Chromosomal variation in Argentine populations of Akodon montensis Thomas, 1913 (Rodentia, Cricetidae, Sigmodontinae)

Abstract

The genus Akodon Meyen, 1833 is one of the most species-rich among sigmodontine rodents and has great chromosome variability. Akodon montensis has a relatively broad distribution in South America, and Argentine populations are located in the southernmost region of its range. Brazilian populations have important chromosomal variability, but cytogenetic data from Argentina are scarce. We performed a chromosome characterization of natural populations of Akodon montensis using conventional staining, C-banding, Ag-NORs and base-specific fluorochromes. A total of 31 specimens from five localities of Misiones Province, in Argentina, were analyzed. The 2n=24 chromosomes was the most frequently observed karyotype. However, five individuals presented 25 chromosomes due to a supernumerary B-chromosome; and one individual had 2n=26 due to one B plus a trisomy for chromosome 11. Additionally, two XY females and two variants of the X chromosomes were found. C-positive centromeric bands occurred in all chromosomes; additional C-bands were observed in some autosomes, the X, Y and B chromosomes. Ag-NORs were observed in five autosomes, and the B chromosome was frequently marked. Fluorochrome banding was similar among karyotypes of the analyzed populations. Comparisons of cytogenetic data among populations of Argentina and Brazil showed the presence of high intraspecific variability in Akodon montensis and some differences among regions.

Revision and analysis of the chromosome variability in the speciose genus Akodon (Rodentia, Sigmodontinae), including new data from Argentina

“…Additionally, some groups are very variable, as the A. cursor where high levels of polymorphisms were reported (Fagundes et al 1998, Silva & Yonenaga-Yassuda 1998. Also, in this last group, species with B-chromosomes, sex-reversed females, and trisomies were detected (Fagundes et al 1998, Silva & Yonenaga-Yassuda 1998, Malleret et al 2016, Labaroni et al 2023. This indicates that these chromosomal variants have not a high negative impact on the fertility and survival of these species.…”

“…The Y chromosome was different in morphology in both lineages but was always wholly heterochromatic. The accumulation of heterochromatin in sex chromosomes is usual in rodents, probably due to genetic degenerations (Labaroni et al 2014, Malleret et al 2016, Buschiazzo et al 2018. In both chromosome complements, the NORs were evidenced in several autosomes, indicating multiple active NORs, as in other Akodon species (Malleret et al 2016).…”

“…Diploid and fundamental numbers range from 2n=44, FNa=44 in A. paranaensis, A. reigi, and A. dolores (Tiranti 1998, González et al 1998, Christoff et al 2000 to 2n=10, FNa=14 in A. diauarum (Silva & Yonenaga-Yassuda 1998). Some species share the karyotype, but others present distinctive chromosome complements (Myers 1989, Gonçalves et al 2007, Malleret et al 2016. Additionally, other species have polymorphisms and polytypisms, as A. dolores in which several species-specific Robertsonian (Rb) variants were described (Bianchi et al 1971, 1979, Wittouck et al 1995, Tiranti 1998.…”

B Chromosomes in Populations of Mammals Revisited

“…Besides Bs, genus Mazama is featured with other kinds of chromosome polymorphisms, involving autosomes and sex chromosomes. This is also the case with Acodon montensis [ 128 ]. On the other hand, genus Apodemus with one third of species with Bs is karyotypically very stable.…”