Raorchestes shillongensis ( Pillai & Chanda, 1973 )

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 shillongensis ( Pillai & Chanda, 1973)

Figure 36; Tables 1, 2, S 12

Chresonymy.

Philautus shillongensis Pillai & Chanda, 1973: 30 .

Philautus ( Philautus) shillongensis — Bossuyt and Dubois (2001): 54.

Pseudophilautus shillongensis — Li et al. (2009): 519.

Philautus shillongensis — Ahmed et al. (2009): 16, 48.

Raorchestes shillongensis — Biju et al. (2010): 1120 (by implication); Boruah et al. (2018): 3 –15.

Comments on taxonomic status.

Raorchestes shillongensis was originally described by Pillai and Chanda (1973) from Malki forest, Shillong, Meghalaya under the genus Philautus . Based on Biju et al. (2010), it was allocated to the genus Raorchestes by implication. Boruah et al. (2018) redescribed this species and identified its phylogenetic status based on newly collected topotypic material and discussed colour polymorphism in this species. During our sampling we collected three adult males ( WII-ADA 1459 – WII-ADA 1461 ) from Risa Forest ( 25.55615°N, 91.89389°E, elevation 1670 m a. s. l.), Shillong, East Khasi Hills District and one adult male ( WII-ADA 1506 ) from Jowai ( 25.45849°N, 92.21247°E, elevation 1410 m a. s. l.), West Jaintia Hills District, Meghalaya. We re-examined the specimens mentioned in Boruah et al. (2018) ( WII 500 – WII 525 ; present voucher number WII-ADA 1921 – WII-ADA 1930 , WII-ADA 1932 , WII-ADA 1933 , WII-ADA 1936 – WII-ADA 1938 , WII-ADA 1951 – WII-ADA 1964 ).

Boruah et al. (2018) mentioned head length slightly greater than width, snout longer than eye length, tibia longer than thigh, metatarsal tubercle absents. However, re-examination of the specimens of Boruah et al. (2018) and the newly collected material we found head slightly wider than its length or width equal to its length, tibia shorter than thigh, inner metatarsal tubercle present but indistinct while outer metatarsal tubercle absent. Boruah et al. (2018) provided a description of male specimen ( WII 503 , present voucher number WII-ADA 1936 ), however our re-examination found that this specimen is a female. Therefore, we provided a revised diagnosis and expanded description of the species below.

Diagnosis.

Small sized Raorchestes, SVL 13.9–20.4 mm in adult males and SVL 15.1–21.0 mm in adult females. Head width equal to or slightly greater than its length ( HL / HW = 0.92–1.01); vomerine teeth absent; snout rounded or sub-ovoid, rarely pointed; snout length less than or equal to eye length ( SL / EL = 0.93–1.05); inter-upper eyelid width slightly less than or equal to eye length ( IUE / EL = 0.81–1.0); nostril equidistant between eye and snout tip or slightly closer to snout tip than eye; nuptial pad present on first finger in males; thigh length greater than tibia length ( TBL / TL = 0.89–0.94); dorsal skin on head and back moderately to heavily tuberculate; dark “) - (“ mark on dorsum or a hourglass shaped mark; a dark bar on inter-upper eyelid space; dark brown cross bar on limbs.

Description of a male specimen ( WII-ADA 1459 ).

Small sized Raorchestes, SVL 18.6 mm; head wider than long; snout rounded in dorsal view and slightly protruding beyond lower jaw in ventral view; snout slightly concave dorsally at internarial space, its length slightly less than eye length ( SL / EL = 0.93); canthus rostralis rounded; loreal concave; internarial distance less than inter upper eyelid width ( IN / IUE = 0.91) and greater than upper eyelid width ( IN /UE = 0.85); inter-upper eyelid width less than eye length ( IUE / EL = 0.81); nostril oval, laterally positioned and obliquely oriented; nostril equidistant between eye and snout tip; tympanum indistinct, round, less than one third of eye length ( HTYD / EL = 0.3); supratympanic fold distinct; vomerine teeth absent; choanae round; tongue posteriorly notched; eye protruding, moderate in size, length less than half of head length ( EL / HL = 0.44); pair of internal vocal sac openings on lower jaw; habitus robust, its length less than half of snout-vent length ( AG / SVL = 0.46).

