Cameron Elissa Z, Edwards Amy M, Parsley Laura M
School of Biological Sciences, University of Tasmania, Hobart, Australia.
School of Biological Sciences, University of Canterbury, Christchurch, New Zealand.
Ann N Y Acad Sci. 2017 Feb;1389(1):147-163. doi: 10.1111/nyas.13288. Epub 2016 Nov 18.
Sex allocation theory predicts biased offspring sex ratios in relation to local conditions if they would maximize parental lifetime reproductive return. In mammals, the extent of the birth sex bias is often unpredictable and inconsistent, leading some to question its evolutionary significance. For facultative adjustment of sex ratios to occur, males and females would need to be detectably different from an early developmental stage, but classic sexual dimorphism arises from hormonal influences after gonadal development. Recent advances in our understanding of early, pregonadal sexual dimorphism, however, indicate high levels of dimorphism in gene expression, caused by chromosomal rather than hormonal differences. Here, we discuss how such dimorphism would interact with and link previously hypothesized mechanisms for sex-ratio adjustment. These differences between males and females are sufficient for offspring sex both to be detectable to parents and to provide selectable cues for biasing sex ratios from the earliest stages. We suggest ways in which future research could use the advances in our understanding of sexually dimorphic developmental physiology to test the evolutionary significance of sex allocation in mammals. Such an approach would advance our understanding of sex allocation and could be applied to other taxa.
性分配理论预测，如果当地条件能使亲本一生的繁殖回报最大化，那么后代的性别比例会出现偏差。在哺乳动物中，出生时的性别偏差程度往往不可预测且不一致，这使得一些人质疑其进化意义。为了实现性别比例的适应性调整，雄性和雌性需要在发育早期就表现出可察觉的差异，但经典的性二态性是在性腺发育后由激素影响产生的。然而，我们对早期性腺前性二态性的最新认识表明，基因表达存在高度二态性，这是由染色体差异而非激素差异导致的。在这里，我们讨论这种二态性将如何与先前假设的性别比例调整机制相互作用并建立联系。雄性和雌性之间的这些差异足以使亲本在最早阶段就能检测到后代的性别，并为偏向性别比例提供可选择的线索。我们提出了一些方法，未来的研究可以利用我们对性二态发育生理学的理解进展来测试哺乳动物中性分配的进化意义。这样的方法将增进我们对性分配的理解，并可应用于其他分类群。
