Department of Biology, University of Kentucky, Lexington, Kentucky 40506.
Evolution. 2018 Nov;72(11):2378-2393. doi: 10.1111/evo.13606. Epub 2018 Oct 4.
Closely related taxa with dissimilar morphologies are often considered to have diverged via natural selection favoring different phenotypes. However, some studies have found these scenarios to be paired with limited or no genetic differentiation. Desmognathus quadramaculatus and D. marmoratus are sympatric salamander species thought to represent a case of ecological speciation based on distinct morphologies, but the results of previous studies have not resolved corresponding patterns of lineage divergence. Here, we use genome-wide data to test this hypothesis of ecological speciation. Population structure analyses partitioned individuals geographically, but not morphologically, into two adjacent regions of western North Carolina: Pisgah and Nantahala. Phylogenetic analyses confirmed the nominal species are nonmonophyletic and resolved deep divergence between the two geographic clusters. Model-testing overwhelmingly supported the hypothesis that lineage divergence followed geography. Finally, ecological niche modeling showed that Pisgah and Nantahala individuals occupy different climatic niches, and geographic boundaries for the two lineages correspond to differences in precipitation regimes across southern Appalachia. Overall, we reject the previous hypothesis of ecological speciation based on microhabitat partitioning. Instead, our results suggest that there are two cryptic lineages, each containing the same pair of morphotypes.
形态差异较大的近缘种通常被认为是通过自然选择而产生的，这种选择有利于不同的表型。然而，一些研究发现，这些情况伴随着有限的或没有遗传分化。Desmognathus quadramaculatus 和 D. marmoratus 是同域分布的蝾螈物种，它们的形态差异被认为代表了生态物种形成的一个案例，但之前的研究结果并没有解决相应的谱系分化模式。在这里，我们使用全基因组数据来检验这种生态物种形成的假设。种群结构分析将个体在地理上而不是形态上划分为北卡罗来纳州西部的两个相邻地区：皮斯加和楠塔哈拉。系统发育分析证实了这两个命名物种不是单系的，并且在两个地理群之间存在很深的分歧。模型测试强烈支持谱系分化遵循地理的假设。最后，生态位模型显示，皮斯加和楠塔哈拉的个体占据不同的气候小生境，并且两个谱系的地理边界与阿巴拉契亚南部降水模式的差异相对应。总的来说，我们拒绝了以前基于微生境划分的生态物种形成的假设。相反，我们的结果表明，有两个隐生种，每个种都包含相同的两种形态型。
