Raorchestes orientalis, 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 orientalis sp. nov.

Figures 23 , 24 , 25; Tables 1, 2, S 12

Holotype.

An adult male ( WII-ADA 1309 ) collected by BB and AD on 10 May 2022 from Deban ( 27.49662°N, 96.38949°E, elevation 380 m a. s. l.), Namdapha Tiger Reserve, Changlang District, Arunachal Pradesh, India .

Paratypes.

Two adult males ( WII-ADA 3202 and WII-ADA 3204 ) collected by R. N. Venkatesh and S. Dutta on 30 April 2023 from Deban ( 27.49178°N, 96.39313°E, elevation 580 m a. s. l.), Namdapha Tiger Reserve, Changlang District, Arunachal Pradesh, India .

Referred material.

Five adult males ( WII-ADA 1339 , WII-ADA 1341 – WII-ADA 1344 ) collected by BB, AD and JV on 13 May 2022 from Motijheel trail ( 27.48585°N, 96.331475°E, elevation 680 m a. s. l.), Namdapha Tiger Reserve ; one adult male ( WII-ADA 1387 ) and one adult female ( WII-ADA 1389 ) collected by BB, AD and VJ on 20 May 2022 from Motijheel trail ( 27.48998°N, 96.33484°E, elevation 530 m a. s. l.), Namdapha Tiger Reserve ; one adult male ( WII-ADA 1367 ) collected by BB, AD and VJ on 14 May 2022 from Kamala Valley ( 27.4595°N, 96.4279°E, elevation 650 m a. s. l.), Namdapha Tiger Reserve ; two adult males ( WII-ADA 3266 and WII-ADA 3267 ) collected by AD, RNV and SD on 29 May 2023 from Kamala Valley ( 27.46148°N, 96.42758°E; elevation 650 m a. s. l.), Namdapha Tiger Reserve ; two adult males ( WII-ADA 3243 and WII-ADA 3244 ) and one adult female ( WII-ADA 3235 ) collected by AD, RNV and SD on 24 May 2023 from Gandhigram ( 27.29512°N, 96.90208°E; elevation 1090 m a. s. l.), Changlang District, Arunachal Pradesh ; one adult male ( WII-ADA 3400 ) collected by RNV on 13 June 2023 from Ranijheel ( 27.53902°N, 96.4888°E, elevation 910 m a. s. l.), Namdapha Tiger Reserve ; two adult males ( WII-ADA 3422 and WII-ADA 3423 ) collected by AD, RNV and JDG on 17 July 2023 from Kalai ( 27.72294°N, 96.4346°E, elevation 1110 m a. s. l.), Kamlang Tiger Reserve, Lohit District, Arunachal Pradesh ; four adult males ( WII-ADA 1628 – WII-ADA 1631 ) collected by BB on 19 July 2022 from Liyai Khunou ( 25.49257°N, 94.29186°E, elevation 2150 m a. s. l.), Senapati District, Manipur .

Diagnosis.

Small sized Raorchestes (Fig. 23 ), SVL 14.6–20.8 mm in adult males and SVL 19.8–21.9 mm in adult females; snout rounded to oval in dorsal view; snout length slightly less than or equal to eye length ( SL / EL = 0.92–1.04); nostrils closer to snout than eye or equidistant between eye and snout tip; inter-upper eyelid width less than or equal to eye length ( IUE / EL = 0.73–1.04); internarial distance greater than or equal to upper eyelid width ( UEW / IN = 0.65–0.95); internarial distance less than or equal to inter upper eyelid width ( IN / IUE = 0.78–1.05); nuptial pad present only on first finger in males; prominent bluntly conical tubercular projections on upper eyelids and posterior part of head; spinules on dorsum; scattered blunt tubercles on dorsum and hindlimbs; “) - (“ dark brown marking on dorsum; three or four dark-brown crossbars on thigh and tibia; short dark stripe present on groin.

Description of holotype.

Holotype is in good condition except for an incision on the ventral side of the right thigh. Adult male with vocal sac, SVL 20.4 mm; head as long as wide; snout rounded in dorsal view, truncated in lateral view, its length equal to eye length and greater than inter-upper eyelid width ( IUE / SL = 0.87); narial region slightly protruding; nostrils oval, obliquely oriented, equidistant between eye and snout tip; loreal region concave; canthus rostralis distinct, rounded and oblique; internarial distance greater than upper eyelid width ( UEW / IN = 0.79) and slightly smaller than inter-upper eyelid width ( IN / IUE = 0.92); tympanum indistinct, round, one third of the eye length ( HTYD / EL = 0.33); supratympanic fold distinct; vomerine teeth absent; choanae round; tongue posteriorly notched; pair of internal slit like openings on lower jaw; trunk more than half of snout-vent length ( AG / SVL = 0.55).

