Amolops monticola ( Anderson, 1871 )

Patel, Naitik G., Garg, Sonali, Das, Abhijit, Stuart, Bryan L. & Biju, S. D., 2021, Phylogenetic position of the poorly known montane cascade frog Amolops monticola (Ranidae) and description of a new closely related species from Northeast India, Journal of Natural History 55 (21 - 22), pp. 1403-1440 : 1412-1422

Amolops monticola ( Anderson, 1871)

Montane cascade frog

( Figures 1–7 ; Tables 1–2, S1–S2)

Taxonomic notes

Amolops monticola ( Anderson 1871) has remained one of the least known cascade frogs since its original description 150 years ago. The species was described based on a single specimen from ‘Darjeeling’ collected at an altitude of ‘3,500 feet’. The original description is based on a specimen with ‘length of body 2’, 10”’ (= 53.34 mm) and several other morphological characters ( Anderson 1871, p. 26). The catalogue number of the described specimen was not stated in the original description, but was subsequently provided as ZSIC 10036 by Sclater (1892). We studied the type that is currently available at ZSI (Zoological Survey of India), Kolkata and found that it largely matches the specimen in the original description ( Figure 3 ). This species has subsequently been reported in checklists from various localities within India (mostly lacking vouchers) and neighbouring countries such as China, Nepal and Bhutan. The report of this species from the Indian State of Nagaland ( Ao et al. 2003) may refer to A. kohimaensis ( Biju et al. 2010) , based on close proximity to its type locality, while reports of A. monticola from other parts of Northeast India ( Sarkar et al. 1992; Mathew and Sen 2010) require re-evaluation. Reports of this species from China (e.g. Hu 1987; Fei 1999; Fei et al. 2009; Li et al. 2010) have been doubted and possibly refer to A. aniqiaoensis ( Jiang et al. 2016) . The reported occurrence of this species in Bhutan has also been doubted ( Wangyal 2014). However, this species was recently included in the checklist of Sikkim amphibians ( Subba et al. 2017) based on new collections with a brief description.

We did not locate A. monticola during our surveys in Darjeeling hills. However, we did collect it from the low-lying Himalayan region in south Sikkim near Tarku Forest block (27.247° N, 88.437° E, elevation 930 m asl), located at an aerial distance of approximately 30 km from the type locality ‘Darjeeling 3,500 feet’ (= 1066.8 m elevation) . The new collection was compared with the holotype, the original description ( Anderson 1871) and the subsequent redescription of A. monticola by Boulenger (1920). We confirm that our new collection from Sikkim represents A. monticola based on the following comparable characters (the holotype characters measured in the present study are indicated in quotes and those for the new collection are given in parentheses): snout-vent size, SVL ‘69.7’ mm, female, ZSIC 10036 (SVL 62.3 mm, female, BNHS 6120 ); ‘head as long as broad or a little longer: HL 24.7; HW 21.5 ’ (head slightly longer than wide, HL 21.0 mm, HW 20.8 mm); (Continued) ‘snout rounded’ (snout rounded in ventral view); ‘loreal region feebly oblique, concave’ (acute to obtuse and concave); ‘nostril equally distant from the eye and from the tip of the snout: NS 4.5 ; EN 4.4 ’ (distance from eye to nostril EN 4.0 nearly equal to the distance from nostril to snout NS 3.9 ); ‘nearly entirely webbed’ (webbing up to the base of the discs on all toes except toe IV); and ‘narrow, feebly prominent, glandular dorso-lateral fold’ (weakly developed dorsolateral folds). An additional male specimen from ‘Darjiling’ was described by Boulenger (1920) for which the mentioned characters (male, SVL 41 mm, specimen probably at Natural History Museum [NHM], London, not studied) ‘with an external vocal sac on each side of the throat’ and ‘a strong pad on the inner side of the first finger’ also match our male specimens from south Sikkim ( Table 2) . The colour characters mentioned in the original description ( Anderson 1871) are also a close match to those of the newly collected population; however, since the holotype is bleached, colour in preservation cannot be reliably compared with the new collection ( Figure 3 ).

Below we provide a detailed description of the available holotype and a newly collected female specimen having a comparable snout-vent size to the holotype, for two reasons: (1) the type specimen is currently in a poor condition due to dehydration, hence reliable measurements for several characters are not possible; and (2) the original description is based largely on meristic characters and presumably without live colouration.

Diagnosis

Amolops monticola is a relatively large member of the A. monticola group, female SVL 62– 70 mm (N = 2), male SVL 38–41 mm (N = 5); outline of the snout rounded in dorsal view; tympanum distinct, 40.5–41.5% (females), 40.4–44.2% (males) of the eye diameter; dorsal skin smooth to shagreened in female, shagreened to granular in male; dorsolateral folds weakly developed; dorsal colouration varying from light to dark brown, reddish brown or ash greyish brown, dorsum without prominent spots or markings in female, but with light-brown spots in breeding male ( Figure 4 ); ventral surfaces without spots or markings; limbs with dark crossbands; foot webbing large, up to the base of the disc on all toes and beyond the third subarticular tubercle on either side of toe IV.

