Otomys willani, Taylor & Kearney & Dalton & Chakona & Kelly & Barker, 2020

OTOMYS WILLANI SP. NOV., WILLAN’S VLEI RAT

Holotype: Ditsong National Museum of Natural History ( TM) No. 49101 (field number BAR1020) is a male, age class 3, probably young adult (sensu Taylor et al., 1993), with intact cranium (skin rotten and discarded), part of a series of specimens collected at Tiffendell , Eastern Cape Province in December 2013 by G. Goldner. The specimen has been included in both morphometric and molecular analyses. The following external measurements were recorded: total length 198 mm, tail length 74 mm, hind length 25/ 22 mm [cu (cum unguis: with claw) / su (sine unguis: without claw)], ear 16.5 mm.

Type locality: Tiffendell, Eastern Cape Province (30.653°S, 27.928°E), South Africa GoogleMaps .

Paratypes: Ten specimens collected from Tiffendell Ski Resort in December 2013. Some have formaldehydepreserved skins and damaged skulls [ TM49094 ( BAR1002 ), male; TM49100 ( BAR1016 ), unknown sex; TM49097 ( BAR1019 ), male; TM49091 ( BAR1021 ), male; TM49095 ( BAR1026 ), male; and TM49098 ( BAR1018 ), unknown sex], one has an intact skull, but the skin was rotten and discarded [ TM49092 ( BAR1001 ), female], and three have damaged skulls and rotten skins that were discarded [ TM49096 ( BAR1006 ), male; TM49093 ( BAR1010 ), male; and TM49099 ( BAR1017 ), unknown sex]. The specimens were decapitated and the brains removed from some individuals, as part of an earlier study by G. Goldner .

Referred specimens having molecular identification: (includes the paratypes mentioned above). From Tiffendell Ski Resort, all collected by G. Goldner in December 2013: TM49099 ( BAR1017 ) , male, unknown age [class 1 (for explanation of relative age/tooth-wear classes, see Taylor et al., 1993)]; TM49098 ( BAR1018 ) , female of unknown age (class 2); TM49092 ( BAR1001 ) , female, unknown age (class 1); TM49094 ( BAR1002 ) , male, unknown age (class 2); TM49096 ( BAR1006 ) ,

F -values are indicated for ANOVA tests; all tests were significant at P <0.01 (***). Superscript letters indicate non-significant subsets of means based on pairwise Tukey’s tests. For abbreviations of variables, see under text for Material and Methods.

male, adult (class 3); TM49093 ( BAR1010 ), male, adult (class 3) ; TM49100 ( BAR1016 ), unknown age (class 1) and sex ; TM49097 ( BAR1019 ), male of unknown age (class 1) ; TM49091 ( BAR1021 ), male of unknown age (class 1); and TM49095 ( BAR1026 ), male of unknown age (class 1). From Asante Sana (− 32.24925S, 24.936E), 2090 m a.s.l. GoogleMaps : DM13662 ( AS 23), skull only of unknown sex, collected 7 June 2009 by Armand Kok. From Mountain Zebra National Park (− 32.521S, 25.686E), 1740–1762 ma.s.l GoogleMaps .: DM13657 ( MZ5 ), skull only, unknown sex, collected 26 July 2009 by Armand Kok .

Referred specimens having only morphological identification: TM22642 , 32 km from Sterkstroom on Queenstown Road , Eastern Cape Province (− 31.7696S, 26.7312E), adult female, collected by A.J. Prinsloo and J.G. Greeff on 26 July 1957 GoogleMaps ; TM22651 , Quqodalo Location, between Glen Grey and Tarkastad , Eastern Cape Province (− 31.7497S, 26.8823E), adult female, collected by J.G. Greeff on 18 October 1955 GoogleMaps ; TM22655 , 32 km on road from Sterkstroom to Queenstown , Eastern Cape Province (− 31.7696S, 26.7312E), adult male, collected by A.J. Prinsloo and J.G. Greeff on 26 July 1957 GoogleMaps ; TM22652 , Matyhantya No. 11 Location, between Tarkastad and Glen Grey , Eastern Cape Province (− 31.7825S, 27.0705E), adult male, collected by J.G. Greeff on 22 October 1957 GoogleMaps ; and TM29521 , Karoo National Park , 9 km NW Beaufort West, Western Cape Province (− 32.2745S, 22.6266E), adult female, collected by I.L. Rautenbach, J.G. De Jager and G. De Graaff on 22 January 1979 GoogleMaps .

Incertae sedis : There were two categories of undetermined specimens that were provisionally referred to O. willani : (1) those specimens without molecular data that were morphologically most like O. willani (e.g. small-sized in cranial dimensions), albeit slightly distinct (see Fig. 3, marked as ‘ O. cf. karoensis sp. 2’): NMB 9606 and NMB 9607, unknown sex, Glen Agricultural College, Free State Province (− 28.875S, 26.375E); NMB 11420, unknown sex, Sandymount Park, Fauresmith, Free State Province (− 29.625S, 25.125E); and (2), those specimens that most closely resembled O. willani in morphology but that belonged to a different mtDNA molecular clade ( Fig. 2): DM 13661 ( MZP 7), female collected at Mountain Zebra National Park (− 32.521S, 25.686E) on 12 February 2010 by Armand Kok.; and DM 13658 ( MZ 2), unknown sex, collected at Mountain Zebra National Park (− 32.521S, 25.686E) on 26 July 2009 by Armand Kok.

