Gray David A, Huang Huateng, Knowles L Lacey
Department of Biology, California State University, 18111 Nordhoff Street, Northridge, California 91330-8303, USA.
Mol Ecol. 2008 Sep;17(17):3836-55. doi: 10.1111/j.1365-294X.2008.03827.x. Epub 2008 Jul 18.
Species pairs that differ primarily in characters involved in mating interactions and are largely sympatric raise intriguing questions about the mode of speciation. When species divergence is relatively recent, the footprint of the demographic history during speciation might be preserved and used to reconstruct the biogeography of species divergence. In this study, patterns of genetic variation were examined throughout the geographical range of two cryptic sister taxa of field crickets, Gryllus texensis and G. rubens; mitochondrial cytochrome oxidase I (COI) was sequenced in 365 individuals sampled from 48 localities. Despite significant molecular divergence between the species, they were not reciprocally monophyletic. We devised several analyses to statistically explore what historical processes might have given rise to this genealogical structure. The analyses indicated that the biogeographical pattern of genetic variation does not support a model of recent gene flow between species. Instead, coalescent simulations suggested that the genealogical structure within G. texensis, namely a deep split between two geographically overlapping clades, reflects historical substructure within G. texensis. Additional tests that consider the concentration of G. rubens haplotypes in one of the two G. texensis genetic clusters suggest a model of speciation in which G. rubens was derived from one lineage of a geographically subdivided ancestor. These results indicate that, despite the contemporary sympatry of G. texensis and G. rubens, the data are indicative of an peripatric origin in which G. rubens was derived from one of the two historical partitions in the species currently recognized as G. texensis. This proposed model of species divergence suggests how the interplay of geography and selection may give rise to new species, although this requires testing with multilocus data. Specifically, the model highlights how that geographical partitioning of ancestral variation in the past may augment the selectively driven divergence of characters involved in the reproductive isolation of the species today.
主要在交配相互作用所涉及的特征上存在差异且在很大程度上同域分布的物种对，引发了关于物种形成模式的有趣问题。当物种分化相对较新时，物种形成过程中种群历史的印记可能会被保留下来，并用于重建物种分化的生物地理学。在本研究中，我们在田野蟋蟀的两个隐存姐妹分类群——德克萨斯蟋蟀（Gryllus texensis）和红蟋蟀（G. rubens）的整个地理分布范围内，研究了遗传变异模式；对从48个地点采集的365个个体的线粒体细胞色素氧化酶I（COI）进行了测序。尽管这两个物种之间存在显著的分子差异，但它们并非相互单系的。我们设计了几种分析方法，以统计学方式探究哪些历史过程可能导致了这种谱系结构。分析表明，遗传变异的生物地理模式并不支持物种间近期基因流动的模型。相反，溯祖模拟表明，德克萨斯蟋蟀内部的谱系结构，即两个地理上重叠的分支之间的深度分化，反映了德克萨斯蟋蟀内部的历史亚结构。考虑到红蟋蟀单倍型在德克萨斯蟋蟀两个遗传簇之一中的集中情况的其他测试，提出了一种物种形成模型，即红蟋蟀源自地理上细分的祖先的一个谱系。这些结果表明，尽管德克萨斯蟋蟀和红蟋蟀目前同域分布，但数据表明其起源是边缘隔离的，其中红蟋蟀源自目前被认定为德克萨斯蟋蟀的物种的两个历史分区之一。这种提出的物种分化模型表明了地理和选择的相互作用可能如何产生新物种，尽管这需要用多位点数据进行检验。具体而言，该模型突出了过去祖先变异的地理分区如何增强如今参与物种生殖隔离的特征的选择驱动分化。
