Abstract
Oecomys 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 Oecomys species, suggesting the presence of a complex of species. The present work had the goal of contributing to the genetic characterization of the genus Oecomys in the Brazilian Amazon. Thirty specimens were collected from four locations in the Brazilian Amazon and three nominal species recognized: Oecomys auyantepui (Tate, 1939), Oecomys bicolor (Tomes, 1860) and Oecomys rutilus (Anthony, 1921). COI sequence analysis grouped Oecomys auyantepui, Oecomys bicolor and Oecomys rutilus specimens into one, three and two clades, respectively, which is consistent with their geographic distribution. Cytogenetic data for Oecomys auyantepui revealed the sympatric occurrence of two different diploid numbers, 2n=64/NFa=110 and 2n=66/NFa=114, suggesting polymorphism while Oecomys bicolor exhibited 2n=80/NFa=142 and Oecomys rutilus 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 Oecomys auyantepui. The data presented in this work reinforce intra- and interspecific variations observed in the diploid number of Oecomys species and indicate that chromosomal rearrangements have led to the appearance of different diploid numbers and karyotypic formulas.
Highlights
The order Rodentia is divided into nine taxonomic families in Brazil
In Brazil 12 species were registered and 9 of which can be found in Amazon biome; O. auyantepui Tate, 1939, O. bicolor (Tomes, 1860), O. concolor (Wagner, 1845), O. paricola (Thomas, 1904), O. rex Thomas, 1910, O. roberti (Thomas, 1904), O. rutilus Anthony, 1921, O. superans Thomas, 1911 and O. trinitatis
Two different diploid numbers were observed along the same bank of the Jatapú River: Karyomorph “a” exhibited 2n=64 chromosomes, a fundamental number = 110, and a karyotypic formula of 16m+6sm+26st+14a+XY (Fig. 2), in which pairs 1, 4, 15, 22, 26, 28, 30 and 31 were metacentric; 2, 3 and 19 were submetacentric; 5-13, 23, 24, 25 and 27 were subtelocentric; and 14, 16, 17, 18, 20, 21 and 29 were acrocentric (Fig. 2a)
Summary
The order Rodentia is divided into nine taxonomic families in Brazil. The family Cricetidae contains the most members, among which the subfamily Sigmodontinae includes 86 genera and 395 species (sensu Reig 1980) according to Prado and Percequillo (2013). 16 species are recognized within this genus (Musser and Carleton 2005, Carleton et al 2009), but only nine species have been studied for karyotypes, showing 11 different diploid numbers, varying between 54 and 86 chromosomes (Table 1). Morphological and morphometric analysis in conjunction with molecular and cytogenetic approaches revealed uncertainty in the delimitation and distribution of Oecomys species, suggesting the presence of a complex of species (Patton and Sherwood 1983, Emmons and Feer 1997, Patton et al 2000, Musser and Carleton 2005, Carleton et al 2009, Flores 2010, Rosa et al 2012)
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