Boiga dightoni (Boulenger, 1894)

Narayanan, Surya, Das, Sandeep, Anvar, Y. Muhammed, Tillack, Frank, Mohapatra, Pratyush P., Gower, David J., Rajkumar, K. P. & Deepak, V., 2023, On the taxonomic validity of Boiga whitakeri Ganesh et al., 2021 with new insights on Boiga dightoni (Boulenger, 1894) (Reptilia: Squamata: Colubridae), Vertebrate Zoology 73, pp. 1-21 : 1

Boiga dightoni (Boulenger, 1894)

Figs 3 , 4 , 5 , 6 , 7

Dipsas dightoni Boulenger 1894, p. 528.

Dipsadomorphus dightoni - Boulenger 1896, p. 69.

Boiga dightoni - Smith 1943, p. 567; Murthy 1984, p. 84; Inger et al. 1984, p. 567; Wallach et al. 2014, p. 103; Kanagavel & Ganesh 2021, p. 67, 68, fig. 1,2; Ganesh et al. 2020, p. 314, fig. 7; Ganesh et al. 2021, p. 449-151, 453.

Boiga whitakeri Ganesh, Mallik, Achyuthan, Shanker & Vogel, 2021 p. 453, fig. 3, syn. nov.

Taxonomic comments.

A detailed description of the external morphology of the holotype of Boiga dightoni (BMNH 1946.1.1.32) is presented by Ganesh et al. (2020). In this work, we provide scale reduction formula and detailed dentition based on microCT scans for the holotype of Boiga dightoni . In addition, we provide a detailed description of the hemipenis of B. dightoni based on a topotypic specimen (ZSI-CZRC-V-7541).

Based on the morphological data from the two specimens collected during this study, including the specimen from the type locality (Peermed, Kerala) of Boiga dightoni , we confidently identify these two specimens as B. dightoni . Our morphological examination of the types and non-type materials of Boiga whitakeri , B. dightoni and B. nuchalis provide evidence that led us to conclude that the holotype of B. whitakeri is conspecific with B. dightoni. This is consistent with our molecular analyses, in which the holotype of B. whitakeri is nested within the samples (including the topotype) that we identify as B. dightoni . On the other hand, the type series (BMNH 74.4.29.933-6) and two other specimens of Boiga nuchalis examined here have 21 dorsal scale rows at midbody (Scale reduction formula; Appendix 2). This further confirms that the paratype (BNHS 1863; Appendix 3) of B. whitakeri is rather B. nuchalis . Because the holotype and paratype of B. whitakeri clearly represent two already described species, we relegate Boiga whitakeri Ganesh, Mallik, Achyuthan, Shanker and Vogel, 2021 to the junior subjective synonymy of Dipsas dightoni Boulenger, 1894.

Morphology.

A medium-sized Boiga (greatest TL 1000 mm (male), 935 mm (female)); 229-249 ventrals, 99-112 divided subcaudals; 13/14 teeth on maxilla and 7 on palatine; dorsal scales smooth, 23:23:19 in rows; dorsal scale reduction from 23 to 21 rows occurs between ventrals 123-144 and the reduction from 21 to 19 occurs between ventrals 148-155. Dorsum reddish dun to olive greenish with dorsal light brown to dark bands. Head with dark marking dorsally (rarely absent) and a dark laterocular stripe present.

Colouration in life and preservative.

Based on the (live and museum) specimens examined and information available from the literature, we report two different colour morphs in B. dightoni .

Morph 1 (n = 5).

Reddish dun-coloured dorsum with faint reddish bands on the body (rarely absent) with or without distinct dark marking on the head, and ventral scales uniformly creamish white (Figs 3A-B , 4 , 6 A-C, G-I, M-O ). Holotypes of both B. dightoni and B. whitakeri are of this colour morph with no markings on the body in preservation. However, it might be noted that the recently collected specimen from Arippa (BNHS 3617) had faint markings on the body at the time of collection (3rd February 2022) that disappeared in the preservative (Figs 2 , 3C-D , 4 , 6 A-C ). This also applies to the holotype of B. whitakeri (Fig. 3B ), which had markings on the body in life that disappeared in the preservative ( Ganesh et al. 2021). A specimen from Aanapara, Kerala reported by Kanagavel and Ganesh (2021) also belongs to this morph, with very faint bands.

Morph 2 (n = 5).

Olive greenish dorsum with black bands (76-80) on the body, with distinct marks on the head and a postocular stripe that ends shortly behind the fissure of the mouth, and irregular small dark blotches along the paraventral scales (Figs 3C-D , 5 , 6D-F, J-L, P-R ). The topotypic specimen (ZSI-CZRC-V-7541) of B. dightoni collected during this study is of this morph (Fig. 3C ) and we observed several specimens from museum collections of this morph including a specimen (ZSI/SRS/S-73) collected from the Anamalais in Southern India.

Based on the specimens examined here, it is also clear that these two colour morphs are not explained by sexual dichromatism because both male and female specimens are known for both morphs. For example, the male specimens BNHS 3597 and ZSI-CZRC-V-7541 and the female specimens BMNH 1946.1.1.32 and BMNH 1940.10.13.19 belong to Morph 1 and 2, respectively. Both the morphs are found in sympatry in at least one location (Arippa, Kerala), so they additionally cannot be explained as purely geographic variation. Furthermore, these colour morphs cannot be currently explained as simple ontogenetic variation, because all the specimens examined here are adults.

Description of hemipenis of ZSI-CZRC-V-7541 (Fig. 7 ).

