CYTOGENETICS OF THE GENUS ARVICANTHIS (RODENTIA, MURIDAE) .1. ARVICANTHIS NILOTICUS FROM REPUBLIC OF BENIN (WEST-AFRICA)

Arvicanthis niloticus is characterized, according to previous karyological studies, by a wide chromosome variability. In distinct populations of its wide area of distribution, the diploid number ranges from between 2n=44 and 2n=62. The present study analysed the karyotype of 13 Arvicanthis niloticus from South Benin, Guinea Gulf (West Africa). The constitutive heterochromatin pattern was evidenced by C-banding and the location of Nucleolar Organiser Regions was assessed by AgNO3 plus G-banding reactions. The G-banding pattern was also performed both on cultured fibroblasts and bone marrow preparations. The 2n=62 and the aFN=74 characterize the South Benin cytotype which was found to be identical to that described for Southern Senegal specimens. A few chromosomal rearrangements (3 pericentric inversions) are enough to transform the Benin cytotype into the ANI-3 cytotype described in animals from Mall and Burkina Faso. A polymorphism of the X chromosome is described; three different forms (i.e. metacentric, submetacentric, and subtelocentric) were observed both in homomorphic and heteromorphic conditions. The problem of intraspecies chromosomal variability in Arvicanthis niloticus is discussed.