Raorchestes boulengeri, 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 boulengeri sp. nov.

Figure 27; Tables 1, 2, S 12

Holotype.

An adult male ( WII-ADA 1539 ) collected by BB on 2 June 2022 from Cherrapunji ( 25.27696°N, 91.69745°E, elevation 1380 m a. s. l.), approximately one kilometre east of Nohkalikai Waterfall, East Khasi Hills, Meghalaya, India .

Paratypes.

Three adult males ( WII-ADA 1540 , WII-ADA 1541 and WII-ADA 1542 ). Collection details are the same as for the holotype .

Diagnosis.

Small sized Raorchestes , adult male, SVL 17.5–19.1 mm; female unknown; head length equal to width; vomerine teeth absent; snout rounded in dorsal view; snout length less than or equal to eye length; snout length greater than inter-upper eyelid width; nostril equidistant between eye and snout tip; bluntly conical tubercles on dorsal aspect of head, upper eyelid, behind eyelid, dorsolateral aspect of trunk, on dorsal aspect of tibia, and tarsus; spinules on dorsum; nuptial pad present on first finger in males; pair of concave dark brown stripes on dorsum; crossbars on forearm, thigh, and tibia; lower arm orange yellowish; supratympanic fold pale yellowish; finger disc yellow; irregular sized white patches on axilla, groin and abdomen.

Description of the holotype.

Holotype is in good condition except for an incision under right thigh; adult male with vocal sacs, SVL 17.9 mm, overall specimen in good condition, a small portion of muscle from ventral side of right thigh was sampled. Body slender, dorsoventrally flattened, head oval in shape, dorsoventrally flattened, length equal to width; snout rounded in dorsal view, acute in lateral view, slightly protruding beyond lower jaw; vomerine teeth absent; choanae round; tongue posteriorly broad and slightly notched medially at posterior end; pair of slit like openings on lower jaw; snout length slightly less than eye length; canthus rostralis distinct, rounded and vertical; loreal region concave; inter-upper eyelid space flat; narial region slightly raised; internarial distance slightly less than inter-upper eyelid width (INS/ IUE = 0.87) and greater than upper eyelid width ( UEW /INS = 0.75); nostril oval, laterally positioned, obliquely oriented, equally positioned between eye and snout tip; eye moderate in size ( EL / HL = 0.45), protruding in life condition; tympanum barely visible, ( HTYD / EL = 0.3); supratympanic fold distinct; trunk slender, dorsoventrally flattened, less than half of snout-vent length ( AG / SVL = 0.45).

Forelimbs slender; forearm slightly longer than hand length; digits with rounded disc, disc on third and fourth finger slightly wider than tympanic diameter; circum-marginal groove on disc present; palmar tubercles barely visible; indistinct flat granules present on palm; subarticular tubercles large distinct and round, proximal ones on finger III and IV smaller than distal subarticular tubercles; subarticular tubercles on finger I – IV = 1: 1: 2: 2; enlarged nuptial pad on first finger; relative length of fingers = I <II <IV <III; webbing among fingers absent.

Hindlimbs slender; thigh length nearly equal to tibia length ( TBL / TL = 0.97) and half of the snout-vent length ( TL / SVL = 0.49); tibia longer than foot length ( FOL / TBL = 0.89); toes with rounded disc; relative length of toes = I <II <V <III <IV; circum-marginal groove present on toe disc; disc on fourth toe as wide as disc on finger III and IV; elliptical inner metatarsal tubercle present, outer one absent; subarticular tubercles visible, round (1: 1: 2: 3: 2); webbing slight, not reaching second subarticular tubercle on fourth toe.

Dorsal skin on head nearly smooth, upper eyelid granular with indistinct blunt tubercles; few tubercles on mandibular region posterior to angle of jaw; tubercles above supratympanic fold and above axilla running dorso-laterally to middle of the trunk; flank granular, becoming distinct ventro-laterally; tubercles and spinules on head and dorsum in preserved condition not distinct as in life; tubercles on forelimb and hindlimb not visible in preserved condition unlike in life; gular skin loose; skin on chest, abdomen, and on ventral aspect of thigh granular, but granules not as distinct on abdomen; ventral side of forelimbs with barely visible flat granules to palm; tibia and tarsus smooth.

