Sympatric Speciation of Tibetan Loaches (Triplophysa) Driven by Dietary Niche Specialization

The Qinghai-Tibeta Plateau is a hotspot for endemic fish biodiversity. Multiple isolated glacial lakes provide an ideal scenario for verifying the speciation mode of highland ichthyofauna. Sympatric speciation, a controversial topic in evolutionary biology, is driven by ecological niche differentiation, including dietary specialization. The coexistence of Triplophysa leptosoma and Triplophysa longianguis in a small semi-enclosed postglacial Sunmcuo Lake makes it an excellent model for testing speciation mechanisms. Phylogenetic and population genetic analyses revealed monophyletic groups of T. longianguis and T. leptosoma. Together with the estimated divergence time, our results confirmed the sympatric speciation of T. longianguis and T. leptosoma. Gut contents and stable isotope analysis demonstrated the overlap of food resources with species-specific private diet items, which is consistent with the observed morphological variations in trophic structures. The sequencing of 16S rRNA genes and LEfSe analysis revealed similar compositions and different functions of the gut microbiota between T. longianguis and T. leptosoma, which might contribute to host adaptation to specialized diets. Overall, the results of the present study identified a new case of sympatric speciation of Triplophysa fish and provided novel insight into sympatric speciation underlying the synergistic mechanism of the gut microbiomes and dietary specialization, which improved our understanding on the formation of endemic fish biodiversity on the Qinghai-Tibeta Plateau.