A MULTIDISCIPLINARY APPROACH TO THE SYSTEMATICS OF THE GENUS ARVICANTHIS LESSON, 1842 (RODENTIA, MURINAE)

The genus Arvicanthis includes several cryptic species, some of which have been primarily identified on a cytogenetic basis. This paper pres ents results on cytogenetics, genetics (allozymes) and geometric morph ometrics of three species from Ethiopia, i.e. A. dembeensis, A. abyssi nicus and A. blicki, and one from West Africa (Benin), Arvicanthis sp. Karyotypes were compared using banding procedures (C-, G- and Ag-NOR- bands). A dembeensis and A. abyssinicus share the same 2n = 62 and dif fer by a pericentric inversion. A. dembeensis has the same ANI-1 cytot ype (Volobouev et al. 1988) found in A. niloticus from terra typica. A . blicki has a lower diploid number (2n = 48) due to Robertsonian fusi ons. Arvicanthis sp. from Benin has also a 2n = 62 karyotype, but with several pericentric inversions corresponding to a variant of the ANI- 3 Volobouev's cytotype. Chromosomal rearrangements were used to assess phylogenetic relationships between species. Multilocus electrophoreti c analysis on 25 loci showed a high genetic differentiation (presumabl y dating to the early Pliocene) between Arvicanthis sp. from Benin and the Ethiopian species (Nei's (D) over bar = 0.847). The highest genet ic affinities are between A. abyssinicus and A. blicki ((D) over bar = 0.079), suggesting a recent Pleistocene speciation, and they are both different from A. dembeensis ((D) over bar = 0.240). Geometric morpho metrics (Relative Warps) were used to show size and shape changes in t he skull of the four species, with 19 landmarks from the dorsal and 22 landmarks from the ventral side of the skull. There are very differen t skull traits between species, with closer relationships between A. d embeensis and Arvicanthis sp. Genetic and cytogenetic evidence suggest that the Benin Arvicanthis belongs to a Western group of populations characterised by different cytotypes and it probably deserves a differ ent name. Moreover, the fact that the karyotype of A. dembeensis is id entical to that of the ''true'' A. niloticus from terra typica (Egypt) suggests a need to test whether it represents a geographic variant of A. niloticus or a different species.