Raorchestes dibangensis, Boruah & Deepak & Das, 2025

Boruah, Bitupan, Deepak, V. & Das, Abhijit, 2025, Revision of bush frogs, Raorchestes and Philautus (Amphibia: Anura: Rhacophoridae) from the northeast Indian biodiversity hotspot with description of thirteen new species, Vertebrate Zoology 75, pp. 517-625 : 517-625

Raorchestes dibangensis sp. nov.

Figure 35; Tables 1, 2, S 12

Holotype.

An adult male ( WII-ADA 1677 ) collected by BB on 7 August 2022 from Abango ( 28.09974°N, 95.89392°E, elevation 410 m a. s. l.), Lower Dibang Valley District, Arunachal Pradesh, India .

Paratype.

An adult male ( WII-ADA 1671 ) collected along with holotype from the same locality .

Diagnosis.

A small sized Raorchestes, SVL 19.6–21.8 mm in adult males, female unknown; head length equal to width; snout rounded, its length equal to or less than eye length; tympanum indistinct; small blunt tubercles on upper eyelid; spinules on middle of dorsum, above supratympanic fold, flank and sparsely present on limb; two indistinct crossbars on thigh and tibia; dorsum pale brown with a pair of faint concave stripes, posterior ends of these stripes distinct near groin; white bar present on inter-upper eyelid space in some individuals; small white spots visible on abdomen in life.

Description of the holotype.

Holotype well preserved except for an incision on underside of right thigh; small sized. Adult male with vocal sac, SVL 21.8 mm; head length equal to width; snout rounded in dorsal view and nearly truncated in lateral view, its length ( 2.9 mm) equal to eye length ( 2.9 mm); nostril obliquely oval in shape, laterally positioned and oblique, closer to snout tip than eye ( NS / EN = 0.69); narial region raised; canthus rostralis smooth, obliqued; loreal region concave; internarial distance equal to inter-upper eyelid width and greater than upper eyelid width ( UEW / IN = 0.68); tympanum indistinct, round, less than one third of eye length ( HTYD / EL = 0.28); supratympanic fold distinct; tongue posteriorly wide and deeply notched; small flat tubercles on tongue; choanae oval; vomerine teeth absent; a pair of slit like openings on lower jaw near angle of jaw; symphysial knob present on lower jaw.

Habitus slender, dorso-ventrally flattened, less than half of snout-vent length ( AG / SVL = 0.44); forelimb slender; hand length greater than forearm length ( FAL / HAL = 0.86); digit with rounded disc; circum-marginal groove present on each disc; third finger longest, relative length of fingers = I <II <IV <III; disc on third finger wider than tympanic diameter ( HTYD /TIIID = 0.73); palmar tubercles barely visible; subarticular tubercles rounded, proximal ones on third and fourth finger smaller than distal ones and indistinct; no webbing among the fingers; finely granular nuptial pad on first finger; hindlimb slender; thigh longer than tibia ( TBL / TL = 0.94) and nearly half snout-vent length ( TL / SVL = 0.48); fourth toe longest; toe with rounded disc, disc width equal to those of fingers; relative length of toes = I <II <III = V <IV; no dermal fringe along fifth toe; webbing slight, not reaching the second subarticular tubercle on fourth toe; small inner metatarsal tubercle present, outer one absent; subarticular tubercles round, proximal subarticular tubercles on toe III – V barely visible; no supernumerary tubercles.

Skin on dorsal aspect of head smooth; snout on dorsal aspect and upper eyelids shagreen; indistinct tubercles on upper eyelid; at least two blunt tubercles on mandibular region, behind angle of jaw; spinules on dorsolateral aspect of trunk and middle of dorsum, starting above posterior part of supratympanic fold, few scattered on anterior and posterior part of dorsum; flank, forelimb and hindlimb smooth on dorsal aspect; throat and chest smooth; gular skin loose; abdomen granular; thigh granular but not as distinct as on abdomen; tibia smooth on ventral aspect.

Colouration in preservative.

Dorsal aspect of head brown; pale white bar on inter-upper eyelid space followed by a slightly darker inverted triangular mark on head; upper eyelid dark grey; loreal region darker than dorsal aspect of head; supratympanic fold dark brown; dorsum darker than head, paler on flank; forelimb pale brown on dorsal aspect; a slight dark brown crossbar on forearm; a similar short bar on hand below fourth finger; hindlimbs pale brown dorsally, slightly darker towards knee; single dark brown cross bar on each thigh; a single cross bar on left tibia and two on right tibia; two crossbars on each tarsus, faint; a short dark brown bar on foot below fifth toe; area around vent darker; chin, throat, chest, abdomen, ventral aspect of limb, hand, and feet creamy white with brown mottling, chin towards the edge of lower jaw heavily mottled.

Colouration in life.

