Leptobrachium aryatium, Purkayastha & Dutta & Gogoi & Sengupta, 2025

Leptobrachium aryatium sp. nov.

Fig. 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 12 View FIGURE 12

Holotype: Adult male ([ ADBUA1085 ]; Fig. 3 View FIGURE 3 ), from Garbhanga Reserve Forest (26.065892°N, 91.752645°E; elevation 230 m a.s.l.), Kamrup Metropolitan District, Assam, India collected on 14 June 2004 by Saibal Sengupta GoogleMaps

Paratypes ( Fig. 4 View FIGURE 4 ). Two adult males ( ADBUA1084 and ADBUGRB6982 ) GoogleMaps and one adult female ( ADBUA0474 ), same collection details as holotype except for the collection date of ADBUA0474 was on 4 April 2005 GoogleMaps .

Diagnosis

Leptobrachium aryatium sp. nov. can be distinguished from other congeners by the following combination of morphological characteristics:

A medium-sized species with adult SVL of 49.0– 55.4 mm in males and 53.2–61.65 mm in females; head wider than long; iris bicoloured, top 1/4th fiery orange with gradually thinning in the middle becoming inverted “V” shaped and the rest is black in colour, with bright-blue sclera; nostril closer to the snout than to the eyes; tympanum indistinct; supratympanic fold distinct extending from behind eye to arm insertion; relative finger lengths: I<IV<II<III; relative toe lengths: I<II<V<III<IV; toe webbing formula: I 0–1 II 0–2 III 0–3 IV 3–1/2 V; large inner and outer metacarpal tubercle present, inner metatarsal tubercle large and spade shaped; dorsal skin sparsely tuberculated with lateral region having most tubercles; dorsum in shades of light to dark uniform grey with prominent black spots, elongated in the lateral region than on the vertebral region; ventrum creamy to white with varying amount of dark infusion.; gular region with prominent black reticulation pattern; dark marking covering the entire tympanum; dark canthal stripe present; dorsal part of tibia with prominent dark blotches forming 4–5 rows; dark blotch at groin present, posterior sides of thighs blackish with white spots; males with a single vocal sac.

Comparison

The colour of iris and scleral ring are important diagnostic feature in identification of the species within the genus Leptobrachium ( Matsui et al. 1999; Hamidy & Matsui 2014; Stuart et al. 2011; Wogan 2012; Yang et al. 2016; Pawangkhanant et al. 2018; Al-Razi et al. 2021) Leptobrachium aryatium sp. nov. has a bicoloured iris having upper 1/4 th fiery orange with a typical getting thinner at the middle becoming inverted “ V ” shaped and the rest is black in colour, with bright-blue sclera versus black or dark-brown in L. abbotti (Cochran) , L. chapaense Bourret , L. gunungense Malkmus , L. hasseltii , L. ingeri Hamidy, Matsui, Nishikawa & Belabut , L. kanowitense Hamidy, Matsui, Nishikawa & Belabut , L. kantonishikawai Hamidy & Matsui , L. lumadorum Brown, Siler, Diesmos & Alcala , L. mangyanorum Brown, Siler, Diesmos & Alcala , L. montanum , L. nigrops Berry & Hendrickson and L. tagbanorum Brown, Siler, Diesmos & Alcala ; black and white or black and blue in L. ailaonicum (Yang, Chen & Ma) , L. banae Lathrop, Murphy, Orlov & Ho , L. boringii Lui , L. buchardi Ohler, Teynié & David , L. guangxiense , L. hainanense Ye & Fei , L. huashen Fei & Ye , L. leishanense (Liu & Hu) , L. leucops Stuart, Rowley, Tran, Le & Hoang , L. liui Pope , L. masatakasatoi Matsui , L. ngoclinhense Orlov , L. promustache (Rao, Wilkinson & Zhang) , L. tenasserimense , L. xanthop Stuart, Phimmachak, Seateun & Sivongxay and L. xanthospilum Lathrop, Murphy, Orlov & Ho ; blue in L. bompu Sondhi & Ohler and L. waysepuntiense Hamidy & Matsui ; reddish or orange scleral ring in L. lunatum Stuart, Som, Neang, Hoang, Le, Dau, Potter & Rowley , L. mouhoti Stuart, Sok & Neang and L. pullus Smith. Leptobrachium aryatium sp. nov. differs from L. hendricksoni Taylor by having dorsum in shades of light to dark uniform grey with prominent black spots versus lavender brown dorsum without any distinct marks, presence of head markings versus absent or indefinite.

