Werner Jan, Griebeler Eva Maria
Institute of Organismic and Molecular Evolution, Evolutionary Ecology, Johannes Gutenberg-Universität Mainz, P.O. Box 3980, 55099, Mainz, Germany.
Naturwissenschaften. 2017 Oct 11;104(11-12):90. doi: 10.1007/s00114-017-1513-1.
Endothermy and its evolution are still an unresolved issue. Here, we present a model which transforms an ectothermic amniote (ancestor) into a derived amniote (descendant) showing many characteristics seen in extant endothermic birds and mammals. Consistent with the fossil record within the ancestral lineages of birds and mammals, the model assumes that mutations in genes which get active during ontogeny and affect body growth resulted in a reduced asymptotic body size and an early growth stop of the descendant. We show that such a postulated early growth stop in the descendant simultaneously increases the growth rate and metabolic rate, and also changes six life history traits (offspring mass, annual clutch/litter mass, number of offspring per year, age and mass at which sexual maturity is reached, age at which the individual is fully grown) of the descendant compared to a similar-sized ancestor. All these changes coincide with known differences between recent ectothermic and endothermic amniotes. We also elaborate many other differences and similarities in biological characteristics supporting the early growth stop. An early stop in growth during ontogeny thus could have played a key role in the evolution of endothermy within the reptilia and therapsids. It generated variability in characteristics of ancestral ectotherms, which was subject to natural selection in the past and resulted in many adaptations linked to endothermy in today's birds and mammals.
恒温性及其进化仍是一个未解决的问题。在此，我们提出一个模型，该模型将变温羊膜动物（祖先）转变为衍生羊膜动物（后代），后者展现出许多现存恒温鸟类和哺乳动物所具有的特征。与鸟类和哺乳动物祖先谱系中的化石记录一致，该模型假设在个体发育过程中活跃且影响身体生长的基因发生突变，导致后代的渐近体型减小和生长提前停止。我们表明，后代中这种假定的生长提前停止同时提高了生长速率和代谢速率，并且与体型相似的祖先相比，还改变了后代的六个生活史特征（后代质量、每年窝卵数/产仔数、每年后代数量、达到性成熟的年龄和体重、个体完全成熟的年龄）。所有这些变化都与近期变温羊膜动物和恒温羊膜动物之间已知的差异相吻合。我们还阐述了支持生长提前停止的生物学特征中的许多其他差异和相似之处。因此，个体发育过程中生长的提前停止可能在爬行纲和兽孔目动物的恒温进化中起到了关键作用。它在祖先变温动物的特征中产生了变异性，这种变异性在过去受到自然选择的影响，并导致了当今鸟类和哺乳动物中许多与恒温相关的适应性变化。
