On the taxonomic validity of Boiga whitakeri Ganesh et al., 2021 with new insights on Boiga dightoni (Boulenger, 1894) (Reptilia: Squamata: Colubridae)

Abstract

Colour polymorphism has been previously reported in several colubrid snakes including Boiga spp. In this paper, we report colour variations within the poorly known southern Indian Boiga dightoni, provide the first molecular data for this species, from two localities (including the type locality) and compare them with data from other congeners. Additionally, we provide detailed dentition and hemipenis descriptions for B. dightoni. Molecular data for B. dightoni show very little difference (0.2–0.4% 16S ; 0.9–1.2% cyt b) to the recently described Boiga whitakeri, also from southern India. We have re-examined and present new information on the pholidosis of the type specimens of B. whitakeri and reconsider its taxonomic status. On the basis of molecular data and overlapping morphological characteristics, we argue that Boiga whitakeri and Boiga dightoni are conspecific, and place B. whitakeri under the subjective synonymy of the latter. Furthermore, we show that colour polymorphism in B. dightoni is a gender-independent character and that both colour morphs are found in high as well as low elevations and partly in sympatry. A revised key to the Boiga ceylonensis complex is provided.

Introduction

The colubrid snake genus Boiga Fitzinger, 1826 is represented by 37 currently recognised species distributed from the southern Palaearctic and the Oriental region to the northern and eastern coasts of Australasia (Uetz et al. 2022). Of these, eight species viz., Boiga beddomei (Wall, 1909), B. dightoni (Boulenger, 1894), B. thackerayi Giri et al., 2019, B. whitakeri Ganesh et al., 2021, B. forsteni (Duméril, Bibron & Duméril, 1854), B. flaviviridis Vogel & Ganesh, 2013, B. nuchalis (Günther, 1875) and B. trigonata (Schneider, 1802) are found in the Western Ghats of peninsular India. Boiga beddomei, B. dightoni, B. thackerayi and B. whitakeri are endemic to the Western Ghats (Ganesh et al. 2021). Among these, Boiga whitakeri is the most recently described species, based on two specimens from the southern Western Ghats (Ganesh et al. 2021). Prior to this, Ganesh et al. (2020) clarified the status of B. ceylonensis and B. beddomei based on morphological data and restricted these taxa to Sri Lanka and India, respectively. Ganesh et al. (2020) speculated that Indian records of B. ceylonensis might actually represent B. thackerayi, which was confirmed subsequently by analysis of molecular data from across the species’ range (Ganesh et al. 2021).

Ganesh et al. (2021) also provided molecular data for the holotype of Boiga whitakeri and all previously unsampled species of the genus Boiga from across peninsular India, except B. dightoni . Boiga dightoni was originally described based on a single female specimen collected from “Pirmed” (now Peermed, Kerala state, India) (Boulenger 1894) and appears to be a rarely encountered snake. Since its description, only a few studies reported the occurrence of this species from different parts of the southern Western Ghats and none so far from the type locality (Inger et al. 1984; Murthy 1984; Kanagavel and Ganesh 2021).

During our recent fieldwork in the southern Western Ghats, we collected two individuals of Boiga sp., one from Peermed and the other from Arippa, Kerala. The specimen from Arippa superficially resembled the holotype of B. whitakeri, in colour and inconspicuous dorsal markings, and the specimen from Peermed resembled the paratype of B. whitakeri in having prominent dorsal bands. We generated molecular and further morphological data for these two individuals and compared them with the types and with non-types of other Boiga spp. from the Western Ghats. In this work, we reassess the taxonomic status of B. whitakeri in light of new data on scale variation, and we report colour polymorphism within Boiga dightoni .

Materials and Methods

Molecular phylogenetics

We generated DNA sequences for two Boiga sp., a specimen (ZSI-CZRC -V-7541) from Peermed, Kerala (9.602710°N, 76.937857°E, 1238 m Above Sea Level (ASL)) approximately 9 km from the type locality of B. dightoni and one more specimen (BNHS 3617) from south of Shencottah gap (Arippa, Kerala, 8.831640°N, 77.038542°E, 195 m ASL) (Fig. 1), and one specimen (BNHS 3618) of Boiga nuchalis (Yercaud, Tamil Nadu, 11.775140°N, 78.214654°E, 1300 m ASL).