Leptobrachium aryatium sp. nov. is a member of L. smithi species complex (see Al-Razi et al. 2021) and thus a close comparison with the member species namely L. rakhinense , L. smithi , L. sylheticum and L. tenasserimense is most relevant for species delimitation. Leptobrachium aryatium sp. nov. differs from L. sylheticum in having obscured tympanum (versus distinct), head little longer than broad, HW/HL: 0.997 (versus wider than long; HW/ HL: 1.159), relative toe length I<II< V < III <IV (versus V <I=II< III <IV), toe web I 0-1 II 0-2 III 0-3 IV 3-½ V (versus I 1-1 II 1-2 III 1-3¼ IV 3½-1 V), inner metatarsal tubercle spade shaped (versus elongated), iris bicoloured, upper ¼ th fiery orange (versus upper ⅓ rd fine red), dorsal side of the body uniformly light to dark grey with prominent black spots/ small blotches (versus dorsum uniform grey with few black spots laterally), lateral side of the body has elongated black patches frequently forming rows (versus laterally may have few black spots without forming rows), ventrally belly creamy to white with varying amounts of dark infusion (versus belly dark grey to black with irregular sparse whitish marbling on chest and anterior part), orange red dots absent, gular with prominent black reticulation (versus tiny orange red dots on lower jaw and gular area), strong supratympanic fold, flanked by dark stripe/blotch (versus distinct supratympanic fold, without dark flank), dorsal part of tibia with 4 – 5 rows of dark markings (vs 2–3 rows of dark markings), groin with dark blotch (versus without blotch); from L. rakhinense in possessing bicoloured iris, upper half fiery orange (versus upper half of iris red), a strong supratympanic fold (versus supratympanic fold is weak), relative finger length II ≤ I <IV < III (vs II <IV <I < III), toe web I 0-1 II 0-2 III 0-3 IV 3-½ V (versus I 1 ½-3 II 1-3 III 2-3½ IV 4-3 V), irregular dark blotches, a ‘Y shaped’ mark may or may not be present, when present this may be complete or broken, bordered with a dark brown rim (versus an inverted ‘Y shaped’ mark on the head without dark rim), the dorsal blotches are without white outline (blotches are outlined with white), dorsal blotches are irregularly arranged (versus another ‘Y shaped’ mark begins just posterior to the eyes and broadens between shoulders), ventrum whitish and speckled heavily with dark markings (versus light colour with small white speckles), eggs are bicoloured (versus unicoloured); from L. tenasserimense in having head little longer than wide HW/HL: 0.98 (versus slightly wider than long HW/HL: 1.029), iris upper half fiery orange (versus bluish green), tympanic hidden (versus distinct), relative finger length II ≤ I <IV < III (versus II <IV <I < III), ventrolateral row of dark spots present (versus absent), strong supratympanic fold (versus weak supratympanic fold). From L. smithi by having obscured tympanum (versus distinct tympanum), broad tongue which is entire posteriorly (versus tongue notched posteriorly), toe web I 0-1 II 0-2 III 0-3 IV 3-½ V (versus I 1-3 II 2½ - 1 III 2 – ½ IV 2-1 V), larval labial tooth formula 1:5+5/5+5:1 (versus 1: 6+6/5+5:1).

Furthermore, the advertisement call of Leptobrachium aryatium sp. nov. exhibits distinct characteristics when compared to its closely related species, L. smithi and L. sylheticum . One note of Leptobrachium aryatium sp. nov. has a duration of approximately 0.5 seconds, with a frequency range spanning 0.5–5 kHz and a dominant frequency centred around 1–2 kHz. The amplitude pattern is characterized by a gradual rise to a peak and subsequent tapering, giving it a smoother temporal structure.

In comparison, one note of L. smithi has a duration of approximately 1.0 seconds (see Matsui et al. 1999) displays a broader frequency range of 1–6.5 kHz, with dominant energy concentrated between 2–3 kHz. The amplitude pattern of L. smithi is highly symmetrical, with a sharp rise and fall around the midpoint of the call. This contrasts with the smoother amplitude pattern observed in Leptobrachium aryatium sp. nov..

