Variance in within-pair reproductive success drives the opportunity for sexual selection annually and over the lifetimes of males in a multi-brooded songbird

In pair-bonding species, male reproductive success consists of "within-pair" offspring produced with their socially-paired mate(s), and "extra-pair" offspring produced with additional females throughout the population. Both reproductive pathways offer distinct opportunities for sexual selection to operate in wild populations, as each are composed of sub-components of mate attraction, female fecundity, and paternity allocation. Identifying key sources of variance and covariance among these components is a crucial step towards understanding the reproductive strategies that males use to maximize fitness both annually and over their lifetimes. We use 16 years of complete reproductive data from a population of black-throated blue warblers (Setophaga caerulescens) to decompose variance in male annual and lifetime reproductive success and thereby identify if the opportunity for sexual selection acts consistently over the lifetimes of individual males and what reproductive strategies likely favor maximum lifetime fitness. The majority of variance in male reproduction was attributable to within-pair sources of variance, but the specific effects of individual components of variance differed annually versus over the lifetimes of individual males. Positive lifetime covariance between within-pair and extra-pair success indicates that males able to maximize within-pair success likely achieve higher overall lifetime fitness via both the within-pair and extra-pair reproductive pathways.