The role of sex steroid hormones against global warming in species with temperature-dependent sex determination

全球变暖威胁着全世界400多种具有温度依赖性性别决定（TSD）的物种，包括许多爬行动物，如海龟。在发育过程中，温度升高会影响性类固醇激素的转化，使其只产生一种性别，进而使种群的性别比例出现危险的偏差。例如，在拥有世界上第三大赤海龟聚集地的卡波佛得角，预计到2100年，3摄氏度的增加将导致>99%的雌性新生海龟。如果这些预测是正确的，这个物种将灭绝，因此我们需要更好地了解性别决定的生理学知识，以便应用于管理策略。自120 Mya的化石记录中首次出现以来，海龟一直暴露在大规模的气候变化中。因此，它们很可能已经进化出了尚未描述的生理机制，可以缓冲温度变化导致的性别比例偏差。重要的是，这些生理变化可能跟不上当前全球变暖的空前速度。但如果他们这样做了，我们预测未来的模型是错误的，因此我们需要重新分配有限的资源，例如重新考虑主要的缓解策略，即迁移巢穴。在海龟中，性别主要是由催化酶芳香化酶将雄激素（睾酮）转化为雌激素（雌二醇）决定的。起初，这些激素的浓度来源于母体转移到卵子中。虽然这种进化机制可能在启动芳香化酶活性方面发挥关键作用，但其受温度的调节以及随后对性别比例的影响仍然完全未知。在胚胎发生的中途，胚胎本身开始产生睾丸激素和芳香酶。该催化过程是温度依赖性的，并且温度是否影响睾酮、芳香酶的浓度或其催化效率仍有待确定。然而，现在有可能在大肠杆菌中表达芳香化酶基因（CYP 19A）。大肠杆菌，并实施体外试验，以揭示性别决定的机制下，不同范围的控制温度和母亲引发条件。到目前为止，新生儿的性别，因此性别比，不能确定非致命的，限制了在濒危海龟性别决定的体内生理机制的研究。在最近的预印本中，我们介绍了一种新方法，该方法基于从一滴血中定量睾酮和雌二醇来确定海龟新生儿的性别，而无需杀死它们。在这里，我们将利用这种方法来测试如何温度依赖性的母体激素转移到鸡蛋提供底物的芳香化酶在发展过程中催化。我们假设这种生理机制，结合孵化温度，形成了调整性别比例的过程，以对抗全球温度升高导致的种群灭绝风险。我们将利用这些新的见解来设计预测模型，并测试缓解策略的效果，例如在不同温度下将巢迁移到孵化场。

Global warming threatens over 400 species with temperature-dependent sex determination (TSD) worldwide including many reptiles such as sea turtles. During development, increasing temperatures affect the conversion of sex steroid hormones to produce only one sex and, in turn, dangerously bias populations' sex ratios. For example, in Cabo Verde, which holds the third largest aggregation of loggerhead turtles (Caretta caretta) in the world, an increase of 3C is predicted to result in >99% female neonates by 2100. If these predictions are correct this species will go extinct, and therefore we need a better physiological understanding of sex determination that can be applied to management strategies. Since their first appearance in the fossil records 120 Mya, sea turtles have been exposed to large scale climatic changes. It is therefore likely they have evolved still undescribed physiological mechanisms that buffer against sex ratio bias driven by temperature variation. Importantly, these physiological changes may not keep up with the unprecedented pace of current global warming. But if they do, our models that predict the future are wrong, and hence we need to redirect limited resources, for instance in rethinking the main mitigation strategy of nest relocation. In turtles, sex is mainly determined by the conversion of androgens (testosterone) to estrogens (estradiol) by the catalytic enzyme aromatase. At first, concentrations of these hormones originate from maternal transfer into the eggs. While this evolutionary mechanism may play a key role in priming the aromatase activity, its regulation by temperature and subsequent influence on sex ratios remains entirely unknown. Half way through embryogenesis, the embryo itself starts producing testosterone as well as the aromatase enzyme. This catalytic process is temperature-dependent, and whether temperature affects the concentration of testosterone, of aromatase or its catalytic efficiency remains to be established. It is, however, now possible to express the aromatase gene (CYP19A) into E. coli and implement in vitro tests to uncover the mechanisms of sex determination under a diverse range of controlled temperatures and maternal priming conditions. Until now, sex of neonates, and therefore sex ratios, could not be determined non-lethally, limiting the study of the in vivo physiological mechanisms underlying sex determination in endangered sea turtles. In a recent pre-print, we introduced a new method based on the quantification of testosterone and estradiol from a blood drop to determine the sex of turtle neonates without killing them. Here, we will exploit this method to test how temperature-dependent maternal hormone transfer into the eggs provides the substrates to be catalysed by the aromatase during development. We hypothesize this physiological mechanism, combined with incubation temperatures, forms the process that adjusts sex ratio against the risks of population extinction driven by globally increasing temperatures. We will use these new insights to design predictive models and test the effect of mitigation strategies such as nest relocation at different temperatures into hatcheries.