Microhyla eos, Biju & Garg & Kamei & Maheswaran, 2019

Biju, S. D., Garg, Sonali, Kamei, Rachunliu G. & Maheswaran, Gopinathan, 2019, A new Microhyla species (Anura: Microhylidae) from riparian evergreen forest in the eastern Himalayan state of Arunachal Pradesh, India, Zootaxa 4674 (1), pp. 100-116 : 105-111

Microhyla eos sp. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:32B8523E-69CC-4EBA-9071-919F40C73B44

Arunachal Chorus Frog

( Figs. 1–4 , Tables 1–3 )

Holotype. ZSIC 14310 , an adult female, from Rani Jheel (27°32’20.5” N, 96°29’17.6” E, 860 m asl), Namdapha National Park , Changlang district, Arunachal Pradesh state, India, collected by S. D. Biju, R. G. Kamei and G. Maheswaran, on 22 May 2011.

Paratypes. ZSIC 14311–14312 , two adult females, collected along with the holotype .

Referred specimen. SDBDU 2011.380 , an adult male, collected along with the types .

Etymology. The species is named after the mythological Greek goddess of dawn called ‘Eos’, personifying the region of its discovery—the easternmost Indian state of Arunachal Pradesh, which is popularly known as the land of dawn-lit mountains or the land of rising sun. The species epithet eos is used as a feminine noun in apposition to the generic name.

Diagnosis. Microhyla eos sp. nov. can be distinguished from all other known Microhyla species by a suite of morphological characters: medium-sized adults (male SVL 21.5 mm, female SVL 26.9–27.8 mm); stout and prominently triangular-shaped body; contrasting colouration and prominent markings on dorsal and lateral surfaces; and prominently dilated finger and toe tips with dorso-terminal grooves, cover rounded distally ( Fig. 2 ).

Description of holotype. Adult female (SVL 27.8), body stout, triangular-shaped; head wider than long (HW 8.4, HL 6.3); snout elliptical to pointed in dorsal and ventral view, rounded in lateral view, its length (SL 3.5) longer than horizontal diameter of eye (EL 2.6); loreal region vertical, indistinct canthus rostralis; interorbital space flat, wider (IUE 2.6) than upper eyelid width (UEW 1.9) and internarial distance (IN 2.3); nostril oval, closer to tip of snout (NS 1.4) than eye (EN 1.6), placed more towards the lateral side of snout; tympanum hidden; supratympanic fold extending from posterior corner of eye to shoulder weakly developed; vomerine teeth absent; tongue small, oval, without papillae. Arms short, forearm length (FAL 5.4) shorter than hand length (HAL 7.9); relative length of fingers I<II<IV<III (FL I 1.4, FL II 2.4, FL III 4.3, FL IV 3.3); tips of all fingers with discs, moderately wide compared to finger width (FD I 0.7, FW I 0.4; FD II 1.4, FW II 0.5; FD III 1.5, FW III 0.6; FD IV 1.2, FW IV 0.6); finger discs with dorso-terminal grooves, cover rounded distally; dermal fringe present on fingers; webbing absent between fingers; subarticular tubercles rather prominent; palmar tubercles weakly developed, outer palmar tubercle (OPTL 0.9) slightly larger than the inner (IPTL 0.8); supernumerary tubercles absent. Hind limbs short, thigh (THL 15.2) shorter than shank (SHL 17.5) and foot (FOL 16.1); distance from base of tarsus to tip of toe IV (TFOL 22.1); relative length of toes I<II<V<III<IV; toe tips dilated with prominent discs (TD I 1.1, TW I 0.4; TD II 1.3, TW II 0.5; TD III 1.6, TW III 0.6; TD IV 1.5, TW IV 0.5; TD V 1.0, TW V 0.5); toe discs with dorso-terminal grooves, cover rounded distally; terminal phalanges of toes Y-shaped; dermal fringe present on toes; foot webbing small: I1 1 / 2 –2 + II1 2 / 3 –3 – III2 1 / 2 –4 – IV4 –– 1 1 / 2 V; subarticular tubercles prominent, all present, circular; inner metatarsal tubercle prominent (IMTL 1.1), oval-shaped; outer metatarsal tubercle, small (OMTL 0.3), rounded; supernumerary tubercles absent ( Fig. 2 ).

