Journal
MOLECULAR ECOLOGY
Volume 23, Issue 14, Pages 3587-3599Publisher
WILEY
DOI: 10.1111/mec.12826
Keywords
Bateman gradient; body size; genetic mating system; operational sex ratio; opportunity for sexual selection; selection gradient
Funding
- Research Council of Norway
- Oceans and Coastal Areas Program [166596]
- National Science Foundation International Research Fellowship Program grant [OISE-0701086]
- Nordic Marine Academy Mobility Grant
- Royal Swedish Academy of Sciences
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The strength of sexual selection may vary between species, among populations and within populations over time. While there is growing evidence that sexual selection may vary between years, less is known about variation in sexual selection within a season. Here, we investigate within-season variation in sexual selection in male two-spotted gobies (Gobiusculus flavescens). This marine fish experiences a seasonal change in the operational sex ratio from male-to female-biased, resulting in a dramatic decrease in male mating competition over the breeding season. We therefore expected stronger sexual selection on males early in the season. We sampled nests and nest-holding males early and late in the breeding season and used microsatellite markers to determine male mating and reproductive success. We first analysed sexual selection associated with the acquisition of nests by comparing nest-holding males to population samples. Among nest-holders, we calculated the potential strength of sexual selection and selection on phenotypic traits. We found remarkable within-season variation in sexual selection. Selection on male body size related to nest acquisition changed from positive to negative over the season. The opportunity for sexual selection among nest-holders was significantly greater early in the season rather than late in the season, partly due to more unmated males. Overall, our study documents a within-season change in sexual selection that corresponds with a predictable change in the operational sex ratio. We suggest that many species may experience within-season changes in sexual selection and that such dynamics are important for understanding how sexual selection operates in the wild.
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