Robertsonian polymorphism, B chromosomes variation and sex chromosomes heteromorphism in the african water rat Dasymys (Rodentia, Muridae).

Chromosome banding analysis (G- and C-bands) of Dasymys rufulus from Senegal, Mali and the Ivory Coast, and D. cf. incomtus from Eastern and South-western Ethiopia was carried out. The diploid numbers (2N) in the former species range between 36 and 39 due to the presence of 0-3 small biarmed heterochromatic B chromosomes, resulting in a corresponding variation of the number of autosomal arms (NFa) between 44 and 50. The basic autosomal set was, however, constant and identical in these specimens. The karyotypes of D. cf. incomtus from Eastern and Western Ethiopia were found to be different (2N = 40 and 38, respectively). Comparison of G-banding patterns of the species studied revealed that they differ from each others by 1-2 Rb fusions/fissions, one paracentric inversion and heteromorphous sex chromosomes resulting from addition/deletion of heterochromatic blocks (X) and pericentric inversion (Y). In the light of the available chromosome banding data, the significance of intraspecies karyotypic variability within D. cf. incomtus and its relevance to the systematics of the genus are discussed.