Karyotype evolution in South American subterranean rodents Ctenomys magellanicus (Rodentia: Octodontidae): chromosome rearrangements and (TTAGGG)n telomeric sequence localization in 2n=34 and 2n=36 chromosomal forms

摘要

Ctenomys is the most numerous genus of South American subterranean rodents with about 60 species distributed from Peru and Brazil to Tierra del Fuego (Argentina). This is one of the most karyotypically diverse clades of mammals known, with diploid numbers ranging from 10 to 70 chromosomes (Reig et al. 1990). For this reason, Ctenomys is very useful to investigate the dynamics of chromosome evolution as well as the process of speciation in mammals. Several lines of evidence suggest that karyotype evolution of Ctenomys involves an increasing trend in both diploid and fundamental numbers (Reig et al. 1990; Massarini et al. 1991; Ortells 1995; Bidau et al. 1996).Ctenomys magellanicus is the southernmost species of the group and the only one living in Isla Grande de Tierra del Fuego (Argentina). This species presents two chromosomal forms, i.e., 2n=34, and 2n=36 (Kiblisky and Reig 1968; Gallardo 1979; Lizarralde 1992). The presence of a constant number of chromosome arms (FN=68) and interstitial C-bands suggests that C. magellanicus underwent a chromosome reorganization through numerical and structural changes (Reig and Kiblisky 1969; Gallardo 1991; Alvarez et al. 1994). A recent study showed that the two chromosomal forms of this species exhibit non significant differences in terms of genetic (estimated by allozyme analysis) and morphological differentiation (Lizarralde et al. 2001). This might indicate a relatively recent karyotypic differentiation, suggesting a chromosomal speciation process.Despite all the studies performed so far, the chromosome rearrangements involved in the karyotype evolution of C. magellanicus are still unknown. Hence, in the present study, we used chromosome banding techniques and fluorescence in situ hybridization with a telomeric probe to metaphase chromosomes of the two chromosomal forms of the species in order to determine the possible chromosomal rearrangements involved in the karyotype evolution of this species.