Megophrys (Xenophrys) dzukou, Mahony & Kamei & Teeling & Biju, 2020

Mahony, Stephen, Kamei, Rachunliu G., Teeling, Emma C. & Biju, S. D., 2020, Taxonomic review of the Asian Horned Frogs (Amphibia: Megophrys Kuhl & Van Hasselt) of Northeast India and Bangladesh previously misidentified as M. parva (Boulenger), with descriptions of three new species, Journal of Natural History 54 (1 - 4), pp. 119-194 : 148-154

Megophrys (Xenophrys) dzukou sp. nov.

Holotype. Adult male ( BNHS 6072 [field tag SDBDU 2007.106 ] [Figures (7 and 8(a)]) from Dzükou Valley, Jakhama circle (25.560555, 94.080555, 2650 m asl.), Kohima district, Nagaland state, Northeast India, collected by RGK and VK on 23 June 2007.

Paratypes. Two adult males ( BNHS 6073 [field tag SDBDU 2007.107 ] ( Figure 8 (b,d)) & BNHS 6074 [field tag SDBDU 2007.108 ]), collected with the holotype .

Referred specimen. One adult male ( SDBDU 2007.109 [ Figure 8 (c,d)]), collected with the holotype .

Holotype description (measurements in mm). Mature male ( SVL 34.2) ( Figures 7 and 8 (a)). Head small, longer than wide ( HW 11.4, HL 11.7, IFE 6.1, IBE 9.5); snout bluntly pointed in dorsal view, obtusely protruding in lateral view, rostral appendage absent ( Figure 7 (c)); loreal region acute, concave; canthus rostralis angular; dorsal region of snout slightly

concave; eye length more than twice maximum tympanum diameter, and shorter than snout ( EL 4.4, TYD 2.0, SL 4.7); eye – tympanum distance ( TYE 2.0) equal to tympanum diameter; tympanum circular, upper border not concealed by supratympanic ridge ( Figure 7 (c)); pupil appears vertically oval in preservation; nostril oval, orientated laterally, closer to eye than snout ( EN 2.2, NS 2.4); internarial distance greater than eyelid width, and narrowest point between upper eyelids ( IN 4.0, UEW 3.7, IUE 3.4); pineal ocellus not visible externally; vomerine ridges small, ovoid, weakly raised, orientated acutely, positioned between to slightly posterior to choanae, equidistant from each other and choanae; vomerine teeth small; maxillary teeth present; tongue large, covers almost entire floor of mouth, cordiform (with weak notch posteriorly), no medial lingual process.

Forelimbs moderately long, thin ( Figure 7 (a,b)); forearms considerably enlarged relative to upper forelimbs, forearm shorter than hand length ( FAL 7.6, HAL 9.2); fingers moderately long, narrow, lateral dermal fringes absent ( Figure 7 (d)), finger length formula I = II <IV < III ( FIL 3.4, FIIL 3.4, FIIIL 6.0, FIVL 4.3); interdigital webbing, and subarticular, supernumerary and metacarpal tubercles absent; thenar tubercles weak; fingertips rounded, not expanded relative to digit widths, with circular pads, terminal grooves on fingertips absent. Hindlimbs long, thin ( Figure 7 (a – b)); thigh shorter than shank and foot (TL 15.6, SHL 17.0, FOL 17.2); toes long, dorsoventrally flattened, weak lateral dermal ridges present ( Figure 7 (e)), relative toe lengths I <II < V < III <IV; toe tips rounded, not dilated, with distinct circular pads, terminal groves on toe tips absent; webbing absent; inner metatarsal tubercle indistinct; subarticular, supernumerary and outer metatarsal tubercles absent; ridge of callous tissue present on ventral surface of all digits.