Skin: Skin of dorsum, lateral surfaces from head up to groin, fore- and hind limbs (including fingers and toes) smooth to shagreened; posterior parts of thigh and cloacal region granular. Ventral surfaces smooth ( Fig. 2 ).

Colour: In life. Dorsal surface of snout light creamish-brown without prominent markings; a dark brown Wshaped marking between the eyes, tapering behind the head, and expanding into a large inverted V-shaped dark brown marking that extends from anterior part of the dorsum at the level of the shoulder towards the lower back and groin; dorsal V-shaped markings intermitted with round or elongate brown spots, V-shaped markings and spots with cream colour outline; forelimbs and hind limbs light brown with dark brown crossbands and elongate spots with cream colour outline; lateral surface of the snout reddish-brown with scattered minute white spots along the upper and lower lip; a prominent cream colour streak extending from posterior corner of the eye to the shoulder; a dark brown lateral band that starts from posterior corner of the eye, widen up to the shoulder, forms an arch over the insertion of forelimb at axilla, and again widens up to the groin with an undulating margin towards the ventral side; remaining parts of flank light brown with scattered black spots; scattered brown spots with cream colour outline above the shoulder; lateral surfaces of thighs with prominent dark brown marking up to the knee; groin light yellowish-brown; a dark brown marking around the cloacal region. Ventral surface of throat and chest light creamishbrown with scattered brown spots; belly greyish-brown; armpits encircled with dark brown marking; ventral surface of forelimbs light brown with dark brown margins; hind limbs light brown with scattered black speckles and spots ( Fig. 2 ). In preservation. All markings observed in life were present in preservation in lighter or slightly bleached colours. Dorsum light greyish-brown with dark greyish-brown markings, fore- and hind limbs light brown with dark greyish-brown crossbands; lateral surfaces greyish-brown with dark blackish-brown markings and spots. Ventral surfaces of throat and chest light grey with scattered brown spots ( Fig. 2 ).

Morphological variations. Morphometric data from the type and referred specimens (male, N = 1; females, N = 3), including the holotype, is provided in Table 2 .

The overall morphology of the paratypes is similar to the holotype with slight variations in colour and markings. ZSIC 14311 and ZSIC 14312 : dorsal markings darker in colour; ZSIC 14311 : ventral markings more prominent.

Secondary sexual character. Female (ZSIC 14310): ova, pigmented on poles (diameter 1.0– 1.6 mm, N = 10).

Morphological comparison. The new species, Microhyla eos , differs from M. annectens , M. arboricola , M. borneensis , M. darreli , M. irrawaddy , M. karunaratnei , M. kodial , M. maculifera , M. minuta , M. nanapollexa , M. orientalis , M.perparva , M. petrigena , M. sholigari , M. superciliaris and M. zeylanica by its relatively larger SVL,> 20 mm (vs. smaller, SVL <20 mm) ( Table 3 ). It specifically also differs from M. arboricola , M. darreli , M. irrawaddy , M. karunaratnei , M. kodial , M. maculifera , M. minuta , M. orientalis , M. sholigari and M. zeylanica by more webbing on feet, fourth toe webbing reaching up to the third subarticular tubercle on either side (vs. absent or rudimentary), and differs from M. annectens , M. borneensis , M. nanapollexa , M.perparva , M. petrigena , M. superciliaris and M. nanapollexa by relatively smaller foot webbing, just above the third subarticular tubercle on either side of toe IV, I1 1 / 2 –2 + II1 2 / 3 –3 – III2 1 / 2 –4 – IV4 –– 1 1 / 2 V (vs. larger, fourth toe webbing extending well beyond the third subarticular tubercle or up to the first subarticular tubercle on either side). Further, it differs from M. achatina , M. annamensis , M. chakrapanii , M. darevskii , M. fanjingshanensis , M. fissipes , M. fodiens , M. fusca , M. gadjahmadai , M. heymonsi , M. malang , M. mantheyi , M. marmorata , M. mukhlesuri , M. mymensinghensis , M. nilphamariensis , M. okinavensis , M. ornata , M. picta , M. pulchella , M. pulverata , M. pineticola , M. rubra and M. taraiensis by toe tips dilated into discs with dorso-terminal grooves, cover rounded distally (vs. without grooves, or with dorso-terminal grooves, cover bifurcate distally); and differs from M. palmipes by nostrils placed more towards the lateral side of snout (vs. towards the dorsal side), and relatively smaller foot webbing, reaching just above the third subarticular tubercle on either side of toe IV (vs. beyond, up to the second subarticular tubercles on either side of toe IV).

