Evolution of a Ureagenic Ability of Japanese Mugilogobjus Species (Pisces: Gobiidae).

Abstract

Interspecific differences in the ability to excrete urea in four gobiid fishes, Mugilogobius abei, M. chulae, M. sp. 1 and M. sp. 2, in response to elevated external ammonia, were compared and set against the phylogenetic relationships of species, following molecular phylogenetic analyses using a portion of mitochondrially-encoded 12S ribosomal RNA and tRNA-Val genes, which were sequenced from five species of Mugilogobius. The resulting tree, based on 710 base pairs of aligned sequences, was statistically robust and indicated two major clades, (M. abei, M. sp. 1 and M. chulae) and (M. parvus and M. sp. 2), respectively. High ureagenic ability was demonstrated in M. abei and M. sp. 1, being sister species according to the phylogenetic analysis, while the remaining species having a low level of ability. The two former species are restricted to temperate and subtropical Japan, whereas the others are widely distributed throughout tropical Asia. The most parsimonious reconstruction of these features suggested that ancestral Mugilogobius, probably widely distributed in tropical Asia, may had low ureagenic ability. The high ureagenic ability of the temperate species may have evolved concurrently with the northward spread of Mugilogobius from the tropical zone.