Otomys irroratus Brants 1827

Otomys irroratus Brants 1827, Het Geslacht der Muizen: 94.

Type Locality: South Africa, Western Cape Province, Cape Town district, near Constantia (fixed by A. Smith, 1834:149, in supplying replacement name typicus; see Meester et al., 1986:250) .

Vernacular Names: Southern African Vlei Rat.

Synonyms: Otomys auratus Wroughton 1906; Otomys bisulcatus F. Cuvier 1829; Otomys capensis G. Cuvier 1830; Otomys coenosus Thomas 1918; Otomys cupreoides Roberts 1946; Otomys cupreus Wroughton 1906; Otomys natalensis Roberts 1929; Otomys obscura (Lichtenstein 1842); Otomys orientalis Roberts 1946; Otomys randensis Roberts 1929; Otomys saundersiae Roberts 1929; Otomys typicus (A. Smith 1834) .

Distribution: Mesic savannah and grasslands of southern Africa—S Western Cape Province to Limpopo Province, South Africa; disjunct populations in W South Africa and in E Zimbabwe and contiguous Mozambique (De Graaff, 1981:146).

Conservation: IUCN – Lower Risk (lc).

Discussion: Bohmann (1952) established a broad, improbably polymorphic definition of O. irroratus, including some 23 subspecies, a concept further enlarged by Dieterlen (1968) and Petter (1982) and collectively enveloping the following forms here (and elsewhere) treated as separate species (see individual accounts): O. anchietae, O. angoniensis, O. barbouri, O. burtoni, O. cuanzensis, O. dollmani, O. jacksoni, O. laminatus, O. maximus, O. orestes, O. tropicalis, O. typus, and O. uzungwensis . Although followed to a greater or lesser extent (e.g., Delany, 1975; Honacki et al., 1982; Kingdon, 1974 b), such an inclusive species construct has been refuted by others who identify O. irroratus proper as a species indigenous to southern Africa, south of the Zambezi River (e.g., De Graaff, 1981; Meester et al., 1986; Misonne, 1974; Taylor and Kumirai, 2001). Morphometrically distinguishable from East African forms, such as O. typus and O. tropicalis, and M3 characteristically possessing 6 laminae compared with 7-8 in those forms (Dollman, 1915; Thomas, 1918 b; Taylor and Kumirai, 2001).

A subject of intensive investigation of intraspecific patterns of differentiation, O. irroratus sensu stricto is becoming a model organism for pursuit of evolutionary questions. Some results suggest "incipient speciation" among the population moieties so far identified (see overview and mapping of chromosomal races by Taylor, 2000 b:Fig. 1), although the different data sets are not necessarily wholly concordant. G-banded comparisons reveal a karyotype that is highly derived (Robinson and Elder, 1987). Extensive cytogenetic variation (2n = 23-32; FN = 24-50) reported among South African population samples (Contrafatto et al., 1992 a, b; Taylor, 2000 b), complemented by examinations of variation in mtDNA (Lamb et al., 1996), protein electrophoresis (Contrafatto et al., 1997; Taylor et al., 1992; Taylor, 2000 b), and reproductive isolating mechanisms (Pillay et al., 1992; 1995 a, b). Correlation of cytotype distributions with climatic variables studied by Taylor et al. (1994 b). Included saundersiae according to Taylor et al. (1993) but afterwards reinstated to species by Taylor et al. (in prep.); see that account. See Bronner et al. (1988, Mammalian Species, 308).