Do females adjust brood sex ratio according to males' genetic structures in a gregarious passerine, the vinous-throated parrotbill Paradoxornis webbianus?

摘要

A growing number of bird species are known to have fine-scale genetic structure during the breeding season, with relatives breeding in close vicinity. Such genetic structure often has fitness consequences for parents, and sex ratio theory predicts that females should respond adaptively when they determine offspring sex. We examined whether or not females allocate offspring sex adaptively in response to the local genetic structures as well as other biotic and abiotic factors in a population of the vinous-throated parrotbill Paradoxornis webbianus, a small passerine with strong flocking habit and various genetic structures among neighbouring males during the breeding season. The average brood sex ratio of hatchlings (secondary sex ratio) did not deviate from parity. In addition, the observed brood sex ratio was independent of the fine-scale genetic structure and other factors including breeding density, clutch size, laying date, parents' quality, and the presence of extrapair paternity. Accordingly, we reject the hypothesis of adaptive sex allocation by female parrotbills in association with local genetic structure and other factors. Instead we conclude that despite the plausible benefits of biased sex allocation, this species determines brood sex ratio via random sex allocation with equal probability of male and female offspring.