Otomys simiensis, Taylor & Lavrenchenko & Carleton & Verheyen & Bennett & Oosthuizen & Maree, 2011

Taylor, Peter J., Lavrenchenko, Leonid A., Carleton, Michael D., Verheyen, Erik, Bennett, Nigel C., Oosthuizen, Carel J. & Maree, Sarita, 2011, Specific limits and emerging diversity patterns in East African populations of laminate-toothed rats, genus Otomys (Muridae: Murinae: Otomyini): Revision of the Otomys typus complex 3024, Zootaxa 3024 (1), pp. 1-66 : 47

Otomys simiensis new species

Figs. 2c , 5 , 6 , 17 ; Table 9

Simien Vlei Rat

Holotype. ZMMU 178757 ; adult male, dry skin and skull, collector’s number 1338; collected by L.A. Lavrenchenko, 4 May 2005.

Type locality. Ethiopia, Simien Mountains National Park , vicinity of Sankaber campsite, 3250 m; 13°14'N, 38°03'E ( GPS reading by collector) .

Diagnosis. A small-sized representative of the O. typus species complex (referred to “Sp. D” above; see Figs. 5 , 6 , 17 and Tables 7, 9). Similar to O. yaldeni but considerably larger externally (HB mean 155 mm in simiensis , cf. 143 in yaldeni ; tail means 83 mm and 72 mm respectively); skull having a narrower interorbital region, less pronounced supraorbital ridges, relatively longer nasal bones, and braincase with flatter dorsal profile ( Fig. 17 ); karyotype distinctive (2N=54, NF=56).

Paratypes. ZMMU 178756 (adult female, dry skin and skull, collector’s number 1336) ; ZMMU 178758 (adult male, dry skin and skull, collector’s number 1352) ; ZMMU 178759 (adult male, dry skin and skull, collector’s number 1353) ; ZMMU 178762 (adult female, dry skin and skull, collector’s number 1429); all four specimens from the type locality, collected by L.A. Lavrenchenko between 4 and 20 May 2005 .

Description. The dorsal pelage is dark brown, with individual hairs having a blackish base, rufous subterminal band, and relatively narrow black tip. Among the guard hairs (17 mm), there are longer bristles (26 mm) that produce the effect of the double-layered fur. Ventral pelage is pale grey, the individual hairs grey at the base and tipped with pale whitish. The ears are blackish, their inner surface covered with short rufous hairs. Dorsal surfaces of the forefeet and hindfeet are dark grey, and the claws are grey. The tail is moderately long (53.4% of HB) and appears distinctly bicoloured, the dorsal caudal hairs relatively long and blackish in contrast to the white ventral hairs.

The skull resembles most other members of the O. typus complex, having a relatively narrow interorbital region, reduced supraorbital ridges, shallow braincase, and short anterior palatal foramen ( Table 9). Anterior face of the lower incisor has two well defined and equally deep grooves. The upper third molar possesses 7 complete laminae; the lower first molar possesses 4 complete laminae.

The chromosomal complement of O. simiensis consists of 2N=54, NF=56; 2m + 52a ( Fig. 2c ).

Otomys simiensis differs from other Ethiopian Otomys (excluding yaldeni ) by the lower number of laminae in the upper third molar (7 versus 8–9) and the double-layered dorsal fur. Amongst other members of typus s.l., simiensis is most like jacksoni which is similar in skull size and shape ( Table 9) and also has 7 laminae in the third upper molar and a similar dark brown colour ( Bohmann 1952); however, jacksoni is much smaller in external dimensions (HB mean 141 mm in jacksoni cf. 155 mm in simiensis ) and has a proportionately shorter tail (45.4% in jacksoni cf. 53.4% in simiensis ). Furthermore molecular data ( Fig. 3 ) clearly demonstrate the genetic separation of these taxa.

Distribution. Known only from the type locality in the Simien Mountains, northern Ethiopia (see above).

