Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA.
Mol Ecol. 2012 Aug;21(15):3776-93. doi: 10.1111/j.1365-294X.2012.05648.x.
Many recent studies on invertebrates have shown how morphology not always captures the true diversity of taxa, with cryptic speciation often being discussed in this context. Here, we show how diversification patterns can be very different in two clades of closely related earthworms in the genus Hormogaster stressing the risk of using nonspecific substitution rate values across taxa. On the one hand, the Hormogaster elisae species complex, endemic to the central Iberian Peninsula, shows morphological stasis. On the other hand, a clade of Hormogaster from the NE Iberian Peninsula shows an enormous morphological variability, with 15 described morphospecies. The H. elisae complex, however, evolves faster genetically, and this could be explained by the harsher environmental conditions to which it is confined-as detected in this study, that is, sandier and slightly poorer soils with lower pH values than those of the other species in the family. These extreme conditions could be at the same time limiting morphological evolution and thus be responsible for the observed morphological stasis in this clade. Contrarily, Hormogaster species from the NE Iberian Peninsula, although still inhabiting harsher milieu than other earthworm groups, have had the opportunity to evolve into a greater morphological disparity. An attempt to delimit species within this group following the recently proposed general mixed Yule-coalescent method showed a higher number of entities than expected under the morphospecies concept, most probably due to the low vagility of these animals, which considerably limits gene flow between distant conspecific populations, but also because of the decoupling between morphological and genetic evolution in the H. elisae complex.
许多最近关于无脊椎动物的研究表明，形态学并不总是能捕捉到分类单元的真实多样性，在这种情况下，隐种形成经常被讨论。在这里，我们展示了两个密切相关的环节动物属 Hormogaster 分支的多样化模式如何存在很大差异，强调了在跨分类单元使用非特异性替代率值的风险。一方面，仅存在于伊比利亚半岛中部的 Hormogaster elisae 物种复合体表现出形态上的静止。另一方面，来自伊比利亚半岛东北部的 Hormogaster 分支表现出巨大的形态变异性，有 15 个已描述的形态种。然而，H. elisae 复合体在遗传上进化得更快，这可以用它所处的更恶劣的环境条件来解释——正如本研究所检测到的，与该家族中的其他物种相比，它所处的环境更沙化、土壤稍差、pH 值更低。这些极端条件可能同时限制了形态进化，从而导致该分支观察到的形态静止。相反，来自伊比利亚半岛东北部的 Hormogaster 物种，尽管仍然生活在比其他蚯蚓群体更恶劣的环境中，但有机会进化出更大的形态差异。尝试按照最近提出的通用混合 Yule 合并方法来界定该组内的物种，结果显示出比形态种概念下预期的更多实体，这很可能是由于这些动物的迁移能力较低，极大地限制了遥远同种群体之间的基因流动，但也由于 H. elisae 复合体中形态和遗传进化的解耦。
