Phylogenies, species boundaries, and marine to freshwater transitions in South American silversides.

SOMMER, J.; C. CONTE-GRAND; R. CIFUENTES; E. HABIT; V. CUSSAC; G. ORTÍ

Providence

Encuentro; American Society of Ichthyologists and Herpetologists Annual Meeting; 2010

A molecular phylogeny of the tribe Sorgentinini reveals significant discordance with previous hypotheses based on morphology. A total of 446 individuals representing 16 out of 23 nominal species were sampled from throughout their range in South America. Mitochondrial cytochrome b DNA sequences were obtained for all specimens and a subsample was analyzed for the S7 nuclear marker. The molecular evidence provided strong support for the monophyly of both included genera and many of the nominal species, but failed to produce diagnostic characters to differentiate two nominal species within Basilichthys (B. microlepidotus and B. australis) and several species within Odontesthes. The latter include the Chilean freshwater species O. mauleanum and O. microlepidotus, the widespread marine taxa O. regia and O. gracilis from the Chilean pacific coast and J. Fernandez Islands, respectively, and several freshwater and marine species from Argentina. Most notably, a clade comprising O. bonariensis and O. argentiniensis and several species recently described from Southern Brazil is strongly supported by the molecular data, but shows poor resolution to differentiate the contained taxa. Although some species are strictly marine or freshwater, two clades identified by the molecular data show strong evidence of repeated historical transitions between marine and freshwater habitats. Phylogenetic reconstruction implies an ancestral marine habitat for this group, with at least five instances of freshwater invasion and some reversals to marine habitat.