Gracixalus medogensis ( Ye and Hu, 1984 )

Tajo, Tage, Upadhyaya K., Radhakrishna, Dikshit Akalabya Sarmah, A. N., Garg, Sonali & Biju, S. D., 2025, Whistles in the reeds: a new country record of the deeply divergent Gracixalus medogensis, with additional insights on Gracixalus frogs (Rhacophoridae) in India, Zootaxa 5659 (4), pp. 511-535 : 520-527

Gracixalus medogensis ( Ye and Hu, 1984)

( Figures 1–6 ; Tables 1 –5)

Philautus medogensis Ye and Hu, 1984

Aquixalus medogensis Fei, Hu, Ye, and Huang, 2009

Gracixalus medogensis Li, Che, Murphy, Zhao, Zhao, Rao, and Zhang, 2009

Remark. The original description and comparison of Gracixalus medogensis ( Ye and Hu, 1984) was brief and based on a single specimen, with no comprehensive comparison conducted with all species known to date. Therefore, below we present a detailed morphological description and comparison for the species.

Specimens examined. SDBDU 2024.6748 , SDBDU 2024.6586 , SDBDU 2024.6579 , and SDBDU 2022.6244 , four adult males , and SDBDU 2024.6580 , an adult female, from Pange in Tale Valley Wildlife Sanctuary , Lower Subansiri district, Arunachal Pradesh state, India ; SDBDU 2023.6393 , SDBDU 2023.6539 , and SDBDU 2023.6568 , three subadults , from Tasi Biidang in Tale Valley Wildlife Sanctuary , Lower Subansiri district, Arunachal Pradesh state, India; and SDBDU 2025.6779 , an adult male, from Tiwarigaon, Lower Dibang Valley district , Arunachal Pradesh state, India (see Distribution and Natural History for more details) .

Diagnosis. Distinguishable from its congeners by a combination of the following morphological characters: (1) relatively small adult size, SVL 24.1–29.7 mm (N = 5) in males, SVL 31.0 mm in female (N = 1); (2) snout rounded to truncate in dorsal view; (3) head longer than wide (HL/HW ratio 1.08–1.10 in males); (4) internarial distance almost equal to diameter of eye (IN/EL ratio 0.94–1.03 in males); (5) vomerine teeth absent; (6) weakly developed spines on upper eyelid (in life); (7) supratympanic fold distinct; (8) tympanum rather distinct; (9) dorsal skin shagreened to granular; (10) ventral skin granular, not semi-transparent; (11) webbing absent on fingers; (12) moderately developed webbing on foot: fourth toe webbing just below the third subarticular tubercle on either side; (13) dorsum green, brownish-green, or brown, with prominent and contrasting markings that extend from interorbital region to posterior region of dorsum, and light brown-yellow colourations along the body side; (14) males with a smooth nuptial pad on finger I.

Adult morphology. Morphological description, based on five adult males. Small adult size ( SVL 24.1 – 29.7 ) with a slender body; head longer than wide (HL/ HW 1.08 – 1.10 ); outline of the snout rounded to truncate in dorsal view, rounded in ventral view, and rounded to vertical in lateral view; canthus rostralis distinct and sharp; loreal region obtuse and concave; interorbital region flat; snout longer than horizontal diameter of eye (SL/ EL 1.15 – 1.36 ); nostril nearer to the tip of snout than eye ( NS / EN 0.68–0.74); internarial distance almost equal to the diameter of eye ( IN / EL 0.94–1.03); interorbital width greater than upper eyelid width ( IUE / UEW 1.35 – 1.50 ); tympanum rather distinct, diameter shorter than eye diameter ( TYD / EL 0.41–0.42); supratympanic fold distinct and extends up to the axilla; vomerine teeth absent; tongue attached anteriorly, deeply notched posteriorly.

Forelimbs relatively slender; relative length of fingers FLI <FLII <FLIV <FLIII; tips of all fingers with well-developed discs having horizontal circummarginal grooves, discs relatively wide compared to finger width, third finger disc width nearly equal to the distance from eye to nostril; webbing absent between fingers; subarticular tubercles prominent, rounded, all present, palmar tubercles indistinct; nuptial pads present on posterolateral surface of finger I.