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

We extracted genomic DNA from liver samples stored in absolute ethanol at –20°C, using the DNeasy (QiagenTM) blood and tissue kit following the manufacturer’s protocol. We amplified partial sequences of two mitochondrial genes, 16S rRNA (16S) and cytochrome b (cyt b). Respective primers for these genes are as follows: 16Sar-L and 16Sbr-H (Palumbi et al. 1991) and CS1L and LTyph2R (Adalsteinsson et al. 2009). PCR conditions were as follows: Fragments of 16S were amplified using an initial denaturation at 95°C for 5 min, followed by 39 cycles of denaturation at 95°C for 45 sec, annealing at 50.4°C for 45 sec and extension at 72°C for 1 min 30 sec. Final extension was at 72°C for 10 min. Fragments of cyt b gene were amplified using an initial denaturation at 95°C for 5 min, followed by 35 cycles of denaturation at 95°C for 45 sec, annealing at 48°C for 45 sec and extension at 72°C for 55 sec. Final extension was at 72°C for 10 min. PCR reactions were carried out in 25 µl reactions containing 11µl of Takara emerald RR310B mastermix, 12 µl of PCR grade H₂O, 0.5 µl of each forward and reverse primers and 1µl (60–80 ng) of template DNA. PCR amplifications were carried out in S1000TM Thermal Cycler (Bio-Rad, USA). Amplified PCR products were run on a 2% agarose gel and viewed with an Essential V4 (UVITEC Cambridge, UK) gel documentation system to confirm the PCR amplification. PCR products were purified and Sanger sequenced in both directions at Barcode Biosciences (Bangalore, India) using the same primers that were used for amplification.

Bidirectional sequences were checked manually using CHROMAS (http://technelysium.com.au/wp/chromas) and aligned using ClustalW with default prior settings implemented in MEGA 7 (Tamura et al. 2011; Kumar et al. 2016). We checked for unexpected stop codons in the protein-coding gene cyt b by translating nucleotide alignments to amino acids in MEGA7 (Kumar et al. 2016). The new sequences generated in this study were concatenated with data for twenty-three other Boiga and three outgroups (Telescopus tripolitanus, T. variegates and Toxicodryas pulverulenta) (Appendix 1).

Maximum Likelihood (ML) analysis was performed using IQ-TREE (Nguyen et al. 2015), implemented in the web server version (http://iqtree.cibiv.univie.ac.at) (Trifinopoulos et al. 2016). The IQ-TREE server used Modelfinder (Kalyaanamoorthy et al. 2017) to find the best-fit evolutionary model for each of the four suggested partitions (16S : TIM2+F+I+G4; Cytb position 1: TIM2+F+G4; Cytb position 2: TN+F+I+G4; cyt b position3: TIM3+F+G4). Bayesian (BI) phylogenetic analysis was carried out with MrBayes 3.2 (Ronquist et al. 2012), with default prior settings and implementing the best-fit models and partitioning scheme as determined by Partition Finder V2. (Lanfear et al. 2017) with default settings. The best-fit scheme comprised three partitions, by gene and codon position (16S and cyt b position 1: GTR+I+G; cyt b position 2: TrN+I+G; cyt b position3: TVM+G). Four separate MCMC runs were initiated from random trees and allowed to run for ten million generations, sampling every 1000 generations. Analyses were terminated when the standard deviation of split frequencies was less than 0.005, the first 25% of trees were discarded as “burn-in”, and trees were constructed under the 50% majority consensus rule. Support for internal branches in ML and BI trees was quantified using Ultrafast Bootstrap (1000 pseudoreplicates) and posterior probability, respectively.

Morphology

We examined 33 specimens of Boiga spp., including Boiga dightoni (n = 9), B. whitakeri (n = 2), B. nuchalis (n = 10), B. thackerayi (n = 4), B. flaviviridis (n = 1) and B. ceylonensis (n = 7) (Appendix 2). Morphological data for B. ranawanei were taken from Samarawickrama et al. (2005) .

The numbers of dorsal scale rows are reported for one head length behind the head, at midbody (i.e., at the level of the ventral plate corresponding to half of the total ventral number), and at one head length anterior to the vent respectively. Dorsal scale row reduction formulae were based on Dowling (1951a) . Ventral scale counts and hemipenial descriptions follow Dowling (1951b) and Dowling and Savage (1960), respectively. The terminal scute is not included in the number of subcaudals. Values for symmetric head characters are given in left/right order.

The following measurements were taken: snout-vent length (SVL); tail length (TL); head length (HL : distance between posterior edge of last supralabial and tip of the snout); head width (HW : at angle of jaws); head depth (HD : height at the occipital region); Frontal length (FL : at the longest point); frontal width (FW : at the widest point on the anterior region); eye diameter (ED : horizontal diameter); eye to nostril distance (E–N : anterior corner of eye to posterior edge of nostril); eye to snout distance (E-S : anterior corner of eye to tip of snout); frontal to snout (FrSN : anterior end of frontal to tip of snout); inter-orbital distance (IO : measured at the anterior edge of eyes); number of dorsal scale rows (DSR). All linear measurements, except SVL and TL were taken using Mitutoyo dial vernier callipers (to 0.1 mm). SVL and TL were measured using a thread and metal scale (to 1 mm).

Among the specimens checked in this study, the holotype (BNHS 3597) of Boiga whitakeri is in a poor state of preservation and the paratype (BNHS 1863) of this species is also damaged, especially its anterior ventral scales. Thus, the number of ventral scales provided here for the paratype of Boiga whitakeri (BNHS 1863) is not complete Appendix 3C). For the ventrals that are damaged, we counted the adjacent dorsal scale rows assuming that one first-row dorsal corresponds to one ventral here.

