Evidence for eight tandem and five centric fusions in the evolution of the karyotype ofAethomys namaquensis A. Smith (Rodentia: Muridae)

G- and C-banded chromosomes ofAethomys namaquensis (2n=24),A. chrysophilus (2n=44), andPraomys coucha (2n=36) are compared and contrasted with publised material on Australian Muridae and North American Sigmodontidae. Direction and types of chromosomal rearrangements are established using cladistic methodology. An acrocentric morphology for chromosomes 5, 14, 15 and 20 (numbering system fromPeromyscus) are proposed as primitive for the common ancestor of the Muridae and Sigmodontidae rodent lineages. Reduced diploid number ofAethomys namaquensis is derived by eight tandem and five centric fusions since divergence from the common ancestor withA. chrysophilus. The two species ofAethomys share one derived metacentric chromosome that distinguishes them fromPraomys. Praomys has unique chromosomes which can be derived from the proposed primitive condition by five centric fusions and five pericentric inversions. It is concluded that karyotypic orthoselection for tandem and centric fusions is best explained by cellular or biochemical mechanisms rather than variation in population characteristics.