Long-term fitness consequences of high yolk androgen levels: sons pay the costs

1. Early growth conditions, for example hormonal environment during embryonic development, may have long-lasting effects on behaviour and phenotype, with subsequent fitness consequences. Yolk androgens have been shown to affect various offspring traits in the short-term, but fitness consequences for either offspring or parents, a prerequisite for studying the adaptiveness of this maternal effect, are poorly known in the wild. 2. We experimentally elevated yolk androgen levels of whole clutches in a wild population of collared flycatchers (Ficedula albicollis) and investigated the long-term effects of yolk androgens on offspring local recruitment, parental return rate, and timing and success of breeding in both parents and offspring in the breeding season(s) following the manipulation. 3. Yolk androgen elevation lowered the local recruitment rate of male, but not female offspring, but had no effect on any breeding parameters of offspring of either sex. Furthermore, yolk androgen elevation of the clutch had no effect on the return rate or any breeding parameters of the parents. 4. Our results indicate that high yolk androgen levels may impose a potential direct fitness cost for male offspring, but no long-lasting additional indirect fitness costs for parents (direct costs of transferring androgens to eggs not considered). Such a sex-specific cost on offspring could constrain yolk androgen deposition and select for sex-specific deposition mechanisms. 5. As yolk androgen levels in this population are heritable, our results on long-term fitness effect of yolk androgens support the idea that hormone-mediated maternal effects may evolve under selection and thereby affect evolutionary processes.