School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia.
School of Medical Sciences, University of New South Wales, Sydney, NSW, Australia.
Mol Biol Evol. 2022 Apr 10;39(4). doi: 10.1093/molbev/msac077.
The repeated evolution of the same traits in distantly related groups (convergent evolution) raises a key question in evolutionary biology: do the same genes underpin convergent phenotypes? Here, we explore one such trait, viviparity (live birth), which, qualitative studies suggest, may indeed have evolved via genetic convergence. There are >150 independent origins of live birth in vertebrates, providing a uniquely powerful system to test the mechanisms underpinning convergence in morphology, physiology, and/or gene recruitment during pregnancy. We compared transcriptomic data from eight vertebrates (lizards, mammals, sharks) that gestate embryos within the uterus. Since many previous studies detected qualitative similarities in gene use during independent origins of pregnancy, we expected to find significant overlap in gene use in viviparous taxa. However, we found no more overlap in uterine gene expression associated with viviparity than we would expect by chance alone. Each viviparous lineage exhibits the same core set of uterine physiological functions. Yet, contrary to prevailing assumptions about this trait, we find that none of the same genes are differentially expressed in all viviparous lineages, or even in all viviparous amniote lineages. Therefore, across distantly related vertebrates, different genes have been recruited to support the morphological and physiological changes required for successful pregnancy. We conclude that redundancies in gene function have enabled the repeated evolution of viviparity through recruitment of different genes from genomic "toolboxes", which are uniquely constrained by the ancestries of each lineage.
在亲缘关系较远的群体中重复出现相同特征（趋同进化）提出了进化生物学中的一个关键问题：是否相同的基因支持趋同表型？在这里，我们探讨了一个这样的特征，即胎生（活体分娩），有定性研究表明，这种特征可能确实是通过基因趋同进化而来的。在脊椎动物中有超过 150 个独立的活体分娩起源，为测试形态、生理和/或怀孕期间基因募集的趋同机制提供了一个独特的强大系统。我们比较了来自 8 种脊椎动物（蜥蜴、哺乳动物、鲨鱼）的转录组数据，这些动物在子宫内孕育胚胎。由于之前的许多研究都检测到了怀孕期间基因使用的定性相似性，我们预计在胎生分类群中会发现基因使用的显著重叠。然而，我们发现与胎生相关的子宫基因表达的重叠并没有超出偶然的预期。每个胎生谱系都表现出相同的核心子宫生理功能。然而，与人们对这种特征的普遍假设相反，我们发现并非所有的胎生谱系都有相同的基因差异表达，甚至在所有的胎生羊膜动物谱系中也是如此。因此，在亲缘关系较远的脊椎动物中，不同的基因被招募来支持成功怀孕所需的形态和生理变化。我们得出的结论是，基因功能的冗余使得胎生通过从基因组“工具包”中招募不同的基因得以在亲缘关系较远的物种中重复进化，而这些基因仅受到每个谱系的祖先的独特限制。
