Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, Iowa 50011, USA.
Evolution. 2010 May;64(5):1331-45. doi: 10.1111/j.1558-5646.2009.00916.x. Epub 2009 Dec 4.
Traditional models predict that organisms should allocate to sex based on their condition relative to the condition of their competitors, tracking shifts in mean condition in fluctuating environments, and maintaining an equilibrium sex ratio. In contrast, when individuals are constrained to define their condition absolutely, environmental fluctuations induce fluctuating sex ratios and the evolutionary loss of condition-dependent sex allocation in short-lived organisms. Here, we present a simulation model of temperature-dependent sex determination (TSD) in fluctuating environments that specifically examines the importance of relativity in defining individual condition. When relativity in condition is allowed to evolve, short-lived organisms evolve switchlike TSD reaction norms and define their condition relative to the annual temperature distribution, thus preventing biased cohort sex ratios in extreme years. Long-lived organisms also evolve switchlike reaction norms, but define condition less relatively and experience biased cohort sex ratios. The predictions are supported by data from painted turtles, where TSD reaction norms exhibit pivotal temperatures of sex determination that partially track mean annual temperature. Examining relativity in amniotic vertebrates provides a conceptual framework for multifactorial sex determination and suggests new ways of exploring adaptive hypotheses of sex allocation by focusing on the importance of frequency-dependent selection on sex.
传统模型预测，生物体应根据其相对于竞争者的状况来分配性别，跟踪波动环境中平均状况的变化，并维持平衡的性别比例。相比之下，当个体受到限制，必须绝对定义其状况时，环境波动会导致性别比例波动，并导致短期生物中条件依赖的性别分配的进化丧失。在这里，我们提出了一个在波动环境中温度依赖的性别决定（TSD）的模拟模型，该模型专门研究了在定义个体状况时相对性的重要性。当允许条件的相对性进化时，短期生物会进化出开关式的 TSD 反应规范，并根据年度温度分布来定义其状况，从而防止在极端年份中出现偏向性的群体性别比例。长期生物也会进化出开关式的反应规范，但定义条件的相对性较低，并经历偏向性的群体性别比例。这些预测得到了来自彩绘龟的数据的支持，其中 TSD 反应规范表现出部分跟踪平均年温度的决定性温度。研究羊膜脊椎动物中的相对性为多因素性别决定提供了一个概念框架，并通过关注对性别频率依赖选择的重要性，为探索适应性性别分配假设提供了新的方法。
