A phylogenetic analysis of the Asian catfish family Sisoridae (Teleostei: Siluriformes), and the evolution of epidermal characters in the group.

Abstract

The phylogenetic relationships of the Asian hillstream catfish family Sisoridae are examined in this study, using a combination of morphological, and mitochondrial and nuclear gene sequence data. The composition of the family is also examined and the hypothesis that the Asian Erethistidae (previously considered part of the Sisoridae) is the sister group of the Neotropical catfish family Aspredinidae is tested with morphological and molecular data. The results of this study indicate that the clade containing the members currently assigned to the Erethistidae is nested within the Sisoridae. The Sisoridae is therefore redefined to include the Erethistidae. The Sisoridae is divided into two clades: the Glyptosterninae and the Sisorinae, with the Sisorinae divided into three subclades in an unresolved trichotomy: the Bagariini, Erethistini and Sisorini. A novel sister group relationship between <italic>Bagarius</italic> and <italic> Glyptothorax</italic> (both comprising the Bagariini) was recovered, and some sisorid taxa previously thought to be monophyletic, e.g. <italic>Hara</italic>, were not recovered as such. A divergence time estimate analysis carried out on some nodes within the Sisoridae suggests that much of the speciation within Sundaic Southeast Asian <italic>Glyptothorax</italic> predates the Pleistocene. While this is expected for elements of the ichthyofauna occurring in the upper reaches of river drainages in the region and expected to undergo the most isolation, the hypothesis that sea level changes during the Pleistocene were the major vicariant events that led to speciation has also been frequently extended to include species occurring in the middle and upper reaches of rivers in existing literature. The results of this study indicate otherwise, and suggest that more intensive studies on the historical biogeography of the upriver elements of the ichthyofauna of river drainages in Southeast Asia is deserving of further study. Some epidermal characters in the Sisoridae, viz. the tubercles on the sides of the body and the epidermal structures of the thoracic region, were examined using both light and scanning electron microscopy in an attempt to elucidate their evolution and phylogenetic significance in the light of the phylogenetic hypothesis obtained. The morphology of these structures appear to be highly influenced by hydrodynamic regimes and the apparent homoplasy observed in them limits their use as phylogenetically. The taxonomic problems associated with the diagnosability of sisorid taxa is discussed and highlighted with the description of a new species of <italic> Erethistoides</italic>.