Molecular phylogenetic relationships of pangasiid and schilbid catfishes in Thailand.

In this study, the phylogenetic relationships among 13 pangasiids and six schilbids of Thailand were reconstructed based on the almost complete mitochondrial cytochrome b (cyt b), 12S rRNA, tRNA-Val and 16S rRNA, as well as the partial nuclear recombination-activating gene 1 (rag1) sequences by using the maximum likelihood and the Bayesian inference methods of phylogenetic reconstruction. The reconstructed phylogeny based on the concatenated sequence data set recovered Pangasiidae and Schilbidae as reciprocally monophyletic groups. Within Pangasiidae, four major clades were recovered, which according to the cyt b genetic distances can be categorized into four genera: Pangasius, Pseudolais, Helicophagus and Pangasianodon. The genus Pangasianodon was strongly supported as the most basal taxon within pangasiids, whereas Pseudolais + Helicophagus were recovered as a sister group of Pangasius. Within the latter, the giant pangasius Pangasius sanitwongsei was recovered as a sister group of the spot pangasius Pangasius larnaudii, Pangasius krempfi as a sister group of Pangasius nasutus + Pangasius conchophilus and Pangasius polyuranodon as a sister species of Pangasius macronema. Other internal phylogenetic relationships, however, were unresolved. Within Schilbidae, Pseudeutropius was supported as the most basal lineage. Eutropiichthys was recovered as a sister group of Clupisoma. The enigmatic Clupisoma sinense was recognized as more closely related to Laides longibarbis than to Clupisoma prateri. Thus, based on the cyt b genetic distances, a recategorization of C. sinense to the genus Laides is suggested. On the basis of a relaxed clock fossil calibration, the divergence of pangasiids and schilbids was estimated to have occurred 14·93 million years before present (b.p.) during the Miocene epoch. The separation between Pangasiidae and Schilbidae took place c. 13·12 Mb.p. during the early middle Miocene. The estimated divergence time of pangasiids is similar to the age of the calibrated fossil, Cetopangasius chaetobranchus, which was discovered in north-central Thailand. This suggests that the oldest pangasiid ancestor diverged into diverse genera in the area.