Hindlimbs relatively long; thigh shorter than shank (TL/ShL 0.90–0.94) and longer than foot (TL/FOL 1.08– 1.13); shank longer than foot (ShL/FOL 1.15–1.25), heels just overlapping when held at right angles to the body; tibiotarsal articulation well below the eyes; relative length of toes TLI <TLII <TLIII <TLV <TLIV; tips of all toes with well-developed discs having distinct circum-marginal grooves; toes moderately webbed, webbing formula: I2 –– 2 + II2 –– 3 – III2 –– 2 + IV2 + –2 – V; subarticular tubercles rounded, distinct; one on toes I and II, two on toes III and V, and three on toe IV; inner metatarsal tubercle oval; outer metatarsal tubercle and supernumerary tubercles absent; dermal ridge along the outer margin of tibia; and tarsal fold absent.

Dorsal surfaces of head, body and limbs shagreened to granular with scattered tubercles, a faint horny ridge extending from the tip of the snout to the vent, relatively less granulation on tympanum; spinules on upper eyelid absent but with tubercles; supratympanic fold distinct, extending from eye to angle of jaw; throat and chest sparsely granular, belly and ventral surface of thighs granular; dermal appendage at vent absent.

Colour in life. Dorsal colouration ranges from light green to dark green, brownish-green, to brown, with an inverse V-shaped dark green or dark brown continuous or discontinuous marking across the back, covering the interorbital region and eyelids, bifurcating into two branches over the shoulders, and reaching the posterior of the back; axilla and posterior surface of flanks light green, greyish-brown, or pale yellowish-white with light to dark brown mosaic pattern; groin yellowish-brown; sides of head light green or light brown with dark brown spots and markings; a broad dark brown stripe extending on either from upper region of snout to anterior part of eye; tympanic region light or dark brown; dorsal surface of fore limbs and hind limbs same colour as dorsum with dark brown transverse bands; dorsal surface of fingers and toes light brown with faint or prominent blackish-brown cross bands; finger and toe tips yellowish-grey; posterior part of the thighs light brown with a reddish tinge. Ventral surfaces of the throat, chest, and belly greyish-white with minute spots (subadult specimens with prominent light brown spots); thighs light brown with a light orange tinge; iris bronze with a network of fine brown reticulations; pupil black.

Colour in preservative. Dorsum (including head) light slate grey, with the inverse V-shaped marking (discussed in life) dark greyish-brown and a few scattered blackish-brown spots; upper eyelids darker than dorsum; snout greyish-brown, sides of head light slate grey with blackish-brown markings; a broad dark greyish-brown stripe extending from upper region of snout to anterior part of eye on either side; dorsal surface of fore limbs (including fingers) and hind limbs (including toes) same colour as dorsum with dark greyish-brown transverse bands; finger and toe tips off white. Ventral surfaces of the throat, chest, and belly greyish-white, belly with dense blackish spots; thighs light grey with prominent (dense) blackish-brown spots.

Variations. Morphometric data from five adult males from Indian regions is given in Table 3 . The populations from Tale Valley Wildlife Sanctuary and Tiwarigaon differ in their dorsal skin texture and colouration. The dorsal colour is green with contrasting dark markings and dorsal skin shagreened to granular with scattered tubercles in all specimens from Tale Valley, whereas the Tiwarigaon specimen is more similar to the typical Gracixalus medogensis reported from Medog, China in having light brown or beige dorsal colouration with contrasting dark brown markings and a relatively smooth to shagreened dorsal skin without prominent tubercles. The specimens from Tale Valley are slightly smaller in male snout-vent size SVL 24.1–27.3 from the Tiwarigaon specimen (SVL 29.7) but otherwise fall in the same size range as the two reported from Medog (SVL 26.5–28.1). The Indian populations also appear to differ slightly from the two reported Chinese specimens (Yu & Hu 1984; Che et al. 2020) in some morphometric measurements, such as head longer than wide (vs. nearly equal or wider than long), thigh shorter than shank (vs. longer), and perhaps slightly smaller eye and tympanum diameters (vs. slightly larger); however, we note that some of these differences could likely be due to the combination of overall apparent variation in snout-vent size as well as the use of varying measurement techniques, rather than true morphological variations.