Location records for both Boiga dightoni and B. nuchalis used for the map (Fig. 1) are based on the literature and specimens examined during the study (Appendix 4). Additionally, we downloaded research-grade data for both of these species from the citizen science portals, iNaturalist (https://www.inaturalist.org) and India Biodiversity Portal (https://www.indiabiodiversity.org). All the records for both species were checked individually wherever we could count the dorsal scales on one side, especially for the records from the southern Western Ghats. Doubtful records or records with poor photographs were not considered for plotting on the mapping and distribution (see also Discussion).

To obtain counts of teeth by a non-invasive procedure, the head of the holotype of Boiga dightoni was subjected to micro-tomographic analysis at the Museum für Naturkunde Berlin, using a Phoenix nanotomX-ray|s tube. The cone-beam reconstruction was performed using the datos|x-reconstruction software (GE Sensing & Inspection Technologies GMBH phoenix|x-raydatos|x 2.0) and the data were visualised in VGStudio Max 2.2. Teeth (including empty sockets) were counted on all dentigerous bones.

Museum specimen number prefixes

BMNH : The Natural History Museum, London, UK; FMNH : Field Museum of Natural History, Chicago, USA; BNHS : Bombay Natural History Society; MCZ : Museum of Comparative Zoology, Cambridge, USA; RMNH-BBSR-R : Regional Museum of Natural History, Bhubaneswar, India; ZMB : Museum für Naturkunde (formerly Zoologisches Museum Berlin), Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany; ZSI-CZRC : Zoological Survey of India, Central Zone Regional Centre, Jabalpur, India; ZSI/SRS/S : Zoological Survey of India, Southern Regional Centre, Chennai, India. Museum acronyms follow Sabaj (2020) .

Results

Molecular phylogenetics

The inferred phylogenies are broadly congruent with those presented by Ganesh et al. (2021) . Boiga ceylonensis is sister to B. dightoni + B. whitakeri with strong support (ML 98, BI 1.0) and this clade is sister to B. nuchalis . Boiga nuchalis from Yercaud (BNHS 3618) is nested with other B. nuchalis from the Western Ghats (Fig. 2). Boiga cf. ranawanei (sensu Ganesh et al. 2021) is sister to B. flaviviridis (a dry zone species found in thorn forests and scrub jungle). The holotype sequence of B. whitakeri is sister to the sample from Arippa (BNHS 3617) with strong and moderate support in BI and ML, respectively (BI 0.98, ML 83) and these two samples are together sister to the B. dightoni from the type locality with strong support (ML 95, BI 1.0) (Fig. 2).

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.

The uncorrected pairwise genetic distance between the two samples of B. dightoni and the holotype of B. whitakeri, is 0.9–1.2% and 0.2–0.4% in cyt b and 16S, respectively (Table 1). These distances are almost all smaller than intraspecific distances for the other congeners B. beddomei 2.5%, B. flaviviridis 2.2%, B. nuchalis 0.4–2.3% and B. thackerayi 0.6–3.6% in cyt b and B. beddomei 0.8%, B. nuchalis 0% and B. thackerayi 0.2–0.8% in 16S .

Table 1. Pairwise genetic distances (%) between the Boiga spp. from the Western Ghats, Eastern Ghats and Sri Lanka for both mitochondrial 16S and cyt b genes.

