Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California, 95060.
Current Address: Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, 55108.
Evolution. 2022 Jun;76(6):1246-1259. doi: 10.1111/evo.14484. Epub 2022 Apr 20.
Budding speciation involves isolation of marginal populations at the periphery of a species range and is thought to be a prominent mode of speciation in organisms with low dispersal and/or strong local adaptation among populations. Budding speciation is typically evidenced by abutting, asymmetric ranges of ecologically divergent sister species and low genetic diversity in putative budded species. Yet these indirect patterns may be unreliable, instead caused by postspeciation processes such as range or demographic shifts. Nested phylogenetic relationships provide the most conclusive evidence of budding speciation. A putative case of budding speciation in the serpentine endemic Clarkia franciscana and two closely related widespread congeners was studied by Harlan Lewis, Peter Raven, Leslie Gottlieb, and others over a 20-year period, yet the origin of C. franciscana remains controversial. Here, we reinvestigate this system with phylogenomic analyses to determine whether C. franciscana is a recently derived budded species, phylogenetically nested within one of the other two putative progenitor species. In contrast to the hypothesized pattern of relatedness among the three Clarkia species, we find no evidence for recent budding speciation. Instead, the data suggest the three species diverged simultaneously. We urge caution in using contemporary range patterns to infer geographic modes of speciation.
物种形成涉及到边缘种群在物种分布范围边缘的隔离，并且被认为是具有低扩散和/或种群间强烈的局部适应的生物的主要物种形成模式。物种形成通常表现为生态上不同的姐妹物种的毗邻、不对称的范围，以及假定的萌芽物种中遗传多样性较低。然而，这些间接模式可能是不可靠的，而是由物种形成后的过程引起的，如范围或人口变化。嵌套的系统发育关系提供了物种形成的最确凿证据。在过去的 20 年里，Harlan Lewis、Peter Raven、Leslie Gottlieb 等人对蛇纹石特有种弗朗西斯卡那·克拉克西亚（Clarkia franciscana）及其两个密切相关的广泛同属种的萌芽物种形成进行了研究，但弗朗西斯卡那·克拉克西亚的起源仍然存在争议。在这里，我们用基因组系统发育分析来重新研究这个系统，以确定弗朗西斯卡那·克拉克西亚是否是一个最近衍生的萌芽物种，在系统发育上嵌套在另外两个假定的祖先生物种之一中。与三种克拉克西亚物种之间假定的亲缘关系模式相反，我们没有发现最近的物种形成的证据。相反，数据表明这三个物种是同时分化的。我们敦促谨慎使用现代范围模式来推断地理物种形成模式。
