Multi-loci molecular phylogeny brings insight into systematics and evolution of genus Tridentiger (Teleostei: Gobiiformes)

The genus Tridentiger Gill, 1859 is comprised of barbeled and non-barbeled species, which is considered as key character to further divide the genus. Our phylogenetic tree based on 5028-bp sequence data of six genes indicated a well-supported sister relationship between the non-barbeled T. nudicervicus and the barbeled T. barbatus and T. microsquamis, with Papuligobius uniporus as the closest outgroup for Tridentiger. Due to lack of significant diagnoses and the common character of tricuspid teeth, Papuligobius is considered a junior synonym of Tridentiger. Moreover, 12S rRNA K2P distance (0.0000–0.0016) between T. microsquamis and T. radiatus fall in the interval of intraspecific distances (0.0000–0.0030), much smaller than the interspecific distances (0.0122–0.1383). Therefore, T. radiatus should be treated as a synonym of T. microsquamis. K2P distances between the southern and northern lineages T. barbatus fall in the interval of interspecific distances in 12S rRNA, Cytb and RAG1 genes, which were delineated as different species in the species delimitations. The mean divergence time between T. kuroiwae in the Ryukyu Islands and its congener, T. brevispinis and T. obscurus in the Japan Archipelago was dated back to 1.53 mya and close to the formation of the Tokara Gap (~1.5 mya), which might be a barrier driving divergence of the three species. However, as many Tridentiger species show different salinity and habitat preferences, ecological factors might also play important roles in evolution of the genus Tridentiger.