Skin of dorsal surfaces of body, limbs, and dorsal and lateral surfaces of head smooth ( Figure 7 (a – b)); tympanum smooth with borders slightly raised; outer edge of upper eyelids each with a short, weak ridge; supratympanic ridge narrow anteriorly, expands posterior to tympanum to become large and glandular, extending from orbit in a straight line to upper tympanum border, broadly curving obliquely downward along posterior border of tympanum, terminating above forearm insertion on each side ( Figure 7 (c)); flanks with few large scattered pustular tubercles; dorsolateral ridge short, thick, well defined, extending from behind supratympanic ridge to ~25% trunk length on each side; weak, ‘ \ / ’ -shaped parietoscapular ridge present, its two sides extending posteriorly from above tympanum, terminating beyond level of axilla; mid-dorsal and sacral ridges absent ( Figure 7 (a – b)); short, obliquely transverse ridges present on dorsal surface of thighs, shanks and forearms. Gular region, chest, abdomen and ventral surfaces of limbs smooth; pectoral glands indistinct; femoral glands moderately large, slightly raised, positioned equidistant from knee and cloaca on posterior surface of thighs; white and black skin asperities present, sparse at axis of lower and upper jaws, and on surrounding tympanic region (absent from tympanum), absent from all remaining surfaces.

Colour: In preservation ( Figure 7 ): Dorsal and lateral surfaces of head and body primarily light greyish-brown; light edged, solid dark brown triangular marking between eyes; longitudinal brown stripe on mid-dorsal snout; barely distinct mid-brown ‘ X ’ -shaped marking on dorsum; dorsal ridges and flank tubercles light brownish-cream with bordering dark brown spots and speckling; front of snout and lateral edge of canthus rostralis dark brown; wide vertical dark brown bar below eyes; dark brown blotch extends from posterior canthus, through tympanum; supratympanic ridges light yellowish-cream; dorsal surfaces of forelimbs and hindlimbs primarily light greyish-brown, suffused with a hint of yellowish-brown primarily on upper arms and thighs; two dark brown blotches on anterior lateral surface of forearms; dorsal surface of outer three fingers with dark brown blotches; lateral (postaxial) surfaces of thighs and shanks with dark brown spots and blotches. Throat, chest, abdomen and ventral surfaces of forelimbs, thighs and shanks primarily pale grey, suffused with yellow on lateral and posterior abdomen and limbs; some small dark brown spots and blotches laterally along abdomen on both sides; area surrounding vent and posterior surfaces of thighs dark brown; ventral surfaces of tarsus and feet dark brown with contrasting light grey callous ridges on toes, grey oval patch on region where inner metatarsal tubercle would be if present; forelimbs and hands ventrally mottled creamish-white and dark greyish-brown with ventral surfaces of digits light grey; femoral glands creamish-white. In life ( Figure 8 (a)): As in preservation but more vivid, i.e. dorsally and laterally mid-brown; no contrasting colouration on groin; iris mahogany brown in life.

Variation. See Table 2 for morphometric variation within the specimen series of four adult males. Paratypes and the referred specimen resemble the holotype for most morphological characters with some exceptions: BNHS 6073 has a vomerine ridge on right side only; short weak ridge on eyelids replaced by small bump on BNHS 6073, BNHS 6074, and SDBDU 2007.109; small flat pectoral glands visible on BNHS 6074 and SDBDU 2007.109; ‘ \ / ’ -shaped parietoscapular ridge absent on BNHS 6074; dorsolateral ridge absent on SDBDU 2007.109, and absent on left side on BNHS 6073; tongue appears rounded posteriorly on SDBDU 2007.109; on SDBDU 2007.109, ‘ X ’ -shaped dorsal marking indistinct ( Figure 8 (c)), triangular marking on dorsal surface of head with dark edges and lighter centre; on BNHS 6073 and SDBDU 2007.109, median longitudinal stripe on dorsal surface of snout replaced by dark brown spots and speckling, and have faint transverse crossbars on dorsal thighs, shanks and tarsus ( Figure 8 (b,c)); paratypes ventrally primarily light yellowish-grey in preservation with small dark brown spots and speckles on throat, chest and abdomen, spots solid on BNHS 6073 ( Figure 8 (d)) and BNHS 6074, and appear as dark rings on SDBDU 2007.109 ( Figure 8 (d)); paratypes also have short dark brown stripe extending from posterior lateral sides of throat to base of forelimbs on each side ( Figure 8 (d)); paratypes with ventral thighs, shanks and dorsal tarsus and feet with small dark brown spots and speckles, except SDBDU 2007.109 which has plain shanks; on all specimens dermal asperities restricted to region surrounding tympanum, and to a band along margin of lower jaw.