Head and body and limbs on top pale greyish brown; a broken pale white bar on inter-upper eyelid space; iris whitish with brown spots and irregular wavy brown lines, golden mottling on upper half of it; a pair of barely visible, faint brown concave stripes on dorsum; single faint brown crossbar on forearm; similar two crossbars on each thigh and tibia and single cross bar on tarsus towards distal end; disc on inner two fingers and inner two toes yellow; ventral aspect of head, abdomen and limbs pale flesh coloured with brown mottling; vocal sac pale yellow and pale semi-transparent,; white spots of irregular size on granules of abdomen; irregular white spots on thigh, tibia, tarsus, and forearm.

Morphological variation.

Morphometric details are given in Table S 12. The paratype does not have a white bar on inter-upper eyelid space; crossbars on limbs not visible in preserved condition unlike holotype; lower jaw and chest heavily mottled with brown unlike holotype.

Morphological comparison.

Raorchestes dibangensis sp. nov. differs from R. andersoni by head length being equal to width (vs. head wider than length); R. annandalii by presence of dense spinules on dorsum (vs. skin on dorsum smooth); it differs from R. barakensis sp. nov. by absence of pattern on groin (vs. enlarged brown patch on groin), two indistinct crossbars present on thigh and tibia (vs. three narrow bands present on thigh and tibia), concave stripes on dorsum indistinct or not visible (vs. concave stripes on dorsum distinct); it differs from R. boulengeri sp. nov., R. dulongensis , R. hekouensis , R. hillisi , R. malipoensis and R. mawsynramensis sp. nov. by larger body size, SVL 19.6–21.8 mm in adult males (vs. 17.5–19.1 mm in R. boulengeri sp. nov., 15.0–19.0 mm in R. dulongensis , 16.1–17.5 mm in R. hekouensis , 15.9–17.7 mm in R. hillisi , 14.6–17.7 mm in R. malipoensis and 16.0– 18.7 mm in R. mawsynramensis sp. nov.); it differs from R. cinerascens nov. comb. by dense spinules on middle of dorsum. (vs. scattered tubercles on dorsum), by presence of two indistinct crossbars on thigh and tibia (vs. three crossbars on thigh and tibia), absence of blotch or pattern on groin (vs. a spot partially encircled by yellow tinge on groin); it differs from R. garo by absence of enlarged dark brown patches and yellow spots on groin and thigh (vs. present); it differs from R. huanglianshan and R. tytthus nov. comb. by snout length being equal to or less than eye length (vs. snout length longer than eye length); it differs from R. jadoh by larger body size in adult males, SVL 19.6–21.8 mm (vs. SVL 13.6–14.0 mm), inter-upper eyelid width being less than eye length (vs. inter-upper eyelid greater than eye length), and thigh length being greater than tibia length (vs. thigh length less than tibia length); it differs from R. jakoid by snout length being less than or equal to eye length (vs. snout length greater than eye length) and thigh length being greater than tibia length (vs. thigh length less than tibia length); it differs from R. lawngtlaiensis sp. nov. by nostril being closer to snout tip than eye (vs. nostril equidistant between eye and snout tip), absence of pattern or blotch on groin (dark brown stripe with white spots), concave stripes on dorsum indistinct (vs. broad dark brown concave stripes on dorsum); it differs from R. longchuanensis by inter-upper eyelid width being smaller than eye length (vs. inter-upper eyelid width greater than eye length); it differs from R. leiktho by larger body size in adult males, SVL 19.6–21.8 mm (vs. SVL 15.7–15.8 mm); it differs from R. menglaensis by snout length being equal to or less than eye length (vs. snout length greater than eye length), and head length being equal to its width (vs. head longer than wide); it differs from R. mindat by larger body size in adult males, SVL 19.6–21.8 mm (vs. SVL 16.7–18.3 mm), dark or white patches absent on groin (vs. enlarged black and white patches present on groin), and absence of white patches on lateral aspect of thigh (vs. enlarged white patches on lateral aspect of thigh); it differs from R. nasuta sp. nov. by rounded snout (vs. snout acute), head length being equal to width (vs. head longer than wide); it differs from R. narpuhensis sp. nov. by presence of dense spinules on the middle of dorsum (vs. scattered tubercles on dorsum), presence of two indistinct crossbars on thigh and tibia (vs. single broad crossbar on thigh and tibia); it differs from R. orientalis sp. nov. by concave stripes on dorsum and crossbars on limbs being faint or not visible (vs. concave stripes on dorsum and crossbars on limbs distinct), absence of blotch or pattern on groin (vs. a short brown stripe on groin); it differs from R. parvulus by larger body size in adult males, SVL 19.6–21.8 mm (vs. SVL 17.0– 18.6 mm), thigh length being greater than tibia length (vs. thigh length smaller than or equal to tibia length); differs from R. rezakhani by head length being equal to width (vs. head wider than long); it differs from R. shillongensis by presence of dense spinules on dorsum (vs. blunt tubercles present on dorsum); it differs from R. yadongensis by head length being equal to width (vs. head wider than long). Raorchestes dibangensis sp. nov. is morphologically close to R. kempiae . A detailed morphological comparison with other congeners is presented in Table 1.

Acoustics.

