Hybomys Thomas 1910

Hybomys Thomas 1910, Ann. Mag. Nat. Hist., ser. 8, 5: 85.

Type Species: Mus univittatus Peters 1876

Species and subspecies: 6 species in 2 subgenera:

Subgenus Hybomys (Hybomys) Thomas 1910

Subgenus Hybomys (Typomys) Thomas 1911

Species Hybomys (Hybomys) badius Osgood 1936

Species Hybomys (Hybomys) basilii Eisentraut 1965

Species Hybomys (Hybomys) lunaris (Thomas 1906)

Species Hybomys (Typomys) planifrons (Miller 1900)

Species Hybomys (Typomys) trivirgatus (Temminck 1853)

Species Hybomys (Hybomys) univittatus (Peters 1876)

Discussion: Hybomys Division. The species have traditionally been arranged into two groups and reflected taxonomically as either subgenera ( Hybomys and Typomys; G. M. Allen, 1939; Carleton and Robbins, 1985; Ellerman, 1941; Misonne, 1969) or genera (Thomas, 1911 b; see Rosevear's [1969] excellent exposition). Morphometric analyses of cranial and dental dimensions by Van der Straeten (1984) showed a closer alliance between the subgenus Hybomys and Dephomys, a West African forest endemic, than with Typomys, and prompted Van der Straeten to argue strongly for recognizing Typomys as a separate genus. But his conclusion was founded on multivariate analyses of continuous variables and ignored discrete character-trait differences; his tree is a phenogram of shape-size similarity, not a cladogram of shared-derived characters hypothesizing phylogenetic affinity. Carleton and Robbins (1985:983) corroborated the dichotomy between Hybomys and Typomys using a suite of qualitative features and chromosomal data, but commented that whether " Typomys and Hybomys merit generic segregation must await an evaluation of character variation among Hybomys and its near relatives." We also note that Hybomys and Typomys share several traits setting them apart from Dephomys (dorsal striping, no pronounced guard hairs, narrower hind foot with short fifth digit, no hypothenar pad, tail shorter than head and body, weaker temporal ridging, shorter incisive foramina, deeper zygomatic notch, larger auditory bullae, and cusp t3 of M1 larger and separate from cusp t2). Additional research is needed to resolve the phylogenetic relationships among Hybomys, Typomys, and other genera of African rainforest murines. Analysis of microcomplement fixation of albumin grouped Hybomys univittatus with Stochomys (Watts and Baverstock, 1995 a), but other genera and species critical to resolving the Typomys-Hybomys problem were not included in their inquiry. Analyses of mtDNA cytochrome b and 12S and 16S rRNA gene fragments placed Hybomys with Dasymys in an African murine clade containing Aethomys, Grammomys, Lemniscomys, Desmomys, Rhabdomys, Pelomys, Mylomys, and Arvicanthis (Ducroz et al., 2001) . The association of Hybomys with Dasymys, Grammomys, and arvicanthines is also supported by DNA/DNA hybridization studies (Chevret, 1994), analyses of nuclear IRBP gene sequences (Lecompte, 2003), and another study of mtDNA cytochrome b sequences (Castiglia et al., 2003 b). Carleton and Robbins (1985) reviewed patterns of morphometric differentiation, qualitative features, chromosomal data, geographic distributions, and ecological and zoogeographical associations of several species, focusing on West African forms but discussing taxonomic problems within the H. univittatus complex.