It is generally accepted that if a female can improve her offspring’s genetics via extra-pair copulations (EPC), it is by
copulating with extra-pair males whose phenotypes are more superior or whose genes are more compatible to hers than those
of her bonded male. Here, we present a model that puts together uncertainties about the male genetic quality, a postcopulatory
sperm bias in favor of the
... [Show full abstract] better or the more compatible genes, and costs that females pay by being choosy about extra-pair
male quality. The model’s conclusions challenge traditional views of good genes explanations of EPC. When phenotypes give
incomplete information about genotypes, a female choosing a phenotypically superior extra-pair male, may nevertheless find
herself trading good genes of a bonded male for poor genes of an extra-pair male. Such “unfortunate sperm replacements” can
limit the female involvement in EPC even when EPC are otherwise cost-free. The model also shows that even a female bonded
to a phenotypically superior male may benefit by EPC, provided that sperm competition is biased toward sperm with more fit
or more compatible genes. Furthermore, if choosiness is sufficiently costly, a female may even do best by copulating with
a random extra-pair male.
KeywordsExtra-pair copulations–EPC–Female strategies–Costs–Mathematical model–Sperm bias–Old males–Good genes–Compatible genes