Ahaetulla flavescens ( Wall, 1910 ) Srikanthan & Adhikari & Mallik & Campbell & Bhatt & Shanker & Ganesh, 2022

Srikanthan, Achyuthan N., Adhikari, Omkar Dilip, Mallik, Ashok Kumar, Campbell, Patrick D., Bhatt, Bharat Bhushan, Shanker, Kartik & Ganesh, Sumaithangi Rajagopalan, 2022, Taxonomic revaluation of the Ahaetulla prasina (H. Boie in F. Boie, 1827) complex from Northeast India: resurrection and redescription of Ahaetulla flavescens (Wall, 1910) (Reptilia: Serpentes: Colubridae), European Journal of Taxonomy 839 (1), pp. 120-148 : 133-142

Ahaetulla flavescens ( Wall, 1910) comb. nov.

Figs 1–9 ; Tables 2–5

Dryophis prasinus flavescens Wall, 1910: 834 .

Dryophis prasinus indicus Mell, 1931: 119–219 . (by implication).

Dryophis prasina – Günther 1858: 159 (part).

Tragops prasinus – Günther 1864: 364. — Theobald 1876: 191.

Dryophis prasinus – Boulenger 1890: 369; 1896: 180 (part).

Dryophis prasinus ‘forma typica’ (non H. Boie in F. Boie, 1827) – Wall 1909a: 354; 1909b: 898; 1910: 834.

Dryophis prasinus flavescens (nec Smith, 1914) – Wall 1910: 834.

Differential diagnosis

A species of Ahaetulla inhabiting Northeast India, defined by the following combination of characters: dorsal scales in 15:15:11–13 smooth rows (vs 13 midbody rows of keeled scales in Proahaetulla Link, 1807 ); rostral appendage absent (vs present in the A. nasuta group and A. pulverulenta groups); presence of a pair of white ventrolateral stripes throughout the body (vs absence of ventrolateral stripes in the A.pulverulenta group); dorsum usually greenish (vs usually brownish in both sexes in the A. pulverulenta and A. laudankia groups; usually brown in females, in A. anomala (Annandale, 1906) , A. perrotetii (Duméril & Bibron, 1854) , A. dispar ( Günther, 1864) and A. travancorica Mallik, Srikanthan, Pal, D’Souza, Shanker & Ganesh, 2020 ); crown uniform and unpatterned (vs crown with black markings and reticulations in A. anomala , A. laudankia Deepak, Narayanan, Sarkar, Dutta & Mohapatra, 2019 and A. fasciolata ); ventrals 194–200 (vs <190 in A. nasuta and A. pulverulenta groups); subcaudals 155–168 (vs <120 in A. perrotetii , A. dispar and A. travancorica ); cloacal scale paired (vs entire in A. mycterizans and A. fasciolata ); supralabials entire (vs 3 rd –4 th supralabials horizontally divided in A. fronticincta ); nasals not in contact with one another (vs in contact with one another above rostral in A. fronticincta ); upper snout surface flat to mildly depressed (vs convex in A. mycterizans ); 8.2–10% divergent in ND4 and 6.5–9.5% in Cytb gene from the SE Asian populations of A. prasina sensu lato.

Etymology

A Latin adjective, derived from Latin verb ‘ flavesco / flavescre ’, meaning ‘turning to yellow’ / ‘becoming yellow’, referring to the yellowish colouration of the type specimens in life (see Wall 1910).

Type material

Lectotype (designated herein)

INDIA • ♀; “ Lakimpur, Assam, Northeast India ”; 27°13′40.8″ N, 94°6′28.8″ E; unknown date; Maj. F. Wall leg.; NHMUK (= BMNH) 1908.6.23.58 .

Paralectotype

INDIA • ♀; same collection data as for lectotype; NHMUK (= BMNH) 1908.6.23.59 .

Other examined material (2 ♂♂, 2 ♀♀)

INDIA – Meghalaya • 1 ♀; Shillong; unknown date; maj. F. Wall leg.; BNHS 1975 (green dorsum); BNHS • 1 ♂; Tura, Garo Hills ; unknown date; H.W. Wells; BNHS 1978 (green dorsum); BNHS . – Assam • 1 ♂; North Lakimpur; unknown date; maj. F. Wall leg.; BNHS 1976 (buff dorsum); BNHS . – Arunachal Pradesh • 1 ♀; Janakamukh, Abor Hills ; 10 Jun. 1912; 32, Sikh pioneers of Indian Museum; BNHS 1979 (green dorsum); BNHS .