Morphological comparison. Morphological comparison of Gracixalus medogensis with other congeners was carried out by using the data obtained from relevant literature ( Boulenger 1893; Bourret 1937; Hu et al. 1978; Ye & Hu 1984; Matsui & Orlov 2004; Nguyen et al. 2008, 2013; Fei et al. 2009; Rowley et al. 2011, 2014, 2020; Mo et al. 2013; Matsui et al. 2015, 2017; Zeng et al. 2017; Chen et al. 2018; Wang et al. 2018; Yu et al. 2019; Che et al. 2020; Le et al. 2021; Boruah et al. 2023; Tran et al. 2023).

Gracixalus medogensis differs from G. gracilipes , G. patkaiensis , G. quangi , and G. supercornutus by its relatively larger male snout-vent size, SVL 24.1–29.7 (vs. smaller: G. gracilipes SVL 20.0–24.0; G. patkaiensis SVL 23.6–26.5; G. quangi SVL 21.0–24.0; G. supercornutus SVL 22.0–24.1), snout rounded to truncate (vs. triangularly pointed), absence of spines or prominent tubercles on upper eyelid (vs. present), opaque ventral skin (vs. translucent), lateral surfaces of head and flank without prominent markings (vs. white, sulphur green or light brown irregular spots or patches), red blood and white bones (vs. green blood and turquoise bones); specifically also differs from G. quangi and G. supercornutus by the absence of a tibiotarsal projection (vs. present); differs from G. seesom by the relatively larger body size, SVL males 24.1–29.7, females 34.9–35.4 (vs. males 21.6–23.0, females 23.2–25.4), presence of nuptial pads on the first finger of males (vs. absence), webbing between fingers absent (vs. rudimentary), and tibiotarsal articulation well below the eyes (vs. well above); differs from G. guangdongensis by snout rounded to truncate (vs. triangularly pointed), absence of a white patch under the eye extending to the tympanum (vs. present), belly skin opaque (vs. semi-transparent); differs from G. lumarius by its smaller body size, SVL males 24.1–29.7, females 34.9–35.4 (vs. larger, males 38.9–41.6 and female 36.3), dorsum green, brownish-green, or brown (vs. yellow), supratympanic folds distinct (vs. indistinct), conical tubercles on dorsum absent (vs. present), webbing between fingers absent (vs. rudimentary); differs from G. quyeti by presence of distinct supratympanic folds (vs. indistinct), conical tubercles on dorsum absent (vs. present), tibiotarsal articulation well below the eyes (vs. reaching up to the snout), webbing between fingers absent (vs. rudimentary); differs from G. sapaensis by the absence of webbing between fingers (vs. rudimentary), dorsum sparsely tuberculated (vs. coarsely scattered with large tubercles), dorsum green, brownish-green, or brown (vs. golden ochre), groin light brown with a yellow tinge and without markings (vs. with light yellow transparent spots laterally in front of the groins); differs from G. tianlinensis by its relatively smaller body size, SVL males 24.1–29.7, females 34.9–35.4 (vs. larger, males 30.3–35.9 and females 35.6–38.7), dorsum green, brownish-green, or brown (vs. brown to beige), nuptial pads only on the first finger (vs. on fingers I and II); differs from G. trieng by its smaller body size, SVL males 24.1–29.7 (vs. larger, males 47.2–41.4), dorsum green, brownish-green, or brown (vs. light brown or yellowish brown), ventral skin uniformly grey with a yellow tinge (vs. mostly yellowish brown with dark mottling and belly pinkish brown), nuptial pads only on the first finger (vs. on fingers I and II), webbing between fingers absent (vs. rudimentary); differs from G. truongi by its relatively smaller body size, SVL males 24.1–29.7, females 34.9–35.4 (vs. larger, SVL males 32.2–33.1, females 37.6–39.3), tibiotarsal articulation well below the eyes (vs. reaching between eyes and nostrils); differs from G. yunnanensis by the absence of webbing between fingers (vs. rudimentary), dorsum green, brownish-green, or brown (vs. yellow brown or red brown), dorsum without conical tubercles (vs. present, small), ventral skin uniformly grey with a yellow tinge (vs. orangish with yellow spots, immaculate, semi-transparent); differs from G. ziegleri by its relatively smaller body size, SVL males 24.1–29.7, females 34.9–35.4 (vs. larger, SVL males 28.1– 30.0, females 36.7–41.2), snout rounded to truncate (vs. triangularly pointed), webbing between fingers absent (vs. rudimentary), tibiotarsal articulation well below the eyes (vs. reaching the tip of snout), dorsum green, brownish-green, or brown (vs. yellowish brown), dorsum without conical tubercles (vs. present).

