Correlated responses to selection on female egg size in male reproductive traits in a butterfly
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Genetic correlations between male and female traits can act as evolutionary constraints and, if involving reproductive traits, potentially influence sexual selection. Artificial selection on egg size in the tropical butterfly Bicyclus anynana has yielded highly divergent lines. Here we report evidence for correlated evolution in male traits. Males from the large-egg selected lines produced significantly heavier spermatophores independent of body size and tended to have more fertile sperm stored in their reproductive tracts than those from the small-egg selected lines. This may be due to an underlying genetic correlation in reproductive effort between the sexes. However, non-fertile sperm number and testis size remained unaffected by selection on egg size. Phenotypic correlations within an unselected population revealed that spermatophore mass and fertile sperm number, but not testis size and non-fertile sperm number, were positively related to male body size, and that larger spermatophores contained more fertile, but not non-fertile sperm. In addition, males provided larger females with bigger spermatophores and more fertile sperm, indicating males may be exercising mate choice during copulation.
KeywordsApyrene sperm Artificial selection Body size Eupyrene sperm Genetic correlation Spermatophore size
We thank David Hosken and John Hunt for discussions and David Hosken for valuable comments on the manuscript. Financial support was provided by the German Research Council (DFG grant no. Fi 846/1-2 and 1-3) to KF, and the Royal Society, the Leverhulme Trust and the European Social Fund to Nina Wedell.
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