Benefits Of Extrapair Mating Research Articles

Benefits of extra-pair mating may depend on environmental conditions—an experimental study in the blue tit (Cyanistes caeruleus)

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.

Female Red-backed Fairy-Wrens (Malurus melanocephalus) do not appear to pay a cost for high rates of promiscuity

ABSTRACT. Males of monogamous species are expected to increase their overall fitness by engaging in extrapair copulations, but the fitness implications of this behavior for females are somewhat less clear. Numerous studies have examined the potential benefits of extrapair mating to females, but the costs of extrapair mating, which may be substantial, are less well studied. Quantifying these costs is critical to understanding the evolution of extrapair mating behavior in females. We examined the costs of extrapair paternity to female Red-backed Fairy-wrens (Malurus melanocephalus) using an 8-year data set that allowed us to examine both short-term and long-term costs. The variability of individual extrapair mating behavior in female Red-backed Fairy-wrens allowed us to compare the parental care, fecundity, and apparent survival of faithful and promiscuous females. We found no effect of the presence of extrapair offspring on the rate at which males provisioned broods. We also found that promiscuous and fait...

Immunocompetence of nestling great tits in relation to rearing environment and parentage

Theoretical models of host–parasite coevolution assume a partially genetic basis to the variability in susceptibility to parasites among hosts, for instance as a result of genetic variation in immune function. However, few empirical data exist for free–living vertebrate hosts to support this presumption. In a cross–fostering experiment with nestling great tits, by comparing nestlings of the same origin we investigated (i) the variance in host resistance against an ectoparasite due to a common genetic origin, (ii) the effect of ectoparasite infestation on cell–mediated immunity and (iii) the variance in cell–mediated immunity due to a common genetic origin. Ectoparasitic hen fleas can impair the growth of nestling great tits and nestling growth was therefore taken as a measure of host susceptibility. A common origin did not account for a significant part of the variation in host susceptibility to fleas. There was no significant overall effect of fleas on nestling growth or cell–mediated immunity, as assessed by a cutaneous hypersensitivity response. A common rearing environment explained a significant part of the variation in cell–mediated immunity among nestlings, mainly through its effect on nestling body mass. The variation in cell–mediated immunity was also related to a common origin. However, the origin–related variation in body mass did not account for the origin–related differences in cell–mediated immunity. The results of the present study thus suggest heritable variation in cell–mediated immunity among nestling great tits.