Morphologically, Gracixalus medogensis is most similar to G. jinggangensis (in the genus Orixalus sensu Dubois et al. 2021 ). Nonetheless, G. medogensis can be differentiated from G. jinggangensis by its predominantly green or brown dorsal colour in life (vs. brown to beige); relatively less granular dorsal skin (vs. more granular); heels barely meeting when flexed hindlimbs are held at right angles to the body axis (vs. heels overlaps); nuptial pads only on the first finger (vs. on fingers I and II). At the same time, our molecular analyses show that G. medogensis does not cluster in the same clade as G. jinggangensis ( Figure 1 ), and the uncorrected pairwise genetic distance between them is up to 10%. As such, we provide a comparison of G. medogensis with the other three species that were assigned to the genus Orixalus by Dubois et al. (2021) for the purpose of future taxonomic clarification. Gracixalus medogensis differs from G. ananjevae by its snout rounded to truncate (vs. slightly pointed), head longer than wide (vs. wider than long), snout longer than horizontal diameter of eye (vs. snout as long as the diameter of eye), relatively less webbing between toes (vs. more webbing); differs from G. carinensis by its snout rounded to truncate (vs. rounded), snout longer than horizontal diameter of eye (vs. shorter), webbing between fingers absent (vs. rudimentary web present), relatively less webbing between toes ( Figures 3–5 ) (vs. more webbing, Figure 4B in Matsui et al. 2017); differs from G. nonggangensis by its relatively smaller male body size, SVL 24.1–29.7 (vs. larger, SVL 29.9–35.3), snout rounded to truncate (vs. rounded), canthus rostralis sharp (vs. rounded), nuptial pads on the first finger (vs. absent), tibiotarsal articulation well below the eyes (vs. reaching up to the tip of snout).

Distribution. Gracixalus medogensis is currently known only from the vicinity of its type locality in Medog County, Tibet in China between elevations of 1400–1500 m asl, from Tale Valley Wildlife Sanctuary in Lower Subansiri district and from Tiwarigaon in Lower Dibang Valley district, Arunachal Pradesh state, India. At Tale Valley, four adult males (SDBDU 2022.6244, SDBDU 2024.6748, SDBDU 2024.6579, and SDBDU 2024.6586) and one adult female (SDBDU 2024.6580) were all collected from Pange and within a radius of two kilometres. SDBDU 2022.6244 was collected on 08 August 2022 by TT, RUK, and SG (27°32’59.89” N 93°53’48.80” E; elevation 1923 m) ; SDBDU 2024.6748 was collected on 28 August 2024 by TT, RUK, SG, and SDB (27°32’49.76” N 93°53’43.82” E; elevation 1891 m) ; SDBDU 2024.6579 was collected on 04 June 2024 by TT, RUK, SG, and SDB (27°32’59.89” N 93°53’48.80” E; elevation 1923 m) ; SDBDU 2024.6580 and SDBDU 2024.6586 were collected on 04 and 06 June 2024, respectively, by TT and RUK (27°32’59.89”N 93°53’48.80”E; elevation 1923 m) . At Tiwarigaon, an adult male SDBDU 2025.6779 was collected on 28 April 2025 by RUK, TT, and SDB (28º13’09.8”N 95°50’24.6”E; elevation 1470 m) .

