Abstract
Schizothoracine fishes distributed in the water system of the Qinghai-Tibetan plateau (QTP) and adjacent areas are characterized by being highly adaptive to the cold and hypoxic environment of the plateau, as well as by a high degree of diversity in trophic morphology due to resource polymorphisms. Although convergent and parallel evolution are prevalent in the organisms of the QTP, it remains unknown whether similar evolutionary patterns have occurred in the schizothoracine fishes. Here, we constructed for the first time a tentative molecular phylogeny of the schizothoracine fishes based on the complete sequences of the cytochrome b gene. We employed this molecular phylogenetic framework to examine the evolution of trophic morphologies. We used Pagel's maximum likelihood method to estimate the evolutionary associations of trophic morphologies and food resource use. Our results showed that the molecular and published morphological phylogenies of Schizothoracinae are partially incongruent with respect to some intergeneric relationships. The phylogenetic results revealed that four character states of five trophic morphologies and of food resource use evolved at least twice during the diversification of the subfamily. State transitions are the result of evolutionary patterns including either convergence or parallelism or both. Furthermore, our analyses indicate that some characters of trophic morphologies in the Schizothoracinae have undergone correlated evolution, which are somewhat correlated with different food resource uses. Collectively, our results reveal new examples of convergent and parallel evolution in the organisms of the QTP. The adaptation to different trophic niches through the modification of trophic morphologies and feeding behaviour as found in the schizothoracine fishes may account for the formation and maintenance of the high degree of diversity and radiations in fish communities endemic to QTP.
Highlights
The Qinghai-Tibetan plateau (QTP), which is renowned as being ‘‘the roof of the world’’, is the world’s largest high-elevation ecosystem, occupying nearly 2.5 million km2, with an average elevation of more than 4,000 m above sea level [1]
Settings for this model were as follows: Base = (0.3059 0.3405 0.0921), Nst = 6, Rmat = (0.6799 19.8065 0.7380 1.2627 9.1259), Rates = gamma, Shape = 0.8461, and Pinvar = 0.4785. Parameters obtained from this analysis were used for the construction of maximum likelihood (ML) and Bayesian inference (BI) phylogenies
The trees showed that the schizothoracine fishes are a well-supported monophyletic group
Summary
The Qinghai-Tibetan plateau (QTP), which is renowned as being ‘‘the roof of the world’’, is the world’s largest high-elevation ecosystem, occupying nearly 2.5 million km, with an average elevation of more than 4,000 m above sea level [1]. The species of Sinocyclocheilus occurs in the eastern QTP and adjacent areas It exhibits degeneration of the eyes and pigments, and a well-developed projection of frontal and parietal bones that adapt to cave environments. Through molecular analyses these have been demonstrated to having originated multiple times from different lineages during the evolutionary history of this genus [8]. It remains unknown whether similar evolutionary patterns have occurred in the schizothoracine fishes distributed in the QTP, due in part to the difficulty in obtaining specimens
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