Sex-specific fitness landscapes in the evolution of egg-laying vs live-birth

从卵生（oviparity）到活产（viviparity）的进化被认为是生物学上伟大而反复的转变之一。在外部发育和孵化的卵生和产卵与生下发育完全的幼崽有很大的不同。不仅涉及到繁殖机制，而且还涉及到产卵和生育物种之间的生态和生活史策略的不同。尽管这是一个非常复杂的进化步骤，但羊膜动物已经进化了很多次：哺乳动物早期有一次，爬行动物有一百多次。虽然整个世系固定在一种或另一种状态，但显然只有具有生殖能力的成年雌性表现出卵生或胎生，即产卵或分娩。然而，根据进化理论，在某种程度上，我们期望种群中的所有个体都经历介于两种可选择的和不同的适应状态之间的中间阶段的后果，例如产卵和生育。我们可以预测——但从未测试过——两性对卵生和胎生的生命历史成本和收益的反应可能不同，这可能对进化产生巨大影响。如果我们想要推断出是什么生态条件导致了生殖模式的变化，那么通过案例研究来精细地理清生养的进化和有机体生物学，包括中间阶段，是至关重要的。我们提出的项目是高度跨学科的，因为它涵盖了生殖生物学，生理学，基因组学和进化理论。这是一种“蓝天”探索科学，它是由对自然界动物多样性及其起源的强烈好奇心所驱动的。这项研究的结果将为我们理解生殖模式进化打开新的大门，并推动未来跨生物系统的研究。虽然哺乳动物似乎与蜥蜴相距甚远，但事实上，我们已经证明，从哺乳动物到爬行动物，在生育方面有着很深的共同基因工具包。因此，我们在蜥蜴身上研究的基因和进化力量也在包括人类在内的许多动物物种中得到了呼应。

The evolution of live-birth (viviparity) from egg-laying (oviparity) is regarded as one of biology's great and repeated transitions. Making and laying eggs, which develop and hatch externally is very different from giving birth to fully developed young. Not only the machinery of reproduction is involved, but also an assortment of ecological and life history strategies differ between egg-laying and live-bearing species. Even though it is a very complex evolutionary step, live-bearing has evolved many times in amniotes: once early in mammals and more than one hundred times in reptiles.While entire lineages fix in one state or the other, obviously only the reproductive adult females express oviparity or viviparity, i.e. lay eggs or give birth. However according to evolutionary theory, to some extent we expect all individuals in a population experience the consequences of being at intermediate phases that lie between two alternative and distinct adaptive states, such as egg-laying and live-bearing. We can predict - but have never tested - that sexes might respond differently to the life-history costs and benefits of being oviparous or viviparous, with potentially dramatic consequences for evolution. Case studies to finely disentangle the evolutionary and organismal biology of live-bearing, including intermediate phases, are vital if we are ever to infer what ecological conditions drive changes in reproductive mode. Our proposed project is highly interdisciplinary as it spans reproductive biology, physiology, genomics, and evolutionary theory. It is "blue-skies" discovery science, which is driven by deep curiosity about the animal diversity of the natural world and how it arose. Outcomes from this study will open new doors in our understanding of reproductive mode evolution and propel future research across biological systems. While mammals might seem far removed from lizards, in fact we have shown that there are deep shared genetic toolkits of live-bearing from mammals to reptiles. Consequently the genes and evolutionary forces we study in lizards also echo across many animal species, including humans.