Forelimbs slender; forearm shorter than hand ( FAL / HAL = 0.91); third finger longest; relative length of fingers = I <II <IV <III; finger width rounded disc; disc on third finger slightly wider than tympanic diameter ( HTYD / FID = 0.77); palmar tubercles indistinct; subarticular tubercles distinct, round, proximal subarticular tubercle on finger II and IV small; fine granular nuptial pad present on first finger; webbing on fingers absent.

Hindlimbs slender; thigh length half of snout-vent length ( TL / SVL = 0.51); tibia slightly shorter than thigh ( TBL / TL = 0.94); fourth toe longest; relative length of toes = I <II <II <V <IV; toe with rounded disc; disc width of fourth toe equal to that of third finger; subarticular tubercles distinct, round, proximal subarticular tubercle on toe IV and V small and indistinct; inner metatarsal tubercle present, its length equal to disc width of first and second toe; outer metatarsal tubercle absent; webbing slight, not reaching second subarticular tubercle on fourth toe.

Skin on dorsal aspect of snout shagreen; inter-upper eyelid space smooth; upper eyelid and loreal region shagreen; bluntly conical tubercles on upper eyelid, posterior part of head not visible in preserved condition unlike in life, pair of enlarged bluntly conical tubercle visible posterior to upper eyelid; one or two tubercles behind angle of jaw; flat granular tubercles present on dorsal surface of tongue; spinules present on dorsum and flank, spinules absent towards vent; forelimb and hindlimb smooth on dorsal aspect, spinules on thigh and tibia not visible unlike in life; head on ventral aspect smooth, gular region indistinctly granular; chest smooth; abdomen, thighs on ventral aspect granular; tibia on ventral aspect granular; two tubercles below vent.

Colouration in life.

Dorsal aspect of head, dorsum, limbs pale greyish brown with slightly darker brown flecks; pair of reddish, blunt tubercles posterior to upper eyelid; a reddish tubercle behind angle of jaw; pair of concave indistinct, brown stripes on dorsum; a broad brown crossbar on forearm; two brown crossbars on thigh and tibia and one on tarsus; diffused brown stripe along supratympanic fold; another similar stripe on upper jaw ventral to eye; irregular white spots along upper jaw; on ventral aspect of head, abdomen, and limbs flesh coloured with brown mottling; pale yellow tinge on gular region; brown patch around vent.

Colouration in preservative.

Colour pattern similar to life coloration; dorsally pale greyish brown, head slightly darker, limbs and flank paler; on ventrum, abdomen and limbs pale cream coloured with brown mottling.

Sexual dimorphism and morphological variation.

Males have a pair of internal vocal sac openings, subgular external vocal sac and nuptial pad on the first finger; head longer than wide in females, but in males head wider than long or width equal to length. Dorsal colour varies from pale greyish brown to pale yellowish brown; concave stripes on dorsum may be broken or faint in some individuals; number of crossbars on thigh and tibia varies between 2–4; axilla and groin may be pale yellow in some individuals; disc on inner two fingers may be pale yellow. Detailed morphometric variation between the individuals of this species is given in Table S 12.

Morphological comparison.

Raorchestes orientalis sp. nov. differs from R. andersoni by short stripe present on groin (vs. large black spot with two yellow spots present on groin); it differs from R. annandalii by skin on dorsum with spinules (vs. skin on dorsum smooth); it differs from R. cinerascens nov. comb. by short stripe present on groin (vs. a spot partially encircled by yellow tinge present on groin), dense spinules on dorsum (vs. scattered tubercles on dorsum); it differs from R. dulongensis by presence of nuptial pad on first finger in males (vs. nuptial pad absent); it differs from R. hekouensis by nuptial pad present only on first finger (vs. nuptial pad present on first and second finger); it differs from R. garo by short stripe present on groin (vs. enlarged dark brown patches with or without white or yellow patches present on groin); it differs from R. hillisi , R. huanglianshan , R. menglaensis , and R. tytthus nov. comb. by snout length being less than or equal to eye length (vs. snout longer than eye length); it differs from R. jadoh and 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 or equal to tibia length (vs. thigh length less than tibia length); it differs from R. kempiae by presence of distinct “) - (“ on dorsum (vs. comparatively faint “) (“ mark on dorsum), 2–4 cross bars on tibia and thigh (vs. three bars on tibia and thigh); it differs from R. leiktho by presence of a pair of concave stripes on dorsum (vs. pair of anteriorly connected stripes on dorsum); it differs from R. longchuanensis by inter-upper eyelid width being less than or equal to eye length (vs. inter-upper eyelid width greater than eye length); it differs from R. malipoensis by short stripe present on groin (vs. black patches present on groin); it differs from R. mindat by short stripe present on groin (vs. enlarged black and white patches present on groin); it differs from R. parvulus by short stripe present on the groin (vs. dark brown marbling enclosing a whitish blotch present on groin); it differs from R. rezakhani by presence of dense spinules on dorsum (vs. scattered tubercles on dorsum); it differs from R. shillongensis by short stripe present on groin (vs. dark brown patch with white crown shaped mark present on groin); it differs from R. yadongensis inter-upper eyelid width being less than or equal to eye length (vs. inter-upper eyelid width greater than eye length). Morphological comparisons with other new species described in this study are given in respective sections and Table 1.

