Phylogenetic analyses

A total of 66 COI sequences of congeners were obtained from GenBank for phylogenetic analyses, including the three sequences obtained in this study (Table 1).

Nucleotide sequences were initially aligned using ClustalX 1.81 (Thompson et al., 1997) with default parameters, and then optimized manually in BioEdit 7.0.5.2 (Hall, 1999) and MEGA 6.0 (Tamura et al., 2013). Mean uncorrected genetic distances (P-distances) between sequences were determined with MEGA 6.0. MODELTEST v.3.06 (Posada & Crandall, 1998) was used to estimate the optimal models of DNA evolution. The best-fitting model selected for COI dataset was K80+I+G for the first and the second codon positions and GTR+G for the third codon position, as suggested by the Akaike Information Criterion (AIC).

Phylogenetic trees were inferred using two different methods: Bayesian inference (BI) and maximum likelihood (ML). BI was conducted in MrBayes 3.1.2 (Huelsenbeck & Ronquist, 2001; Ronquist & Huelsenbeck, 2003). Metropolis-coupled Markov chain Monte Carlo (MCMCMC) analyses were run with one cold chain and three heated chains for four million generations and sampled every 1 000 generations. Five independent MCMCMC runs were performed and 1 000 trees were discarded as burn-in. Confidence in tree topology was assessed by posterior probability (BI PP) (Huelsenbeck & Ronquist, 2001). The ML analyses were conducted using Treefinder (Jobb et al., 2004). The COI sequence of Cyrtodactylus elok Dring was used as an outgroup following Luu et al. (2016a). Confidence in tree topology was tested by non-parametric bootstrap analysis (ML BS) with 1 000 replicates (Felsenstein, 2004). We a priori regarded tree nodes with bootstrap (ML BS) values of 70% or greater and posterior probabilities (BI PP) values over 0.95 as sufficiently resolved, ML BS values between 70% and 50% (and BI PP between 0.95 and 0.90) were regarded as tendencies, and ML BS values below 50% (BI PP below 0.90) were considered unresolved (Felsenstein, 2004; Huelsenbeck & Hillis, 1993).

Cyrtodactylus thathomensis p. nov. (Figure 3, Figure 4, Figure 5 and Figure 6)

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Figure 3

Male holotype of Cyrtodactylus thathomensis sp. nov. (ZMMU R-14919)

A: General view of holotype in situ; B: Precloacal region with row of femoral and precloacal pores separated by diastema; C: Postcloacal spurs (see arrow); D: Lateral side of the head with supralabials and infralabials scalation; E: Ventral surface of the head with mental scalation; F: Dorsum surface with the rows of enlarged tubercles. Photos by E.L. Konstantinov (A) and R.A. Nazarov (B–F).

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Figure 4

Female paratype of Cyrtodactylus thathomensis sp. nov. (ZISP 29731)

A: General view of preserved paratype with original tail; B: Lateral side of the head with supralabials and infralabials scalation; C: Shape of rostral and surrounding scales; D: Ventral surface of the head with mental scalation; E: Precloacal region with row of enlarged femoral and precloacal scales with pit and pitless scales; F: Medial row of enlarged subcaudal scales. Photos by R.A. Nazarov.

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Figure 5

Female paratype of Cyrtodactylus thathomensis sp. nov. (ZMMU 15384)

A: General view of preserved paratype with original tail; B: Lateral side of the head with supralabials and infralabials scalation; C: Shape and scalation of rostral (supranasals in contact with each other); D: Ventral surface of the head with mental scalation; E: Precloacal region with row of enlarged femoral and precloacal scales with pit and pitless scales; F: Medial row of enlarged subcaudal scales. Photos by R.A. Nazarov.

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Figure 6

Live female paratype of Cyrtodactylus thathomensis sp. nov. (ZISP 29731) in dorsal view (Photo by E.L. Konstantinov)

Holotype: ZMMU R-14919-1 (Figure 3); an adult male from the north-western slope of a limestone hill (N18°59′48.9″, E103°35′30.6″; alt. 271 m a.s.l.) near Ban (=Village) Thathom, Xiangkhoang Province, Laos. Collected on 14 May 2008 by E. L. Konstantinov and A. S. Chulisov.

Paratypes: ZMMU R-15384 and ZISP 29731; two adult females from the same locality

Diagnosis: Cyrtodactylus thathomensis sp. nov. can be distinguished from all other congeneric species by its medium body size (maximal known SVL 75.5 mm); dorsal tubercles in 14–18 rows at midbody; midbody scale rows 30–36 across belly between ventrolateral skin folds; a continuous series of 10–12 pore-bearing (male) or pitted (females), enlarged precloacal scales, separated by a diastema from a series of enlarged femoral scales bearing 18 or 19 pores (male) or 1–9 pits (females) on each femur; absence of precloacal groove; transversely enlarged median subcaudal scales; and four dark dorsal bands between limb insertions.

