Differential effects of steroid hormones on levels of genetic variance in a wild bird: possible mechanism of maternal-effects x genetic variance interaction?

Abstract

Genetic variation is one of the key concepts in evolutionary biology and an important prerequisite of evolutionary change. Still, we know very little about processes that modulate its levels in wild populations. In particular – we still are to understand why genetic variances often depend on environmental conditions. One of possible environment-sensitive modulators of observed levels of genetic variance are maternal effects. In this study we attempt to experimentally test the hypothesis that maternally-transmitted agents (e.g. hormones) may influence the expression of genetic variance in quantitative traits in the offspring. We manipulated the levels of steroid hormones (testosterone and corticosterone) in eggs laid by blue tits in a wild population. Our experimental setup allowed for full crossing of genetic and rearing effects with the experimental manipulation. We observed, that birds treated with corticosterone exhibited a significant decrease in genetic variance of tarsus length. We also observed less pronounced, marginally significant effects of hormonal administration on the patterns of genetic correlations between traits expressed under varying pre-hatching hormonal conditions. Our study indicates, that maternally transmitted substances such as hormones may have measurable impact on the levels of genetic variance – and hence, on the evolutionary potential of quantitative traits.