Abstract

It is widely hypothesized that the evolution of female extra-pair reproduction in socially monogamous species reflects indirect genetic benefits to females. However, a critical prediction of this hypothesis, that extra-pair young (EPY) are fitter than within-pair young (WPY), has rarely been rigorously tested. We used 18 years of data from free-living song sparrows, Melospiza melodia, to test whether survival through major life-history stages differed between EPY and WPY maternal half-siblings. On average, survival of hatched chicks to independence from parental care and recruitment, and their total lifespan, did not differ significantly between EPY and WPY. However, EPY consistently tended to be less likely to survive, and recruited EPY survived for significantly fewer years than recruited WPY. Furthermore, the survival difference between EPY and WPY was sex-specific; female EPY were less likely to survive to independence and recruitment and lived fewer years than female WPY, whereas male EPY were similarly or slightly more likely to survive and to live more years than male WPY. These data indicate that extra-pair paternity may impose an indirect cost on females via their female offspring and that sex-specific genetic, environmental or maternal effects may shape extra-pair reproduction.

Highlights

  • Extra-pair mating, and multiple mating by a female within one reproductive cycle more generally, occurs in a wide range of organisms [1,2]

  • We used comprehensive data from a resident population of song sparrows with high natal and breeding philopatry to test whether survival through major life-history stages differed between extra-pair and within-pair maternal half-siblings, and whether these effects depended on offspring sex or natal season

  • Indirect genetic benefits are often suggested to be one main force driving female extra-pair reproduction, some previous studies found that extra-pair young (EPY) tend to have lower survival than within-pair young (WPY) [5]

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Summary

Introduction

Extra-pair mating, and multiple mating by a female within one reproductive cycle more generally, occurs in a wide range of organisms [1,2]. We tested whether differential survival of EPY versus WPY through these life-history stages differed between males and females or early and late season broods and showed differential sex- or environment-specific effects.

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