Phylogeny of the Genus Pseudecheneis (Sisoridae) with an Explanation of Its Distribution Pattern

In the present paper, the cladistics method was used to analyze the phylogenetic relationships of 6 recorded species in the genus Pseudecheneis. Bagarius yarrelli and Glyptothorax honghensis were designated as outgroup species. Seventy-three characters of external morphology, internal myology, and osteology were chosen for comparison. Five ingroup species were included, but not P. sympelvicus because the examination of its myological and osteological characters is incomplete. All characters were set as unordered with equal weighting, and the data matrix produced a single most-parsimonious tree with a tree length of 110 steps, a consistency index of 0.7364, and a retention index of 0.6947. Meanwhile, a bootstrap test was conducted to verify the reliability of the results. The matrix was analyzed for different conditions: P. sympelvicus was combined into the ingroup and all characters were ordered. Each method yielded a single most-parsimonious phylogenetic tree whose structure was completely consistent with each other. The cladogram shows that all species in Pseudecheneis form a monophyletic group and can be divided into 2 clades: one includes P. paviei and P. intermedius, and the other includes the remaining 4 species (P. immaculatus, P. sulcatus, P. sulcatoides, and P. sympelvicus). Based on fossil records of the Sisoridae and the phylogenetic tree of Pseudecheneis, it is inferred that the genus Pseudecheneis originated in the Late Pliocene. With the uplift of the Qinghai-Xizang Plateau, this genus has differentiated 4 times, an inference consistents with the geography of the river systems in Yunnan Province, China.