One note of L. sylheticum has a duration of approximately 0.3 seconds (see Al-Razi et al. 2021) with a frequency range of 0.5–4 kHz and a dominant frequency around 2 kHz. The amplitude pattern of L. sylheticum is more variable, displaying multiple peaks and valleys within its short call duration.

These acoustic differences, particularly in call duration, frequency range, dominant frequency, and amplitude pattern, clearly differentiate Leptobrachium aryatium sp. nov. from L. smithi and L. sylheticum , supporting its recognition as a distinct species.

Description of holotype

Adult male in a good state of preservation, with SVL 54.0 mm; Head large, broad and flattened, almost as broad as long (HWAJ/HL: 0.94), snout gently rounded, gently sloping in profile, projecting beyond lower jaw; nostrils round, oriented dorsally, located on the canthus rostralis, closer to tip of snout than to eye (NS/EN: 0.38); canthus rostralis distinct, rounded; loreal region deeply concave; internarial distance less than half of the interorbital distance; eyes very large, bulging, distinctly projecting from sides of head in lateral and dorsal view, eye diameter one third of the snout length (ED/SL: 75); interorbital distance almost twice the upper eyelid width (UE/IOS: 0.52); tympanum indistinct, vomerine teeth absent; tongue large, broad and lacking posterior notch; vocal sac single, gular. Forelimb long (FLL/SVL: 0.65), all fingers free of webbing, tips rounded and slightly swollen; relative finger lengths: I=II<IV< III; two prominent large palmar tubercles, not contacting each other medially, much larger than finger tips, inner palmar tubercle rounded in shape and slightly smaller than the ovate outer palmar tubercle; subarticular tubercles not distinct.

Hind limbs long almost the size of SVL (HLL/SVL: 0.98), slender; heels do not contact each other when legs held at right angles to body; tibiotarsal articulation of adpressed limb reaches the angle of the jaw. Toes with thick lateral dermal fringes reaching to the toe tips; toe webbing well-developed and thick, toe webbing formula: I 0–1 II 0–2 III 0–3 IV 3–1/2 V. Tips of all toes rounded, notably swollen; relative toe lengths: I<II< III < V <IV. Subarticular tubercles not distinct, replaced by smooth low callous ridges, inner metatarsal tubercle distinct, spade shaped, outer metatarsal tubercle absent.

Skin smooth with a few white granules located ventral to the tympanum and the ventro-lateral region. A supratympanic ridge from eye to insertion of armpit present.

Colouration in life

( Fig. 5 View FIGURE 5 )

The dorsal and dorsolateral regions of the body exhibit irregularly shaped blotches of varying sizes. Dorsal blotches are slightly darker than the base color at the center, with a dark brown to black border, while dorsolateral blotches are uniformly dark brown. A distinct Y-shaped mark may be present on the forehead, which can be either complete, broken, or absent altogether.When present, the Y-shaped blotch is outlined with a broad dark brown rim.A dark streak extends from the tip of the snout, terminating just before the nostril. Another broad dark streak runs from the nostril to the anterior corner of the eye, while an irregularly shaped streak extends from behind the eye to the angle of the jaw. A sub-triangular dark blotch is located below the eye, extending towards the upper lip. The ventrolateral region contains numerous dark blotches. The dorsal surfaces of the arms and shanks are marked with thin, discontinuous bars, and the dorsal surface of the thighs exhibits dark reticulations. Similarly, the dorsal surfaces of the hands and feet also bear discontinuous bars. The ventral side is heavily speckled, with more pronounced markings on the posterior half and throat. The ventral surfaces of both the forelimbs and hindlimbs are marked with dark blotches.

Variation

Variation of the type series in morphometric characters is presented in Table 1 View TABLE 1 . The external morphology and coloration of the paratypes match those described for the holotype, with no significant deviations. The tympanum is obscure in all examined specimens, including individuals of both sexes and subadults, confirming that this is a consistent diagnostic feature distinguishing Leptobrachium aryatium sp. nov. from L. smithi and L. sylheticum .

Furthermore, none of the examined specimens exhibit a uniform grey dorsum as seen in L. sylheticum . Instead, all individuals display prominent black blotches on the dorsum and tibia, with lateral body markings forming distinct elongated patterns. These features remain consistent across the type series.

