Mastomys pernanus Kershaw 1921

Mastomys pernanus Kershaw 1921, Ann. Mag. Nat. Hist., ser. 9, 8: 568.

Type Locality: SW Kenya, Amala (Mara) River; see G. M. Allen (1939:406) and Misonne and Verschuren (1964:655) for details.

Vernacular Names: Dwarf Mastomys.

Distribution: Published records are from SW Kenya, N Tanzania, and Rwanda (Misonne and Verschuren, 1964; see map inVan der Straeten, 1999:228).

Conservation: IUCN – Data Deficient.

Discussion: Known by very few specimens. Ellerman (1941) listed pernanus as a distinctive species of Rattus in the subgenus Mastomys, but earlier G. M. Allen (1939) had treated it as a species of Myomys . Robbins and Van der Straeten (1989) claimed this a possibility. Misonne and Verschuren (1964, 1966 b), however, discussed the problem and concluded that pernanus should be associated with Mastomys, an arrangement endorsed by Van der Straeten (1999). Van der Straeten (1999) studied and measured all known specimens (except those from Rwanda extracted from raptor pellets and a skull from Tanzania reported by Misonne and Verschuren, 1964, which could not be found in the Koninklijk Belgisch Instituut voor Natuurwetenschappen at Brussels). His principal component analysis contrasting two specimens of M. pernanus with holotypes of taxa in Praomys, Mastomys, Myomys, Myomyscus, and Hylomyscus indicated M. pernanus could be a dwarf Mastomys . Van der Straeten (1999) and Granjon et al. (1997 b) suggested that molecular data might provide sharper resolution of M. pernanus ’s affinities. Recent analyses of complete mtDNA cytochrome b (Lecompte et al., 2002 b) and nuclear IRBP gene (Lecompte, 2003) sequences did not cluster M. pernanus with the other species of Mastomys tested ( M. coucha, M. huberti, M. erythroleucus, M. natalensis, and M. kollmannspergeri [reported as verheyeni]), but aligned it with Heimyscus and species of Hylomyscus . Keeping pernanus within Mastomys renders that genus polyphyletic, but extracting it will require additional analyses using a broader array of genes to determine if pernanus is the sole member of a separate genus related to Hylomyscus or to be included within that genus (see discussion in Lecompte, 2003).