Phylogenetic Studies of the Rodent Family Gerbillidae: I. Chromosomal Evolution in the Southern African Complex

Chromosomes of several southern African gerbils were examined and compared by G- and C-banding techniques: Desmodillus auricularis, Gerbillurus paeba, G. vallinus, Tatera afra, T. brantsii, and T. leucogastor. Intraspecific chromosomal variation involves an inversion and a euchromatic addition in G. paeba, and heterochromatic additions in G. vallinus and the Tatera species. Chromosomal evolution in the southern African gerbils has been characterized by a minimum of 7 centric fissions, 6 centric fusions, 1 tandem fusion, 7 inversions (one unfixed), 6 translocations, and numerous but individually variable constitutive heterochromatic additions. The close affinity of the genera Tatera and Gerbillurus is confirmed by cladistic analysis of chromosomal data. Gerbillurus paeba (2n = 36) and G. vallinus (2n = 60) evidently arose from a common ancestor that had a 2n = 44; events leading to the former were fusions, to the latter fissions. This illustrates the hazard of assuming either a general decrease or increase in diploid numbers for any group of mammals.