Karyotypic and molecular polymorphisms in Ctenomys torquatus (Rodentia: Ctenomyidae): taxonomic considerations

The rodent genus Ctenomys (tuco-tucos) comprises more than 60 described species, and shows extraordinary inter- and intraspecific karyotypic variation. The most widely distributed species of Ctenomys in Brazil is C. torquatus. Although several cytogenetic studies have been done, the karyotypic variability of this species is still poorly known. In this paper we report two new diploid numbers for C. torquatus: 2n = 40 and 2n = 42, both showing AN = 72. The new distribution limits of C. torquatus here reported include localities in the southern, central and western parts of Rio Grande do Sul (RS) State in southern Brazil. The phylogenetic relationship between C. torquatus from Alegrete, RS, and Ctenomys sp. from Corrientes, Argentina, is described by means of mtDNA cytochrome b analysis. Although both entities share similar karyotypes and sperm morphology, these two species are not phylogenetically close.