Secondary sexual characters. This species is currently known from male specimens only and have the following characters which are usually unique to males of Megophrys : weakly raised nuptial pads covered with brown micro-asperities present, covering most of dorsal surface of base of Finger I, narrowing distally, extending onto base of distal phalange on inner dorsal side; nuptial pad large on Finger II, covering>50% of dorsal surface of digit, widest proximally, extending to distal phalange on inner side; external vocal sac indistinct; internal vocal slits present near rear of lower mandible; forearms considerably enlarged relative to upper forelimbs; fleshy projection above cloaca absent.

Morphological comparisons. Megophrys dzukou sp. nov. (adult males, N = 4) differs from the following species that have not yet been assigned to a subgenus or species group through molecular analyses: from M. damrei and M. shuichengensis by much smaller adult size, male SVL 34.2 – 35.3 mm (vs. M. damrei : adult male SVL 47.7 – 57.1 mm, N = 7 [Mahony 2011; Neang et al. 2013]; M. shuichengensis : adult male SVL 102.0 – 118.3 mm, N = 8 [ Tian et al. 2000]); from M. feii by larger adult size, male SVL 34.2 – 35.3 mm (vs. adult male SVL 24.3 – 25.1 mm, N = 4), and nuptial pads on fingers of males present (vs. absent) ( Yang et al. 2018).

Megophrys dzukou sp. nov. differs from M. parva s.s. by SHL≤FOL (vs. FOL<SHL), FIL = FIIL (vs. FIL <FIIL), dorsolateral ridges short, ca. 25% trunk length (vs.>70% trunk length), fingertips not expanded relative to finger width (vs. slightly expanded).

Megophrys dzukou sp. nov. differs from all currently named members of the M. (X.) megacephala SG based on the following combinations of characters: from the following by smaller male adult size, SVL 34.2 – 35.3 mm (vs. M. ancrae, SVL 39.1 – 45.0 mm, N = 8; M. megacephala, SVL 45.9 – 53.4 mm, N = 7; M. serchhipii, SVL 36.1 – 46.7 mm, N = 25), further from M. ancrae by digit tips not expanded terminally (vs. digit tips distinctly expanded terminally), small raised bump or short ridge on outer upper eyelids present (vs. a short, sharp horn-like tubercle on outer upper eyelids present), further from M. megacephala by considerably narrower head, HW/SVL 33.0 – 33.9% (vs. HW/SVL 40.2 – 45.1%, N = 12), further from M. serchhipii by SHL≤FOL (vs. FOL<SHL), tympanum circular (vs. oval), toes dorsoventrally flattened (vs. rounded); differs from Megophrys awuh sp. nov. by slightly smaller adult male size, SVL 34.2 – 35.3 mm (vs. SVL 35.7 – 41.1 mm, N = 4), relative forearm length, FAL/SVL 22.2 – 24.1% (vs. FAL/SVL 24.5 – 26.3%), narrow lateral ridges on toes present (vs. absent), dorsolateral ridges vary from absent to ~25% trunk length (vs. typically extend the entire trunk length), parietoscapular ridge ‘ \ / ’ -shaped when present (vs. ‘ V ’ -shaped when present); differs from M. oropedion by loreal region moderately acute (vs. vertical), dorsolateral ridges ≤25% trunk length (vs.>75% trunk length), toes dorsoventrally flattened (vs. not dorsoventrally flattened), dermal asperities restricted to margin of lower mandible and area surrounding tympanum on males (vs. dermal asperities always also present on dorsum and dorsal surfaces of hind limbs on males), vomerine ridges narrow (vs. rounded posteriorly); differs from M. zunhebotoensis by slightly larger adult male size, SVL 34.2 – 35.3 mm (vs. male SVL 28.4 – 33.9 mm, N = 22), narrow lateral ridges on toes present (vs. absent), dermal asperities absent on dorsal surface of body and hindlimbs (vs. present).

For comparisons with the third new species described below refer to the comparison sections for that species.

Etymology. The specific epithet ‘dzukou’ is a toponym based on the type locality of Dzükou Valley. The name is treated as a noun in apposition.

