卵胎生由卵生物种逐渐延长胚胎体内发育时间进化产生的繁殖模式，有母体死亡率高、生育力或繁殖输出低、后代遗传多样性低等选择劣势。卵胎生劣势补偿机制的关键科学问题是：卵胎生物种是否相对增大母体腹腔空间提高生育力或繁殖输出？是否相对提高胚胎代谢率缩短孕期降低母体捕食风险？是否增加同窝不同父权后代比例提高后代遗传多样性？已知卵胎生蛇比相同大小的卵生蛇产更多、更大的后代，但两者腹腔空间无异，故蛇类中须检验的假设是：1、卵胎生蛇应有较高的胚胎代谢率以缩短孕期降低母体捕食风险；2、卵胎生蛇应有较高的同窝不同父权后代比例以提高后代遗传多样性。申请人拟用3组、每组2种同属或同亚科繁殖模式不同但同域分布的蛇为材料，检验假设1和2。申请人将测定实验室现有的3科、14种其它蛇的后代父权，通过比较不同繁殖模式蛇的同窝不同父权比例检验假设2的普适性。从生理和后代遗传多样性角度探讨爬行动物卵胎生劣势补偿机制为原创性工作。

Evolving from oviparity through gradual increases in the length of intrauterine development, viviparity offers pervasive benefits by lowering embryonic mortality, accelerating developmental rate, optimizing the phenotype of offspring, freeing females from having to find egg-laying sites, and providing the mother the chance to select the sex of her offspring in species with temperature-dependent sex determination, but it entails several costs of which the most important three are decreased fecundity or reproductive output, increased maternal mortality, and reduced genetic diversity among offspring as a consequence of reduced matings or clutches. This raises the question of whether viviparous females compensate for the costs of viviparity by increasing the amount of space available to hold eggs, by accelerating the rate of embryonic development to shorten gestation length, and/or by increasing the frequency of multiple paternity. To answer this question, one virtually needs to test three hypotheses. First, body plans should differ between oviparous and viviparous females, and in particular, selection should favor the evolution of a larger abdomen size (and thus, a larger body-volume) in viviparous females. Second, the rate of embryonic development should be higher in viviparous species, as the selective advantage accruing from reduced gestation length can be translated into enhanced maternal fitness in viviparous species because prolonged retention of eggs and impaired locomotor capacity during prenancy increase predation risks. Third, the frequency of multiple paternity should be higher in viviparous species, as the selective advantage accruing from increased multiple paternity can be translated into increased genetic diversity among offspring. Evidence from snakes has showed that viviparous females do compensate for reduced fecundity or reproductive output by producing more and larger offspring in single reproductive episodes than do oviparous females of the same body size, but they do so not by increasing the relative size of body-volume. Thus, for this group of animals the focus should be laid on the latter two hypotheses that have never been tested in any animal taxa. We will use three pairs of snakes of which each includes two coexisting species with different reproductive modes to test these two hypotheses by comparing heart and metabolic rates of embryos, offspring performance and multiple paternity between oviparous and viviparous species. We will also examine the frequency of multiple paternity in another 14 snakes using samples (hatchlings and their mothers) collected over the past decade to test whether the third hypothesis (the second hypothesis that will be tested in this study) mentioned above is generalisable to snakes. Our study is the first to address the question of whether reptiles can compensate for selective disadvantages of viviparity by modifying the rate of embryonic development and the frequency of multiple paternity.