爬行动物胚胎发育可塑性在卵胎生进化中发挥着重要作用，卵胎生进化伴随的胚胎低氧可得性是影响胚胎发育及后代表型的潜在驱动力。虽然卵胎生进化起源的冷气候假说和母体操纵假说都认为驱动卵胎生进化的关键环境因子是温度，但均忽视了与温度梯度相关的其他气候因子的影响，因此需要从卵胎生物种的胚胎及新生幼体的生理适应角度，探讨爬行动物卵胎生进化过程中胚胎适应母体输卵管内低氧环境的生理机制。本项目拟以同科不同繁殖模式的爬行动物为研究对象，通过实验操纵新生卵的孵化氧环境，比较不同氧分压下胚胎发育速度、孵化成功率和新生幼体表型的差异；测定、比较不同繁殖模式下新生幼体的呼吸代谢水平差异；实验控制环境温度和氧分压，比较不同繁殖模式下新生幼体的低氧耐受能力。本研究通过探讨低氧条件下爬行动物的胚胎发育可塑性及胚胎适应低氧的生理机制，为卵胎生进化成因的低氧假说提供实验证据。

The developmental plasticity has an important role in the evolutionary transition from oviparity to reprilian viviparity. The reduced availability of oxygen associated with with parity-mode transition is a key factor potentially affecting embryonic development and offspring phenotype. Many hypotheses have been proposed to uncover the selective forces leading to the evolution of viviparity within squamate reptiles. Of these hypotheses, the cold-climate hypothesis and the maternal manipulation hypothesis are most frequently cited. Both hypotheses agree on the idea that viviparity has evolved in squamate reptiles for thermal reasons; that is thermal differentials between the uterus and the nest resulting from maternal thermoregulation are the key to the evolution of viviparity. However, the two hypotheses both ignore the role of other climatic factors that vary along thermal gradients. The hypoxia hypothesis purports that natural selection associated with low oxygen availability may lead to prolonged embryo retention within the female’s body, where placental structures are designed to provide optimal levels of oxygen to allow embryonic development. However, the prolonged egg retention will lead to embryonic development retardation and malformation, because oviparous females cannot meet the dramatically increased oxygen consumption in the late period of embryonic development. Previous studies have shown that embryonic differentiation and growth rates, water uptake, duration of incubation, growth of the chorioallantoic membrane, egg survival and hatchling size are affected negatively by hypoxia, which suggests the hypoxia hypothesis. Here we will use four species pairs of squamate reptiles of which each has one oviparous and one viviparous species of the same family to test the hypothesis. Specifically, we will determine metabolic rates at embryonic and hatchling stages and manipulate oxygen concentration to determine hypoxic tolerance. If the hypothesis is true, then the following three predictions can be expected. First, embryos of viviparous species should have an accelerated blood circulation and heart rate, increased heart volume and elevated number of hemocytes, thus being more likely to meet oxygen demands in the late stages of development. Second, neonates of viviparous species should maintain a lower level of respiratory metabolism, thus being better able to survive the oxygen-limited environment within females, especially at the end of pregnancy. Third, viviparous species should have an elevated hypoxic tolerance, thus being better able to adapt to the hypoxic environment, inside or outside the oviduct. This study aims to explore the physiological constraints and phenotypic plasticity caused by hypoxia, and to uncover the adaptation mechanism that may explain the evolutionary transition from oviparity to viviparity. Data generated from this study will provide experimental evidence for the validation of the hypoxia hypothesis for the evolution of reptilian viviparity.