Praomys melanotus, G. M. Allen & Loveridge, 1933

Carleton, Michael D. & Stanley, William T., 2012, Species limits within the Praomys delectorum group (Rodentia: Muridae: Murinae) of East Africa: a morphometric reassessment and biogeographical implications, Zoological Journal of the Linnean Society 165 (2), pp. 420-469 : 441-444

PRAOMYS MELANOTUS G. M. ALLEN & LOVERIDGE, 1933, NEW RANK ( FIGS 6–9 ; TABLES 5, 6)

Praomys tullbergi melanotus G. M. Allen & Loveridge, 1933: 106 ; type locality – ‘Nyamwanga, Poroto Mountains , northwest end of Lake Nyasa, Tanganyika Territory’ [ Tanzania] ; type specimen – MCZ 26287, an adult male collected 21 March 1930 by A. Loveridge .

Praomys jacksoni melanotus, G. M. Allen, 1939: 410 (specific reallocation, retention as valid subspecies).

Rattus [( Praomys )] tullbergi melanotus, Ellerman, 1941: 208 (name combination).

Rattus [( Praomys )] jacksoni melanotus, Swynnerton & Hayman, 1951: 316 (name combination, retention as valid subspecies).

Distribution: Southern Highlands of south-western Tanzania (Livingstone Mts, Poroto Mts, Mt Rungwe) and contiguous Misuku Mts in northern Malawi ( Fig. 10 ); known elevation 1524–2410 m.

Morphological description and comparisons: Allen & Loveridge (1933: 106) succinctly described the pelage characteristics of P. melanotus in their description of the taxon.

‘A very dark saturated race: general color above, including muzzle to eyes, the forehead, ears and central area of the back, dark blackish brown, many of the hairs entirely black, others with minute subterminal ochraceous rings [bands] that are barely noticeable; on the sides of the face and body and on the nape, these rings [bands] are longer, producing a dull rufous to ochraceous wash over these areas. Lower surfaces dull grayish white, the hairs everywhere with slaty bases. The tail, which equals the head and body in length, is blackish all around, with narrow rings... The feet are very dark smoky brown, with silvery toes’.

The more deeply saturated, somber appearance of the upperparts of P. melanotus has been emphasized in comparisons with P. delectorum or P. taitae (then ranked as subspecies of P. jacksoni – Hatt, 1940; Swynnerton & Hayman, 1951; Lawrence & Loveridge, 1953), which commonly exhibit a brighter dorsum and sides ( Figs 8 , 9 ). The flanks of P. melanotus are nearly as dark as the middle dorsum; whereas, in P. delectorum and P. taitae proper, the sides noticeably grade to paler, dominated by buffy brown to russet tones. The dark quality of P. melanotus extends to the epidermal pigmentation of the pinnae and tail, which are dusky to nearly black compared with medium brown in typical P. delectorum and P. taitae ( Fig. 9 ); the underside of the tail in P. melanotus is as dark as or only slightly paler than the dorsal surface. The underparts of P. melanotus are typically dark grey, an impression imparted by the long, deep slate, basal band of ventral hairs and their short white terminal band. The bellies of P. melanotus and P. taitae overlap in the intensity of greyness, the former tending toward darker and the latter paler ( Fig. 8 ). We have not observed the strong buffy overwash on the venters of P. melanotus skins, a trait commonly encountered in series of P. delectorum . In P. melanotus , the dark brown dorsal ground colour extends at least over the tarsus and usually onto the top of the metatarsus, forming a sharp contrast to the silvery white hairs investing the toes. The particoloured hindfoot typical of P. melanotus usefully distinguishes it from samples of P. taitae , whose tarsus-metatarsus is wholly white ( Fig. 9 ).

Compared with P. delectorum and P. taitae , the skull of P. melanotus is characterized by larger size and ample proportions, a general assertion sustained by univariate sample statistics ( Table 5) and by results of the several multivariate analyses (see Patterns of morphometric variation). Although nearly all dimensions statistically emphasize the larger craniodental size of P. melanotus relative to P. delectorum or P. taitae , the distinction is less obvious when inspecting individual skulls of mixed age classes. The immediately conspicuous differences of P. melanotus are its broader zygomatic plate ( Fig. 7 ), as indicated by the deeper zygomatic notch when viewed dorsally ( Fig. 6 ), and the robust molar rows.

