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A novel test of the phenotype-linked fertility hypothesis reveals independent components of fertility
Section of Ethology, Dept. of Anim. Environ. and Health, Swed. Univ. of Agricultural Sciences, PO Box 234, Skara SE 532 31, Sweden, Evolution and Ecology Group, School of Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
Linköping University, Department of Physics, Chemistry and Biology, Zoology .
Dept. of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom.
2004 (English)In: Philosophical Transactions of the Royal Society of London. Biological Sciences, ISSN 0962-8436, Vol. 271, no 1534, 51-58 p.Article in journal (Refereed) Published
Abstract [en]

The phenotype-linked fertility hypothesis predicts that male sexual ornaments signal fertilizing efficiency and that the coevolution of male ornaments and female preference for such ornaments is driven by female pursuit of fertility benefits. In addition, directional testicular asymmetry frequently observed in birds has been suggested to reflect fertilizing efficiency and to covary with ornament expression. However, the idea of a phenotypic relationship between male ornaments and fertilizing efficiency is often tested in populations where environmental effects mask the underlying genetic associations between ornaments and fertilizing efficiency implied by this idea. Here, we adopt a novel design, which increases genetic diversity through the crossing of two divergent populations while controlling for environmental effects, to test: (i) the phenotypic relationship between male ornaments and both, gonadal (testicular mass) and gametic (sperm quality) components of fertilizing efficiency, and (ii) the extent to which these components are phenotypically integrated in the fowl, Gallus gallus. We show that consistent with theory, the testosterone-dependent expression of a male ornament, the comb, predicted testicular mass. However, despite their functional inter-dependence, testicular mass and sperm quality were not phenotypically integrated. Consistent with this result, males of one parental population invested more in testicular and comb mass, whereas males of the other parental population had higher sperm quality. We found no evidence that directional testicular asymmetry covaried with ornament expression. These results shed new light on the evolutionary relationship between male fertilizing efficiency and ornaments. Although testosterone-dependent ornaments may covary with testicular mass and thus reflect sperm production rate, the lack of phenotypic integration between gonadal and gametic traits reveals that the expression of an ornament is unlikely to reflect the overall fertilizing efficiency of a male.

Place, publisher, year, edition, pages
2004. Vol. 271, no 1534, 51-58 p.
Keyword [en]
Female preference, Gallus, Phenotypic integration, Sexual ornaments, Sperm quality genes, Testicular asymmetry
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-45838DOI: 10.1098/rspb.2003.2577OAI: diva2:266734
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2010-06-28Bibliographically approved

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