Suggested common name. We suggest ‘ Dzükou Valley Horned Frog ’ as a suitable English language common name.

Distribution. Known only from the type locality ( Figure 2 ). The Dzükou Valley is a highelevation valley located on the southern side of Mt. Japfü (3044 m), the second-highest peak in Nagaland state. The valley itself forms part of the border between the states of Nagaland and Manipur, so it is likely that this species will also be found in the Manipur portion of the valley. The Dzükou Valley is drained by two major streams, the Japfü and Dzükou rivers, which are tributaries of the Barak (Ahu) River. The valley is bordered by two community protected areas, the Puliebadze Wildlife Sanctuary (10923 ha) and the Khonoma Nature Conservation and Tragopan Sanctuary (2500 ha).

Habitat and natural history. Dzükou Valley is characterised by an abundance of highelevation grassland, surrounded by temperate broadleaf forest, and subtropical broadleaf forest on the lower slopes. Specimens were collected from around a small forest pool fed by a small, shallow, slow-moving stream. The stream was immediately bordered by grasses and low vegetation but otherwise flowed through a mixed broadleaf and bamboo forest. Frogs were found on leaf litter surrounding the pool at approximately 20:00 h. Presumably disturbed by the collectors ’ presence, one specimen was collected from amongst submerged leaf litter in the pond itself. No male vocalisations were heard during the collection period.

Conservation. Despite quite extensive sampling in the forested areas on the lower slopes surrounding the Dzükou Valley, where this species is generally replaced by other small-sized Megophrys species, no further individuals of Megophrys dzukou sp. nov. were found. Due to the uniqueness of the habitat found in the Dzükou Valley, and its elevational isolation from neighbouring high-elevation areas, it is possible that this species may be endemic to the type locality. The community protected areas cover primarily forested areas but the valley itself is increasingly becoming more popular for tourism (trekking and camping), which brings with it the associated anthropogenic threats. There is currently no official mechanism or infrastructure in place to deal with the fallouts of increasing tourism. Further research on this species is essential to estimate its population size, biology and ecology in order to determine whether the species requires active conservation.

Remarks. The DNA sequences for Megophrys dzukou sp. nov. used in our phylogenetic analyses were generated in Mahony et al. (2017) with the identification ‘M. sp. [1] ’. Mahony et al. (2017) and the phylogenetic results presented herein ( Figures 1, S1 , & S3) resolved this high-elevation species as the sister taxon to the low elevation M. ancrae currently known only from ca. 320 km northeast of Dzükou Valley, in eastern Arunachal Pradesh, and estimated the divergence of these two species to have occurred at ca. 5 MY ( Mahony et al. 2017, fig. 1).

Figures

Figure 1. ML phylogenetic tree of the subgenus Megophrys (Xenophrys) based on the concatenated mt +nuDNA alignment. Bootstrap values ≥95% are represented by a black spot; 80–95% represented by a grey spot; <80% not given. Numbers next to species names correspond with specimen numbers in Table 1.

Figure 2. Topographic distribution map of the Megophrys (X.) megacephala SG taxa: Left. All taxa from Northeast India and surrounding countries: diamonds represent type localities; circles represent referred localities based on examined specimens; circles with central dot represent identifications based on literature where sufficient evidence was available (see Remarks sections); Right. Inset rectangle enlarged to show the distributions of species from more densely sampled southern Nagaland and northern Manipur states, Northeast India. Blue lines represent major rivers; grey lines represent international borders.

Figure 7. Megophrys dzukou sp. nov. adult male holotype (BNHS 6072: SVL 34.2 mm) in preservation, from Kohima district, Nagaland state, India: (a). dorsal view; (b). ventral view; (c). profile view of head; (d). ventral view of hand; (e). ventral view of foot.

Figure 8. Megophrys dzukou sp. nov. from Kohima district, Nagaland state, India: (a). adult male holotype (BNHS 6072: SVL 34.2 mm) in life; (b–d). adult males in preservation showing variation: (b). paratype (BNHS 6073: SVL 35.1 mm), dorsal view; (c). referred specimen (SDBDU 2007.109: SVL 35.3 mm), dorsal view; (d). left, paratype (BNHS 6072) and right, referred specimen (SDBDU 2007.109), ventral view.