Intense genomic reorganization in the genus (Rodentia, Sigmodontinae): comparison between DNA barcoding and mapping of repetitive elements in three species of the Brazilian Amazon.

Thomas, 1906 is one of the most diverse and widely distributed genera within the tribe Oryzomyini. At least sixteen species in this genus have been described to date, but it is believed this genus contains undescribed species. Morphological, molecular and cytogenetic study has revealed an uncertain taxonomic status for several species, suggesting the presence of a complex of species. The present work had the goal of contributing to the genetic characterization of the genus in the Brazilian Amazon. Thirty specimens were collected from four locations in the Brazilian Amazon and three nominal species recognized: (Tate, 1939), (Tomes, 1860) and (Anthony, 1921). COI sequence analysis grouped , and specimens into one, three and two clades, respectively, which is consistent with their geographic distribution. Cytogenetic data for revealed the sympatric occurrence of two different diploid numbers, 2n=64/NFa=110 and 2n=66/NFa=114, suggesting polymorphism while exhibited 2n=80/NFa=142 and 2n=54/NFa=90. The distribution of constitutive heterochromatin followed a species-specific pattern. Interspecific variation was evident in the chromosomal location and number of 18S rDNA loci. However, not all loci showed signs of activity. All three species displayed a similar pattern for 5S rDNA, with only one pair carrying this locus. Interstitial telomeric sites were found only in . The data presented in this work reinforce intra- and interspecific variations observed in the diploid number of species and indicate that chromosomal rearrangements have led to the appearance of different diploid numbers and karyotypic formulas.