Karyotypic Relationship between Akodon azarae and A. boliviensis (Rodentia, Sigmodontinae).

Abstract

Summary The genus Akodon, comprising more than 60% of the species of the Akodontini, widely distributed in South America, presents many interesting cytogenetic atributes, such as an ample karyotypic variation (2n=10-52), intraspecific and intrapopulational polymorphisms of the autosomes and of the gonosomes, and, as in both species here studied, XY fertile females. We report a cytogenetic comparative study of A. azarae (2n=38) and of A. boliviensis (2n=40) specimens. In these species, only the sex chromosomes, the first autosomal pair and the small bibrachial autosome characteristic of the genus, can be identified in conventional preparations. Chromosome relative lengths of each species were determined from G-banded karyotypes, and a schematic representation of the G-banding patterns is presented. The comparison of these patterns shows that 16 autosomal pairs are "shared" chromosomes, corresponding to 88.3% of the autosomal complement of A. azarae and to 87.5% of that of A. boliviensis. Furthermore, A. azarae pair 2 (8.23% of its autosomal complement) has a banding pattern homologue to pair 15 and most of pair 12 of A. boliviensis, which indicates that this chromosome of A. azarae would basically result from a tandem translocation. Apparently, no correspondence exists between the remaining pair 16 of A. azarae and pair 11 of A. boliviensis. Key words Akodontini, Akodon boliviensis, Akodon azarae, Chromosomes, G-bands.The genus Akodon (Reig 1986(Reig , 1987 is the most polytypic of the akodontine tribe of the South American Sigmodontinae, comprising more than 60% of the species of the tribe (Apfelbaum and Reig 1989, Reig 1987). Its species are extensively distributed in South America, and can be found in different habitats through most part of the subcontinent. This genus is cytogenetically very interesting, not only because of its systematic complexity, but also due to the considerable karyotypic variation existent (2n= 10-52), the intraspecific variation concerning the autosomes and the sex chromosomes, and the presence of species with fertile XY females

Chromosomal localization of telomeric sequences in three species of <i>Akodon</i> (Rodentia, Sigmodontinae)

“…The long arm of pair 1 of A. dolores, considered to be homologous to pair 1 of A. boliviensis and A. azarae (Bianchi and Merani, 1984;Lisanti et al, 2000), did not exhibit the proximal IT observed in these chromosomes (the short arm is not conserved in these species). A more detailed analysis of the Gbanding patterns (Fig.…”

“…1A, B). This chromosome pair is represented by two telocentric pairs in A. boliviensis and A. azarae, among several akodontine species (Bianchi and Merani, 1984;Lisanti et al, 2000). Comparison of the G-banding patterns did not reveal any rearrangement corresponding to this interstitial signal (Fig.…”

“…However, a karyotype comparison of G-banding patterns of A. azarae and A. boliviensis (Lisanti et al, 2000) showed that 16 chromosome pairs (approximately 88 % of their autosomal sets) were conserved between these species. No rearrangements involving chromosomes of the size of those presenting ITs could be detected at this level.…”