Due to comparable snout-vent size, dorsal markings and the overall external morphology, Microhyla eos could be confused with known congeners such as M. aurantiventris , M. berdmorei , M. beilunensis , M. butleri , M. fanjingshanensis , M. mixtura and M. pulchra , however, it differs from all of these species by a suite of morphological characters discussed below.

Microhyla eos differs from M. aurantiventris by its toe discs with dorso-terminal grooves, cover rounded distally (vs. with dorso-terminal grooves, cover bifurcate distally); dorsal skin smooth to shagreened (vs. presence of scattered tiny rounded tubercles); absence of mid-dorsal dermal ridge (vs. presence of a weak discontinuous middorsal dermal ridge); and ventrally, belly and throat light creamish to greyish-brown in life (vs. bright orange-yellow colouration).

Microhyla eos differs from M. berdmorei by its snout elliptical to pointed in dorsal and ventral view (vs. round- ed to subovoid); toe discs with dorso-terminal grooves, cover rounded distally (vs. with dorso-terminal grooves, cover bifurcate distally); and relatively smaller foot webbing, just above the third subarticular tubercle on either side of toe IV, I1 1 / 2 –2 + II1 2 / 3 –3 – III2 1 / 2 –4 – IV4 –– 1 1 / 2 V (vs. larger, extending beyond the first subarticular tubercle on either side of toe IV, I1– 1II 1–1 + III1–1 1 / 2 IV1 1 / 2 – 1V) ( Fig. 3 ).

Microhyla eos differs from M. beilunensis , M. fanjingshanensis and M. mixtura by its snout elliptical to pointed in dorsal and ventral view (vs. rounded in M. beilunensis and M. fanjingshanensis , and rounded to subovoid in M. mixtura ); prominently dilated toe tips with dorso-terminal grooves, cover rounded distally (vs. with dorso-terminal grooves and cover bifurcate distally in the other three species); and relatively more webbing on foot, just above the third subarticular tubercle on either side of toe IV, I1 1 / 2 –2 + II1 2 / 3 –3 – III2 1 / 2 –4 – IV4 –– 1 1 / 2 V (vs. rudimentary, below the third subarticular tubercle on either side of toe IV, I2–2 1 / 2 II 2– 3III 3– 4IV 4– 3V in M. beilunensis , and I2–2 1 / 2 II 2–3 – III3 –– 4 – IV4 –– 3V in M. mixtura ; rudimentary webbing at bases in M. fanjingshanensis ) ( Fig. 3 ).

Microhyla eos differs from M. butleri by its snout elliptical to pointed in dorsal and ventral view (vs. rounded); dorsal skin smooth to shagreened (vs. presence of tubercles); toe discs with dorso-terminal grooves, cover rounded distally (vs. with dorso-terminal grooves, cover bifurcate distally); and presence of a prominent cream colour streak extending from posterior corner of the eye to the shoulder (vs. absent). Further, five recognised synonyms are currently available under M. butleri ( Microhyla boulengeri Vogt ; Microhyla latastii Boulenger ; Microhyla grahami Stejneger ; Microhyla sowerbyi Stejneger ; and Microhyla cantonensis Chen ). However, based on previous exami- nation of type specimens and synonymisation actions ( Parker 1928; Bourret 1942), as followed by Nguyen et al. (2019), we consider all these taxon to be conspecific with M. butleri Boulenger.

