Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA.
School of Biological Sciences, Illinois State University, Normal, IL 61790, USA.
Integr Comp Biol. 2019 Oct 1;59(4):1081-1088. doi: 10.1093/icb/icz036.
Most organisms experience thermal variability in their environment; however, our understanding of how organisms cope with this variation is under-developed. For example, in organisms with temperature-dependent sex determination (TSD), an inability to predict sex ratios under fluctuating incubation temperatures in the field hinders predictions of how species with TSD will fare in a changing climate. To better understand how sex determination is affected by thermal variation, we incubated Trachemys scripta eggs using a "heat wave" design, where embryos experienced a male-producing temperature of 25 ± 3°C for the majority of development and varying durations at a female-producing temperature of 29.5 ± 3°C during the window of development when sex is determined. We compared the sex ratios from these incubation conditions with a previous data set that utilized a similar heat wave design, but instead incubated eggs at a male-producing temperature of 27 ± 3°C but utilized the same female-producing temperature of 29.5 ± 3°C. We compared the sex ratio reaction norms produced from these two incubation conditions and found that, despite differences in average temperatures, both conditions produced 50:50 sex ratios after ∼8 days of exposure to female-producing conditions. This emphasizes that sex can be determined in just a few days at female-producing conditions and that sex determination is relatively unaffected by temperatures outside of this short window. Further, these data demonstrate the reduced accuracy of the constant temperature equivalent model (the leading method of predicting sex ratios) under thermally variable temperatures. Conceptualizing sex determination as the number of days spent incubating at female-producing conditions rather than an aggregate statistic is supported by the mechanistic underpinnings of TSD, helps to improve sex ratio estimation methods, and has important consequences for predicting how species with TSD will fare in a changing climate.
大多数生物在其环境中都会经历温度变化，但我们对生物如何应对这种变化的理解还很不完善。例如，在温度依赖型性别决定（TSD）的生物中，无法预测在野外波动的孵化温度下的性别比例，这阻碍了对具有 TSD 的物种在气候变化下的表现的预测。为了更好地了解性别决定如何受到热变异性的影响，我们使用“热浪”设计孵化了 Trachemys scripta 卵，其中胚胎在发育的大部分时间内经历产生雄性的温度为 25 ± 3°C，而在性别决定的发育窗口期间，经历产生雌性的温度为 29.5 ± 3°C 的不同持续时间。我们比较了这些孵化条件下的性别比例与之前利用类似热浪设计但在产生雄性的温度为 27 ± 3°C 但利用相同产生雌性的温度为 29.5 ± 3°C 的孵化条件下的数据。我们比较了这两种孵化条件产生的性别比反应规范，发现尽管平均温度存在差异，但在暴露于雌性产生条件下约 8 天后，两种条件都产生了 50:50 的性别比例。这强调了性别可以在雌性产生条件下仅几天内确定，并且性别决定相对不受该短窗口之外的温度影响。此外，这些数据表明，在温度变化的情况下，恒温等效模型（预测性别比例的主要方法）的准确性降低。将性别决定概念化为在雌性产生条件下孵化的天数，而不是综合统计数据，这得到了 TSD 的机制基础的支持，有助于改进性别比例估计方法，并对预测具有 TSD 的物种在气候变化下的表现具有重要意义。
