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 presents results on cytogenetics, genetics (allozymes) and geometric morphometrics of three species from Ethiopia, i.e. A. dembeensis, A. abyssinicus 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 differ by a pericentric inversion. A. dembeensis has the same ANI-1 cytotype (Volobouev et al. 1988) found in A. niloticus from terra typica. A. blicki has a lower diploid number (2n = 48) due to Robertsonian fusions. 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 electrophoretic analysis on 25 loci showed a high genetic differentiation (presumably dating to the early Pliocene) between Arvicanthis sp. from Benin and the Ethiopian species (Nei's (D) over bar = 0.847). The highest genetic 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 morphometrics (Relative Warps) were used to show size and shape changes in the skull of the four species, with 19 landmarks from the dorsal and 22 landmarks from the ventral side of the skull. There are very different skull traits between species, with closer relationships between A. dembeensis 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 different name. Moreover, the fact that the karyotype of A. dembeensis is identical 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.