title: 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.
authors.affiliation: Department of Zoology, University of Otago, Dunedin, New Zealand.
authors.forename: Yu-Hsun
authors.initials: YH
authors.lastname: Hsu
authors.forename: Julia
authors.initials: J
authors.lastname: Schroeder
authors.forename: Isabel
authors.initials: I
authors.lastname: Winney
authors.forename: Terry
authors.initials: T
authors.lastname: Burke
authors.forename: Shinichi
authors.initials: S
authors.lastname: Nakagawa
mesh_terms: D000818:Animals; D005260:Female; D056084:Genetic Fitness; D016014:Linear Models; D008297:Male; D052586:Mating Preference, Animal; D008957:Models, Genetic; D010641:Phenotype; D046370:Sparrows / Q000235:genetics*
keywords: genetic compatibility; genetic constraints; good genes; male manipulation; polyandry; sexual conflict