Microhyla eos could also be confused with M. pulchra , a species found in neighbouring regions of China, due to its triangular-shaped body and similar dorsal colouration and markings. However, it differs from M. pulchra by relatively smaller adult size, male SVL 21.5, N = 1; female SVL 26.9–27.8, N = 3 (vs. larger, male SVL 23–28, N = 8; female SVL 31–32, N = 3); presence of prominent discs on finger and toe tips (vs. absent); and finger and toe discs with dorso-terminal grooves, cover rounded distally (vs. without grooves). Further, since the new species may be confused with M. pulchra because of similarities in dorsal colour and markings, a specific comparison of this character is provided: dorsal surface of snout light creamish-brown without prominent markings (vs. light greyishbrown with prominent dark brown concentric markings from snout to the upper eyelids); absence of dark coloured streak connecting the posterior ends of the upper eyelids (vs. dark brown streak connecting the posterior ends of the upper eyelids); W-shaped dark brown marking between the upper eyelids connected to a large inverted V-shaped dark brown marking extending from anterior part of the dorsum towards the lower back and groin (vs. absence of W-shaped marking between the upper eyelids, presence of a large inverted V-shaped dark brown marking not connected to the streak connecting the posterior ends of the upper eyelids); area surrounding the inverted V-shaped marking light brown with discontinuous dark brown markings (vs. with prominent and continuous light grey inverted U-shaped concentric bands, extending from upper eyelids to the groin); a continuous dark brown lateral band starting from posterior corner of the eye to the groin (vs. discontinuous dark lateral markings); and lateral surfaces of thigh with prominent dark brown marking up to the knee (vs. light greenish-yellow with brown patches).

Microhyla eos also differs from four previously available names currently under the synonymy of Microhyla pulchra . The taxon Ranina symetrica David was described with a brief description and differentiated from M. pulchra mainly based on dorsal colour and patterns. Due the non-availability of the type, we examined few samples from close vicinity of the type locality in the Sichuan Province of China (CIB 68812) that showed close resemblance with M. pulchra . Another taxon, Microhyla hainanensis Barbour was described from the Hainan Island of China largely based on differences in body shape and colour. We studied one of the four syntypes (MCZ 2435) and based on characters mentioned in the original description, we found it to match with specimens of M. pulchra from China (CIB 95457). We also examined the holotype (ZMB 24097) of the third available name, Microhyla melli Vogt and found it to be comparable with M. pulchra , especially due to absence of discs and grooves on finger and toe tips as in M. pulchra (vs. prominent finger and toe discs with dorso-terminal grooves, cover rounded distally in M. eos ). The fourth nomen Microhyla major Ahl , which was described from China (Guangdong Province) is also comparable with M. pulchra from China (CIB 68886). Hence, all the four available synonyms ( M. symetrica , M. hainanensis , M. melli and M. major ) cannot be confused with the new species M. eos , chiefly by two digit tip characters, i.e., finger and toe tips with discs (vs. absent), and finger and toe discs with dorso-terminal grooves, cover rounded distally (vs. absent).

Further, Microhyla eos differs from another similar sized species, M. rubra , by absence of shovel-shaped inner and outer metatarsal tubercles (vs. present); and presence of prominent and contrasting dorsal colouration and markings (vs. dorsum reddish-brown without prominent markings).

Although the new species is phylogenetically close to members of the Microhyla zeylanica group ( M. darreli , M. karunaratnei , M. laterite , M. sholigari and M. zeylanica ) and another Southeast Asian taxon ( M. superciliaris ) (see ‘Phylogenetic relationship’), it is clearly distinguishable from all these species by its larger adult size, male SVL 21.5 N = 1; female SVL 26.9–27.8, N = 3 (vs. smaller, <20.0 in both males and females); nostrils placed towards the lateral side of the snout (vs. placed dorsally); finger and toe tips with well-developed discs having dorso-terminal grooves, cover rounded distally (vs. small finger discs without grooves, and small toe discs with circum-marginal grooves in M. zeylanica or dorso-terminal grooves with cover bifurcate distally in all other species).

