Nyctibatrachus sabarimalai Garg, Suyesh, Sukesan & Biju, 2017, sp. nov.

Nyctibatrachus sabarimalai sp. nov.

urn:lsid:zoobank.org:act:4517569C-ECCA-49C9-B1C3-A1B6E4FD6F00

Sabarimala Night Frog

(Figs. 1, 8 and 9; Tables S1–S8)

Holotype. ZSI/WGRC/V/A/927, adult male, from Pamba (09°24 17.6 N 77°0 4 11.6 E, 210 m), Pathanamthitta district, Kerala state, India, collected by SDB and SG on 17 July 2016. Paratypes. ZSI/WGRC/V/A/928–931, four adult males collected along with the holotype, and ZSI/WGRC/V/A/932, adult female, collected from the same locality as holotype, by SDB, SG, RS, SS on 0 2 July 2015.

Etymology. The species is named after Sabarimala, a pilgrim site located inside the Periyar Tiger Reserve, from the surroundings of which the type series was collected. The species name is considered as a noun in the genitive case.

Diagnosis. Nyctibatrachus sabarimalai can be distinguished from known congeners by the following combination of morphological characters: (1) miniature-sized adult males (SVL 12.3–13.2 mm, N = 5); (2) head longer than wide (male HW/HL ratio 82.4–89.8%, N = 5); (3) presence of weakly developed dorsolateral glandular folds separated by scattered granular projections; (4) third finger disc slightly wider than finger width (male FDIII 0.3– 0.4, FWIII 0.2–0.3, N = 5), with dorso-terminal groove and cover bifurcate distally; (5) fourth toe disc slightly wider than toe width (male TDIV 0.5–0.6, TWIV 0.3–0.4, N = 5), with dorso-terminal groove and cover bifurcate distally; (6) presence of single palmar tubercle; (7) foot webbing absent; (8) thigh nearly equal to shank length (male TL/SHL ratio 98.4–101.6%, N = 5); (9) thigh nearly equal to foot length (male TL/FOL ratio 96.9–101.6%, N = 5); and (10) shank nearly equal to foot length (male SHL/FOL ratio 98.4–100%, N = 5).

Morphological comparison. Nyctibatrachus sabarimalai can be distinguished from all its congeners, expect N. anamallaiensis, N. athirappillyensis sp. nov., N. beddomii, N. deccanensis, N. kempholeyensis, N. manalari sp. nov., N. minimus, N. minor, N. pulivijayani sp. nov., N. robinmoorei sp. nov. and N. webilla sp. nov., by its smaller male snout-vent size, SVL 12.3–13.2 mm (vs. larger, 18.1–76.9 mm), absence of webbing between toes (vs. present) and dorsal skin not prominently wrinkled and/or granular (vs. prominently wrinkled and/or granular); differs from N. athirappillyensis, N. deccanensis and N. kempholeyensis by absence of webbing between toes (vs. present); differs from N. minor by its dorsal skin without distinct dorsolateral glandular folds separated by an ‘X’ pattern on anterior half of back (vs. present); and differs from N. webilla by its third finger disc with dorso-terminal groove and cover bifurcate distally (vs. without dorso-terminal groove). Because of the comparable snout-vent size, Nyctibatrachus sabarimalai could be confused with the previously known species N. anamallaiensis, N. beddomii and N. minimus, and the new species N. manalari, N. pulivijayani and N. robinmoorei. However, N. sabarimalai differs from N. anamallaiensis by its head longer than wide, male HW/HL ratio 82.4– 89.8%, N = 5 (vs. head wider than long, male HW/HL 115.7–126.1%, N = 5), relatively Garg et al. (2017), PeerJ, DOI 10.7717/peerj.3007 32/50 larger male HL/SVL ratio of 38.3–41.5%, N = 5 (vs. male HL/SVL ratio of 30.3–37.4%, N = 5), relatively larger male SL/HL ratio of 35.8–40.8%, N = 5 (vs. male SL/HL ratio of 29.4–34.9%, N = 5), and eye length smaller than snout length, male EL/SL ratio 70–84.2%, N = 5 (vs. larger, male EL/SL ratio 125–140%, N = 5).

Nyctibatrachus sabarimalai differs from N. beddomii its dorsolateral glandular folds separated by scattered granular projections (vs. dorsal skin finely granular), relatively smaller snout-vent size, male SVL 12.3–13.2 mm, N = 5 (vs. male SVL 13.3–18.0 mm, N = 10), and head longer than wide, male HW/HL ratio 82.4–89.8%, N = 5 (vs. head wider than long, male HW/HL 106.6–129.3%, N = 10).

Nyctibatrachus sabarimalai differs from N. minimus its dorsolateral glandular folds separated by scattered granular projections (vs. dorsal skin with faint and interrupted glandular folds), and head longer than wide, male HW/HL ratio 82.4–89.8%, N = 5 (vs. head width nearly equal or larger than head length, male HW/HL 95.7–108%, N = 10).

