Incubation temperature and parental identity determine sex in the Australian agamid lizard Ctenophorus pictus

Sex determination in Australian agamid lizards show a complex framework of different mechanisms, varying even among closely related taxa. It is clear that discrete classification of these species as either having genetic (GSD) or environmental sex determination (ESD) does not agree with empirical data. Although many species in this group show temperature-dependent sex determination (TSD), recent evidence suggests additional genetic or epigenetic effects. A proposed model explaining the adaptive significance and evolution of TSD in short-lived agamids predicts that selection will favor temperature-biased sex ratios in species with intense male-male competition. Here we use experimental incubation at (near) constant temperatures to test whether the sex of Australian painted dragons (Ctenophorus pictus) is influenced by temperature, building on previous research yet to have reached an agreement regarding the role of temperature in this species. In the present study, incubation temperature and parental identity affected hatchling sex suggesting that environment and genetics may work in concert to determine sex in this species. Although our results are consistent with TSD, our data cannot rule out a temperature-by-sex effect on egg or hatchling mortality. However, our findings together with the observed differences of sex determination systems in closely related species within this genus may provide novel opportunities to address fundamental questions in the evolution of sex determination systems.

澳大利亚鬣蜥科蜥蜴的性别决定机制呈现出复杂的多元架构，即便在亲缘关系密切的类群之间也存在差异。将这些物种简单划分为仅具备遗传性别决定（genetic sex determination, GSD）或仅具备环境性别决定（environmental sex determination, ESD）的离散类型，显然与实证研究数据不符。尽管该类群中的诸多物种表现出温度依赖型性别决定（temperature-dependent sex determination, TSD），但新近研究证据表明还存在额外的遗传或表观遗传调控效应。有学者提出了一套解释短命鬣蜥科物种TSD适应性意义与演化历程的模型，该模型预测：在雄性间竞争激烈的物种中，自然选择会倾向于偏爱温度偏向性的性别比例。本研究通过（近乎）恒定温度的人工孵化实验，探究澳大利亚彩绘龙（Ctenophorus pictus）的性别是否受温度调控，该研究建立在既往相关研究的基础之上——此前学界尚未就温度在该物种中的作用达成一致意见。本研究中，孵化温度与亲本身份均会影响幼体的性别，这表明环境与遗传因素可能协同作用以决定该物种的性别。尽管我们的研究结果与TSD模式相符，但本研究数据无法排除温度与性别的交互作用对卵或幼体存活率产生影响的可能性。然而，结合本研究的发现与该属内近缘物种间已观测到的性别决定系统差异，本研究或可为解答性别决定系统演化领域的核心问题提供全新的研究契机。