Polyandry in coal tits Parus ater: fitness consequences of putting eggs into multiple genetic baskets

Schmoll T, Schurr FM, Winkel W, Epplen JT, Lubjuhn T. Polyandry in coal tits Parus ater: fitness consequences of putting eggs into multiple genetic baskets. JOURNAL OF EVOLUTIONARY BIOLOGY. 2007;20(3):1115-1125.Females of many species mate with multiple males within a single reproductive cycle. One hypothesis to explain polyandry postulates that females benefit from increasing within-brood genetic diversity. Two mechanisms may render sire genetic diversity beneficial for females, genetic bet-hedging vs. non-bet-hedging. We analysed whether females of the socially monogamous coal tit (Parus ater) benefit via either of these mechanisms when engaging in extra-pair (i.e. polyandrous) mating. To obtain a measure of within-brood genetic diversity as a function of paternal genetic contributions, we calculated a sire diversity index based on the established Shannon-Wiener Index. In 246 broods from two consecutive years, sire genetic diversity had no effect on either the mean or the variance in brood fitness measured as offspring recruitment within 4 years after birth. The hypothesis that benefits of increasing sire diversity contribute to selection for female extra-pair mating behaviour in P. ater was therefore not supported