Sex allocation and progress in the studies on offspringsex ratio of birds

Abstract

Sex allocation has caught much attention because it is related to life strategies, individual fitness and population dynamics. Birds, a class of vertebrates with extremely high species diversity and abundance, are ideal subjects for the study of sex allocation. Several classic hypotheses have been proposed, such as evolutionary stable strategy and Trivers-Willard hypothesis. Offspring sex ratio is a direct observation of sex allocation, so the factors influencing offspring sex ratio are key to the understanding of sex allocation between males and females. Currently, the field focuses on the research of environmental, parental and offspring factors. However, up to date it is still an open question which factor determines the offspring sex ratio, and much work needs to be done before we know to what extent parents can regulate offspring sexes. In this review, we summarize the progress in the factors influencing the offspring sex ratio, presenting a spectrum of offspring sex ratio studies from the classic hypotheses to empirical studies.