Dissertation Research: Temperature Dependent Sex Determination in the Giant River Turtle Podocnemis Expansa from Colombian Amazonia

Janson 9800679与哺乳动物和鸟类不同，许多海龟物种的胚胎可以发育成两性，这取决于它们生长的温度。一般来说，在特定的敏感期，高温会诱导分化为雌性，而低温会诱导雄性分化。这项建议的目的是模拟濒临灭绝的亚马逊巨型河龟Podocnmeis expansa的性别决定随温度的变化。与以前的努力不同，这个新模型将包括野外经历的自然温度波动，以及受控的实验室实验。将进行以下具体实验：1)恒温人工孵化；2)移一和移两次实验，即卵从雌性转移到雄性产生温度，反之亦然；3)不同深度和遮荫条件下的半自然孵化和自然孵化。通过这些实验，PI将确定性别比例与温度的关系，发育的温度敏感期的时间，以及温度波动对性别比例的影响。采购经理人指数将提出，所有这些关系背后的单一变量是敏感期结束时积累的热量。PI将测量不同实验和自然孵化条件下的累积热量，并将这个变量与发育速度和幼体性别比联系起来。这些结果应该提供了一个模型，解释了海龟在自然界中的性别比例，并将有助于设计这种濒危研究物种的管理计划。

Janson 9800679 Unlike mammals and birds, embryos of many turtle species can develop into either sex, depending on the temperature at which they are raised. As a rough rule, high temperatures during a particular sensitive period induce differentiation into females and low temperatures induce males. The purpose of this proposal is to model temperature-dependent sex determination of the endangered Amazonian Giant River Turtle, Podocnmeis expansa. Unlike previous efforts, this new model will include natural fluctuations of temperature as experienced in the field, as well as controlled laboratory experiments. The following specific experiments will be conducted: 1) Artificial incubation at constant temperatures; 2) Shift-one and shift-twice experiments, where eggs are transferred from female to male-producing temperatures and vice versa; 3) Seminatural incubation at different depths and shade conditions, and natural incubation. With these experiments the PIs will determine the relationship of sex ratios to temperature, the timing of the temperature-sensitive period of development, and the effects of fluctuating temperatures on sex ratios. The PIs will propose that the single variable underlying all these relationships is the amount of heat accumulated by the end of the sensitive period. The PIs will measure accumulated heat under different experimental and natural incubation regimes and relate this variable to rate of development and hatchling sex ratios. The results should provide a model that explains sex-ratios in nature for turtles in general, and will be useful in designing management plans for this endangered study species.