Karyotypic Evolution in Ctenomys (Rodentia, Ctenomyidae)

Cytogenetic relationships among Andean species of Ctenomys were examined by use of nondifferentially stained chromosomes, C-band patterns, and sperm morphology. Chromosomal diversity shows evolutionary karyotypic pathways that are remarkably varied. C-band analyses indicate that tandem fusions and other non-Robertsonian mechanisms account for the variation observed in the genus. Evolution of heterochromatin has proceeded through whole-arm additions and euchromatin transformation. Evolutionary trends toward an increase or decrease in chromosome number have been independent of heterochromatic changes. Heterochromatic short arms do not account for the large number of metacentric chromosomes. Accordingly, neither high nor low fundamental numbers per se represent derived conditions in this taxon.