Redescription of holotype, ZSIC 10036 (measurements in mm)

A medium-sized adult female (SVL 69.7), body rather robust; head longer than wide (HL 24.7; HW 21.5; MN 19.9; MFE 16.4; MBE 8.8); snout rounded in dorsal, ventral and lateral views, its length (SL 9.5) longer than horizontal diameter of eye (EL 8.2); loreal region acute to obtuse, concave; indistinct canthus rostralis; interorbital space flat, narrower (IUE 7.2) than upper eyelid width (UEW 8.8) and wider than internarial distance (IN 6.5); nostril oval, almost as close to the tip of snout (NS 4.5) as eye (EN 4.4); tympanum rather distinct (TYD 3.4), 41.5% of eye diameter (EL 8.2), nearly 1.2 times larger than distance from tympanum to eye (TYE 2.8); pineal ocellus present between the eyes; vomerine ridge present, at an angle of 90° relative to the body axis, closer to each other than choanae, longer than distance between them; tongue large, emarginate, lingual papilla absent; supratympanic fold rather indistinct ( Figure 3 ). Arms moderately long, forearm length (FAL 16.6) shorter than hand length (HAL 17.9); relative length of fingers I <IV <II <III (FL I 8.9, FLII 11.0, FLIII 14.7, FLIV 10.3), tips of fingers with discs except on finger I, discs moderately wide compared to finger width except on finger I (FDI 1.9, FWI 1.8; FDII 2.3, FWII 1.1; FDIII 3.0, FWIII 1.1; FDIV 3.0, FWIV 1.1), finger discs with circummarginal grooves, except on finger I; dermal fringe present on fingers; webbing absent between fingers; subarticular tubercles rather prominent and rounded, formula 1, 1, 2, 2 ( Figure 3 ); two metacarpal tubercles, elongate. Hind limbs long, heels overlapping when legs at right angle to the body; thigh (TL 39.5) shorter than shank (SHL 42.1) and longer than foot (FOL 32.0); distance from base of tarsus to tip of toe IV (TFOL 53.5);relative length of toes I <II <V <III <IV; toe tips dilated with prominent discs (TDI 2.3, TDII 2.6, TDIII 2.6, TDIV 2.4, TDV 1.9), toe discs with circummarginal grooves, slightly narrower than discs of toes I and IV; foot webbing large: I1– 1II1–1III1–1 1/3IV1 1/3–1V, extending up to the base of discs on toes I, II, III and V, and beyond the third subarticular tubercle on either side of toe IV with narrow extension to the base of disc; subarticular tubercles prominent, all present, oval; inner metatarsal tubercle prominent (IMTL 3.5), oval; outer metatarsal tubercle absent; supernumerary tubercles absent.

Skin of dorsum smooth to shagreened, posterior parts of thigh and cloacal region sparsely granular; lateral surfaces from the head to the groin and fore- and hind limbs (including fingers and toes) smooth; flank and groin smooth to shagreened; supratympanic fold rather indistinct;dorsolateral fold weakly developed; two rictal glands, the anterior gland continuous with the upper lip. Ventral surfaces smooth ( Figure 3 ).

Colour in preservation. Dorsum yellowish brown; lateral surfaces of the head lighter than dorsum; ventral surfaces light grey ( Figure 3 ).

Description of topotype, BNHS 6120 (measurements in mm)

