Institute for Applied Ecology, University of Canberra, Canberra, ACT, Australia. georges @ aerg.canberra.edu.au
Sex Dev. 2010;4(1-2):7-15. doi: 10.1159/000279441. Epub 2010 Jan 29.
Vertebrates show an astonishing array of sex determining mechanisms, including male and female heterogamety, multiple sex chromosome systems, environmental sex determination, parthenogenesis and hermaphroditism. Sex determination in mammals and birds is extraordinarily conservative compared to that of reptiles, amphibians and fish. In this paper, we explore possible explanations for the diversity of sex determining modes in reptiles, and in particular, address the prevalence of reptilian temperature-dependent sex determination (TSD) and its almost haphazard distribution across the reptile phylogeny. We suggest that reptiles are predisposed to evolving TSD from genotypic sex determination (GSD) by virtue of the uniquely variable thermal environment experienced by their embryos during the critical period in which sex is determined. Explicit mechanisms for canalization of sexual phenotype in the face of high thermal variation during development provide a context for thermolability in sex determination at extremes and the raw material for natural selection to move this thermolability into the developmental mainstream when there is a selective advantage to do so. Release of cryptic variation when canalization is challenged and fails at extremes may accelerate evolutionary transitions between GSD and TSD.
脊椎动物表现出令人惊讶的性别决定机制，包括雄性和雌性异型性、多种性染色体系统、环境性别决定、孤雌生殖和雌雄同体。与爬行动物、两栖动物和鱼类相比，哺乳动物和鸟类的性别决定机制非常保守。在本文中，我们探讨了爬行动物性别决定模式多样性的可能解释，特别是解决了爬行动物中温度依赖性性别决定（TSD）的普遍存在及其在爬行动物系统发育中的几乎随意分布问题。我们认为，由于其胚胎在决定性别时所处的关键时期经历了独特的可变热环境，因此，爬行动物具有从基因型性别决定（GSD）进化为 TSD 的倾向。在发育过程中面对高温度变化时，对性表型进行 canalization 的明确机制为极端温度下性别决定的热敏性提供了背景，并且当这样做具有选择优势时，为自然选择将热敏性推向发育主流提供了原材料。当 canalization 在极端情况下受到挑战和失败时，隐匿变异的释放可能会加速 GSD 和 TSD 之间的进化转变。
