Comments: | Cabrera (1961; based on Osgood, 1946) and Nowak (1999) listed two subgenera: Chacomys (C. conoveri only) and Ctenomys (all other species). The validity of subgenus Chacomys has not been supported by subsequent studies (Cook and Yates, 1994; Lessa and Cook, 1998). Thomas (1916c) placed C. leucodon in the subgenus Haptomys, an arrangement that is supported by sequence divergence (Lessa and Cook, 1998). Penis morphology appears to be useful in examining relationships among species (Balbontin et al., 1996). Sperm morphology (Feito and Gallardo, 1982; Vitullo et al., 1988; Vitullo and Cook, 1991) has been used to suggest two major divisions but the sequence analysis of D’Elía et al. (1999) does not support those lineages. A mendocinus group was designated by Massarini et al. (1991a) composed of morphologically similar species: australis, azarae, mendocinus, porteousi, and C. sp. from Chasicó. Freitas (1994) included flamarioni and rionegrensis within this group, a conclusion supported by sequence analysis (D’Elia et al., 1999). In contrast with the predominant mode of speciation within the genus Ctenomys associated with chromosomal rearrangements (Ortells, 1995; Reig and Kiblisky, 1969), members of the mendocinus group share relatively uniform karyotypes. Although a karyotype of 2n=48 is predominant, limited polymorphism has been reported in a single pair of chromosomes in populations of azarae and porteousi (Massarini et al., 1998) resulting in karyotypes with a 2n=46-48. |