Natural history. The habitat of Gracixalus medogensis at Tale Valley Wildlife Sanctuary, Arunachal Pradesh lies in evergreen forests with a moderate to closed canopy cover. During opportunistic searches, specimens were located on shrubs near small hill streams, primarily during the rainy season from April–August, and occasionally from September–December, although no calling activity was observed during the latter period. The peak calling activity of this species was noted during the months of June and July in the vicinity of Pange forest camp. In August, only a few isolated calls were heard at Tasi Biidang, also located within the Tale Valley Wildlife Sanctuary, and subadults were subsequently collected in September. The calling sites were mostly located in densely forested areas and inside bamboo thickets growing on hilly slopes (or cliffs) with slow flowing streams at their base. Calling animals were also located in isolated bamboo patches in forested plains. At most of the locations, animals were recorded calling from heights of 1–3 metres above the ground and perched on bamboo culms, nodes, branches, or leaves. However, on few instances calling males were also observed approximately 30 cm above the ground on blades of bamboo grass or thin branches. Over 10 calling males and three females were observed on a hilly slope overgrown with bamboo thickets in a single night at around 20:00 h in July, three hours after moderate rainfall. It was observed that the calling started as early as 17:30 h and subsided by around 23:30 h. The individuals were highly sensitive and stopped calling upon the slightest disturbance in their immediate vicinity. At another sampling site, Tiwarigaon that is located ~ 200 km away and at a relatively lower elevation, the habitat is dominated by a lush canopy of tall evergreen trees, creating a dense forest cover. Interspersed among these tall trees is a well-developed understorey of various shrubs. A stream flows through the specific site, and the sloping terrain along its banks consists of protruding rocks of various sizes, with small shrubs and bamboo grass growing at their bases. The individuals at Tiwarigaon were observed calling from heights of either less than 1.5 metres or over 20 metres above the ground. One calling individual was located and collected from the edge of a small protruding rock along the stream bank at around 20:00 h in late April.

Vocalisation. Vocal repertoire ( Figure 6 ; Table 4 ). The male calls of Gracixalus medogensis were recorded at Pange (Tale Valley Wildlife Sanctuary) on 04 June 2024, at around 21:00 h, from a bamboo patch located at a height of 1.5 m above ground. Ambient air temperature at the time of recording was 17.2 °C (dry bulb) and 16.8 °C (wet bulb). We analysed a total of 67 calls produced by a single individual. The vocal repertoire of G. medogensis consisted of two types of single note calls (type 1 and type 2) both of which had a non-pulsatile structure. The produced calls were stereotypical and delivered in call groups that could be differentiated into two call types. The type 1 calls were longer, whistle-like, and always the first call in a call group, followed by the shorter type 2 calls. Type 1 calls were always constant and showed a single occurrence. The number of calls in each call group ranged from 4−28 (N = 7). The longer type 1 calls (N = 7) had a mean call duration of 192.2 ms, with a mean rise time of 88.1 ms and a mean fall time of 104.11 ms. The dominant frequency was at 3.01 kHz. The spectrum showed harmonics between 2.97−3.06 kHz, 5.94−6.16 kHz, 9.09−12.27 kHz, and 14.6−15.37 kHz. The shorter type 2 calls (N = 60) were the most commonly produced call type. They had a mean call duration of 26.6 ms, with a characteristic mean rise time of 6.2 ms and a mean fall time of 20.3 ms. The spectrum showed no harmonics and the overall dominant frequency was 2.96 ± 0.03 kHz (2.89−3.01 kHz).

Call comparison. We compared the calls of Gracixalus medogensis with the published calls of seven other species. The calls of G. medogensis can be differentiated from those of G. guangdongensis , G. jinggangensis , and G. tianlinensis by their higher mean dominant frequency, 3.01 kHz for type 1 and 2.96 kHz for type 2 calls (vs. lower, 2.4−4, 2.6, and 2−3 kHz, respectively); and from G. gracilipes , G. quangi , and G. supercornutus by a lower dominant frequency, 3.01 kHz for type 1 and 2.96 kHz for type 2 calls (vs. higher, 4.1−5.1, 4.1–4.7, and 3.6−4.1 kHz, respectively). The calls of G. medogensis can be differentiated from those of G. patkaiensis by their lower dominant frequency, 3.01 kHz for type 1 and 2.96 kHz for type 2 calls (vs. higher, 4.35−4.61 kHz for type 1 and 3.1−4.61 kHz for type 2). Due to the presence of highly variable and non-stereotypical calls in G. gracilipes , G. patkaiensis , G. quangi , and G. supercornutus , the call durations of their ‘introductory notes’ or ‘whistles’ (150−250, 45–229, 370, and ~370 ms, respectively) fell in the range of the call duration of G. medogensis (131.5−236.3 ms), whereas the ‘clicks’ of the same species were relatively less variable. The type 2 calls of G. medogensis differed from the ‘clicks’ of G. gracilipes , G. patkaiensis , G. quangi , and G. supercornutus by having a longer call duration, 21.4−29.9 ms (vs. shorter, 6−20, 7–65, 10, and 6−9 ms, respectively); and from the ‘clicks’ of G. guangdongensis and G. jinggangensis by having a shorter call duration, 21.4−29.9 ms (vs. longer, 40−50 and 47–67 ms, respectively).

