|Distribution:||NE Africa: Libya, Egypt (Osborn and Helmy, 1980), Sinai Peninsula (Saleh and Basuony, 1998), N Sudan, Ethiopia (identified by chromosomal traits; Sokolov et al., 1992, 1993), and Djibouti (Pearch et al., 2001); see Bates (1994); W and S distributional limits unresolved.|
Subgenus Acomys. Musser and Carleton (1993) presented a broad definition of A. cahirinus that included some of the species listed here (airensis, chudeaui, dimidiatus and its synonyms, johannis and seurati) and had a geographic range extending from NW Africa to S Pakistan (as mapped by Bates, 1994, who followed Musser and Carleton, 1993). A growing body of published research, mostly by French scientists, has rendered Musser and Carleton’s view simplistic and an underestimate of the actual number of species. As currently understood, the geographic distribution of A. cahirinus centers in NE Africa, and the species is distinguished from A. airensis, A. chudeaui, A. dimidiatus, A. johannis, and A. seurati by dental characters (Denys et al., 1994), chromosomal traits (Volobouev et al., 1991, 1996, 2002b; 2n = 36 for A. cahirinus, 2n from 38 to 68 for the other species), and mtDNA cytochrome b sequences (Barome et al., 2000, 2001a, b); see accounts of those species.
Morphological and geographic definition of A. cahirinus remains incomplete; some of the taxa listed here as synonyms may belong to other species. El Ashmawy (1990), for example, documented different G- and C-banding patterns in cahirinus and hunteri from Egypt. Osborn and Helmy (1980), however, noted the ample evidence of intergradation between hunteri (described from NE Sudan) and cahirinus but no indication that hunteri intergrades with the more southern cineraceus. We provisionally include viator (type locality NC Libya) in the synonymy of A. cahirinus, but Osborn and Helmy (1980) recorded smaller measurements for that form in Egypt (occurs only in extreme SW corner of the country) compared with all the other samples of A. cahirinus, and Denys et al. (1994) described the molar morphology of viator as distinct from that of A. cahirinus. Ranck (1968) provided detailed descriptions of pelage and habitat for samples from Libya that he assigned to viator. Whether the latter represents the easternmost segment of A. cahirinus, is a separate species, or a population of some other Acomys (the Algerian seurati, for example) will have to be determined by cytogenetic, molecular, and additional morphological inquiries.
Setzer (1959:95) claimed melanistic A. cahirinus to be "almost exclusively commensal" or, if not actually caught in houses, collected in cultivated fields adjacent to villages. Osborn and Helmy (1980:298) noted that melanism is common in the Egyptian population "because it is the commonest mouse in buildings and houses. Some have been taken in gardens, date groves, and rocky hills and cliffs bordering the Nile Delta and Valley." The rat is also numerous in tombs and temples where the melanism becomes diluted.