Call

( Fig. 6 View FIGURE 6 )

A typical advertisement call has 4– 6 notes lasting from 0.8– 1.2 sec. The dominant frequency is approximately 1031.25 Hz, with a fundamental frequency starting at 515.625 Hz, and the frequency range spanning from 656.25 Hz to 1218.75 Hz, indicating some variability. The crest factor is 2.3219, suggesting a sharp peak in the call. Energy distribution varies across the call, with a significant portion concentrated at the beginning (around 3.5% between 10– 50% of the call's start) and towards the end (around 2.75% from 50– 10% of the call's end). The pulse duration at 50% energy is about 0.54 seconds, showing a quick rise and fall in intensity. The pulse shape indices (0.71429 for onset and 0.93 for offset) suggest a relatively smooth rise and decay. Harmonic content is present, with relative amplitudes of H1 at -0.90777 dB and H3 at -2.802 dB, though the fundamental frequency carries most of the call’s energy.

Description of tadpole

( Fig 7–8 View FIGURE 7 View FIGURE 8 , Table 2 View TABLE 2 )

Dorsal view of the tadpole shows an elliptically shaped body widening in the centre. Ventral side is translucent with four and half circular intestinal coils; faintly visible in some tadpoles. Tadpoles were moderatly sized, snout blunt but rounded in both dorsal and ventral views. Body is about 90% of the total length (BL/SVL: 0.895 ± 0.004) and it is maintained from Gosner stage 26 to 42. Body is depressed (BH/BL: 0.370 ± 0.014), is widest in the middle and the body length is almost twice the body width (SVL/BW: 1.89 ± 0.01), 143% of the body height (BW/BH: 1.428 ± 0.015). Head is little more than 1/4th of snout vent length (HL/SVL: 0.3067 ± 0.0035); head longer than broad (HL/HD: 1.4503 ± 0.0244); Eyes are large and bulging (ED/HL: 0.291 ± 0.011) positioned and directed dorso-laterally. Eye is more than one-third of the interorbital distance (ED/IOS: 0.352 ± 0.013). Nostril openings oblong, positioned dorso-laterally, without narial flap of skin and narrowly spaced. Internarial space is much less than interorbital distance (INS/IOS: 0.335 ± 0.007). Nostrils are located closer to the eye than to the snout tip (EN/NS: 0.6232 ± 0.009). Mouth is placed ventrally, suggesting its benthic, suctorial habit. Oral disc, placed antero-ventrally is non-emarginate, with narrowly curved jaw sheath, with narc shaped upper jaw and U shaped lower jaw. Oral disc is double the length to its width (ODL/ODW: 2.3697 ± 0.065); LTRF: 1:5+5/5+5:1. Spiracle tube is long (SPL/HL: 0.366 ± 0.010), opening is oval and it is sinistral. Vent tube medial, long, positioned marginally and is attached to ventral fin.

Tail is long, longer than snout vent length was (SVL/TL: 0.770 ± 0.002); Tail tip broadly rounded; the upper part of tail fin begins where the tail meets the body, the lower fin starts at ventral terminal end of the body. Tail musculature strong, tail muscle height 3/4 th of maximum tail height (TMH/MHT: 0.6718 ± 0.0046). Glands on the body surface is absent.

Oral disc is with marginal and sub-marginal papillae, maxillary papillae has narrow dorsal gap. The upper labium is seen to consist of six embryonic tooth ridges with A1 complete and A2-A6 has medial gap. Relative length of upper labial tooth rows with medial gap was found to be gradual and was A2>A3>A4>A5>A1>A6. The lower labium was found to consist of six labial tooth rows, P1–P5 with median gap in between and P6 complete. Relative length of lower labial tooth rows with medial gap was found to be P4>P5>P6>P3>P2>P1. The number of teeth present in each tooth row of upper labium increased from stage 25 to 40, the number of teeth each tooth raw in stage 36 were A1: 62, A2: 139, A3: 116, A4: 94, A5: 71 and A6: 39. Whereas the number of teeth present in each tooth row of lower labium, i.e., P1, P2, P3, P4, P5 and P6 were 22, 64, 84, 132, 97 and 89 respectively in stage 36.

Coloration: Dorsally light brown with small, rounded speckles, while ventral side is a translucent white. Tail muscles feature irregularly distributed dark marking of various shapes and sizes.

