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Operational sex ratio and density do not affect directional selection on male sexual ornaments and behaviour


Head, M L; Lindholm, A K; Brooks, R (2008). Operational sex ratio and density do not affect directional selection on male sexual ornaments and behaviour. Evolution, 62(1):135-144.

Abstract

Demographic parameters including operational sex ratio (OSR) and population density may influence the opportunity for, and
strength of sexual selection. Traditionally, male-biased OSRs and high population densities have been thought to increase the
opportunity for sexual selection on male sexual traits due to increased male competition for mates. Recent experimental evidence,
however, suggests that male-biased OSRs might reduce the opportunity for sexual selection due to increased sexual coercion
experienced by females. How OSR, density, and any resultant changes in the opportunity for sexual selection actually affect
selection on male sexual traits is unclear. In this study, we independently manipulated OSR and density in the guppy (Poecilia
reticulata) without altering the number of males present. We recorded male and female behavior and used DNA microsatellite
data to assign paternity to offspring and estimate male reproductive success. We then used linear selection analyses to examine
the effects of OSR and density on directional sexual selection on male behavioral and morphological traits.We found that females
were pursued more by males in male-biased treatments, despite no change in individual male behavior. There were no differences
in sexual behavior experienced by females or performed by males in relation to density. Neither OSR nor density significantly
altered the opportunity for sexual selection. Also, Although there was significant multivariate linear selection operating on males,
neither OSR nor density altered the pattern of sexual selection on male traits. Our results suggest that differences in either OSR or
density (independent of the number of males present) are unlikely to alter directional evolutionary change in male sexual traits.

Demographic parameters including operational sex ratio (OSR) and population density may influence the opportunity for, and
strength of sexual selection. Traditionally, male-biased OSRs and high population densities have been thought to increase the
opportunity for sexual selection on male sexual traits due to increased male competition for mates. Recent experimental evidence,
however, suggests that male-biased OSRs might reduce the opportunity for sexual selection due to increased sexual coercion
experienced by females. How OSR, density, and any resultant changes in the opportunity for sexual selection actually affect
selection on male sexual traits is unclear. In this study, we independently manipulated OSR and density in the guppy (Poecilia
reticulata) without altering the number of males present. We recorded male and female behavior and used DNA microsatellite
data to assign paternity to offspring and estimate male reproductive success. We then used linear selection analyses to examine
the effects of OSR and density on directional sexual selection on male behavioral and morphological traits.We found that females
were pursued more by males in male-biased treatments, despite no change in individual male behavior. There were no differences
in sexual behavior experienced by females or performed by males in relation to density. Neither OSR nor density significantly
altered the opportunity for sexual selection. Also, Although there was significant multivariate linear selection operating on males,
neither OSR nor density altered the pattern of sexual selection on male traits. Our results suggest that differences in either OSR or
density (independent of the number of males present) are unlikely to alter directional evolutionary change in male sexual traits.

Citations

31 citations in Web of Science®
36 citations in Scopus®
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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Uncontrolled Keywords:Density, guppies, microsatellite paternity analysis, operational sex ratio, opportunity for sexual selection, selection analysis, sexual coercion
Language:English
Date:2008
Deposited On:11 Feb 2008 12:17
Last Modified:05 Apr 2016 12:15
Publisher:Wiley-Blackwell
ISSN:0014-3820
Publisher DOI:10.1111/j.1558-5646.2007.00277.x
Related URLs:http://www.blackwell-synergy.com/doi/abs/10.1111/j.1558-5646.2007.00277.x

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