Description

Lectotype ( Figs 3 , 5 )

MEASUREMENTS (in mm). Body elongated, tapering anteriorly and posteriorly, slightly compressed laterally, slightly narrower at mid-body, mid-body width 7.5, flatter on ventral side. Total length 1335.0; snout to vent length 840.0. Head wider than the neck, head length 27.5, elongated anteriorly; slightly wider, head width 13.2; slightly depressed, head depth 11.6. Eyes lateral, circular in shape with oval with horizontal pupil; horizontal eye diameter 5.1 and vertical eye diameter 3.7; interorbital distance 7.4. Snout acuminate, canthus rostralis prominent; eye to snout distance 11.6, sub-equal to head width; eye to nostrils distance 8.0, inter-narial distance 5.4. Tail elongated, complete, tail length 495.0, relative tail length 37.0%.

SCALATION. Dorsal scales smooth, without any keels; dorsal scales are generally even-sized, comparatively smaller which are close to vent and the anterior end of body. Paravertebral scales broader than other dorsal scale rows, with rounded posterior margin.Anterior scale rows 15 (on neck): mid-body scale rows 15 (at mid-body): posterior scale rows 13 (near vent), arranged in oblique series. Ventrals 206, angulate laterally, preventrals 3; cloacal scales slightly enlarged, paired; subcaudals 168, pairs. Rostral deep and wider at its base; distinctly visible and narrowly grooved in dorsal aspect, without nasal appendage, projects beyond tip of lower jaw when viewed from below. Nasal slightly elongated, laterally oriented, contacting anteriorly with the rostrum on each side. Nostrils distinct, rounded, laterally oriented, situated on posterior surface of the nasal scale on each side. Internasals paired, contacting each other at midline, anteriorly contacting rostral, posteriorly contacting prefrontal and contacting nasal laterally on each side. Loreals two, subequal in size, anterior set of loreals contacting internasals on both sides, posterior loreal contacting anterior on right side. On left side, posterior loreal separated from anterior by 2 nd, 3 rd supralabials and lower edge of prefrontal contact. Supraocular single, enlarged, broader posteriorly, roughly triangular in dorsal aspect on each side. Preocular single, broad, reaching upper surface of head and contacting prefrontal and frontal on each side; on anterior side contacting the posterior parts of loreals. Fourth supralabial divided horizontally ( Fig. 5 ). Postoculars two, upper one larger in size, contacting supraocular above and lower postocular below; lower postocular contacting 6 th supralabial below on each side. Prefrontal paired, roughly rectangular in shape, contacting frontal posteriorly. Frontal single, roughly bell-shaped, situated in middle of two supraoculars, contacting parietal scales posteriorly. Parietal scales paired, large, much wider, roughly pointed posteriorly and sub-equal to supraocular scales in size. Each parietal scale, anteriorly contacting supraocular, fairly touching upper postocular, laterally in contact with upper temporals, posteriorly in contact with three small scales on each side. Temporals 2+2 on both sides; posterior set contacting three comparatively large sized scales on both sides. Supralabials 9 on both sides, 4 th –6 th contacting the eye and 7 th being the largest. Mental small, much wider than long, subtriangular in shape, wedged between 1 st pair of infralabials. Two pairs of genials; anterior set sub-equal to posterior set; both longer than broad; both pairs are in long midline contact. Infralabials 9, 11; 1 st infralabial on each side elongate compared to the rest, medially contacting each other; 1 st –4 th infralabials contacting anterior set of genials; 4 th and 5 th infralabials contacting posterior pair of genials.

COLOURATION IN ETHANOL. Body overall greyish-brown to olive brown, a few small, pale yellowish patches along the trunk. Head mostly faded with grey or bluish grey colour; rostral, upper and lower labials faded grey to off-white, inter-scale colouration on anterior body black white; posteriorly at few places brownish white. Venter cream to light shades of grey; off-white ventrolateral stripe present from neck up to tail tip.

Paralectotype ( Fig. 4 )

Total length 1006.0; snout to vent length 631.0; tail length 375.0; relative tail length 37.2%; head length 28.5; head width 10.9; head depth 10.0.; eye diameter 5.5; eye snout tip distance 10.6; eye nostril distance 7.2; interorbital distance 9.9. Anterior scale rows 15; mid-body scale rows 15; posterior scale rows 13; ventrals 203; pre-ventrals 3; cloacal scale 1; subcaudals 155 pairs; supralabials 9 (4 th –5 th touching eye); infralabials 9 (1 st –5 th touching genials); loreal 3; preocular 1; postoculars 2; temporals 2+2; dorsum brownish-green; venter of a lighter shade as dorsum; chin, throat and labials dirty white.