Natural history

( Fig. 9–11 View FIGURE 9 View FIGURE 10 View FIGURE 11 )

Leptobrachium aryatium sp. nov. is a slow-moving, nocturnal frog that inhabits the foothills of tropical moist deciduous forests and moist sal forests, often associated with evergreen undergrowth. During the study period, the species was found in several microhabitats including grass beds, small bushes, and on dry to moist leaf litter. Coupling pairs were also observed in slow-moving hill stream riffles, which serve as breeding sites for egg-laying. The adults were found to be active between April and August. Mass calling is most commonly observed during the monsoon and breeding season. Females begin approaching calling males between 1900 and 2100 hours. As a female approaches, the male intensifies his calling rate, increasing from 0.17 to 0.67 calls per minute. The male and female then engage in a cyclic chase, with the male attempting to grasp the female from behind. Successful coupling occurs when the male secures the female in inguinal amplexus, holding her at the groin area with his forearms. The amplecting pair then moves towards a slow-moving side pool of the stream to lay eggs. If the female escapes the male’s grasp, she moves away, prompting the male to resume calling in search of a new mate.

The tadpoles were observed inhabiting sections of hill streams with extremely slow to nearly stagnant water flow. They were found at depths ranging from 0.145 m to 0.485 m, in areas with substrates varying from rocky to sandy. At the slightest sign of danger, the tadpoles swiftly retreated to the sandy stream bed..

Distribution

( Fig. 1 View FIGURE 1 )

Leptobrachium aryatium sp. nov. is reported to have a wide occurrence in Assam, parts of Meghalaya, Manipur and Mizoram ( Dutta et al. 2013) but due to the possibility of cryptic diversity within the species, we currently restrict the distribution of species within Garbhanga reserve forest, Rani reserve forest, Amchang Wildlife Sanctuary, Kulsi reserve forest, Maayang hills and Borduar reserve forest in Kamrup and Kamrup Metro district of Assam and Nongkhyllum Wildlife Sanctuary and Nongpoh in Ri-Bhoi district of Meghalaya.

Etymology: The specific epithet aryatium is derived from the name "Arya," referring to Arya Vidyapeeth College, a prestigious educational institution in Guwahati, Assam, India, and the Latin suffix "-tium," which is often used to imply honor or association. The name aryatium is created to signify "in honor of Arya," paying tribute to the college's significant role in advancing education, research, and the academic development of numerous students and scholars. By naming this species Leptobrachium aryatium , the authors aim to commemorate Arya Vidyapeeth College’s legacy, particularly its contributions to the field of herpetology and its support of scientific research in Assam. This species stands as a symbol of the institution's enduring influence in nurturing knowledge and research, especially in the natural sciences.

The present discovery of Leptobrachium aryatium sp. nov., alongside the recent description of L. sylheticum from Sylhet, Bangladesh, and Tripura, Northeast India ( Al-Razi et al. 2021), suggests that the Leptobrachium species in this region may be closely affiliated to L. aryatium , L. sylheticum , or represents an un-described species. This finding raises questions about earlier reports of L. smithi sensu stricto from Northeast India. For instance, Dutta et al. (2013) identified L. smithi in this region, but it is increasingly likely that those populations may represent Leptobrachium aryatium sp. nov., L. sylheticum , or other undescribed species. Given the morphological overlap between these species and the cryptic nature of their diversity, earlier identifications could have been misattributed. This emphasizes the need for molecular analyses alongside traditional morphological assessments to accurately identify cryptic species ( Wogan, 2012).

In light of these findings, we recommend that L. smithi be excluded from the faunal inventories of India until concrete molecular and morphological evidence confirms its presence. The populations currently attributed to L. smithi are better understood as Leptobrachium aryatium sp. nov. or L. sylheticum , pending further taxonomic revisions to clarify species boundaries ( Dutta et al. 2013; Al-Razi et al. 2021). Accurate species identification is critical for conservation efforts, as misidentification may result in ineffective management strategies for species with distinct ecological requirements.

The discovery of Leptobrachium aryatium sp. nov. underscores the importance of continued taxonomic investigation in Northeast India where further cryptic diversity within Leptobrachium is likely to be uncovered. Ongoing research and molecular analyses will be crucial for refining our understanding of amphibian diversity in the region and ensuring that conservation efforts are appropriately directed.