Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, United States.
Yale Institute of Biospheric Studies, Yale University, New Haven, CT, United States.
Evolution. 2023 Nov 2;77(11):2442-2455. doi: 10.1093/evolut/qpad156.
A fundamental goal of evolutionary biology is to understand the mechanisms that generate and maintain biodiversity. Discovery and delimitation of species represent essential prerequisites for such investigations. We investigate a freshwater fish species complex comprising Etheostoma bellator and the endangered E. chermocki, which is endemic to the Black Warrior River system in Alabama, USA, a global hotspot of temperate freshwater biodiversity. Phylogenomic analyses delimit five geographically disjunct species masquerading as E. bellator. Three of these new species exhibit microendemic distributions comparable to that of E. chermocki raising the possibility that they also require protection. The species of the complex are found in streams flowing over carbonate rock and they are separated by waterways flowing over siliciclastic rock, a geographic pattern dictated by the underlying stratigraphy and structural geology. Over time, rivers have eroded downward through layers of siliciclastic rocks in the basin, gradually exposing underlying carbonate rock, the substrate of suitable habitat today. Our results suggest that episodic dispersal to patches of suitable habitat set the stage for allopatric speciation in the species complex. Our study suggests that the presence of heterogeneous rock can facilitate dispersal-mediated allopatric speciation in freshwater organisms in the absence of external tectonic or climatic perturbations.
进化生物学的一个基本目标是理解产生和维持生物多样性的机制。物种的发现和划界是此类研究的必要前提。我们研究了一个包含 Etheostoma bellator 和濒危物种 E. chermocki 的淡水鱼类物种复合体，E. chermocki 是美国阿拉巴马州黑武士河流域的特有物种，该地区是温带淡水生物多样性的全球热点地区。系统基因组学分析将五种地理上分离的物种划分为 E. bellator。其中三种新物种表现出与 E. chermocki 相当的微地方性分布，这增加了它们也需要保护的可能性。该复合体中的物种存在于流经碳酸盐岩的溪流中，它们被流经硅质碎屑岩的水道隔开，这种地理模式是由底层地层和构造地质学决定的。随着时间的推移，河流通过盆地中的硅质碎屑岩层向下侵蚀，逐渐暴露了下面的碳酸盐岩，这就是今天适宜栖息地的基底。我们的研究结果表明，偶然扩散到适宜栖息地斑块为物种复合体的异域物种形成奠定了基础。我们的研究表明，在没有外部构造或气候干扰的情况下，异质岩石的存在可以促进淡水生物的扩散介导的异域物种形成。
