Molecular phylogenetics and ecological diversification of the transisthmian fish genus Centropomus (Perciformes : Centropomidae)

Phylogenetic relationships among the 12 recognized fish species in the New World genus Centropomus (Pisces, Centropomidae) were analyzed using allozym e electrophoresis and 618 bp of the mitochondrial DNA 16S ribosomal RNA (rR NA) gene. Molecular phylogenetic trees were generally consistent with previ ously published partial hypotheses based on morphological evidence. However , previously undefined sister group relationships between major species gro ups were resolved using molecular data, and phylogenetic hypotheses for Cen tropomus based on 16S rRNA sequences were better supported than were allozy me-based hypotheses. The high level of congruence among the trees inferred from the nuclear and mitochondrial characters provided a firm phylogenetic basis for analysis of ecological diversification and molecular evolution in the genus. Compared to basal Centropomus species, members of the most nest ed species group were significantly larger in body size and occupied a mari ne niche only peripherally utilized by their congeners. We also observed su bstitution rate heterogeneity among 16S rRNA lineages; in contrast to expec tations based on "metabolic rate" and "generation interval" models, relativ e substitution rates were faster than expected for the group of large-bodie d snooks. Using the Pliocene rise of the Central American isthmian marine b arrier to calibrate rates of 16S ribosomal gene evolution in Centropomus, w e found that the rates for the genus were similar to those reported for hig her vertebrates. Analysis of the three sets of transisthmian geminate taxa in Centropomus indicated that two of the pairs were probably formed duping the Pliocene rise of the isthmus while the third pair diverged several mill ion years earlier. (C) 1999 Academic Press.