Variation ( Table 4 ; also see Wall 1910)

The examined non-type specimens agree well with the type specimens and show the following intraspecific variations:

MEASUREMENTS (in mm). Total length 1059–1141; snout to vent length 679–768; tail length 373–380; head length 25.6–29.2; head width 9.5–9.6; head depth 7.0–7.1; horizontal eye diameter 4.5–4.6; vertical eye diameter 2.4–3.1; eye to nostrils distance 7.0–8.3; eye to snout tip distance 9.7–10.5; internarial distance 3.5–5.2; interorbital distance 7.3–9.1; mid-body width 7.1–7.7; internasal length 3.5–3.9; prefrontal length 3.6–5.7; frontal length 6.8–8.7; parietal length 5.3–7.3.

SCALATION. Ventrals 197–200; pre-ventrals 3; supralabials 8 or 9; infralabials 8 or 9; anterior scale row 15; mid-body scale row 15, posterior scale row, 11–13; subcaudals, 155–183. BNHS 1975 has 3 loreals on each side and single pre-subocular, contacting 4 th supralabial below and preocular above.

COLOURATION IN LIFE ( Figs 6–7 ). Usually verdant green above, with fluorescent green on the ventral side. A pair of creamy white ventrolateral stripes extends from near neck up to the tip of the tail. Labials, chin and mental region whitish to cream coloured. Inter-scalar skin with alternating black and white ragged bands. Iris yellowish-green with black horizontal pupil. On occasions, body overall yellowish-brown, with minute black dots along the trunk. Venter cream to light brown, flanked on either side by off-white ventrolateral stripes from neck up to tail tip.

Distribution and natural history

Ahaetulla flavescens comb. nov. is currently known from four Northeast Indian states: Arunachal Pradesh, Assam, Mizoram and Meghalaya ( Fig. 8 ) ( Wall 1910; Ahmed et al. 2009). This species was perhaps first recorded in Northeast India, under the name A. prasinus auctorum by Cantor (1847) who mentioned specimens from Bengal and Assam. The following localities were subsequently reported for this taxon, under the name A. prasina: Bengal ( Günther 1858, 1864), Eastern Himalayas, Sikkim, Katchar, Naga, Jaintea and Khasi hills, ( Theobald 1876), Darjeeling, Cherrapunji, Duffla hills, Naga hills, Sibsagar and Cachar ( Sclater 1891), Eastern Himalayas, Assam and Bengal ( Boulenger 1890, 1896). Wall (1906, 1909a, 1909b) recorded this species from near Darjeeling and Jalpaiguri in Assam.

Judging by the geographic continuity and lack of morphological differences, we hypothesise that populations inhabiting other parts of Northeast India and immediately neighbouring areas of other countries could represent A. flavescens . Like other members of this group, A. flavescens is a diurnal, arboreal species inhabiting the wet hill forest tracts of Northeast India ( Whitaker & Captain 2004; Ahmed et al. 2009). It is reported to be live-bearing, as Whitaker & Captain (2004) state “females bear 4-10 live young [in] May-June”, without reference to any country. However, Wall (1910) reported three “eggs” inside a type specimen that was collected in March–April. Given the current knowledge on the reproduction of members of this genus ( Das 2002; Whitaker & Captain 2004; Wallach et al. 2014), we hypothesise that Wall was probably referring to the caul or outer amniotic layer encapsuling the embryos of viviparous snake species. Wall (1910) also reported the presence of a gecko in its gut content. Based on our primary field observations, A. flavescens is somewhat temperamental with some individuals becoming defensive when restrained, displaying their open-mouth gape and striking forwards with a jerky motion.