Etymology: The species is named for Dr Ken Willan, a South African rodent biologist who conducted pioneering research into the social ecology and reproductive biology of Otomys and other African rodents. He designed the ‘Willan trap’, which significantly improved the trap success of catching notoriously trap-shy Otomys ( Willan, 1979) .

Description: Like all members of the genus, it is a relatively large, robust, vole-like rodent, with a large blunt head, short tail and shaggy pelage. Otomys willani is the smallest member of the genus found in southern Africa, having a mass of 75–83 g (mean 78.2 g, N = 4), total length of 170–198 mm (mean 184 mm, N = 2), tail of 59–74 mm (mean 64.5 mm, N = 4), hindfoot (cu) of 21.5–25.5 mm (mean 23.5 mm, N = 9) and ear 15–20 mm (mean 17.3 mm, N = 4) (data obtained from Phukuntsi et al., 2016: supplementary material). The pelage colour is overall darkish brown with reddish to orange tints, but the facial vibrissae are a pallid creamy-brown colour ( Phukuntsi et al., 2016). The upper and lower incisors each have single deep grooves and an additional shallow groove in the lower incisors. The lower M1 has four laminae; upper M3 has seven (in one specimen examined) or six laminae (in ten specimens examined).

Diagnosis: Otomys willani can be distinguished in the field from co-occurring O. auratus and O. sloggetti within its range in the southern escarpment of South Africa. It is pallid-russet in colour dorsally. Compared with O. sloggetti , the body is darker reddish in colour, and this species has smaller body measurements than O. sloggetti . In O. willani , the pelage is grizzled owing to interspersed black- and russet-coloured hairs (based on the colour of subterminal bands), whereas in O. sloggetti it is much less grizzled owing to many fewer black hairs intermixed with pale-buff-coloured hairs ( Fig. 5). Compared with O. willani , O. karoensis has a more pallid-buff rather than pale-russet wash owing to the subterminal section of the guard hairs being buff to pale brown as opposed to russet. Compared with specimens of O. auratus , O. irroratus and O. laminatus , in addition to its distinctly smaller size, the dorsal colour of O. willani is conspicuously paler that the last-mentioned three species in spite of having a similar hue ( Fig. 5).

Although sample sizes are variable owing to the poor state of preservation of some skins, the series from Tiffendell is instructive, with O. willani being distinctly smaller than O. sloggetti in body size without overlap [e.g. mean mass was 78 g (75–83 g, N = 4) in O. willani and 127 g (116–158 g, N = 5) in O. sloggetti ; total body length was 170–198 mm in two individuals of O. willani and 224 mm in one O. sloggetti individual; mean hindfoot (cu) length was 23.5 mm (21.5–25.5 mm, N = 9) in O. willani and 27.9 mm (26.5–30.5 mm, N = 7) in O. sloggetti ]. The tail of O. willani is relatively longer (mean 64.5 mm, N = 4, 35% of total length) than in O. sloggetti (mean 67.5, N = 2, 30% of total length). In the case of co-occurring O. willani and O. auratus , as mentioned above, the latter species is much darker buff-brown in colour and also distinctly larger in body and cranial size. In terms of craniodental characters, O. willani is easily distinguished from O. sloggetti by having at least one conspicuous groove on the lower incisor (none in O. sloggetti ) and a round-shaped petrotympanic foramen (slit shaped in O. sloggetti ). On craniometric grounds, O. willani is easily separated from both O. auratus and O. irroratus on its smaller size, there being minimal or no overlap in most cranial variables (see Table 3; e.g. O. willani has GLS <37 mm, MXTL <9 mm and PAL <20 mm, cf. minimal values exceeding the values of these variables in the case of O. auratus and O. irroratus ). Only in the case of IOC is O. willani significantly smaller than O. karoensis ( Table 3). As shown by PCA ( Fig. 3), O. willani and O. karoensis are completely separated on PC3, which is defined as a shape vector. contrasting IOC and PAL (positive loadings) and NAW (negative loadings). Otomys karoensis generally has a disproportionately large interorbital, longer palatal length (and palatal foramina; Fig. 4) and disproportionately narrow nasal bone relative to O. willani , reflected in the ratio of IOC/NAW (0.69 in O. karoensis and 0.66 in O. willani ). In addition to these subtle morphological differences, the two species are phylogenetically distinct from each other based on mtDNA data, and they are not even sister species; instead, O. karoensis is sister to O. laminatus ( Figs 2, 3). The two species are also geographically and ecologically separated, with O. karoensis occurring mainly in fynbos biome habitats in the Cape Fold Belt Mountains and O. willani occurring in grassland biome habitats in the Southern Escarpment.

Distribution and biology: The species occurs along the Southern Great Escarpment at elevations> 1000 m a.s.l., from the Karoo National Park near Beaufort West in the west to Giant’s Castle in KwaZulu-Natal Province in the east ( Fig. 1). Small-sized specimens from two localities on the central plateau of South Africa north of the Drakensberg, referred to as O. cf. karoensis sp. 2 (dark blue circles in Fig. 1), are provisionally referred here to O. willani .