	CYT B	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17
1	Boiga “ whitakeri ” BNHS 3597
2	Boiga dightoni BNHS 3617	1.2
3	Boiga dightoni ZSI-CZRC -V-7541	0.9	1.2
4	Boiga ceylonensis	5.1	5.2	5.0
5	Boiga nuchalis BNHS 3618	5.3	5.3	4.3	6.4
6	Boiga nuchalis CESS_192	5.2	5.3	4.3	6.3	0.4
7	Boiga nuchalis CESS_081	5.7	5.3	4.6	6.0	1.6	1.9
8	Boiga nuchalis CESS_003	5.4	5.9	5.0	6.5	1.6	1.4	2.3
9	Boiga barnesii	13.3	13.2	12.8	14.2	13.6	13.0	13.5	13.2
10	Boiga beddomei CESS_444	8.9	8.6	7.9	9.4	8.7	8.1	8.5	8.5	14.0
11	Boiga beddomei CESS_418	9.3	9.1	8.3	9.4	8.4	7.7	8.3	8.1	13.7	2.4
12	Boiga cf. ranawanei	14.5	15.0	14.8	14.8	15.1	14.3	14.8	14.2	14.8	13.4	13.7
13	Boiga flaviviridis	13.2	13.7	13.3	13.5	14.0	12.9	12.6	13.3	16.1	13.2	13.3	9.3
14	Boiga flaviviridis CESS_529	13.4	13.0	12.6	13.1	13.3	12.9	12.9	13.2	15.7	13.5	13.3	9.1	2.2
15	Boiga thackerayi CESS_271	13.9	14.3	13.7	14.9	13.8	13.2	13.1	13.5	14.5	13.5	13.3	11.1	13.1	12.5
16	Boiga thackerayi CESS_443	13.6	13.8	13.4	14.6	13.7	13.1	13.0	13.4	14.6	13.1	13.1	10.8	12.7	12.2	0.6
17	Boiga thackerayi CESS_292	14.2	14.2	14.1	14.6	14.3	13.6	13.3	14.1	14.6	13.8	14.1	11.1	12.7	12.0	3.6	3.3
18	Boiga thackerayi BNHS_2371	13.6	14.1	13.8	14.6	14.0	13.1	13.0	13.4	14.7	13.1	13.1	10.5	12.5	12.2	0.6	0.0	3.3
	16S	1	2	3	4	5	6	7	8	9	10	11	12	13	14
1	Boiga “ whitakeri ” BNHS 3597
2	Boiga dightoni BNHS 3617	0.2
3	Boiga dightoni ZSI-CZRC -V-7541	0.4	0.2
4	Boiga ceylonensis	0.8	0.6	0.4
5	Boiga nuchalis CESS_003	0.7	0.9	0.7	1.1
6	Boiga nuchalis CESS_081	0.6	0.8	0.6	1.0	0.0
7	Boiga nuchalis CESS_192	0.6	0.8	0.6	1.0	0.0	0.0
8	Boiga barnesii	4.0	3.7	4.0	4.0	4.6	4.6	4.6
9	Boiga beddomei CESS_418	1.5	1.7	1.9	2.3	1.8	1.7	1.7	3.3
10	Boiga beddomei CESS_444	1.7	1.9	2.1	2.5	2.4	2.3	2.3	3.8	0.8
11	Boiga cf. ranawanei	3.6	3.8	3.6	4.0	3.5	3.4	3.4	4.6	3.1	4.0
12	Boiga flaviviridis CESS_529	2.9	2.7	2.5	2.5	3.1	3.1	3.1	3.8	3.4	3.8	2.7
13	Boiga thackerayi CESS_292	1.9	2.1	2.3	2.3	2.6	2.5	2.5	3.5	2.1	2.5	3.4	2.9
14	Boiga thackerayi CESS_443	2.7	2.5	2.7	2.7	3.5	3.4	3.4	3.1	2.5	2.9	3.6	3.4	0.8
15	Boiga thackerayi CESS_271	2.7	3.1	3.4	3.4	3.5	3.4	3.4	3.8	2.5	2.9	3.4	3.6	0.8	0.2

Morphological comparison of B. dightoni and B. whitakeri

Both specimens of Boiga sp. (ZSI-CZRC -V-7541 and BNHS 3617) collected during this study match well with the holotype of B. dightoni based on scalation data, mainly in having 23 MDSR (also see scale reduction formula for more characters). However, these two specimens differ significantly in scalation from B. whitakeri (based on data provided by Ganesh et al. 2021), despite the strong molecular similarity. MDSRs in B. dightoni are predominantly 23 from the 10^th ventral throughout most of the midbody (up to ventrals 123–144) in all of the specimens examined during the study, but the point of reduction from 23 to 21 differs slightly among the specimens examined (see scale reduction formula below). Boiga whitakeri is diagnosed from congeners mainly based on the presence of 19 MDSR as provided in the original description (Ganesh et al. 2021), but we counted 23 rows in the holotype (scale redcution formula and Table 2). Due to the poor state of preservation, we were unable to acquire the complete scale reduction formula for the paratype of B. whitakeri (BNHS 1863) but it has 21 MDSR until the level of the 145^th ventral and 19 DSR at the level of the 160^th ventral. This matches the dorsal scale reduction range of the sympatric Boiga nuchalis (see scale redcution formula). Furthermore, except for the dorsal scale rows, there is a close similarity in the arrangements of head scalation, ventrals and subcaudals between specimens identified as belonging to these “three” species (Table 2).

Table 2. Meristic and morphometric data (in mm) for Boiga dightoni and Boiga nuchalis examined in this study.