Remarks: In keeping with the taxonomic conventions of the era, Allen & Loveridge (1933) described their darkly saturated, montane form as a subspecies of another Praomys , in this instance P. tullbergi , a species described from lowland tropical forest in West Africa. Their conviction about specific relationship was not strong, for they opined (1933: 107) that East African forms of Praomys are ‘instead a distinct species, jacksoni ... having the outer cusp [= t3] of the first transverse lamina in the upper m1 well developed instead of obsolete’. Although they confusingly named melanotus as a race of P. tullbergi, Allen & Loveridge (1933) nonetheless concluded that ‘This race is closely related to P. jacksoni ... and the subspecies delectorum ’. Their insights anticipated the taxonomic research and revised classifications of the middle 1900s, in which melanotus came to be allocated as a subspecies or full synonym of either P. jacksoni or P. delectorum ( Allen, 1939; Swynnerton & Hayman, 1951; Davis, 1965; Misonne, 1974). According to the traits of the Praomys delectorum species group reviewed above, melanotus Allen & Loveridge (1933) decidedly belongs with this complex; moreover, our morphometric results support its validity as a separate species.

Ansell & Dowsett (1988: 116) identified their samples from the Misuku Mts and Nyika Plateau as an indeterminate subspecies of Praomys delectorum sensu lato (s.l.), citing an unpublished study by J. Sidorowicz, who ‘found no statistical difference in skull and external dimensions between specimens from northeastern Zambia, the Misuku Hills, and the Poroto Mts’. We certainly concur as specimens we examined from two of those localities, Misuku Mts and Poroto Mts, represent one and the same species, P. melanotus . Actually, the problematic affinity of the Praomys from the Misuku Mts was earlier highlighted by Lawrence (in Lawrence & Loveridge, 1953: 45), who first discerned the barely perceptible cranial differences between the skulls of P. melanotus and P. delectorum and thought ‘the Misuku series is intermediate towards melanotus ’. We salute her keen perceptions.

The geographical range of P. melanotus requires refinement. Its core distribution is apparently localized to the forested highlands that envelope northern Lake Malawi and are bounded to the north-east by the Makambako Gap. To the north-west, no examples of the Praomys delectorum complex have been collected on the Ufipa Plateau, western Tanzania, or from mountains in northern Zambia. Instead, those highlands are inhabited by another species of Praomys , P. jacksoni , also a member of a different species group ( Ansell, 1978; Carleton & Stanley, 2005). Praomys melanotus may be reasonably expected to occur in extreme north-eastern Zambia and further south in Tanzania, e.g. wherever pockets of moist montane forest occur on the Nyika Plateau and the Viphya Mountains that stretch south of the Plateau. Specimens identified as Praomys delectorum s.l. have been reported for these regions ( Hanney, 1962, 1965; Ansell & Ansell, 1973; Ansell, 1978; Ansell & Dowsett, 1988; Happold & Happold, 1989), but these determinations require confirmation from a fresh perspective.

Natural history notes: Samples of Praomys melanotus were collected during two surveys of the Southern Highlands in 1998 and 2008. A faunal survey of the south-western slopes of Mt Rungwe in August– September 1998 recovered P. melanotus in forested habitats from 1870 to 2410 m, the lowest and highest elevations within the Southern Highlands sampled by Stanley and colleagues. In 2008, P. melanotus was vouchered in montane forests of the Madehani and Kitulo Plateaux, Livingstone Mts, the eastern slope of Mt Rungwe, and the inner slope of the Ngosi Crater, Poroto Mts.

Trap success for P. melanotus (number captured/ number of trap-nights ¥ 100) ranged from 2.1 to 12.8% across all sites surveyed, but was generally higher on Mt Rungwe (6.0–12.8%) than in either the Poroto or Livingstone Mts (1.2–4.2%). A striking example of this contrast was recorded in 2008 near the village of Bujingijila, where the eastern slope of Rungwe and the western edge of the Livingstone Mts were sampled on the same days with equal trapping effort. Although the two sites were about 5 km apart, trap success for P. melanotus was 1.2% for the Livingstone site and 7.4% for the Rungwe lines. Further study is needed to test whether this pattern holds across time and, if so, what reasons contribute to the apparently lower abundance of this rodent in this area of the Livingstone Mts compared with nearby Rungwe forests.

Of 67 females inspected across all surveys in the Southern Highlands, 12 (17.9%) were pregnant. The crown–rump length of the embryos ranged from 2 to 20 mm with an average of 8.4 mm. The maximum number of embryos in any uterine horn was 5. The average length and width of the testes of 129 males measured was 12.5 (range = 4–17) by 7.7 (2–10) mm; a large majority, 83.7%, possessed convoluted epididymides (N = 127).

