Sorenson L, Santini F, Alfaro M E
Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA.
J Evol Biol. 2014 Aug;27(8):1536-48. doi: 10.1111/jeb.12405. Epub 2014 May 30.
Sharks occupy marine habitats ranging from shallow, inshore environments to pelagic, and deepwaters, and thus provide a model system for testing how gross habitat differences have shaped vertebrate macroevolution. Palaeontological studies have shown that onshore lineages diversify more quickly than offshore taxa. Among onshore habitats, coral reef-association has been shown to increase speciation rates in several groups of fishes and invertebrates. In this study, we investigated whether speciation rates are habitat dependent by generating the first comprehensive molecular timescale for shark divergence. Using phylogenetic comparative methods, we rejected the hypothesis that shelf (i.e. onshore) lineages have higher speciation rates compared to those occupying deepwater and oceanic (i.e. offshore) habitats. Our results, however, support the hypothesis of increased speciation rates in coral reef-associated lineages within the Carcharhinidae. Our new timetree suggests that the two major shark lineages leading to the extant shark diversity began diversifying mostly after the end-Permian mass extinction: the squalimorphs into deepwater and the galeomorphs into shelf habitats. We suggest that the breakdown of the onshore-offshore speciation rate pattern in sharks is mediated by success in deepwater environments through ecological partitioning, and in some cases, the evolution of morphological novelty.
鲨鱼占据着从浅海近岸环境到远洋和深海的海洋栖息地，因此提供了一个模型系统，用于测试总体栖息地差异如何塑造脊椎动物的宏观进化。古生物学研究表明，陆上谱系的多样化速度比近海类群更快。在陆上栖息地中，珊瑚礁关联已被证明会提高几组鱼类和无脊椎动物的物种形成率。在这项研究中，我们通过生成首个全面的鲨鱼分化分子时间尺度，研究了物种形成率是否依赖于栖息地。使用系统发育比较方法，我们拒绝了以下假设：与占据深水和海洋（即近海）栖息地的谱系相比，陆架（即陆上）谱系具有更高的物种形成率。然而，我们的结果支持了真鲨科中与珊瑚礁相关的谱系物种形成率增加的假设。我们新的时间树表明，导致现存鲨鱼多样性的两个主要鲨鱼谱系大多在二叠纪末大灭绝之后开始分化：角鲨形类进入深水，真鲨形类进入陆架栖息地。我们认为，鲨鱼陆上 - 近海物种形成率模式的打破是由在深水环境中通过生态位划分取得的成功介导的，在某些情况下，也是由形态新奇性的进化介导的。
