title: Benefits of extra-pair mating may depend on environmental conditions-an experimental study in the blue tit (Cyanistes caeruleus).
abstract: Extra-pair mating constitutes a relatively common reproductive strategy in many socially monogamous bird species. This strategy may considerably improve reproductive success of males, but female benefits from extra-pair matings still remain unclear and empirical evidence is scarce. This may be because genetic benefits of extra-pair mating are not always revealed. It is possible that they are shown only in unfavourable environmental conditions and hence problems arise with detecting differences between within- and extra-pair offspring whose performance is measured under favourable conditions. In order to test this prediction, we manipulated environmental conditions by altering brood sizes of blue tits and compared phenotypic characteristics of within- and extra-pair offspring in mixed-paternity broods. We found that extra-pair young exhibited a higher response to phytohemagglutinin in comparison to within-pair young, but this was only observed among nestlings from experimentally enlarged broods. These results indicate that genetic benefits may interact with the environment, and thus benefits of extra-pair mating are likely to become visible only when conditions are relatively unfavourable.
authors.affiliation: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
authors.forename: Aneta
authors.initials: A
authors.lastname: Arct
authors.forename: Szymon M
authors.initials: SM
authors.lastname: Drobniak
authors.forename: Edyta
authors.initials: E
authors.lastname: Podmokła
authors.forename: Lars
authors.initials: L
authors.lastname: Gustafson
authors.forename: Mariusz
authors.initials: M
authors.lastname: Cichoń
keywords: Birds; Cell-mediated immunity; Extra-pair paternity; Indirect benefits