CONICET | Buscador de Institutos y Recursos Humanos

Rodentsare a very diverse group with large chromosome variability. One of the mostspecies rich linage in the Neotropics, is the Sigmodontinae. Among them, thetribe Abrotrichini was recently defined and its taxonomy and phylogeny were mostlyelucidated through molecular and morphological evidence. Meanwhile, chromosomedata were only secondarily used because of fragmentary information. In this contribution,we conduct a chromosome characterization of Abrothrixhirta, A. olivacea, A. andinaand Paynomys macronyx, review the cytogeneticbackground of the tribe, and contrast it with molecular data. Chromosomes wereanalyzed by conventional and differential techniques. All Abrothrix species presented 2n=52/FNa=56, with a high similarityin the banding patterns reflecting a conserved karyotype, which does notcoincide with its high molecular variability. In turn, P. macronyx have 2n=54/FNa=58-59, varying due to a heteromorphicpair of autosomes. In addition, in this last species, different morphologies ofthe X chromosome and the presence of B-chromosomes were detected. Heterochromatin was involved in thesevariants. The telomeric probe in P. macronyx marks terminal regions ofall chromosomes. B-chromosomes generated strong telomeric signals. The Ag-NORsbanding revealed the same patterns in Abrothrixand Paynomys. Cytogenetic datasupport phylogenetic relationships previously proposed and suggest that the speciousgenus Abrothrix could have retainedthe ancestral karyotype of the subfamily. In the tribe, the relativelyconserved chromosome complement contrasts with its high molecular variability.This indicates decoupling between the rates of chromosomal and moleculardivergence, as observed in other rodent lineages. In abrotrichines, chromosomeevolution was slower.