Ecology. The holotype and paratypes of O. simiensis were captured in tree-heather forest (trees: Erica arborea , Hypericum revolutum ; shrub: Rosa abyssinica ) with open grassy patches. At higher altitudes, this species is replaced by O. typus s.s., a common inhabitant of the afroalpine zone in the Simien Mountains National Park (e.g., Chennek area, 13°15’N, 38°13’E, 3800 m).

Etymology. The rugged Simien Mountains, to which the new species is apparently endemic, dominate the northern plateau of Ethiopia and contain its highest peaks. The name combines the stem Simien with the Latin suffix “ensis,” meaning “native of” or “characteristic of” the place indicated by the stem.

Figures

FIGURE 2. Giemsa stained karyotypes of (a) Otomys helleri (= “Sp. B”; n=6), O. fortior (n=6) and O.typus s.s. (n=1) (2n=58, NFa=58), (b) Otomys yaldeni sp. nov. (= “Sp. A”; n=1; 2n=56, NFa=54), and (c) Otomys simiensis sp. nov. (= “Sp. D”; n=4; 2n=54, NFa=54).

FIGURE 3a. Bayesian phylogeny inferred from cyt b sequences partitioned by codon position for 34 East African specimens of O. typus s.l. and O. tropicalis s.l. in relation to representatives of seven Otomys species and Parotomys brantsii from eastern, western and southern Africa. Representatives of nine murine taxa served as outgroups (see Appendix 1). Nodal support indices for the main clades (annotated 1 to 8) and subclades (a, b, c, d and e), as well as supported deeper nodes (A, H, I, M, N, O) are given beside the phylogram in the following order: Bayesian posterior probabilities (BPP)/ bootstrap support from 1000 replicates for maximum likelihood (MLbs), under an unpartitioned GTR+I+G model/ unweighted parsimony (UwPbs), six-parameter-weighted parsimony partitioned by codon positions (6PPbs)/ neighbour-joining using uncorrected p-distances (Njpbs)/ neighbour-joining using GTR+I+G-corrected distances (Njcbs). Estimated divergence dates (Myr) for the major lineages identified in the cyt b phylogeny are indicated to the left of each node. Bayesian estimation of divergence times was conducted under a relaxed clock model using BEAST v.1.4. Four well established murine fossil calibration points were specified (Pocock 1987; Rowe et al. 2008, see text).

FIGURE 5. Principal components analysis (PCA) based on nine craniometric variables indicating scatter of individuals on PC1 and PC2 (a) and PC2 and PC3 (b) from six pre-defined taxon-groups of Ethiopian Otomys in relation to existing type specimens of fortior and degeni and new holotypes designated for new species (see Taxonomic Summary). Open squares = O. typus s.s., open triangles = O. fortior; open diamonds = O. yaldeni sp. nov. (= Sp. A); closed squares = O. helleri (= Sp. B); open circles = O. cheesmani sp. nov. (= Sp.C); closed diamonds = O. simiensis sp. nov. (= Sp. D); cross = degeni. Type specimens indicated; normal font indicates existing holotypes; bold font represents newly designated holotypes (see Taxonomic Summary).

FIGURE 6. Canonical variates analysis (plot of first two canonical variates) of six defined taxon-groups of Ethiopian Otomys based on nine craniometric variables. Position of individuals form “unknown” sample from Oromiya, Jimma (asterisks) predicted a posteriori. Open squares = O. typus s.s. (Mt Guna); Closed squares = O. fortior; open circles = O. helleri (= “Sp. B”); closed circles = O. yaldeni sp. nov. (= “Sp. A”); open triangles = O. cheesmani sp. nov. (= “Sp. C”); closed triangles = O. simiensis sp. nov. (= “Sp. D”).

FIGURE 17(a–c). Photographs comparing dorsal, ventral and lateral views of the skulls of holotype of Otomys yaldeni (ZMMU 162594).