The right hemipenis is fully everted and removed in situ for further analysis. The hemipenis is sub-cylindrical and moderately elongate (length: 17.0 mm, maximum width: 5.7 mm), extending to the 7th subcaudal. The sulcus is undivided, bounded by thick walls on both sides, and terminates at the centre of the lobe. It can be differentiated into three zones; the proximal zone is covered with 4-6 rows of spines (~40% of the total length), the middle zone with 5 or 6 rows of spinulate flounces arranged transversely (~35% of the total length), and the distal calyculate area (~25%) with 4 or 5 rows of irregular calyces with papilate edges. The sulcus spermaticus is exposed before entering the calyculate area. There is not much variation in the arrangements of spines and body calyces on sulcate and asulcate sides. The overall structure of the hemipenis of ZSI-CZRC-V-7542 is similar to that described for ZSI-CZRC-V-7541.

Dentition based on the holotype of B. dightoni (BMNH 1946.1.1.32) (left/right order).

Maxillary bone with 13/14 prediastemal teeth, followed by a distinct diastema that is as long as the socket of the last prediastemal tooth and followed by two distinctly enlarged, grooved and posteriorly bent postdiastemal teeth. Prediastemal teeth increase in size posteriorly, the anterior three distinctly posteriorly hooked, the following with less pronounced curvature. On the left side, prediastemal teeth 1, 4, 5, 7, 9, 11, and 13 missing, maxilla broken behind the diastema. On the right side, prediastemal teeth 2-4, 6, 8, 10, 12, 13 and anterior postdiastemal tooth are missing.

Palatine bone with 7/7 posteriorly curved teeth, anterior ones as long as the middle prediastemal teeth, slightly decreasing in size posteriorly. Teeth 1, 5 and 7 are loose, and tooth 3 missing on left side. Teeth 1, 3 and 5 are loose on the right side. Lateral to each palatine tooth is a single replacement tooth at different growth stages. Pterygoid bone with 18/16 posteriorly curved teeth, first one half as long as last palatine tooth, gradually decreasing in size posteriorly, last one minute. Teeth 2, 4, 6, 8, 10, 12, and 14-16 missing on left side, teeth 2, 4, 6, 8, and 10 loose, and 11, 13, and 15 missing on right side. The posterior 45% of the pterygoid bone is without teeth.

Mandibular bone with 20/20 posteriorly curved teeth, shorter than maxillary and palatine teeth, gradually decreasing in size posteriorly. Medial to each mandibular tooth is a single replacement tooth in different growth stages. Teeth 1, 3-7, 9, 11, 13, 15-17, and 19 missing, tooth 2 loose on left side, teeth 1, 3, 5, 7, 9, 11, 13, 15, 17, and 19 missing, and tooth 2 loose on right side. Mandibular bone broken behind tooth 13 on left side.

Distribution.

Based on currently available data, Boiga dightoni is widely distributed in the southern Western Ghats (south of the Palghat Gap), at elevations of 9-1258 m (Appendix 4). Murthy (1984) extended the northern range of this species to Topslip in Anamalais. Murthy (1984) reported 23 dorsal scale rows at midbody for the specimen he collected, which is known only for B. dightoni among Western Ghats’ Boiga . The identity of this specimen (ZSI/SRS/S-73) is confirmed by photographs presented by Murthy (1984). With an additional specimen from the same locality (ZSI-CZRC-V-7541), we reconfirm the distribution of B. dightoni in Topslip in the Anamalai hills. The northernmost known distribution of B. dightoni is based on a specimen (BNHS 1842) from Palagapandy in the Nelliyampathy Hills, Kerala, a specimen that was previously ( Ganesh et al. 2020) misidentified as B. nuchalis. The southernmost known occurrence of this species is Ponmudi in Kerala (Fig. 1 ). Thus, B. dightoni is found only south of the Palghat Gap in the Western Ghats. Boiga dightoni in parts of its range is probably sympatric with B. nuchalis and B. thackerayi immediately south of the Palghat Gap, based on distribution data (Fig. 1 ) and the sequences reported by Ganesh et al. (2021).

Figures

Figure 1. Updated distribution of Boiga dightoni and B. nuchalis in the Western Ghats and B. nuchalis in peninsular India.

Figure 2. ML phylogeny showing relationships of the newly sampled Boiga (in blue) and sequences of other available congeners. ML bootstrap support and BI posterior probability support = /> 75 or 0.75 is shown at each internal branch. Holotype of B. whitakeri (BNHS 3597) labelled in red. Inset image: head closeups of the respective samples in life or freshly roadkill specimen (BNHS 3617). Outgroups are pruned from this tree.

Figure 3. Representative images of B. dightoni in life. Morph 1: A Uncollected individual from Arippa, Kerala (female), B BNHS 3597 (male); Morph 2: C ZSI-CZRC-V- 7541 (male), D uncollected individual from Arippa, Kerala (male).

Figure 4. Representative image of B. dightoni Morph 1. A - B BMNH 1946.1.1.32 (female), C - D BNHS 3617 (female), E - F FMNH 217699 (male). Scale bar = 5 cm.

Figure 5. Representative image of B. dightoni Morph 2. A - B ZSI-CZRC-V- 7541 (male), C - D BNHS 1842 (unknown), E - F ZSI-CZRC-V- 7542 (male). Scale bar = 5 cm.

Figure 6. Head closeup showing colour and pattern in B. dightoni Morph 1: A - C BNHS 3617, G - I BNHS 3597, M - O BMNH 1946.1.1.32; Morph 2: D - F ZSI-CZRC-V- 7542, J - L BNHS 1842 and P - R ZSI-CZRC-V- 7541. Scale bar = 10 mm.

Figure 7. Hemipenis of Boiga dightoni (Right organ of ZSI-CZRC-V- 7541). A sulcate view; B asulcate view; C apex view. Scale bar = 10 mm.