Forelimbs slender, hand longer than forearm ( FAL / HAL = 0.9); relative length of fingers = I <II <IV <III; finger with rounded disc; disc width of the third and fourth fingers equal to tympanic diameter; circum-marginal groove present on each disc; subarticular tubercles distinct, round except the proximal subarticular tubercle on third and fourth fingers, which are smaller in size and indistinct; palmar tubercles not visible; no webbing on hand.

Hindlimbs slender; thigh length less than half of snout-vent length ( TL / SVL = 0.47) and longer than tibia length ( TBL / TL = 0.93); relative length of toes = I <II <V <III <IV; toe with rounded disc; disc width equal to those of fingers; circum-marginal groove present on each disc; subarticular tubercles distinct round except proximal ones on fourth and fifth toes; indistinct inner metatarsal tubercle present; outer metatarsal tubercle absent; webbing slight, reaching second subarticular tubercle on fourth toe.

Skin on dorsal aspect of snout and head smooth; indistinct tubercular projection on snout; upper eyelid shagreen with distinct blunt tubercles, which are not clearly visible in preserved condition; enlarged blunt tubercles on inter-upper eyelid space, behind upper eyelid, temporal and parietal regions, and anterior part of dorsum; similar tubercles but smaller in size, scattered on dorsum, spreading towards dorsolateral side; flat granular tubercles scattered on flank; lateral aspect of head smooth with prominent tubercles on mandibular region behind angle of jaw; tubercles scattered on dorsal aspect of forearm and tibia; on ventrum, lower jaw smooth; gular skin loose; chest smooth; abdomen and thighs granular; tibia smooth; flat granular tubercles sparsely present on ventral aspect of hand and foot.

Colouration in life.

Dorsal aspect of snout and head brown with dark brown irregular spots; dark-brown bar on inter-upper eyelid space; loreal region below canthus rostralis and area between nostril and snout tip dark brown; supratympanic fold dark brown; a broad dark brown patch ventral to eye; dorsum brown, paler towards flank; a pair of dark brown concave stripes on dorsum, broken at the middle, posterior ends extending to groin; forelimb and hindlimb brown dorsally; a dark brown crossbar on each forearm, thigh and tibia; finger and toe disc with pale yellow tinge; on ventrum, head, abdomen and limbs flesh-coloured with brown and white mottling; dense brown mottling along the border of lower jaw; enlarged dark brown patch around vent.

Colouration in preservative.

Pale greyish brown on dorsal aspect; dark brown markings on head, back and limb visible as in life. On ventrum, head, abdomen and limb pale cream coloured; brown mottling visible on ventral aspect, white mottling not visible unlike life colouration.

Sexual dimorphism and morphological variation.

Males have a pair of internal vocal sac openings on the lower jaw; an external subgular vocal sac; and a nuptial pad on the first finger. Morphometric variations are given in Table S 12. Dorsal colouration varies among the individuals which was discussed in Boruah et al. (2018).

Morphological comparison.