For differences with Nyctibatrachus manalari, N. pulivijayani and N. robinmoorei see comparison of those species.

Description of holotype (measurements in mm). Adult male (SVL 12.8); head small, longer than wide (HW 4.4, HL 4.9); snout rounded in dorsal and lateral views, its length (SL 1.9) longer than horizontal diameter of eye (EL 1.4); loreal region obtuse with indistinct canthus rostralis; interorbital space flat, wider (IUE 1.6) than upper eyelid (UEW 0.8) and internarial distance (IN 1.3); nostril closer to eye (EN 0.8) than tip of snout (NS 1.2); tympanum indistinct; vomerine ridge present, bearing numerous small teeth, at an angle of 70° to body axis, closer to each other than choanae, longer than the distance between them; tongue emarginated, bearing no median lingual process. Forearm (FAL 2.6) shorter than hand length (HAL 2.8), finger length formula: I <II <IV <III, finger discs slightly wider compared to finger width (FDI 0.2, FWI 0.1; FDII 0.2, FWII 0.1; FDIII 0.3, FWIII 0.2; FDIV 0.2, FWIV 0.2), finger disc with dorso-terminal groove, cover bifurcate distally; subarticular tubercles prominent, oval, single, all present; prepollex distinct, oval; single palmar tubercle, oval, distinct; nuptial pads present. Thigh length (TL 6.7) nearly equal to shank (SHL 6.6) and foot (FOL 6.6), relative digit lengths I <II <V II III <IV, toe discs slightly wider compared to toe width (TDI 0.4, TWI 0.3; TDII 0.4, TWII 0.3; TDIII 0.5, TWIII 0.3; TDIV 0.5, TWIV 0.4; TDV 0.4, TWV 0.3), toe disc with dorso-terminal groove, cover bifurcate distally; foot webbing absent; subarticular tubercles well developed, oval, single, all present; inner metatarsal tubercle present, oval; outer metatarsal tubercle weakly developed.

Skin of snout shagreened to granular, upper eyelids with a few prominent glandular warts especially on the margins, presence of weakly developed dorsolateral glandular folds separated by scattered granular projections; sides of head, anterior and posterior parts of back, and upper and lower parts of flank with scattered glandular projections; subocular gland indistinct; upper surface of arms and legs with minute granular projections; ventral surfaces smooth; a pair of prominent femoral glands present on the ventral surface of thighs. Colour of holotype. In life. Dorsum dark-brown, with a pair of light brown longitudinal bands starting from behind the eyelids and extending up to the middle of dorsum, another light brown stripe between the eyes demarcating a triangular light brown patch on the snout (Fig. 8 C); lateral sides of head light greyish-brown with scattered white spots, upper eyelids dark brown (Fig. 8 C); upper and lower parts of flank light grey with scattered white spots; forelimbs (including fingers) and hind limbs (including toes) light brown with dark grey transverse bands. Ventral surfaces greyish-white, hand and foot lighter in color than abdomen (Fig. 8 F). In preservation. Dorsum dark grey, with a pair of light grey longitudinal bands starting from behind the eyelids and extending up to the middle of dorsum, another light grey stripe between the eyes demarcating a triangular light grey patch on the snout; lateral sides of head light grey, anterior and posterior parts of flanks greyish-white, upper eyelids dark grey (Fig. 8 I); forelimbs (including fingers) and hind limbs (including toes) light grey with grey transverse bands. Ventral surfaces greyish-white.

Variations. Morphometric data from five adult males and an adult female, including the holotype, is given in Table S6. Overall, the colour and meristic characters of the paratypes are similar to the holotype. Colour in preservation. ZSI/WGRC/V/A/930–932: dorsum lighter grey in colour with light brown markings; ZSI/WGRC/V/A/928: ventral surface of hindlimbs with a few scattered grey speckles.

Secondary sexual characters. Male (ZSI/WGRC/V/A/927), femoral glands present (Figs. 8 G and 8H), nuptial pads present. Female (ZSI/WGRC/V/A/932), large pigmented eggs present (diameter 2.4 ± 0.5mm, N = 10).

Vocalization. Male (ZSI/WGRC/V/A/929) of Nyctibatrachus sabarimalai produced a single type of call. Calls were not delivered in groups and had a pulsatile temporal structure. The call had duration of 139.9 ms and six pulses were delivered at a rate of 45.6 pulses/s. The call envelope was characterized by a rise time of 1.9 ms, fall of 137.9 ms, and the overall dominant frequency of 4.4 kHz (Table S8; Figs. 9 A–9D).

Distribution and natural history. Nyctibatrachus sabarimalai is currently known only from its type locality, which is located close to Sabarimala in Periyar Tiger Reserve, south of Palghat gap in the Western Ghats state of Kerala. Individuals were located under leaf litter in a shallow forest stream or under the grasses on wet rocky terrain. A calling male was found positioned next to an egg clutch (10 eggs) deposited inside a slit on a tree stump about one foot above ground. Males were observed calling both during the day (between 15:00–17:00 h) and night (20:00–22:00 h).