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

与哺乳动物和鸟类不同，许多海龟的胚胎可以发育成任何一种性别，这取决于它们生长的温度。一般来说，在特定的敏感时期，高温会诱导分化为雌性，低温会诱导分化为雄性。本研究的目的是模拟濒危的亚马逊河龟（Podocnmeis expansa）的温度依赖性性别决定。与之前的研究不同，这个新模型将包括实地经历的自然温度波动，以及受控的实验室实验。具体实验如下：1)恒温人工孵育；2) shift- 1和shift- 2实验，将卵子从雌性转移到雄性，反之亦然；3)不同深度和荫蔽条件下的半自然孵化和自然孵化。通过这些实验，pi将确定性别比与温度的关系、对温度敏感的发育时期的时间以及温度波动对性别比的影响。pi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制度下的累积热量，并将这一变量与发育速度和孵化性比联系起来。研究结果将提供一个模型，解释自然界中海龟的性别比例，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.