A medium-sized adult female (SVL 62.3), body rather robust; head slightly longer than wide (HL 21.0; HW 20.8; MN 18.4; MFE 14.6; MBE 8.4); snout rounded in dorsal, ventral and lateral views, its length (SL 8.5) longer than horizontal diameter of eye (EL 7.9); loreal region acute to obtuse, concave; indistinct canthus rostralis; interorbital space flat, nearly equal (IUE 5.1) to upper eyelid width (UEW 5.0) and shorter than internarial distance (IN 6.5); nostril oval, almost as close to the tip of snout (NS 3.9) as eye (EN 4.0); tympanum rather distinct (TYD 3.2), 40.5% of eye diameter (EL 7.9), nearly 1.4 times larger than distance from tympanum to eye (TYE 2.3); pineal ocellus present between the eyes; vomerine ridge present, bearing four large teeth, at an angle of 90° relative to the body axis, closer to each other than choanae, longer than distance between them; tongue large, rounded to cordate, emarginate, lingual papilla absent; supratympanic fold rather indistinct ( Figure 5 ). Arms moderately long, forearm length (FAL 15.7) shorter than hand length (HAL 17.8); relative length of fingers I <II <IV <III (FL I 7.0, FLII 7.4, FLIII 12.1, FLIV 9.4), tips of fingers with discs except on finger I, discs moderately wide compared to finger width except on finger I (FDI 1.6, FWI 1.5; FDII 2.2,FWII 1.0; FDIII 3.0,FWIII 1.0; FDIV 2.9, FWIV 1.0), finger discs with circummarginal grooves, except on finger I; dermal fringe present on fingers; webbing absent between fingers; subarticular tubercles rather prominent and rounded,formula 1, 1, 2, 2; one supernumerary tubercle each on fingers I, II and III and two on finger IV ( Figure 5 ); two metacarpal tubercles,elongate. Hind limbs long, heels overlapping when legs at right angle to the body; thigh (TL 38.0) shorter than shank (SHL 41.8) and longer than foot (FOL 34.4); distance from base of tarsus to tip of toe IV (TFOL 53.0); tibiotarsal articulation reaching up to the snout tip; relative length of toes I <II <V <III <IV; toe tips dilated with prominent discs (TDI 1.8, TDII 2.2, TDIII 2.3, TDIV 2.3, TDV 2.0) toe discs with circummarginal grooves,slightly narrower than discs of toes I and IV;dermal fringe on preaxial side of toe I and postaxial side of toe V; foot webbing large: I1–1II1–1III1–1⅓IV1⅓–1V, extending up to the base of discs on toes I, II, III and V, and beyond the third subarticular tubercle on either side of toe IV with narrow extension to the base of disc; subarticular tubercles prominent, all present, oval; inner metatarsal tubercle prominent (IMTL 3.2), oval; outer metatarsal tubercle absent; supernumerary tubercles absent.

Skin of dorsum smooth to shagreened,posterior parts of thigh and cloacal region granular; lateral surfaces from the head to the groin and fore- and hind limbs (including fingers and toes) smooth; lateral surfaces of head smooth; flank and groin smooth to shagreened; supratympanic fold rather indistinct; dorsolateral fold weakly developed; two rictal glands, the anterior gland continuous with the upper lip. Ventral surfaces smooth ( Figure 5 ).

Colour in life. Dorsum greyish brown, without any prominent spots other than a few scattered creamy-white obscure spots on dorsal parts of the head and posterior back; a lightbrown streak extending from snout to the anterior end of eye;a broad light-brown band from the posterior end of eye to the axilla, including tympanic region; groin and posterior part of flank light brown with light-creamy-white reticulations, and anterior part of flank dark-slate coloured; rictal glands creamy white; anterior and posterior parts of thigh yellowish brown with light-brown reticulations; upper half of the iris golden brown, lower half dark brown; dorsal surfaces of fore limbs lighter than dorsum with prominent dark cross-bands, dorsal surfaces of hind limb blackish brown with black cross-bands; foot webbing light brown with dark-grey reticulations. Ventral surfaces of throat,chest and belly yellowish white; throat,chest and anterior part of belly with obscure greyish spots; fore- and hind limbs flesh-red without markings; foot webbing light grey with dark-grey spots ( Figure 4 ). Colour in preservation. Dorsum light brown with an ash-blue tinge, fore- and hind limbs (including fingers) light brown with an ash-blue tinge and blackish cross-bands; lateral surfaces of the head brown with ash-blue tinge, especially on the tympanic region; rictal glands creamy white; flank and groin dark grey with scattered light-grey spots and faint reticulations. Ventral surfaces creamy white ( Figure 5 ).

Morphological variations

Morphometric data of two females (including the holotype) and four males are provided in Table 2. Dorsal colour slightly variable from light brown to dark brown to slate grey, with or without yellowish tinge. In life. WIIADA 543 (male): dorsal skin shagreened to sparsely granular, especially towards the posterior part; dorsum light brown with a yellow tinge and scattered blackish-brown spots; cross-bands on limbs prominent. WIIADA 544 (male): dorsal skin shagreened to prominently granular; dorsum light brown with a yellow tinge and scattered blackish-brown spots; crossbands on limbs prominent. WIIADA 545 (male): dorsal skin shagreened to prominently granular; dorsum light brown with a yellow tinge and scattered blackishbrown and creamy-white spots; cross-bands on limbs prominent. In preservation. WIIADA 541 (male): dorsal skin shagreened with scattered black spots; cross-bands weakly developed. WIIADA 546 (male): dorsal skin shagreened, posterior part of dorsum sparsely granular, with scattered black spots; cross-bands on limbs obscure. WIIADA 542 (male): dorsal skin smooth to shagreened, posterior part of dorsum sparsely granular; cross-bands on limbs obscure. WIIADA 540 (male): dorsal skin smooth, without any prominent spots; cross-bands on limbs rather prominent.