Comments

Das & Chaturvedi (1998) remarked that Dryophis prasinus flavescens Wall, 1910 was described based on six syntypes. We clarify here that Wall only included the three buff-coloured snakes as part of the type series, whereas the green-coloured specimens were termed “forma typica”. Das & Chaturvedi (1998) remarked that BNHM (= BNHS) 1976, a buff-coloured specimen from Lakimpur, Assam is an extant syntype. Wall (1910) reported a ventral range of 200–209 including preventrals and 155–174 subcaudals, whereas the ventral count of BNHS 1976 is 183, clarifying that it is not a syntype. Das & Chaturvedi (1998) commented that other syntypes may in fact exist, without mentioning any repository. Our investigation proved that they are in London, registered as NHMUK (= BMNH) 1908.6.23.58–59 ( Fig. 6 ). Apart from congruence in locality, collector and sex of the snakes, the ventral and subcaudal counts also match well. Wall (1910) reported 205 ventrals for both snakes and 155, 167 subcaudals, whereas we counted 203, 206 ventrals (+ 1 to 3 preventrals) and 155, 168 subcaudals. Wall (1910) gave measurements for only one of his syntypes from Lakhimpur, total length 5’7’’ (= 1701 mm), tail length 1’7.5’’ (= 495 mm). The tail length of the lectotype (NHMUK 1908.23.6.58) matched fully, although its total length was only 1335 mm. Above all, Wall (1910) stated that 4 th supralabial is divided on the right side, which completely matches with the NHMUK (= BMNH) 1908.23.6.58 specimen. Lastly, Das & Chaturvedi (1998) stated that Smith (1943) erroneously credited the taxon authorship of Dryophis prasinus flavescens to Smith (1915; sic, for 1914) and the type locality was given as Trang Pen, Siam. We further add that Smith’s treatment and usage of this nomen was only a chresonym, when he followed Wall’s subspecies arrangement upon finding a buff variety in Siam, i.e., Thailand (see our chresonymy for unambiguity). In essence, we here demonstrate that the first two buff-coloured female snakes Wall dealt with while describing A. flavescens are indeed NHMUK (= BMNH) 1908.6.23.58–59.

Here, we clarify the confusions about the identity of the type specimens, rediscover and redescribe the type specimens, prove the specific distinction of this nominal taxon and resurrect it as a valid species. Hence, we evoke Art.74.7 of the Code (ICZN 1999) and designate NHMUK (= BMNH) 1908.6.23.58 as the lectotype of Dryophis prasinus flavescens Wall, 1910 . The chosen lectotype is the larger of the two type specimens, has characters that enable its unambiguous recognition, has precise provenance data and is deposited in a scientific institution of permanent record.

Figures

Fig. 1. Maximum Likelihood tree based on Cytb, ND4 and 16S genes, showing the phylogenetic position of Ahaetulla flavescens (Wall, 1910) comb. nov. (red), with respect to other congeners, especially the A. prasina complex (blue, green, purple and brown).

Fig. 2. The bPTP output trees generated from three mitochondrial loci ML trees. Blue coloured branches and black bars indicate monophyly of that lineage, where validity of lineages is further ascertained with genetic divergence (genetic p-distance) and geographic isolation. The grey bars indicate the genetic distance (G1) and geographic isolation (G2) among lineages. The values on clades indicate the posterior probability. The A. prasina complex (Lineage 1 and Lineage 2) from northeast India shows a very low genetic divergence with continuous geographic distribution.

Fig. 3. Dryophis prasinus var. flavescens Wall, 1910, lectotype (NHMUK 1908.6.23.58). Entire profile, dorsal and ventral views. Photo: ©The Trustees of the Natural History Museum, London.

Fig. 4. Dryophis prasinus var. flavescens Wall, 1910, paralectotype (NHMUK 1908.6.23.59). Entire profile, dorsal and ventral views. Photo: ©The Trustees of the Natural History Museum, London.

Fig. 5. Dryophis prasinus var. flavescens Wall, 1910, lectotype (NHMUK 1908.6.23.58). Head close-up showing the divided 4th supralabial on right side, a unique identifying character in ascertaining its type status. Photo: ©The Trustees of the Natural History Museum, London.

Fig. 6. Dryophisprasinusvar. flavescensWall, 1910,lectotype (NHMUK 1908.6.23.58)and paralectotype (NHMUK 1908.6.23.59). Jar label. Photo: ©The Trustees of the Natural History Museum, London.

Fig. 7. Ahaetulla flavescens (Wall, 1910) comb. nov. Live uncollected specimens from Arunachal Pradesh, showing the unusual buff or yellowish-brown colouration. Photo: Bharat Bhushan Bhatt.

Fig. 8. Ahaetulla flavescens (Wall, 1910) comb. nov. Live uncollected specimen from Mizoram, showing the usual green colouration which is dominant in this species. Photo: Ajay Karthik.

Fig. 9. Map of Northeast India, showing the distribution records of Ahaetulla flavescens (Wall, 1910) comb. nov.; red star represents the type locality.