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

性类固醇激素在性别决定与温度相关的物种中对抗全球变暖的作用

• 批准号: NE/V001205/1
• 负责人: Justin Travis
• 金额: $ 25.98万
• 依托单位: University of Aberdeen
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV001205%2F1
• 关键词: role; sex; steroid; hormones; against

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.

全球变暖威胁着全球400多种具有温度依赖性性别决定（TSD）的物种，其中包括海龟等许多爬行动物。在发育过程中，温度升高会影响性类固醇激素的转换，只产生一种性别，从而危险地影响种群的性别比例。例如，在世界上第三大红海龟（Caretta Caretta）聚集的佛得角，预计到2100年，3摄氏度的增长将导致99%的雌性新生海龟。如果这些预测是正确的，这个物种将会灭绝，因此我们需要对性别决定有更好的生理理解，从而应用于管理策略。自从海龟在120万年前的化石记录中首次出现以来，它们就一直面临着大规模的气候变化。因此，它们很可能已经进化出了尚未描述的生理机制，以缓冲由温度变化引起的性别比例偏差。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。但是，如果他们这样做，我们预测未来的模型是错误的，因此我们需要重新定向有限的资源，例如重新考虑巢迁移的主要缓解策略。海龟的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，这些激素的浓度源于母体转移到卵子中。虽然这一进化机制可能在启动芳香化酶活性中起关键作用，但温度对其调节及其对性别比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酮和芳香酶。这一催化过程依赖于温度，温度是否影响睾酮浓度、芳香化酶或其催化效率仍有待确定。然而，现在有可能将芳香化酶基因（CYP19A）表达到大肠杆菌中，并实施体外测试，以揭示在不同范围的控制温度和母体启动条件下的性别决定机制。到目前为止，新生海龟的性别和性别比都无法以非致命性的方式确定，这限制了对濒危海龟性别决定的体内生理机制的研究。在最近的一篇预印本中，我们介绍了一种新的方法，该方法基于对血液中睾酮和雌二醇的定量分析，可以在不杀死海龟的情况下确定新生海龟的性别。在这里，我们将利用这种方法来测试温度依赖的母体激素转移到卵子中如何在发育过程中提供由芳香化酶催化的底物。我们假设这种生理机制与孵化温度相结合，形成了调整性别比例的过程，以应对全球气温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。