Previously, data from chromosomes, hemoglobin electromorph mobility and banding patterns, and spermatozoal and bacular morphologies indicated that populations traditionally identified as A. chrysophilus in southern Africa consisted of two groups: chrysophilus and another species unidentified by scientific name (Breed, 1995a; Breed et al., 1988; Gordon and Rautenbach, 1980; Gordon and Watson, 1986; Visser and Robinson, 1986, 1987); the two are claimed to be indistinguishable in external morphology. This other species has recently been identified as A. ineptus, which, in addition to the traits listed above, can be distinguished by mtDNA cytochrome b sequences (Linzey, et al., 2003).

The two species were thought to be extensively sympatric in the Southern African Subregion (Taylor, 2000b), a conclusion based upon morphometric analyses of cytogenetically identified voucher specimens and material of unknown cytotypes (Chimimba, 1998; Chimimba et al., 1999). Using positively identified specimens, however, Linzey et al. (2003) provided an altered hypothesis of distributions that indicates their geographic ranges are mostly parapatric with a narrow zone of overlap and sympatry (a site in Limpopo Province of South Africa is the only confirmed record of syntopy) along lowlands of the Limpopo River drainage in NE South Africa. Aethomys ineptus occurs in the remainder of C, N, and E South Africa (see that account), and of the two, A. chrysophilus is the only one to range extensively outside that country. Samples from NW Tanzania have 2n = 50 and were identified as Aethomys cf. chrysophilus (Fadda et al., 2001b), which is the same 2n characterizing southern African samples of A. chrysophilus; 2n = 44 is diagnostic for A. ineptus (Chimimba, 1998; Chimimba et al., 1999). With the revised definition of A. chrysophilus offered by Linzey et al. (2003), the intraspecific analysis of samples from southern Africa suggesting the presence of two subspecies (Chimimba, 2000) requires reevaluation.

Recently, Castiglia et al. (2003b) characterized Tanzanian A. chrysophilus by chromosomal (C- and G-banding) and molecular traits (complete mtDNA cytochrome b sequence) and compared results with similar data for Zambian A. kaiseri. The 2n = 50 shared by the two species also characterizes A. bocagei (Matthey, 1954; Visser and Robinson, 1986), and Castiglia et al. (2003b:85) suggested this is ". . . the ancestral chromosomal number. . ." for Aethomys. Divergence between the two species from a common ancestor occurred 5-4 million years ago, as derived from the cytochrome b sequence analyses.

Non-geographic variation associated with sex and age in A. chrysophilus reported by Chimimba and Dippenaar (1994). Several regional studies reported distributional, ecological, and taxonomic information for samples from Mt Kilimanjaro (Grimshaw et al., 1995), Bazaruto Arch. off the coast of S Mozambique (Downs and Wirminghaus, 1997), and the Southern African Subregion (de Graaff, 1997y).