Independently evolving species in asexual bdelloid rotifers.
Independently evolving species in asexual bdelloid rotifers.
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DOI：
10.1371/journal.pbio.0050087
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发表时间：
2007-04
期刊：
影响因子：
9.8
通讯作者：
Barraclough, Timothy G
中科院分区：
文献类型：
--
作者：
Fontaneto, Diego;Herniou, Elisabeth A;Boschetti, Chiara;Caprioli, Manuela;Melone, Giulio;Ricci, Claudia;Barraclough, Timothy G
无性繁殖是物种为什么存在的理论的一个重要测试案例。如果无性支系表现出与有性支系相同的离散变异模式，这将挑战传统观点，即有性是物种多样化所必需的。然而，缺乏关键证据：所有假定的例子都涉及具有最近或正在进行的重组历史的生物体，并且依赖于对遗传和表型变异模式的视觉解释，而不是对替代进化情景的正式测试。在这里，我们展示了一个经典的无性分支--蜈蚣轮虫--已经分化成不同的进化物种。对轮虫属的密集采样表明，存在分离良好的遗传簇，表明独立进化。此外，结合遗传和形态分析揭示了取食形态上的分化选择，表明了生态位分化。一些经历不同选择的形态上一致的群体包含几个基因簇，这与有性有机体中神秘物种的发现是相同的。我们的结果表明，有性生物物种形成的主要原因，种群隔离和分化选择，在无性支系中具有相同的质量效应。这项研究还展示了结合分子和形态分析如何为物种的进化本质提供新的线索。不同物种的进化通常被认为完全是有性繁殖有机体的属性。然而，事实上，几乎没有证据表明无性群体是否会分化为物种。我们发现，一类著名的无性动物--蜈蚣类轮虫，已经分化成与有性种群大致相同的不同物种。我们使用DNA序列和扫描电子显微镜对颌骨形态的测量，调查了世界各地不同栖息地的单一分支--轮藻属的多样性。形态和DNA序列数据联合分析的新统计方法证实了物种的两个基本性质，即独立进化和自然选择导致的生态分化。这两个特性并不总是一致来定义明确的物种群体，但这一发现在性群体中也很常见。结果表明，性别不是物种形成的必要条件。这些方法提供了增加我们对广泛生物体物种边界性质的理解的潜力。对遗传和形态数据的最新分析表明，著名的无性种群--蜈蚣轮虫已经分化为不同的物种，性别并不是物种形成的必要条件。
Asexuals are an important test case for theories of why species exist. If asexual clades displayed the same pattern of discrete variation as sexual clades, this would challenge the traditional view that sex is necessary for diversification into species. However, critical evidence has been lacking: all putative examples have involved organisms with recent or ongoing histories of recombination and have relied on visual interpretation of patterns of genetic and phenotypic variation rather than on formal tests of alternative evolutionary scenarios. Here we show that a classic asexual clade, the bdelloid rotifers, has diversified into distinct evolutionary species. Intensive sampling of the genus Rotaria reveals the presence of well-separated genetic clusters indicative of independent evolution. Moreover, combined genetic and morphological analyses reveal divergent selection in feeding morphology, indicative of niche divergence. Some of the morphologically coherent groups experiencing divergent selection contain several genetic clusters, in common with findings of cryptic species in sexual organisms. Our results show that the main causes of speciation in sexual organisms, population isolation and divergent selection, have the same qualitative effects in an asexual clade. The study also demonstrates how combined molecular and morphological analyses can shed new light on the evolutionary nature of species. The evolution of distinct species has often been considered a property solely of sexually reproducing organisms. In fact, however, there is little evidence as to whether asexual groups do or do not diversify into species. We show that a famous group of asexual animals, the bdelloid rotifers, has diversified into distinct species broadly equivalent to those found in sexual groups. We surveyed diversity within a single clade, the genus Rotaria, from a range of habitats worldwide, using DNA sequences and measurements of jaw morphology from scanning electron microscopy. New statistical methods for the combined analysis of morphology and DNA sequence data confirmed two fundamental properties of species, namely, independent evolution and ecological divergence by natural selection. The two properties did not always coincide to define unambiguous species groups, but this finding is common in sexual groups as well. The results show that sex is not a necessary condition for speciation. The methods offer the potential for increasing our understanding of the nature of species boundaries across a wide range of organisms. New analyses of genetic and morphological data reveal that the bdelloid rotifers, a famous asexual group, have diversified into distinct species and that sex is not a necessary condition for speciation.