Are extra‐pair males different from cuckolded males? A case study and a meta‐analytic examination

Abstract

Traditional models for female extra-pair matings assume that females benefit indirectly from extra-pair mating behaviour. Under these so-called adaptive models, extra-pair males are hypothesized to have more compatible genotypes, larger body size, exaggerated ornaments or to be older than cuckolded males. Alternatively, ('nonadaptive') models that consider female extra-pair matings to be a by-product posit that female extra-pair mating can be maintained even if there is no benefit to females. This could happen if, for example, males gained fitness benefits from extra-pair mating, while female and male extra-pair mating behaviours were genetically correlated. Extra-pair males are also expected to be older and larger if this improves their ability to convince or coerce females to mate. We investigated whether a female's extra-pair mates differed from her cuckolded mate in both genetic and phenotypic traits by analysing data from an insular house sparrow population. We found that extra-pair males were older than cuckolded males, consistent with both models. However, in contrast to the expectations from from adaptive models, extra-pair and cuckolded males were of similar genetic relatedness, and hence expected compatibility, with the female, and had comparable body size and secondary sexual traits. We also updated previous meta-analyses examining differences between extra-pair and cuckolded males. The meta-analytic results matched results from our house sparrow case study. Although we cannot completely exclude indirect benefits for females, nonadaptive models may better explain female extra-pair matings. These neglected alternative models deserve more research attention, and this should improve our understanding of the evolution of mating systems.

Predictably Philandering Females Prompt Poor Paternal Provisioning

“…Thus, the female paired with such a male may gain EPOs while, simultaneously, the male may not provide a high level of paternal care. Extrapair sires are predominantly older males (Wetton et al 1991;Cleasby and Nakagawa 2012;Hsu et al 2015), which could mean that correlated differences in parental investment between males with and without EPP could indirectly be driven by male age. Several studies have shown that older males are better at obtaining EPPs and also invest more into paternal care than younger males (Kempenaers and Sheldon 1997;Houston and McNamara 2002;Velando et al 2006;Hammers et al 2012).…”

“…We sampled DNA from nearly every fledged sparrow caught on Lundy, which we then genotyped at 13 polymorphic microsatellite loci (Schroeder et al 2011a;Hsu et al 2015). The usefulness of these loci for parentage analysis is documented elsewhere (Dawson et al 2012).…”

“…Typically, in each year, 99% of chicks that survived past the age of 2 days were genotyped and assigned paternity (Schroeder et al 2011a). Overall, from 2000 to 2012, we assigned paternity to more than 96% of chicks that were alive as hatchlings (Hsu et al 2015).…”

“…Despite these theories, the empirical evidence for indirect benefits is conflicting (e.g., Møller and Alatalo 1999;Arnqvist and Kirkpatrick 2005;Rosivall et al 2009;Hsu et al 2014;Bowers et al 2015). Meta-analyses have also provided conflicting results for whether females gain fitness benefits from having extrapair offspring (EPO; Akçay and Roughgarden 2007;Arct et al 2015) and even suggest that female infidelity is costly (Hsu et al 2015). To further our understanding of the evolution of female polygamy, it is crucial to understand not only the benefits but also the costs of females producing EPO .…”

“…Distinguishing between these two hypotheses would be informative about whether females pay for infidelity with reduced paternal care and further our understanding of the evolution of mating systems and parental investment. Notably, if the between-male effect hypothesis is supported, then this would reduce the argument for infidelity being costly to females and therefore also reduce the need to identify a counteracting female benefit (Griffith et al 2002;Akçay and Roughgarden 2007; see also Forstmeier 2014;Hsu 2015;Nakagawa et al 2015).…”