Secondary sexual characters

Female (BNHS 6120): mature ova not found, and probably the time of collection was outside the breeding season. Male: loose skin on either side of the throat in calling males (lemon yellow in life) and smooth nuptial pad on finger I.

Distribution and natural history

This species is currently known to occur only in the low-lying Himalayan regions in and around its type locality of ‘ Darjeeling’ in West Bengal State and south Sikkim district in Sikkim State, India ( Figures 2 and 7 ) . Our collection of this species from south Sikkim (collected by NGP on 24 October 2018) was from a small stream located near Tarku forest block (27.247° N, 88.437° E at 930 m asl elevation) . The stream was 220 cm wide and 20 cm deep at the middle. Air temperature at the sampling site was 22.2°C, wet bulb temperature was 15.4°C, water temperature was 18.1°C and relative humidity of 76.8% was noted. Seven males and one female of the species were encountered in about 1 hour between 19:30 and 20:30 hrs. All the individuals were sampled within 1 m distance adjacent to the stream. Individuals occupied rocks and boulders at heights of up to 1 foot. No individual was observed farther away from the stream. The female was found on a boulder near the pool section of the stream. A pair of bright yellow vocal sacs was observed in all seven male individuals found during the survey, although calling activities were not observed. At the sampling site, this species was found along with A. cf. marmoratus , which was more abundant in the area compared to A. monticola , as more than 20 individuals of the former species were encountered with the same sampling effort. Considerable anthropogenic disturbance was observed at the sampling locality, which can impact the stream habitat negatively due to the removal of ground vegetation and substrate for activities such as construction.

Figures

Figure 1. Bayesian consensusphylogram for 167 taxa representing members of the genus Amolopsand five outgroup species, based on 2001 bp of concatenated mitochondrial DNA (16S, COI, and ND2 genes). Voucher numbers and associated details are referenced in Table S1. Bayesian posterior probabilities (BPP) and RAxML bootstrap support (BS) values>50% are denoted above and below the branches, or separated by an oblique (/) mark, respectively.Black vertical bars beside the terminal nodes indicate Amolops species recognised based on Bayesian and ML inferences; grey bars and open rectangles indicate putative species delimited in the bPTP analysis with support values of>90% or <90%, respectively. The genus comprises eight major species groups following Wu et al. (2020), as indicated with coloured bars on the extreme right and corresponding circles on the internal and terminalnodes.Four subgroups are observed within the focal Amolops monticola group. Illustrations representing species groups were prepared based on published photographs.

Figure 2. (a) The type localities of all known members of the Amolops monticola species group. Geographical coordinates and their source information are referenced in Table S2. Illustrations for species are prepared based on type images or subsequently published photographs. (b) The number of A. monticola group species originally described from different Asian countries, based on their type localities. (c) The number of A. monticola group species currently recognised to occur in different countries. An asterisk (*) after the species name indicates a provisionally grouped species.

Figure 3. Holotype (ZSIC 10036, adult female) of Amolops monticola in preservation:(a) dorsal view; (b) ventral view; (c) lateral view of head; (d) ventral view of hand; (e) ventral view of foot; (f) schematic illustration of webbing on foot.

Figure 4. Topotypes of Amolops monticola in life: (a, b) adult female, BNHS 6120: (a) dorsolateral view; (b) dorsal view; (c–e) adult male, WIIADA 544: (c) lateral view; (d) dorsolateral view; (e) dorsal view; (f) dorsolateral view (adult male, WIIADA 545); (g) lateral view of head (adult female, BNHS 6120); (h) ventral view of head showing loose skin of the vocal sacs (adult male, WIIADA 544).Photographs: NGP.

Figure 5. Topotype of Amolops monticola in preservation, an adult female, BNHS 6120: (a) dorsal view; (b) ventral view; (c) lateral view of head; (d) ventral view of hand; (e) ventral view of foot; (f) schematic illustration of webbing on foot.

Figure 6. Topotype of Amolops monticola in preservation, an adult male, WIIADA 544: (a) dorsal view; (b) ventral view; (c) lateral view of head; (d) dorsal view of hand showing nuptial pad on finger I; (e) ventral view of hand; (f) illustration of tip morphology on finger I; (g) illustration of tip morphology on finger III; (h) ventral view of foot; (i) schematic illustration of webbing on foot.

Figure 7. (a) Distribution map of all known members of the Amolops monticola species group found in India; (b) inset rectangle enlarged to show the type locality of Amolops monticola ‘Darjeeling’ and the rediscovered locality in south Sikkim. An asterisk (*) after the species name indicates members whose type locality is in India. A question mark (?) indicates a doubtful record. Geographical coordinates and their source information are referenced in Table S2.