Specimens examined (121, as follows): MALAWI: Misuku Mts , Matipa-Wilindi Ridge, 6000 ft ( MCZ 44012, 44013 , 44015–44020 , 44244 , 44250 ) .

TANZANIA: Iringa Region, Makete District, Livingstone Mts, Madehani Forest , 2100 m ( FMNH 204710 , 204711 , 204713 , 204717 , 204719 , 204720 , 204722 , 204726 , 204728 ) ; Ukinga Mts, Madehani ( MCZ 26259, 26387 , 26389 , 26390 , 26392–26394 , 26411 ) . Mbeya Region, Rungwe District, Poroto Mts, Ngozi Crater , 2250 m ( FMNH 205286–205290 , 205292 , 205294 , 205295 , 205297 , 205299 , 205300–205302 , 205308 , 205309 , 205311 , 205312 ) ; Poroto Mts, Igale ( MCZ 26497) ; Poroto Mts, Nyamwanga ( MCZ 26285– 26288 , 26290 , 26310 , 26327 ) ; Rungwe , 5000 ft ( AMNH 81375 , 81377 , 81378 ) , 5650 ft ( AMNH 81376 ) ; Mt Rungwe, Ilolo ( MCZ 26292, 26293 , 26295– 26297 ) ; Rungwe District, Rungwe Forest Reserve , 5 km E Ilolo, 1870 m ( FMNH 163627 , 163630 , 163631 , 163633 , 163635–163637 , 163640 , 163644 , 163645 , 163647–163649 , 163653 , 163655 , 163658 , 163659 , 163660 , 163662 , 163663 , 163665 , 163668 , 163675 , 163676 , 163682 , 163683 , 163685 , 163697 , 163698 , 163704 , 163708 , 163712 , 163714 , 163720 , 163721 , 163725 , 163726 , 163729 , 163731 , 163734–163738 ) ; Rungwe District, Rungwe Forest Reserve, 7 km E and 2.5 km N Ilolo , 2410 m ( FMNH 163740–163749 , 163751–163756 ) .

Figures

Figure 6. Dorsal (top row) and ventral (bottom row) views (about 2¥) of adult crania of the three species of the Praomys delectorum group recognized here: A, P. delectorum (FMNH 181214; ONL = 29.0 mm), a male from Lichenya Hut, Mt Mulanje, 1840 m, Malawi; B, P. melanotus (FMNH 163682; ONL = 29.9 mm), a female from 5 km east of Ilolo, Rungwe Forest Reserve, Mt Rungwe, 1870 m, Tanzania; C, P. taitae (FMNH 153979; ONL = 28.7 mm), a male from 3 km east and 0.7 km north of Mhero, Chome Forest Reserve, South Pare Mts, 2000 m, Tanzania.

Figure 7. Lateral view (about 2¥) of adult crania of the three species of the Praomys delectorum group (same specimens as illustrated in Fig. 6): A, P. delectorum; B, P. melanotus; C, P. taitae.

Figure 8. Dorsal (left set) and ventral (right set) views of adult round skins (about 0.5¥), illustrating ‘typical’ pelage patterns of the three species of the Praomys delectorum group recognized here: AA′, P. delectorum (FMNH 181237; Total Length = 223 mm), a male from Chisongeli Forest, Mt Mulanje, 1575 m, Malawi; BB′, P. melanotus (FMNH 205299; Total Length = 234 mm), a male from Ngozi Crater, Poroto Mts, 2250 m, Tanzania; CC′, P. taitae (FMNH 150346; Total Length = 240 mm), a male from 4.5 km ESE of Amani, East Usambara Mts, 900 m, Tanzania.

Figure 9. Examples of the Praomys delectorum group as photographed in the field: Top, P. melanotus from Ngozi Crater in the Poroto Mountains, Southern Highlands; Bottom, P. taitae from Mount Malundwe, central Eastern Arc Mountains. Darker pigmentation of the epidermal surfaces is typical of individual P. melanotus compared with P. taitae; also note the extension of dark hairs onto the metatarsum as characteristic of P. melanotus versus a wholly white metatarsum and phalanges in most P. taitae. Hindfoot length averages about 23–25 mm; photographs by W. T. Stanley.

Figure 10. Distributions of the three species of the Praomys delectorum group based on specimens documented herein (see species accounts). The patchy occurrence of Praomys across this region is closely linked to equally patchy associations of wet montane forest (areas shaded pale grey, as extracted from World Wildlife Fund Ecoregions, USGS Digital Atlas of Africa).