Species	B. dightoni	B. dightoni	B. dightoni	B. dightoni	B. dightoni	B. dightoni	B. dightoni	B. nuchalis	B. nuchalis	B. nuchalis	B. nuchalis	B. nuchalis	B. nuchalis
Voucher	BNHS 3617	BNHS 1842	ZSI-CZRC -V-7541	ZSI-CZRC -V-7542	BMNH 1946.1.1.32	FMNH 217699	1940.10.13.19	74.4.29.935	74.4.29.934	74.4.29.933	74.4.29.936	BNHS 3618	BNHS 3619
Location	Arippa, Kerala	Palagapandy, Kerala	Peermed, Kerala	Topslip, Tamil Nadu	Travancore	Ponmudi, Kerala	Kottayam, Kerala	Malabar, Western Ghats	Malabar, Western Ghats	Malabar, Western Ghats	Malabar, Western Ghats	Yercaud, Tamil Nadu	Wayanad, Kerala
Sex	Female	Unsexed	Male	Male	Female	Male	Female	Male	Female	Male	Juvenile Female	Female	Female
HL	22.46	21.8	27.9	21.56	26.2	NA	24	20.3	21.2	25.5	12.3	16.64	15.5
HW	13.1	15.8	16.3	13.51	15.8	NA	14.2	10.79	13.9	15.85	7.3	12.65	10.6
HH	8.1	9.1	9.58	9.37	10	NA	9.2	6.7	9.4	10.5	4.5	6.31	5.4
FL	5.3	5.7	6.16	6.2	6	NA	5.83	5.2	5	5.94	3.96	4.22	4.5
FW	4.9	5.4	5.19	5.1	5.6	NA	5.9	4.4	4.1	5.4	2.85	3.45	3.8
FrSN	4.7	5	6.4	4.86	6.5	NA	6.05	5.2	5.15	6.73	2.85	4.2	3.5
E-S	5.8	6.3	7.6	5.7	NA	NA	NA	NA	NA	NA	NA	4.8	4.3
E-N	4.1	3.9	4.5	3.3	NA	NA	NA	NA	NA	NA	NA	3.1	2.7
ED	3.9	4.3	4.6	4.2	NA	NA	NA	NA	NA	NA	NA	3.2	3
IO	7.1	NA	9.3	7.4	NA	NA	NA	NA	NA	NA	NA	5.6	5.1
SVL	824	832	1000	780	935	932	760	740	722	1010	335	586	465
TL	206	92	268	203	234	245	191*	200	181	255*	80	157	120
Bands on body	not visible	80	76	80	not visible	NA	65	71	85	80	84	98	52 Visible
Bands on tail	not visible	18+	28	not visible	not visible	NA	10	16	21	25	33	22-26	not visible
Preoculars	1,1	1,1	1,1	1,1	1,1	1,1	1,1	1,1	1,1	1,1	1,1	1,1	1,1
Postoculars	2,2	2,2	2,2	2,2	2,2	2,2	2,2	2,2	2,2	2,2	2,2	2,2	2,2
Supralabials	8,8	8,8	8,8	8,8	8,8	8,8	8,8	8,8	9,8	8,8	8,8	8,8	8,8
Infralabials	11,11	11,11	11,11	11,11	12,11	13,12	12,12	11,11	12,11	11,11	11,11	11,11	11,11
Temporals	2+4/2+3	2+4/2+3	3+4/2+3	3+4/2+4	2+3/2+3	4+4/3+4	3+3/3+3	3+3/3+3	3+4/3+4	2+2/2+3	2+4/2+4	3+4/3+4	3+3/3+4
Preventrals	2	1	2	2	2	3	2	2	2	2	2
Ventrals	246	249	239	239	241	248	229	242	233	240	244	239	230
Subcaudals	76+	110	103/104	102	99	112	87*	104	95	99*	102	98	100
Anal	single	single	single	single	single	single	single	single	single	single	single	single	single
DSR	23:23:17	23:23:17	23:23:17	23:23:17	23:23:17	21/23/15	23:23:17	21:21:15	21:21:15	21:21:15	21:21:15	23:21:15	23:21:15
* indicates an incomplete tail.

Dorsal scale row reduction formulae for some of the Boiga specimens examined in this study presented below. *between ventral 9 and 14 counts are not possible because of the damaged vertebral region. Additionally, there are several reductions and additions of the paravertebral scale row between the corresponding ventrals of 194 to 209. *** dorsal scales damaged and is not possible to find the area of scale reduction:

Boiga dightoni

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Boiga “ whitakeri ”

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Boiga dightoni (Boulenger, 1894) Figs 3, 4, 5, 6, 7; Tables 1, 2

Dipsas dightoniBoulenger 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 whitakeriGanesh, 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 (3^rd 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.

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.

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.

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.

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 7^th 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.

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.

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) .

Discussion

Intraspecific colour polymorphism has been reported in several colubrid genera (Pavón-Vázquez et al. 2011; van Rooijen et al. 2011; Cox and Davis Rabosky 2013; Palacios-Aguilar et al. 2022). Within Boiga, colour polymorphism is known in B. forsteni, B. multifasciata (Blyth, 1861), B. multomaculata (Boie, 1827), B. ochracea (Theobald, 1868), B. irregularis (Bechstein, 1802), and B. drapiezii (Boie, 1827) (Mohapatra et al. 2009; Tillack et al. 2021; Weinell et al. 2021). Our results demonstrate that B. dightoni is polymorphic in colouration with no marked sexual dimorphism or obvious ontogenetic or geographic component to this variation.

The holotype of Boiga dightoni (in preservative) is uniform in colour without dorsal markings and this probably led to several misidentifications in the past. Beyond the specimens examined here, it is probable that several individuals of B. dightoni are misidentified as B. nuchalis based on colour pattern. For example, at least two records (https://www.inaturalist.org/observations/37460080, 86841689) identified as B. nuchalis may actually represent B. dightoni . As mentioned above, only a few records of B. dightoni are available in the literature and this might be mainly because of its overall similarity with B. nuchalis, a much more commonly encountered species that partly overlaps in geographic range with the former. It is likely that, at least in some places, these two species are sympatric. Hence, we hereby caution against identifying these species solely based on the colour pattern, especially from the southern Western Ghats where both B. dightoni and B. nuchalis are present. Our results highlight the importance of careful examination of type specimens when describing new, similar and closely related species, especially in the absence of molecular data. Wherever possible, it is also preferable to select well-preserved and undamaged specimens when designating name-bearing types.

