MacLeod Amy, Rodríguez Ariel, Vences Miguel, Orozco-terWengel Pablo, García Carolina, Trillmich Fritz, Gentile Gabriele, Caccone Adalgisa, Quezada Galo, Steinfartz Sebastian
Zoological Institute, Technische Universität Braunschweig, Mendelssohnstrasse 4, Braunschweig 38106, Germany Department of Animal Behavior, University of Bielefeld, Bielefeld 33501, Germany.
Zoological Institute, Technische Universität Braunschweig, Mendelssohnstrasse 4, Braunschweig 38106, Germany.
Proc Biol Sci. 2015 Jun 22;282(1809):20150425. doi: 10.1098/rspb.2015.0425.
The effects of the direct interaction between hybridization and speciation-two major contrasting evolutionary processes--are poorly understood. We present here the evolutionary history of the Galápagos marine iguana (Amblyrhynchus cristatus) and reveal a case of incipient within--island speciation, which is paralleled by between-island hybridization. In-depth genome-wide analyses suggest that Amblyrhynchus diverged from its sister group, the Galápagos land iguanas, around 4.5 million years ago (Ma), but divergence among extant populations is exceedingly young (less than 50,000 years). Despite Amblyrhynchus appearing as a single long-branch species phylogenetically, we find strong population structure between islands, and one case of incipient speciation of sister lineages within the same island--ostensibly initiated by volcanic events. Hybridization between both lineages is exceedingly rare, yet frequent hybridization with migrants from nearby islands is evident. The contemporary snapshot provided by highly variable markers indicates that speciation events may have occurred throughout the evolutionary history of marine iguanas, though these events are not visible in the deeper phylogenetic trees. We hypothesize that the observed interplay of speciation and hybridization might be a mechanism by which local adaptations, generated by incipient speciation, can be absorbed into a common gene pool, thereby enhancing the evolutionary potential of the species as a whole.
杂交和物种形成这两个形成鲜明对比的主要进化过程之间的直接相互作用所产生的影响，目前还了解得很少。我们在此展示了加拉帕戈斯海鬣蜥（Amblyrhynchus cristatus）的进化史，并揭示了一个岛内初期物种形成的案例，与此同时还存在岛间杂交的情况。深入的全基因组分析表明，海鬣蜥在大约450万年前与其姐妹类群加拉帕戈斯陆鬣蜥分化，但现存种群之间的分化时间极为年轻（不到5万年）。尽管从系统发育角度来看海鬣蜥表现为一个单一的长分支物种，但我们发现岛屿之间存在很强的种群结构，并且在同一岛内有一个姐妹谱系初期物种形成的案例——表面上是由火山活动引发的。两个谱系之间的杂交极为罕见，但与来自附近岛屿的迁徙个体的频繁杂交却很明显。由高度可变标记提供的当代情况表明，物种形成事件可能在海鬣蜥的整个进化历史中都有发生，尽管这些事件在更深层次的系统发育树中并不明显。我们推测，观察到的物种形成和杂交之间的相互作用可能是一种机制，通过这种机制，初期物种形成产生的局部适应性能够被纳入一个共同的基因库，从而增强整个物种的进化潜力。
