Abstract
Female polyandry has the potential to prolong sexual selection to continue after copulation allowing males to compete over fertilisation through sperm competition, and females to favour certain males’ sperm. However, post-copulatory mechanisms are notoriously hard to observe, particularly in internal fertilisers.
In the promiscuous fowl, techniques are established enabling investigation of both pre- and post-copulatory mechanisms in both sexes. We have investigated how risk of sperm competition, incest, and also male personality influence sexual selection by shaping pre- and post-copulatory responses.
Shaped by the risk of sperm competition, males sexually harass females. Females respond by sexual resistance and preferentially initiate copulations when males show less sexually interest in them. Further, during copulation, males allocate sperm differentially according to the level of sperm competition they face, but also dependent on their own personality. Males routinely perform ‘aspermic’ copulations, to which females respond by re-mating at a lower propensity. The female response therefore offers an explanation to this seemingly non-adaptive male behaviour. Under the risk of inbreeding, both sexes prefer unrelated individuals as sexual partners, however only females discriminate against kin at a post-copulatory level. Males counter-act this cryptic female choice by inseminating more sperm to their sisters –yet another response that primarily makes sense in the light of the other sex’ reply.
Taken together, both sexes show sex-specific, but also counter-acting responses to the behaviour of other sex, generating a potential for sexual conflict over re-mating and sperm use in this species.
Dr. Hanne Løvlie
EGI, Department of Zoology
University of Oxford