During this study, we also examined the type series of Boiga thackerayi . In the original description (Giri et al. 2019), the midbody scales were reported as being disposed in 17 rows for the holotype (BNHS 3569) and paratype (BNHS 3571), and 19 for the other paratype (BNHS 3570). Based on this, Ganesh et al. (2021) used 17–19 midbody scale rows as a character for B. thackerayi in their key. However, our examination reveals that these two individuals (BNHS 3569 and BNHS 3571) also have 19 midbody scale rows (Appendix 5), the same as the other specimen (BNHS 2372). Here, we provide the correct scale reduction formulae for these two specimens (Appendix 5) and update an identification key to the B. ceylonensis complex.

Revised key to the species in the Boiga ceylonensis complex of Western Ghats, India and Sri Lanka, modified from Ganesh et al. (2021)

1a	Midbody scale rows 19	2
1b	Midbody scale rows 21, temporal scales larger than body scales	B. nuchalis
1c	Midbody scale rows 23, temporal scales subequal to body scales	B. dightoni
2a	Dorsum greenish	B. flaviviridis
2b	Dorsum brownish	3
3a	Subcaudals > 110 pairs, preocular 1	B. beddomei
3b	Subcaudals > 110 pairs, preocular 2	B. ranawanei
3c	Subcaudals < 110 pairs	4
4a	Ventrolateral white blotches absent	5
4b	Ventrolateral white blotches present	6
5	Crown markings on parietals conspicuous and dark; bands dark, prominent	B. ceylonensis
6a	Preocular 1; dorsum barred	B. thackerayi
6b	Preoculars 3; dorsum blotched	B. barnesii

Acknowledgements

We thank the Kerala Forest Department for permits (WL10-636/2021 dated 16/10/2021) and support.BNHSfolks, Bivash Pandav (Director,BNHS), Rahul Khot, Saunak Pal, Vithoba Hegde and Omkar Adhikari for their support during the visits to the collections and Abhijit Das (Scientist, WII) for his support. We thank Hopeland for sharing images and locality information for Boiga species from Tamil Nadu. We thank Saunak Pal (Fig.3B) and Dhruvaraj S (Fig.3C) for sharing their photographs of Boiga dightoni . We are grateful to Kristin Mahlow (Museum für Naturkunde Berlin, Germany) for providing micro-CT scans of Boiga dightoni and other Boiga spp. relevant to this study. SD, MAY and RKP thank PS Easa, Edge team and Benjamin Tapley for all the support and encouragement.

We thank Ashok Captain for his support and advice on Indian snake taxonomy. We thank Dhanu Paran, Vinu J George, Amal Varghese and Akhil KS for their hospitality, Jishnu N, Arun Vijayakumar, Siddharth S, Joju CT, Lal V, Nihal J, Sanjay C, Vignesh B, Nithin D, Ameer K, Santhosh KT, Aravind, Amirtha Balan and Nobin Raja for their support in the field. Patrick Campbell, NHM, London for his support to DV and loans to Frank Tillack. K. A. Subramanian, Office in charge, ZSI Chennai and S. R. Ganesh, Chennai Snake Park Trust for sharing images of the specimen at ZSI, Chennai. SN thanks Kartik Shanker for access to the specimen at CES, Bangalore. SN thanks Aravind NA (Senior Fellow, ATREE) for his support at ATREE. We thank the National Geographic grant (NGS-63816R-19) for the support for fieldwork and museum visits. VD’s contribution was supported in part by the Humboldt fellowship hosted by Uwe Fritz at the Senckenberg Dresden. We thank Saunak Pal and an anonymous reviewer for their comments on the initially submitted version of this manuscript.

Appendix 1

Genbank voucher numbers for the samples used in this study. New sequences generated for this study are marked in bold.

Species Voucher no. Location CYT B 16S

Boigabarnesii RAP0452 Sri Lanka KC347469 KC347345

Boigabeddomei CESS 418 Mhadei WLS, Goa MT733292 MT734906

Boigabeddomei CESS 444 Mahabaleswar, Maharashtra, India MT733294 MT734908

Boigabourreti ZISP 32786 Mang Canh, Kon Plong, Kon Tum, Vietnam MN962356 –

Boigaceylonensis RS-Y Sri Lanka KC347467 KC347347

Boigacf.ranawanei RAP0450 Sri Lanka KC347466 KC347346

Boigacyanea CHS553 — MK201410 MK194064

Boigacynodon — Palawan Islands, Philippines KC010340 AF139566

Boigadendrophila — — AF471089 –

Boigadightoni BNHS 3597 DevarMalai, Tamil Nadu, India MT733284 MT734897

Boigadightoni ZSI-CZRC -V-7541 Peermed, Kerala, India OP948298 OP955936

Boigadightoni BNHS 3617 Arippa, Kerala, India OP948299 OP955937

Boigadrapiezii LSUHC7295 — KX660482 KX660210

Boigaflaviviridis — Meghamalai, Tamil Nadu, India MN508360 –

Boigaflaviviridis CESS 529 Horsley hills, Andhra Pradesh, India MT733297 MT734911

