Flexibility in the timing of parturition: the key to viviparity in lizards?

灵活的分娩时间：蜥蜴胎生的关键？胎生蜥蜴的胚胎通常从蛋黄中获得足够的营养。那么，为什么胎盘营养在某些物种中进化，它开辟了什么新的机会？答案可能在于出生时间的灵活性所带来的优势，这是通过在妊娠期间向胚胎补充转移储存脂质而实现的。我们认为，这提供了一个关键的机会，进化的分歧：一些高山物种利用灵活的分娩，其他物种取代可选的胎盘营养与专性转移。我们独特的实验方法，使用两个经过充分研究的胎生石龙子分支，将导致关于胎生演化的新的可检验的假设。

Flexibility in the timing of parturition: the key to viviparity in lizards? Embryos of viviparous lizards usually gain adequate nutrients from yolk. Why then has placentotrophy evolved in some species, and what new opportunities has it opened up? The answer may lie in the advantages gained from flexibility in the timing of birth, made possible by supplementary transfer of storage lipids to embryos during gestation. We argue that this provides a pivotal opportunity for evolutionary divergence: some alpine species exploit flexible parturition; other species replace optional placentotrophy with obligate transfer. Our unique experimental approach, using two well-researched clades of viviparous skinks, will result in new testable hypotheses about the evolution of viviparity.