CHARACTERIZATION OF 2 DISTINCT SPECIES OF ARVICANTHIS (RODENTIA, MURIDAE) IN WEST-AFRICA - CYTOGENETIC, MOLECULAR AND REPRODUCTIVE EVIDENCE

The unstriped grass rat, Arvicantilis Lesson 1842, is one of the most common genera of murid rodents in African savannas. However, from a sy stematic viewpoint, very little is known about this group. Following r ecent investigations which showed karyotypic variability within the sp ecies A. niloticus, the present study attempts to clarify the nature a nd distribution of these chromosomal variants, as well as to determine their taxonomic rank. The chromosomes of 15 individuals from differen t West African localities were prepared from fibroblast cultures, and R- and C-banded karyotypes were constructed. In addition, the levels o f genetic divergence (DNA/DNA hybridization) and reproductive isolatio n (attempted crossbreeding in captivity) were examined. The results co nfirm the existence of two differentiated karyomorphs, differing by nu merous chromosomal rearrangements such as pericentric inversions and t ranslocations, as well as differences in the quantity of constitutive heterochromatin. These karyomorphs appear to be genetically and reprod uctively isolated and are parapatrically distributed; their areas of d istribution correspond to the sahelian and sudano-guinean domains, res pectively. The distinctness of these karyomorphs, the absence of hybri ds in laboratory crosses, and the pronounced genetic divergence provid e good evidence for the recognition of two distinct sibling species. W e propose to keep the designation A. niloticus for the northern saheli an form and discuss the naming alternatives for the other.