Acoustics.

The calls of R. orientalis sp. nov. were recorded in Deban, Namdapha Tiger Reserve on 10 May, 2022 and in Kamala Valley, Namdapha Tiger Reserve on 16 May 2022 at 19: 25 hrs and 19: 30 hrs at ambient temperatures of 25.8 ° C and 22.7 ° C respectively. The description of calls is based on 60 calls including those of the two individuals ( WII-ADA 1309 and WII-ADA 1367 ). The calls are single type, non-pulsatile, emitted as a single call at start, gradually emitting calls in groups (2–6 calls per group) (Fig. 24 ). The mean call duration is 24.6 ± 2.79 ms (15–28 ms) with a rise time of 1.13 ± 0.39 ms (1–3 ms) and a fall time of 23.43 ± 2.85 ms (13–27 ms). The mean interval between calls is 220.92 ± 23.13 ms (162–295 ms) when calls emitted in groups. The dominant frequency is 3958.52 ± 202.2 Hz (3617.6–4177.4 Hz). A detailed comparison of the advertisement calls with those of the congeners is presented in Table 2.

Phylogenetic relationship and genetic divergence.

Raorchestes orientalis sp. nov. is sister to two other new species with strong node support ( UFB 100 , PP 1) (Figs 2 , 3 ). The genetic divergence with its congeners is 3.2–9.1 % in the 16 S, 9.3–18.7 % in the cyt b and 6.0–14.9 % in the COI genes (Table S 7 A – C).

Etymology.

The specific epithet is derived from the word “oriental” meaning eastern, in reference to its distribution in the easternmost part of India.

Suggested common name.

Eastern bush frog.

Distribution and natural history.

Raorchestes orientalis sp. nov. is currently known from Namdapha Tiger Reserve, Kamlang Tiger Reserve and Gandhigram Village in Arunachal Pradesh, and Liyai Khunou in Manipur (Fig. 25 A ). Calling males were recorded among understorey of evergreen forest at approximately one metre height above ground (Fig. 20 C, D ). In Gandhigram this species was recorded among shrubs near small streams in the forests and near human settlements.

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 20. Habitat at the type localities of Raorchestes species of northeast India. A Forest trail at Tura Peak, the type locality of R. garo and R. kempiae; B forest cover and adjacent lowlands of Garo Hills, from Daribokgre; C a landscape view of forest covers and D a forest trail at Namdapha TR, type localities of R. orientalis sp. nov. and R. nasuta sp. nov.; E hills at Mawsynram, near the type locality of R. mawsynramensis sp. nov.; F Nohkalikai Waterfall and forest cover at the type locality of R. boulengeri sp. nov. in Cherrapunji; G dry stream bed and vegetation in Maruwacherra, near Barail WLS, the type locality of R. barakensis sp. nov. and H forest around Jaintia Hills in Narpuh WLS, at the type locality of R. narpuhensis sp. nov.

Figure 23. Raorchestes orientalis sp. nov. A Dorsal view, B ventral view of holotype (WII-ADA 1309) in preserved condition; C dorsal view of WII-ADA 1389 in preserved condition; D dorsolateral view and E ventral view of holotype in life (inset image showing granular skin of abdomen); F WII-ADA 3423 in life; G-J WII-ADA 1387 in life, G dorsolateral view (inset image showing enlarged bluntly conical tubercles on upper eyelids), H ventral view, I groin, J posterior view of thighs; K an uncollected calling male from Kamala Valley, Namdapha TR; L WII-ADA 1631 in life. Scale bar = 10 mm.

Figure 24. Comparative spectrograms and oscillograms illustrating representative calls of four species of Raorchestes described in this study. A, B Oscillograms, C spectrogram, D power spectrum. The call marked with an arrow on top in A is expanded in B.

Figure 25. Distribution of Raorchestes species in northeast India. A Raorchestes rezakhani and four other closely related species; B Raorchestes annandalii and three new species. Type localities are denoted by stars, and other localities are denoted by circles.