A new species of fish-eating rat, genus (Sigmodontinae), from Ecuador.

Background: Inthis study, the genetic substructure and morphology of the species was evaluated. A nuclear marker and mitochondrial maker were used to examine phylogeographic structure and to estimategenetic distances. Two statistical measurement analyses were applied to morphological data.

Results: These data recovered two morphologically distinct phylogeographic groups corresponding to populations on the eastern and western slopes of the Andes. Further, these eastern and western Andean slope populations of are 8.5 % divergent using sequence data from cytochrome- (0.8 % divergent in the interphotoreceptor retinoid-binding protein gene).

Conclusions: Populationscurrently assigned to constitutea species complex. The name is here restricted to western Andean slope populations. Populations on the eastern slope of the Andes are assigned to a new species, to which the authors assign the name sp.nov.