Colouration in life.

Head dorsally brown; anterior part of inter-upper eyelid space slightly reddish brown; indistinct, brown inverted triangular mark on head starting from inter-upper eyelid space and extending posteriorly; dorsum reddish brown, pair of broad dark brown stripes on dorsum, inwardly curved and outer margins diffused toward flank, starting from posterior end of upper eyelid, extending up to groin; tip of tubercles on head, upper eyelid, dorsum and flank white; lateral aspect of head pale greyish brown with brown mottling on it, small irregular white and faint brown patches on lips; supratympanic fold cream coloured, lower end broad, faint brown stripe in front of supratympanic fold staring from posterior corner of the eye to angle of jaw; lateral aspect trunk pale greyish brown with pinkish tinge and brown mottling on it; few large white patches on groin, ventrolateral aspect of flank and axilla; lower arm dorsally orange yellow, forearms and hands pale brown; a slightly darker crossbar on forearm; finger disc yellow, brown mottling on fourth finger disc; hind limb pale brown, short dark brown crossbars on thigh, tibia, and tarsus, base of thigh dorsally pale yellowish, tibio-tarsal articulation and outer lateral aspect of tarsus reddish brown; disc of inner three toes yellow; ventrally gular region with brown and white mottling, abdomen with irregular white patches and brown mottling.

Colouration in preservative.

Dorsally head pale brown; upper eyelid dark grey; a slightly darker greyish brown reversed triangular mark on head, staring between upper eyelids extending posteriorly, posterior end of the marking diffused; loreal region slightly darker, remaining lateral aspect of head paler; dorsum anteriorly pale brown, pair of pale cream coloured broad stripes, inwardly curved, both stripes merge and diffused posteriorly; forelimb, hindlimb, and digital discs dorsally pale yellowish with brown mottling; faint brown crossbars on forearm, thigh, and tibia. Ventrally pale yellowish with brown mottling.

Morphological variation.

Detailed morphometric variations are provided in Table S 12. In addition, pair of stripes on dorsum prominent in the paratypes than holotype; tubercles behind upper eyelid and spinules on dorsum prominent in WII-ADA 1541 than that of other paratypes and holotype; crossbar on forearm and tibia prominent in WII-ADA 1542 than that of other type specimens; skin on dorsal aspect of snout and head shagreen in WII-ADA 1540 and WII-ADA 1541 ; snout tip slightly more pronounced in WII-ADA 1541 than holotype and other paratypes.

Morphological comparison.

Raorchestes boulengeri sp. nov. differs from R. andersoni by head length being equal to width (vs. head length less than width), position nostril equidistant between eye and snout tip (vs. nostril closer to snout tip than eye); it differs from R. annandalii by presence of dark brown and white patches on groin (vs. no pattern on groin), presence of dense spinules on dorsum (vs. scattered tubercles on dorsum); it differs from R. cinerascens nov. comb. by snout length being greater than inter-upper eyelid width (vs. snout length equal to inter-upper eyelid width), position of nostril equidistant between eye and snout tip (vs. nostril closer to snout tip than eye); it differs from R. dulongensis by head length being equal to head width (vs. head longer than its width), nuptial pad present on first finger in males (vs. nuptial pad absent); it differs from R. garo by smaller body size, SVL 17.5–19.1 mm in adult males (vs. SVL 19.9–26.9 mm in adult males); it differs from R. hekouensis by presence of nuptial pad only on first finger (vs. nuptial pad present on first and second finger); it differs from R. hillisi and R. menglaensis by head length being equal to head width (vs. head longer than wide), snout length being less than or equal to eye length (vs. snout length greater than eye length); it differs from R. huanglianshan by inter-upper eyelid width being less than eye length (vs. inter-upper eyelid width greater than or equal to eye length); it differs from R. jadoh by larger body size in adult males, SVL 17.5–19.1 mm (vs. SVL 13.6–14.0 mm), and inter-upper eyelid width being less than eye length (vs. inter-upper eyelid width greater than eye 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. leiktho by larger body size in adult males, SVL 17.5–19.1 mm (vs. SVL 15.7–15.8 mm), position of nostril equidistant from eye and snout tip (vs. nostril closer to snout tip than eye); it differs from R. longchuanensis and R. yadongensis by inter-upper eyelid width being smaller than eye length (vs. inter-upper eyelid width greater than eye length); it differs from R. malipoensis by inter-upper eyelid width being smaller than eye length (vs. inter-upper eyelid width greater than or equal to eye length); it differs from R. mindat by presence of comparatively smaller white patches on groin (vs. enlarged black and white patches present on groin), absence of white patches on lateral aspect of thigh (vs. enlarged white patches on lateral aspect of thigh); it differs from R. parvulus by thigh length greater than tibia length (vs. thigh length smaller than or equal to tibia length), three crossbars present on thigh and tibia (vs. one on thigh and one or two on tibia); it differs from R. rezakhani by head length being equal to width (vs. head wider than long), snout length being greater than inter-upper eyelid width (vs. snout length less than or equal to inter-upper eyelid width); it differs from R. shillongensis by presence of dense spinules on back (vs. skin on dorsum moderately or heavily tuberculated); it differs from R. tytthus nov. comb. by snout length being less than or equal to eye length (vs. snout longer than eye length), position of nostril equidistant between eye and snout tip (vs. nostril closer to snout tip than eye); morphologically R. boulengeri sp. nov. is close to R. mawsynramensis sp. nov. A detailed morphological comparison of this species with its congeners is summarized in Table 1.