Boigaforsteni RAP0540 Sri Lanka KC347468 KC347348

Boigairregularis — — FJ710794 AF139551

Boigajaspidea LSUHC7656 Endau-Rompin, Johor, West Malaysia KX660484 KX660212

Boigakraepelini CHS115 — MK201272 MK193920

Boigamultomaculata CHS760 — MK201511 MK194200

Boiganigriceps LSUHC7020 — KX660485 KX660213

Boiganuchalis BNHS 3618 Yercaud, Tamil Nadu, India OP948300 –

Boiganuchalis CESS 003 Coorg, Karnataka, India MT733270 MT734883

Boiganuchalis CESS 081 Meppadi,Wynad, Kerala, India MT733274 MT734887

Boiganuchalis CESS 192 Kolli Hills, Tamil Nadu, India MT733282 MT734895

Boigaochracea CAS215390 Yinpaungtaing Village, Yin Ma Bin Township, Sagaing, Myanmar MN962367 –

Boigaquincunciata CAS221434 Putao Dist. Myanmar KX660451 KX660177

Boigaschultzei KU 327776 Estrella Falls Park, Estrella, Narra, Palawan,Philippines MN962368 –

Boigasiamensis LSUHC8502 O’lakmeas, Pursat Province, Cambodia KX660487 KX660215

Boigathackerayi CESS_ 271 Thadiyandamol, Karnataka, India MT733286 MT734899

Boigathackerayi BNHS 2371 Koyna, Maharashtra, India MN508359 –

Boigathackerayi CESS 292 KalakadMundanthurai Tiger Reserve, Tamil Nadu, India MT733287 MT734900

Boigathackerayi CESS 443 Mahabaleswar, Maharashtra, India MT733293 MT734907

Boigatrigonata RS-143 Sri Lanka KC347475 KC347349

Boigawestermanni — India MG428713 MG428711

Telescopustripolitanus BEV9377 Mauritania JX315531 MK372141

Telescopusvariegatus — — MK373093 MK372142

Toxicodryaspulverulenta CAS220642 — KX660460 KX660187

Appendix 2

List of Boiga specimens examined in this study. Specimens examined for scale reductions are marked in bold.

Boigadightoni (n = 9)

Morph 1.BMNH1946.1.1.32 (Holotype), female,SVL: 935 mm, Peermed, Kerala, India; BNHS3597 (Holotype of B.whitakeri ), male,SVL: 500 mm, Devarmalai, Tamil Nadu, India;FMNH217699, male,SVL: 932 mm, Ponmudi hills, Kerala, India; BNHS3617 , female,SVL: 824 mm, Arippa, Kerala, India

Morph 2.BMNH1940.10.13.19, female,SVL: 760 mm, Kottayam, Kerala, India;BNHS1842,SVL: 832 mm; Palakappandi, Nelliyampathy, Kerala, India; ZSI-CZRC-V-7541 , male,SVL: 780 mm, Peermed, Kerala, India; ZSI-CZRC-V-7542 , male,SVL: 780 mm, Topslip, Anamalais, Tamil Nadu, India; BMNH1940.10.13.19 , female,SVL: 760 mm, Kottayam, Kerala, India;ZSI/SRS/S-73, sex unknown,SVL: 545 mm, Topslip, Anamalai Tiger Reserve, Tamil Nadu, India.

Boigabeddomei (n = 1).BMNH69.8.28.123 (Lectotype) Female,SVL: 660 mm, Matheran, India.

Boigaceylonensis (n = 7).BMNH1946.1.1.29 (Lectotype), sex unknown,SVL: 770 mm, Ceylon; Paralectotypes:BMNH1946.1.4.78, female,SVL: 250 mm, Ceylon;BMNH1946.1.4.79, male,SVL: 481 mm, Ceylon;BMNH1946.1.4.80, female,SVL: 528 mm;BMNH1945.1.4.71, male,SVL: 507 mm;BMNH1945.1.4.75, male,SVL: 735 mm, Ceylon;BMNH1945.1.4.81, female,SVL: 632 mm, Ceylon.

Boigaflaviviridis (n = 1).BMNH1911.9.8.4 (holotype), sex unknown,SVL: 790 mm, Berhampur, Odisha, India.

Boiganuchalis (n = 10).BMNH74.4.29.933 , male,SVL: 1010 mm; BMNH74.4.29.934 , female,SVL: 722 mm; BMNH74.4.29.935 , male,SVL: 740 mm;BMNH74.4.29.936, juvenile female,SVL: 335 mm, Malabar, Western Ghats, India; BNHS3618 , female,SVL: 586 mm, Yercaud, Tamil Nadu, India; BNHS3619 , female,SVL: 465 mm, Wayanad, Kerala, India; BNHS1863 (paratype of B.whitakeri ), sex unknown,SVL: 677 mm, Pullompara, Kerala; CAS 17247, male, SVl: 257 mm, Anamallai, India;ZMB6039, female,SVL: 555 mm, Nilgherries (Nilgiris, Tamil Nadu, India);MCZ3876, male,SVL: male, Madras, India.

