The contribution of extra-pair paternity to the variation in lifetime and age-specific male reproductive success in a socially monogamous species

In socially monogamous species, extra-pair paternity (EPP) is predicted to increase variance in male reproductive success beyond that resulting from genetic monogamy, thus increasing the ‘opportunity for selection’ (maximum strength of selection that can act on a trait). This prediction is challenging to investigate in wild populations because lifetime reproduction data are often incomplete. Moreover, age-specific variances in reproductive success have been rarely quantified. We analysed 21 years of near-complete social and genetic reproduction data from an insular population of Seychelles warblers (Acrocephalus sechellensis). We quantified the contribution of EPP to lifetime and age-specific opportunities for selection in males. We also compared the variance in male genetic reproductive success (RS) vs. social (‘apparent’) reproductive success (RSap) to assess if EPP increased the opportunity for selection over that resulting from genetic monogamy. EPP contributed substantially to the ...