Phylogenetic relationship. Phylogenetic analysis based on a combined mitochondrial 16S and nuclear BDNF gene dataset recovered Microhyla eos sp. nov. as a deeply divergent sister lineage to the clade containing members of the Microhyla zeylanica species group ( M. darreli , M. karunaratnei , M. laterite , M. sholigari and M. zeylanica ) with high to moderate support. Further, it shows moderately supported sequential relationship with Southeast Asian species M. superciliaris , followed by clade containing M. aurantiventris + M. butleri ( Fig. 4 ). All other relationships within the genus were largely in agreement with recent studies (e.g., Garg et al., 2018a; Zhang et al., 2018).

Genetic divergence. Based on the analysed mitochondrial 16S rRNA fragment, Microhyla eos sp. nov. differs from its closest genetic relatives by the following uncorrected p-distances: M. laterite (6.5%), M. darreli (6.7%), M. superciliaris (6.8%), M. karunaratnei (7.1%), M. sholigari (7.3%), M. zeylanica (7.9%), M. aurantiventris (8.5%), and M. butleri (8.9%). Further, it shows sequence divergence of> 8% from all other studied Microhyla species ( Table 1 ).

Distribution and natural history. Microhyla eos sp. nov. is currently known only from its type locality Rani Jheel in Namdapha National Park, Arunachal Pradesh, India ( Fig. 1 ). ZSIC 14310 and ZSIC 14312 were collected from swampy forest floor on the fringes of a thickly vegetated lake located inside a tropical semi-evergreen forest patch. ZSIC 14311 and SDBDU 2011.380 were found under leaf litter away from water bodies.

Figures

FIGURE 1. The type locality of Microhyla eos sp. nov., Rani Jheel in Namdapha National Park, in the state of Arunachal Pradesh, Northeast India.

FIGURE 2. Type specimens of Microhyla eos sp. nov. A–K, Holotype, ZSIC 14310, an adult female: A, dorsolateral view in life; B, dorsal view in preservation; C, ventral view in preservation; D, lateral view in life; E, lateral view of head in preservation; F, ventral view of hand in preservation; G, third finger tip; H, ventral view of foot in preservation; I, schematic illustration of webbing on foot; J, fourth toe tip; K, terminal phalanx of fourth toe; L, Paratype, ZSIC 14311, an adult female, dorsolateral view in life. Scale bars: 5 mm.

FIGURE 3. Schematic comparison of Microhyla eos sp. nov. with morphologically close congeners from South and Southeast Asia. A, Dorsolateral colouration and markings in life; B, dorsal markings; C, lateral markings; D, schematic illustration of structure and shape of digit tip on third finger (left) and fourth toe (right); E, schematic illustration of webbing on foot. Microhyla berdmorei, SDBDU 2018.3852, Barail, Assam, India; M. beilunensis, CIBA980059, Chaiqiao, Zhejiang Province, China; M. eos sp. nov., ZSIC 14310, Rani Jheel, Arunachal Pradesh, India; M. mixtura, dorsolateral and dorsal views in life (voucher not preserved, China), dorsolateral view, CIB 65706, Wanyuan Country, Sichuan Province, China; M. pulchra, dorsolateral and dorsal views in life (voucher not preserved, China), dorsolateral view, CIB 68886, Yizhang, Hunan Province, China. Image credits: M. Zhang (M. beilunensis, A–C), J. Jiang (M. mixtura, A–B; M. pulchra, A–B).

FIGURE 4. Maximum Likelihood phylogram depicting the phylogenetic position and relationships of Microhyla eos sp. nov. based on 1,230 bp of the mitochondrial 16S rRNA and the nuclear BDNF gene sequences. Bayesian Posterior Probabilities (BPP) and RAxML bootstrap values of> 50% are indicated above and below the branches, respectively.