Molecular systematics of morphologically similar fishes in the Schizothoracinae in Nanmenxia River, with implication for morphological convergent evolution

摘要

With the human activities and changes of water system due to uplifts of Qinghai-Tibetan Plateau, the gene flow between the schizothoracine fishes distributed in the Nanmenxia River and other upper reaches of Yellow River has been limited for a long time. As a small and isolated group in a special niche, the investigation of its taxonomic status and evolutionary mechanism is important to further understand what has caused the rapid speciation and high levels of fishes biodiversity in Qinghai-Tibetan Plateau. In this study, the complete sequences of the mitochondrial cyt b gene from 29 individuals of schizothoracine fishes in Nanmanxia River and 19 individuals representing other relatively closed species were sequenced. Among the aligned sequences of 29 individuals of schizothoracine fishes in Nanmanxia River, 100 (8.77%) nucleotide sites were variable, and a total of 16 haplotypes identified. The phylogenetic analyses showed that 5 haplotypes（NMX3, 6, 7, 13, 15）from Nanmanxia River clustered with the relatively closed species Gymnocypris eckloni and Gymnocypris przewalskii, and together formed a monophyletic clade with high boostrap values (99% for the MP tree and 98% for Bayesian tree); the rest 11 haplotypes (NMX1, 2, 4, 5, 8, 9, 10, 11, 12, 14, 16) together with Schizopygopsis pylzovi from the upper reaches of Yellow River formed another monophyletic clade (99% for both the MP tree and Bayesian tree). The sequence divergence between two groups distributed in different clades showed significant (average 7.42%), and together with the results of phylogenetic analyses suggested that the schizothoracine fishes in Nanmanxia River may be morphological similar species complex consisted of two species, Gymnocypris eckloni and Schizopygopsis pylzovi. The natural selective pressure resulted from the changes of water system and climatic conditions due to uplifts of the plateau, may have promoted the adaptive convergence of the morphological characters[Acta Zoologica Sinica 52(5): 862 – 870, 2006].