Genetic and morphological variability in South American rodent Oecomys (Sigmodontinae, Rodentia): evidence for a complex of species

The rodent genus Oecomys (Sigmodontinae) comprises similar to 16 species that inhabit tropical and subtropical forests in Central America and South America. In this study specimens of Oecomys paricola Thomas, 1904 from Bel,m and Maraj island, northern Brazil, were investigated using cytogenetic, molecular and morphological analyses. Three karyotypes were found, two from Bel,m (2n = 68, fundamental number (FN) = 72 and 2n = 70, FN = 76) and a third from Maraj island (2n = 70, FN = 72). No molecular or morphological differences were found between the individuals with differing cytotypes from Bel,m, but differences were evident between the individuals from Bel,m and Maraj island. Specimens from Bel,m city region may represent two cryptic species because two different karyotypes are present in the absence of significant differences in morphology and molecular characteristics. The Maraj island and Bel,m populations may represent distinct species that have been separated for some time, and are in the process of morphological and molecular differentiation as a consequence of reproductive isolation at the geographic and chromosomal levels. Thus, the results suggest that O. paricola may be a complex of species.