Acoustics.

The calls of R. boulengeri sp. nov. recorded in its type locality on 2 June 2022 at 18: 15 hrs at an ambient temperature of 25.9 ° C. The call description is based on 40 calls from the holotype ( WII-ADA 1539 ). The calls are single type, non-pulsatile (Fig. 24 ), emitted as a single call at the beginning and gradually modified in groups (2 calls per group). The mean call duration is 25.03 ± 3.48 ms (20–31 ms) with a rise time of 1 ms and fall time of 24.1 ± 3.47 ms (20–30 ms). The mean interval between calls is 187.06 ± 13.18 ms (173–216 ms) when calls were emitted in groups. The dominant frequency is 3740.33 ± 20.81 Hz (3703.7–3789.8 Hz). The call of R. boulengeri sp. nov. differs from the call of its sister species R. mawsynramensis sp. nov. by the following characters: call duration of R. boulengeri sp. nov. is generally longer, 20–31 ms (vs. call duration 13–20 ms), inter-call interval is lower, 173–216 ms (vs. inter-call interval 1127–2133 ms), and peak frequency range is lower, 3703–3789 Hz (vs. 4263–4608 Hz). A detailed comparison of the advertisement calls with those of the congeners is presented in Table 2.

Phylogenetic relationship and genetic divergence.

Raorchestes boulengeri sp. nov. is sister to R. mawsynramensis sp. nov. (Figs 2 , 3 ). The genetic divergence between these two species is 2.5–2.9 % in the 16 S, 3.9–4.4 in the cyt b, and 3.6–3.9 % in the COI genes. The genetic divergence of R. boulengeri sp. nov. with other congeners varied between 3.4–9.8 % in the 16 S, 9.3–18.0 % in the cyt b and 6.0–14.6 % in the COI genes (Table S 7 A – C).

Etymology.

This species is named after George Albert Boulenger for his contribution to Indian herpetology, particularly bush frogs.

Suggested common name.

Boulenger’s bush frog.

Distribution and natural history.

Raorchestes boulengeri sp. nov. is currently known only from the type locality (Fig. 25 A ). Calling individuals of this species were recorded on shrubs and bamboo thickets in a small isolated forest patch. The forest patch was surrounded by grasslands. A small stream was present approximately 300 m west of the forest. Other sympatric anuran species recorded in the area were Amolops sp. and Minervarya sp.

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 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.

Figure 27. Raorchestes boulengeri sp. nov. A – C Holotype (WII-ADA 1539), A dorsal view and B ventral view in preserved condition, C holotype in life. D – F Paratype (WII-ADA 1542) in preserved condition, D dorsal view, E ventral view, F lateral view of head. Scale bar = 10 mm.