PNAS：马科动物基因组与物种形成理论
一项研究发现，包括马、驴和斑马在内的马科动物的进化史与物种形成的某些理论相矛盾。尽管细节丰富的马科动物化石记录常常作为进化的例子，导致现代马科动物多样性的一系列事件仍然不清楚。
为了填补这些动物的进化历史——目前代表这一历史的只有马和家驴的遗传史——Ludovic Orlando及其同事对每一个现存的驴和斑马物种的基因组进行了测序，因此也就让这个属的现存物种的基因组记录变得完整。此外，这组作者使用一个博物馆样本描述了斑驴这种自从20世纪00年代早期灭绝的斑马物种的基因组特征。这组作者扫描了这些基因组，识别出了参与了诸如嗅觉、免疫应答和运动力等特征的48个适应环境的基因。
此外，这些基因组序列揭示出了一个高度动态的种群统计学历史，在气候变化之后在不同的大陆上同步扩张和崩溃。或许最令人吃惊的是，尽管染色体结构极端分离——这一特征被认为阻止了物种之间的繁殖——这组作者识别出了杂交的例子。这些发现提示，马科动物可能充当染色体结构和基因流相互作用从而影响物种形成的一个模型。
原文标题：Speciation with GENE flow in equids despite extensive chromosomal plasticity
原文摘要：Horses, asses, and zebras belong to a single genus, Equus, which emerged 4.0–4.5 Mya. Although the equine fossil record represents a textbook example of evolution, the succession of events that gave rise to the diversity of species existing today remains unclear. Here we present six genomes from each living species of asses and zebras. This completes the set of genomes available for all extant species in the genus, which was hitherto represented only by the horse and the domestic donkey. In addition, we used a museum specimen to characterize the genome of the quagga zebra, which was driven to extinction in the early 1900s. We scan the genomes for lineage-specific adaptations and identify 48 genes that have evolved under positive selection and are involved in olfaction, immune response, development, locomotion, and behavior. Our extensive genome dataset reveals a highly dynamic demographic history with synchronous expansions and collapses on different continents during the last 400 ky after major climatic events. We show that the earliest speciation occurred with gene flow in Northern America, and that the ancestor of present-day asses and zebras dispersed into the Old World 2.1–3.4 Mya. Strikingly, we also find evidence for gene flow involving three contemporary equine species despite chromosomal numbers varying from 16 pairs to 31 pairs. These findings challenge the claim that the accumulation of chromosomal rearrangements drive complete reproductive isolation, and promote equids as a fundamental model for understanding the interplay between chromosomal structure, gene flow, and, ultimately, speciation.
原文地址：http://www.PNAS.org/content/early/2014/11/26/1412627111.abstract
作者：Hákon Jónsson等人
