séminaire du pôle évolution du vivant - vendredi 18 novembre 2011

The Paradox of Polyandry

Tommaso Pizzari, University Oxford

vendredi 18 novembre 2011, 9 h 45, amphithéâtre Ampère


Female promiscuity (polyandry) is emerging as an evolutionary mechanism with fundamental and far-reaching consequences. In particular, polyandry prolongs sexual selection after copulation by forcing the gametes of different males to compete for fertilization. However, the way polyandry affects sexual selection remains unclear. The commonly-held view that polyandry increases sexual selection has been challenged by recent work suggesting that polyandry might in fact weaken sexual selection. Resolving this fundamental debate has been difficult because it requires extensive information on mating behaviour as well as paternity for the whole male population. Here, we show that in replicate semi-natural groups of red junglefowl, Gallus gallus, polyandry was the most important source of variation in male reproductive success, confirming its fundamental role in sexual selection. Polyandry decreased the strength of pre-copulatory sexual selection relative to that of post-copulatory sexual selection, and susbtantially weakened the overall intensity of sexual selection. We further illustrate the differential effect of polyandry on pre- and post-copulatory sexual selection by considering the example of male social status, a key determinant of male reproductive success in this species. In groups with low polyandry, status was strongly sexually selected because dominant males mated with more females, while in more polyandrous groups, dominant males could defend a higher share of paternity by mating repeatedly with the same female. These results contribute to resolve the debate of polyandry and sexual selection, by revealing that polyandry dynamically affects pre- and post-copulatory sexual selection differentially.