Data from: Seasonal shifts in sex ratios are mediated by maternal effects and fluctuating incubation temperatures

Sex-specific maternal effects can be adaptive sources of phenotypic plasticity. Reptiles with temperature-dependent sex determination (TSD) are a powerful system to investigate such maternal effects because offspring phenotype, including sex, can be sensitive to maternal influences such as oestrogens and incubation temperatures. In red-eared slider turtles (Trachemys scripta), concentrations of maternally derived oestrogens and incubation temperatures increase across the nesting season; we wanted to determine if sex ratios shift in a seasonally concordant manner, creating the potential for sex-specific maternal effects, and to define the sex ratio reaction norms under fluctuating temperatures across the nesting season. Eggs from early and late season clutches were incubated under a range of thermally fluctuating temperatures, maternally derived oestradiol concentrations were quantified via radioimmunoassay, and hatchling sex was identified. We found that late-season eggs had higher maternal oestrogen concentrations and were more likely to produce female hatchlings. The sex ratio reaction norm curves systematically varied with season, such that with even a slight increase in temperature (0·5 °C), late-season eggs produced up to 49% more females than early-season eggs. We found a seasonal shift in sex ratios which creates the potential for sex-specific phenotypic matches across the nesting season driven by maternal effects. We also describe, for the first time, systematic variation in the sex ratio reaction norm curve within a single population in a species with TSD.性别特异性母体效应可作为表型可塑性的适应性来源。具有温度依赖型性别决定（temperature-dependent sex determination, TSD）的爬行动物是研究此类母体效应的理想模型体系，因为包括性别在内的后代表型会受到雌激素、孵化温度等母体因素的调控。在红耳滑龟（Trachemys scripta）中，母体源性雌激素浓度与孵化温度均会随筑巢季推移而升高。本研究旨在探究性别比例是否会随季节呈现同步变化，从而产生性别特异性母体效应的潜在可能，并明确筑巢季内波动温度条件下的性别比例反应规范。研究人员采集了筑巢季早期与晚期的龟卵，在一系列热波动温度条件下进行孵化；通过放射免疫分析法定量检测母体源性雌二醇浓度，并鉴定孵化幼龟的性别。研究发现，筑巢晚期的龟卵母体雌激素浓度更高，且更易孵化出雌性幼龟。性别比例反应规范曲线随季节呈现系统性变化：即使温度仅小幅升高0.5℃，筑巢晚期龟卵产生的雌性个体比例较早期龟卵最高可提升49%。本研究证实了筑巢季内性别比例的季节性变化，这为母体效应驱动下的跨季节性别特异性表型匹配提供了潜在可能。此外，本研究首次在具有TSD的物种种群中，报道了单一种群内性别比例反应规范曲线的系统性变异。