Female promiscuity unconstrained by male paternity guards: an experiment on bluethroats

It is a well-established fact that many socially monogamous bird species are genetically polygamous due to the frequent occurrence of extra-pair copulations (EPCs). Recent studies have shown that females benefit from performing EPCs, by producing offsprin g of higher reproductive value. In bluethroats (Luscinia s. svecica), females gain genetic benefits from EPCs through an enhancement of offspring immunocompetence. The fitness benefit seems to arise from a higher compatibility between the genomes of the f emale and the extra-pair mate(s). However, despite the potential benefit of producing extra-pair offspring, many females do not. These females might be faithful because their social partner is the most compatible among the ones available to them. Alternat ively, females might be constrained e.g. by the presence of the pair mate and not succeed in obtaining extra-pair offspring even if they try. Here, we will investigate the mechanism by which females select compatible partners and why some females appear t o be faithful, by experimentally removing one potentially inportant constraint on female extra-pair behaviour, namely the presence of the pair male. By combining temporary male detention with paternity analysis and genotyping of spermatozoa on col lected egg membranes, this project will shed new light on female promiscuity in birds.