Figures

FIGURE 1. Map of the Northeast region of India and neighbouring countries showing the genetically verified distribution of Gracixalus medogensis (China: blue circle; India: light and dark green circles) and G. patkaiensis (red, orange, and pink circles). The type localities are indicated with an asterisk (*) symbol inside the circles. Administrative boundaries are based on maps published by the Survey of India (www.surveyofindia.gov.in).

FIGURE 2. Maximum Likelihood phylogram for the genus Gracixalus sensu lato, based on mitochondrial 16S rRNA, showing the phylogenetic position of the new populations (in bold face) of G. medogensis and G. patkaiensis from Arunachal Pradesh, India. Values on the branches indicate Ultrafast Bootstrap Support (UBS>50%) and Bayesian Posterior Probabilities (BPP>50%), respectively. Voucher details in the taxon labels are referenced in Table 1. Type species of Gracixalus sensu stricto and Orixalus are indicated with asterisk symbols at the nodes.

FIGURE 3. External morphology of Gracixalus medogensis from Pange, Tale Valley WLS, Arunachal Pradesh, India, in life. A–D. Dorsolateral view: A. SDBDU 2024.6748 (male); B. SDBDU 2024.6579 (male); C. SDBDU 2024.6748 (male); D. SDBDU 2024.6586 (male); E–G. Dorsal view: E. SDBDU 2023.6568 (subadult); F. SDBDU 2024.6748 (male); G. SDBDU 2024.6585 (female); H–J. Ventral view: H. SDBDU 2023.6393 (subadult); I. SDBDU 2024.6586 (male); J. SDBDU 2024.6748 (male); K–M. Ventral view: K. SDBDU 2024.6586 (male); L. SDBDU 2024.6585 (female); M. SDBDU 2024.6748 (male); N, O. Hand: N. ventral view, SDBDU 2024.6586 (male); O. dorsal view, SDBDU 2024.6586 (male); P, Q. Foot: P. ventral view, SDBDU 2024.6586 (male); R. dorsal view, SDBDU 2024.6586 (male); S–U. Frontal view: S. SDBDU 2024.6586 (male); T. SDBDU 2024.6585 (female); U. SDBDU 2024.6748 (male); V. posterior view of thighs; W. dorsal view of thighs. Photographs: S. D. Biju and Tage Tajo.

FIGURE 4. External morphology of Gracixalus medogensis from Tiwarigaon, Arunachal Pradesh, India (SDBDU 2025.6779, male). A–F. In life: A. dorsolateral view; B. dorsal view; C. ventral view; D. dorsolateral view; E. ventral view of hand; F. ventral view of foot. G. In preservation: dorsal view. Photographs: S. D. Biju.

FIGURE 5. Gracixalus medogensis, in preservation. A–F. SDBDU 2024.6748: 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 foot webbing.

FIGURE 6. Acoustic properties of a typical male advertisement call of Gracixalus medogensis and G. patkaiensis from Arunachal Pradesh, India. A–F. G. medogensis: A. Oscillogram for 30 s call segment; B. oscillogram for 10 s call segment; C. oscillogram for 1.0 s call segment; D. spectrogram for 1.0 s call segment; E. oscillogram for 0.3 s call segment of type 1 call; F. oscillogram for 0.1 s call segment of type 2 call; G–I. G. patkaiensis: G. oscillogram for 1.0 s call segment; H. spectrogram for 1.0 s call segment; I. oscillogram for 0.1 s call segment.