The calls of R. dibangensis sp. nov. were recorded in Abango, Arunachal Pradesh on 7 August 2022 at 18: 30 hrs. The call description is based on 40 calls of the paratype ( WII-ADA 1671 ). The calls are pulsatile, single type, emitted at regular intervals, not in groups (Fig. 31 ). The amplitude of the calls increases gradually. The number of pulses per call varies from 2 to 3 (2.28 ± 0.45 pulses / call), call starts with two pulses and after attaining maximum amplitude the number of pulses per call increases to three. The mean call duration is 69.1 ± 21.29 ms (58–127 ms) with a rise time of 34.73 ± 21.06 ms (1–50 ms) and a fall time of 42.6 ± 48.11 (11–126 ms). Call rise time is longer when calls consist of two pulses and shorter when there are three pulses. Conversely, call fall time decreases when the calls have two pulses and increases when the calls consist of three pulses. The mean call interval between calls is 291.05 ± 119.17 ms (48–514 ms). The pulse duration varies between 10–15 ms (13.22 ± 1.69 ms) with a pulse rate of 18.68 ± 1.59 pulses / sec (16.95–22.22 pulses / sec). The mean dominant frequency is 3275 ± 51.14 Hz (3143.8–3316.1 Hz). Raorchestes dibangensis sp. nov. have comparatively longer call rise time than its sister species R. kempiae (call rise time 1–50 ms in R. dibangensis sp. nov. vs. call rise time 1 ms R. kempiae ). A detailed comparison of the advertisement calls with those of the congeners is presented in Table 2.

Phylogenetic relationship and genetic divergence.

Raorchestes dibangensis sp. nov. is sister to R. kempiae ( UFB 100 , PP 1.0; Figs 2 , 3 ). These two species have genetic divergence of 2.6–3.3 % in the 16 S gene. The genetic divergence with its congeners included in this study are 4.6–9.3 % in the 16 S, 9.0–19.6 % in the cyt b and 5.0–15.6 % in the COI genes (Table S 7 A – C).

Etymology.

The specific epithet is a toponym derived from the name of the river “Dibang” in Arunachal Pradesh. The type locality of this species lies in the Dibang valley.

Suggested common name.

Dibang Valley bush frog.

Distribution and natural history.

Currently this species is known from the type locality (Fig. 19 B ). On 7 August 2022, two calling individuals were recorded from a degraded forest patch, along the bank of Simari River, on the opposite side of Abango Village (Fig. 33 B ). The individuals were calling from a leaf approximately one metre above ground around 18: 00 hrs. The habitat at the recorded site was degraded vegetation with climbers and large trees. The type locality is approximately one kilometre southwest of Mehao Wildlife Sanctuary.

Figures

Figure 2. A, B Maximum likelihood tree inferred from the concatenated data set (16 S, cyt b, COI and RHO) for Raorchestes species from northeast India, Indo-Burma and Indo-China. Outgroups are not shown in this tree. Numbers at the internal branches represent ultrafast bootstrap values (UFB). Values below 50 are not shown. Scale bar: substitutions per site.

Figure 3. A, B Bayesian tree inferred from the concatenated data set (16 S, cyt b, COI and RHO) for Raorchestes species from northeast India, Indo-Burma and Indochina. Outgroups are not shown in the tree. Numbers at the nodes represent posterior probability (PP) value. Values <0.5 are not shown. Scale bar: substitutions per site.

Figure 19. Distribution of Raorchestes species in northeast India. A Raorchestes garo and three others closely related new species; B Raorchestes kempiae, R. shillongensis, R. mindat and three new species. Type localities are denoted with stars.

Figure 31. Comparative spectrograms and oscillograms illustrating representative calls of three species of Raorchestes. A, B Oscillograms, C spectrogram, D power spectrum. The call marked with an arrow on top in A is expanded in B.

Figure 33. Habitat at the type localities of Raorchestes species in northeast India. A Lowland forest stream at the type locality of R. lawngtlaiensis sp. nov. in Ngengpui WLS; B landscape view of Mehao WLS from Abango, type locality of R. dibangensis sp. nov. in Abango; C. hill stream and riparian habitat at the type locality of R. shillongensis in Malki, Shillong; D landscape view of the hills at Pumdunlong, the type locality of R. monolithus sp. nov. at Willong Khullen Village; E landscape view of hills and lowland areas at Khonoma, the type locality of R. khonoma sp. nov.; F forest cover at Bompu, Eaglenest WLS at the type locality of R. eaglenestensis sp. nov.; G hill stream and forest cover at Abor hills, habitat of R. magnus sp. nov.; H landscape view of Abor hills and adjacent lowland areas, habitat of R. arunachalensis sp. nov.

Figure 35. Raorchestes dibangensis sp. nov. A Dorsal and B ventral view of holotype (WII-ADA 1677) in preserved condition. C – E paratype (WII-ADA 1671) in preserved condition, C dorsal view, D ventral view, E lateral view of head. F Dorsolateral and G ventral view of holotype in life. Scale bar = 10 mm.