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

Abstract

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.

An endemic new species of tuco-tuco, genusCtenomys(Rodentia: Ctenomyidae), with a restricted geographic distribution in southern Brazil

“…Although the members of this species group from Corrientes are closely related to C. torquatus with respect to karyotype morphology, they are phylogenetically distant ( Fig. 6B; Fernandes et al 2009b;Giménez et al 2002).…”

“…The percent of variance explained for each axis is given in parentheses. from 2n ¼ 40 to 46, with a metacentric 1st pair and Robertsonian rearrangements thought to be responsible for the variation in chromosome numbers (Fernandes et al 2009b).…”

“…1). Morphological similarities between their karyotypes were previously investigated by Fernandes et al (2009b), in order to address their taxonomic status. In addition, cytochrome-b sequences were used to reconstruct phylogenetic relationships, which showed that C. torquatus and the species from Corrientes form 2 reciprocally monophyletic clades.…”

“…Finally, C. torquatus, the nominate species of the group, inhabits the grasslands of southern Rio Grande do Sul, Brazil, and northern Uruguay. Despite its wide geographic range, there is a most common and widespread chromosomal form (2n ¼ 44), and only some restricted karyotypic polymorphisms in the southern (2n ¼ 46) and western (2n ¼ 40 and 42) parts of its distribution (Fernandes et al 2009b;Freitas and Lessa 1984;Gonçalves and Freitas 2009).…”

Integrative lineage delimitation in rodents of the Ctenomys Corrientes group

“…A total of seven populations have been studied up to now in the proximities to the Iberá wetland: four located at the western margins of the wetland, two in the east and one isolated on a sandy elevation surrounded by waterlogged lowlands located in the center of the wetland (Figure 2). In mtDNA studies (Fernandes et al 2009, Caraballo et al 2012) their membership to the Corrientes group was confirmed rejecting its affinity to C. torquatus. With the exception of Curuzú Laurel, which falls apart probably due to incomplete lineage sorting, all the Iberanan populations form a monophyletic group (Caraballo et al 2012(Caraballo et al , 2016.…”