Boigathackerayi (n = 4).BNHS3569 (holotype), male,SVL: 870 mm,BNHS3570 (paratype), female,SVL: 493 mm; BNHS3571 (paratype), female,SVL: 552 mm, Koyna, Satara, Maharashtra, India;BMNH74.4.29.66, male,SVL: 531 mm, Anamalais, India.

Appendix 3

Boiganuchalis (paratype of “ B.whitakeri ”,BNHS1863) showing the dorsal (A), ventral (B) and damaged ventral scales (C).

https://binary.pensoft.net/fig/796592

Appendix 4

Gazetteer of confirmed locality records for Boigadightoni and B.nuchalis in India. Localities where we verified only images for confirmation are marked with an asterisk.

Species Current locality Latitude Longitude

Boiganuchalis * Bekkinjaddi, Audala, Karnataka, India 14.73401 74.75821

Boiganuchalis * Guddekeri, Karnataka, India 13.56631 75.1342

Boiganuchalis * Honnavar, Karnataka, India 14.27975 74.44393

Boiganuchalis * Magod Falls, Karnataka, India 14.86487 74.75922

Boiganuchalis Mavinagudi, Karnataka, India 14.92432 74.82812

Boiganuchalis * Guddekeri, Karnataka, India 13.56631 75.1342

Boiganuchalis * Mayfield, Tamil Nadu, India 11.55756 76.43534

Boiganuchalis * Rockwood Estate, Tamil Nadu, India 11.53503 76.40159

Boiganuchalis * Hope Estate, Tamil Nadu, India 11.58956 76.06355

Boiganuchalis * Pilloor, Tamil Nadu, India 11.30443 76.80602

Boiganuchalis * Adderly Estate, Nilgiris, Tamil Nadu, India 11.35901 76.85699

Boiganuchalis Kolli hills, Tamil Nadu, India 11.295 78.377

Boiganuchalis Yercaud, Shervaroys, Tamil Nadu, India 11.83435 78.24079

Boiganuchalis Sirumalai hills, Tamil Nadu, India 10.20065 77.99901

Boiganuchalis * Shimoga, Karnataka, India 13.51287 75.14139

Boiganuchalis * Yevakapadi, Karnataka, India 12.20958 75.64052

Boiganuchalis Kasargod, Kerala, India 12.49293 75.27597

Boiganuchalis Coorg, Karnataka, India 12.20958 75.64052

Boiganuchalis Attakatti, Anamalai Tiger Reserve, Tamil Nadu, India 10.44754 76.9861

Boiganuchalis Mannarkad, Kerala, India 11.05046 76.47072

Boiganuchalis Vythiri, Wayanad, Kerala, India 11.51478 76.03951

Boiganuchalis Siruvani, Tamil Nadu, India 10.987 76.622

Boiganuchalis Vazhachal, Kerala, India 10.303 76.593

Boiganuchalis * Chimmini dam road, Kerala, India 10.43104 76.49101

Boiganuchalis Taliparamba, Kerala, India 12.022472 75.363804

Boiganuchalis * Kervashe Village, Karnataka, India 13.258421 75.081153

Boiganuchalis Kalpetta, Wyanad, Kerala, India 11.588 76.1

Boiganuchalis Pullompara, Kerala, India 10.086 76.511

Boiganuchalis Iruppu falls, Kerala, India 11.969 75.985

Boiganuchalis Thadiyendamol, Karnataka, India 12.229 75.623

Boiganuchalis * Potachipara, Bramagiri, Karnataka, India 12.077 75.805

Boiganuchalis Forests of west coast of Malabar, Kerala, India 11.545426 75.757901

Boigadightoni Peermade, Kerala 9.576675 77.03061

Boigadightoni Aanapara, Ponmudi hills 8.69 77.1

Boigadightoni Ponmudi, Kerala, India 8.752984 77.12104

Boigadightoni Devermala, Kerala, India 9.173 77.261

Boigadightoni Arippa, Kerala, India, Kerala, India 8.832483 77.03245

Boigadightoni * Coutrallam, Tamil Nadu, India 8.923837 77.25514

Boigadightoni Kottayam, Kerala, India 9.579248 76.54887

Boigadightoni Topslip, Tamil Nadu, India 10.46901 76.84185

Boigadightoni Manampalli, Anamalai Tiger Reserve, Tamil Nadu, India 10.35406 76.87829

Boigadightoni * Kalakad Mundanthurai Tiger Reserve, Tamil Nadu, India 8.880428 77.28482

Boigadightoni Palagapandy, Nelliampathy, Kerala, India 10.56112 76.7304

Appendix 5

Scale reduction formula for the two Boigathackerayi type specimens atBNHS, Mumbai, India.

Appendix 6

Representative images of live B.nuchalis : A Wayanad, Kerala (uncollected), B Attakatti, ATR, Tamil Nadu (uncollected), C Yercaud, Tamil Nadu (BNHS3618).

https://binary.pensoft.net/fig/796593

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