Raorchestes shillongensis differs from R. andersoni by presence of dark brown patch with white crown shaped mark or only diffused brown patch on groin (vs. large black irregular spot with two yellow spots present on groin); it differs from R. dulongensis by head length being less than or equal to width (vs. head longer than wide); 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 , R. menglaensis by head length being less than or equal to width (vs. head longer than wide); it differs from R. huanglianshan by snout length being smaller than or equal to eye length (vs. snout length greater 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 tibia length (vs. thigh length less than tibia length); it differs from R. leiktho by the presence of a pair of concave stripes on dorsum from above axilla to groin (vs. absent); it differs from R. malipoensis by presence of dark-brown patch with white crown shaped mark or only diffused brown patch on groin (vs. black patches present on groin and inner lateral aspect thigh); it differs from R. mindat by absence of dark or 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 the lateral aspect of thigh); it differs from R. longchuanensis and R. yadongensis 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. parvulus by thigh length being greater than tibia length (vs. thigh length smaller than or equal to tibia length); it differs from R. tytthus nov. comb. by snout length being greater than or equal to inter-upper eyelid width (vs. snout length less than inter-upper eyelid width). Morphologically R. shillongensis closely resembles R. annandalii . However, it differs from R. annandalii by concave stripes on dorsum connected medially forming “) - (” shaped marking (vs. concave stripes on dorsum not connected medially). Morphological comparisons of R. shillongensis with our newly described species are provided in their respective sections and in Table 1.

Acoustics.

The calls of R. shillongensis were recorded in Risa Forest, Shillong on 23 May 2022 between 19: 00–20: 00 hrs at ambient temperatures of 19.7 ° C – 20.7 ° C. The call description is based on 130 calls including from two individuals ( WII-ADA 1459 and WII-ADA 1460 ). Calls are of a single type, non-pulsatile, and emitted in groups (2–59 calls per group; Fig. 31 ). The mean call duration is 18.55 ± 3.26 ms (12–22 ms) with a rise time of 1 ms and a fall time of 17.55 ± 3.26 ms (11–21 ms). The mean interval between calls is 241.53 ± 14.45 ms (215–281 ms). The dominant frequency is 3720.28 ± 22.38 Hz (3660.6–3746.8 Hz). A detailed comparison of the advertisement calls with those of other congeners is presented in Table 2.

Phylogenetic relationship and genetic divergence.

Raorchestes shillongensis is sister to R. jadoh and an undescribed lineage from Manipur in ML analysis (Fig. 2 ) while it recovered as sister to R. jadoh in BI analysis with weak nodal support (Fig. 3 ). The genetic divergence of R. shillongensis from other congeners is 2.8–8.9 % in the 16 S gene, 8.0–18.3 % in the cyt b gene, and 6.5–16.4 % in the COI gene (Table S 7 A – C).

Distribution and natural history.

Raorchestes shillongensis is distributed within the Shillong Plateau (Fig. 19 B ). The geographical distribution and habitats (Fig. 33 C ) of this species are discussed by Boruah et al. (2018). We recorded this species from Jowai, West Jaintia Hills in the State of Meghalaya. Wangyal et al. (2020) reported this species from Bhutan which is most likely a misidentification. There is no evidence for the presence of R. shillongensis north of the Brahmaputra Valley. This species is known to lay 8– 17 eggs on the ground under leaf litter, where the eggs undergo direct development ( Boruah et al. 2017). Raorchestes shillongensis is known to exhibit territorial behaviour, with males engaging in combat ( Boruah and Das 2020).

Remarks.

Bossuyt and Dubois (2001) doubted the identity of this species as it is morphologically similar to R. annandalii and mentioned that R. shillongensis could be a junior synonym of R. annandalii . However, these two species are phylogenetically distinct and not related to each other (Figs 2 , 3 ). Moreover, R. annandalii is geographically separated from R. shillongensis which is distributed north of the Brahmaputra valley in Sikkim, Darjeeling and Eastern Nepal ( Bossuyt and Dubois 2001; Subba et al. 2017; Khatiwada et al. 2021) while R. shillongensis is restricted to Shillong plateau which is south of the Brahmaputra Valley.

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 36. Raorchestes shillongensis. A – E WII-ADA 1459, A dorsal view and B ventral view in preserved condition, C dorsal view, D dorsolateral view, E ventral view in life. F Dorsolateral view of WII-ADA 1461 in life; G – J WII-ADA 1506 in life, G dorsolateral view, H ventral view, I lateral view showing groin, J posterior view of thighs; K, L two uncollected calling males from Shillong, Meghalaya. Scale bar = 10 mm.