Arvicanthis ansorgei Thomas 1910

Arvicanthis ansorgei Thomas 1910, Ann. Mag. Nat. Hist., ser. 8, 5: 353.

Type Locality: Bissau Guinea, Gunnal.

Vernacular Names: Sudanian Arvicanthis.

Distribution: Grasslands and bush in Sudanian savannas from Gambia (Fadda and Corti, 2001) and S Senegal (Casamance region south of Gambia River; Granjon et al., 1992) through S Mali, Burkina-Faso, and Niger (Dobigny et al., 2002 b; Ducroz et al., 1998; Volobouev et al., 2002 a) to S Chad (Fadda and Corti, 2001); limits of range unresolved.

Discussion: 2n = 62, FNa = 74-76 (Volobouev et al., 2002 a). This is the species originally separated from samples of A. niloticus by its chromosomal features and identified as ANI-3 (Volobouev et al., 1987, 1988 a; Ducroz et al., 1997). Subsequent analyses incorporating chromosomal refinements, DNA/DNA hybridization, cross-breeding experiments in the laboratory, three-dimensional geometric morphometrics, and mtDNA cytochrome b sequences (Ducroz, 1998; Ducroz et al., 1997, 1998; Fadda and Corti, 2001; Volobouev et al., 2002 a), demonstrated that ansorgei is not a geographic form of A. niloticus but a separate species. The two are sympatric along the southern course and in most of the Inner delta of Niger River in Mali (Volobouev et al., 2002 a), but elsewhere the "... distribution of the two species is largely parapatric and follows the latitudinal patterns of the West-African biogeographical domains, which are related to the latitudinal patterns of annual rainfuall in this region" (Sicard et al., 2004:5). The range of A. ansorgei is generally south of A. niloticus, which inhabits the more arid Sahelian and N Sudanian savannas, and north of A. rufinus, found in the more humid S Sudanian-Guinean savannas and adjacent evergreen forest belt. In Senegal, A. ansorgei occurs only south of the Gambia River while A. niloticus inhabits drier habitats north of the Gambia (Granjon et al., 1992). Phylogenetic analysis of mtDNA cytochrome b sequences by Ducroz et al. (1998) indicated A. ansorgei to be more closely related to samples from East Africa (Tanzania and SW Uganda) than to those from Central Africa (Benin and Central African Republic), a discordance with similarities based upon Procrustes distances, which readily distinguished West African from East African assemblages (Fadda and Corti, 2001).

The holotype of ansorgei was not used in any of the analyses cited above, but it is the only taxon described from a place close to where samples of the ANI-3 chromosomal type were collected, and Volobouev et al. (2002 a) thought it reasonable to use ansorgei as the correct name; no synonyms have been identified.