; X chromosome
    National Category
    Evolutionary Biology
    Identifiers
    urn:nbn:se:liu:diva-147130 (URN)10.1111/evo.13434 (DOI)000427676800011 ()29430636 (PubMedID)
    Note

    Funding Agencies|Royal Physiographic Society in Lund; Swedish Research Council; Helge Ax:son Johnsons stiftelse

    Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2023-10-25
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  • 6.
    Iinatti 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.
    Elias, Phoebe
    Linköping University, Department of Physics, Chemistry and Biology, Biology. Linköping University, Faculty of Science & Engineering.
    Thompson, Josephine
    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.
    Deleterious mutations show increasing negative effects with age in Drosophila melanogaster2020In: BMC Biology, E-ISSN 1741-7007, Vol. 18, no 1, article id 128Article in journal (Refereed)
    Abstract [en]

    Background In order for aging to evolve in response to a declining strength of selection with age, a genetic architecture that allows for mutations with age-specific effects on organismal performance is required. Our understanding of how selective effects of individual mutations are distributed across ages is however poor. Established evolutionary theories assume that mutations causing aging have negative late-life effects, coupled to either positive or neutral effects early in life. New theory now suggests evolution of aging may also result from deleterious mutations with increasing negative effects with age, a possibility that has not yet been empirically explored. Results To directly test how the effects of deleterious mutations are distributed across ages, we separately measure age-specific effects on fecundity for each of 20 mutations inDrosophila melanogaster. We find that deleterious mutations in general have a negative effect that increases with age and that the rate of increase depends on how deleterious a mutation is early in life. Conclusions Our findings suggest that aging does not exclusively depend on genetic variants assumed by the established evolutionary theories of aging. Instead, aging can result from deleterious mutations with negative effects that amplify with age. If increasing negative effect with age is a general property of deleterious mutations, the proportion of mutations with the capacity to contribute towards aging may be considerably larger than previously believed.

    Download full text (pdf)
    fulltext
  • 7.
    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.

  • 8.
    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.

    Download full text (pdf)
    fulltext
  • 9.
    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.

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