Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
Am J Phys Anthropol. 2012 Mar;147(3):409-16. doi: 10.1002/ajpa.22008. Epub 2012 Jan 27.
Activity period plays a central role in studies of primate origins and adaptations, yet fundamental questions remain concerning the evolutionary history of primate activity period. Lemurs are of particular interest because they display marked variation in activity period, with some species exhibiting completely nocturnal or diurnal lifestyles, and others distributing activity throughout the 24-h cycle (i.e., cathemerality). Some lines of evidence suggest that cathemerality in lemurs is a recent and transient evolutionary state (i.e., the evolutionary disequilibrium hypothesis), while other studies indicate that cathemerality is a stable evolutionary strategy with a more ancient history. Debate also surrounds activity period in early primate evolution, with some recent studies casting doubt on the traditional hypothesis that basal primates were nocturnal. Here, we used Bayesian phylogenetic methods to reconstruct activity period at key points in primate evolution. Counter to the evolutionary disequilibrium hypothesis, the most recent common ancestor of Eulemur was reconstructed as cathemeral at ∼9-13 million years ago, indicating that cathemerality in lemurs is a stable evolutionary strategy. We found strong evidence favoring a nocturnal ancestor for all primates, strepsirrhines and lemurs, which adds to previous findings based on parsimony by providing quantitative support for these reconstructions. Reconstructions for the haplorrhine ancestor were more equivocal, but diurnality was favored for simian primates. We discuss the implications of our models for the evolutionary disequilibrium hypothesis, and we identify avenues for future research that would provide new insights into the evolution of cathemerality in lemurs.
活动期在灵长类动物起源和适应的研究中起着核心作用，但有关灵长类动物活动期的进化历史仍存在基本问题。狐猴特别有趣，因为它们的活动期存在明显的变化，有些物种表现出完全的夜间或日间生活方式，而其他物种则在 24 小时周期内分配活动（即，日中性）。一些证据表明，狐猴的日中性是一种新近和短暂的进化状态（即，进化不平衡假说），而其他研究表明，日中性是一种具有更古老历史的稳定进化策略。关于早期灵长类动物进化中的活动期也存在争议，一些最近的研究对基干灵长类动物是夜间活动的传统假说提出了质疑。在这里，我们使用贝叶斯系统发育方法来重建灵长类动物进化过程中的关键时期的活动期。与进化不平衡假说相反，Eulemur 的最近共同祖先被重建为约 9-1300 万年前的日中性，这表明狐猴的日中性是一种稳定的进化策略。我们发现了强烈的证据支持所有灵长类动物、原猴类和狐猴类的夜间祖先，这增加了以前基于简约性的发现，为这些重建提供了定量支持。对有胎盘类动物祖先的重建则更为模棱两可，但白天活动则有利于灵长类动物。我们讨论了我们的模型对进化不平衡假说的影响，并确定了未来研究的途径，这些研究将为狐猴的日中性进化提供新的见解。