Description of holotype: Adult male. SVL 70.3 mm. TailL 79.0 mm (last 54 mm regenerated). Head relatively long (HeadL 20.1; HeadL/SVL 0.29) and wide (HeadW 13.4; HeadW/HeadL 0.67), not markedly depressed (HeadH 8.4), distinct from neck. Loreal region inflated, canthus rostralis slightly prominent. Snout elongate (SnOrb/HeadL 0.41), rounded, longer than orbit diameter (OrbD/SnOrb 0.62). Scales on snout small, rounded to oval, granular to weakly conical, mostly homogeneous, larger than those on crown, interorbital, and occipital regions. Eye relatively large (OrbD/HeadL 0.25); pupil vertical with crenelated margins; supraciliaries short, larger anteriorly. Ear opening vertically oval, of moderate size (EarL/HeadL 0.06); orbit to ear distance subequal to orbit diameter (OrbEar/OrbD 1.02). Rostral much wider (3.5 mm) than deep (2.0 mm); rostral crease straight, starting from the upper middle of the rostral, going down half the rostral height. Two enlarged supranasals separated from one another by one internasal. Rostral contacting first supralabial on each side, nostrils, two supranasals and one internasal. Nostrils rounded, more or less laterally directed, each surrounded by supranasal, rostral, first supralabial and two postnasals. Three or four rows of small scales separate orbit from supralabials. Mental triangular, wider (3.4 mm) than deep (2.2 mm). A single pair of greatly enlarged postmentals in broad contact behind mental, each bordered anteromedially by mental, anterolaterally by first infralabial, posterolaterally by an enlarged lateral chinshield, and posteriorly by two granules (in total three granules contact the postmentals) (Figure 3E). Supralabials to mid-orbital position 9/9, enlarged supralabials to angle of jaws 10/11. Infralabials 9/9 (Figure 3D). Interorbital scale rows across narrowest point of frontal bone 30.

Body moderately slender, relatively short (AG/SVL 0.43) with poorly defined, non-denticulate, ventrolateral skin folds. Dorsal scales weakly heterogeneous, domed, with tubercles about four times size of adjacent dorsal scales extending from neck onto tail base, smaller tubercles on postocular region, crown and occiput; tubercles smooth or bearing a very small keel, tubercles on posterior trunk and sacral region most prominent. Dorsal tubercles in 18 rows at midbody, typically separated from one another by two dorsal granules (Figure 3F). Paravertebral tubercles 26. Ventral scales larger than dorsal scales, smooth, oval and subimbricate, largest in precloacal region. Midbody scale rows across belly between ventrolateral folds 30. Gular region with homogeneous, smooth, juxtaposed granular scales. A patch of enlarged precloacal scales on top of which lies a continuous series of ten pore-bearing scales, separated by a diastema of 3/4 enlarged poreless scales from a continuous series of 19/18 pore-bearing femoral scales. Enlarged femoral scales nearly two times the size of the scales of the adjacent anterior scale row (Figure 3B). No precloacal groove. Hemipeneal bulges evident. Postcloacal spurs bearing 6/5 enlarged conical scales (Figure 3C).

Scales on palm and sole smooth, rounded to oval or hexagonal, slightly domed. Scalation on dorsal surfaces of hind limbs similar to body dorsum with enlarged tubercles interspersed among smaller scales; tubercles smaller and rare on forelimbs. Forelimbs and hind limbs moderately long (ForeaL/SVL 0.16, TibiaL/SVL 0.19), moderately slender. Digits long, slender, inflected at interphalangeal joints, all bearing robust, slightly recurved claws. Basal subdigital lamellae broad, oval to rectangular, without scansorial surfaces; lamellae distal to digital inflection narrow; SLF4 17/17; SLT4 20/20. Subcaudals scales larger than supracaudal scales, forming a row of strongly enlarged transverse plates.

Coloration in preservative: Dorsal ground color of head, neck, body, limbs and tail light brown. Dorsal surface of head with irregular dark brown markings. Rostral, supralabials and infralabials dark brown, posterior ones heavily maculated with beige. On each side a postocular stripe reaching the nape but not meeting the one of the opposite side as it breaks into spots (i.e., a discontinuous nuchal collar). Upper surface of limbs showing irregular dark brown bands. Dorsum showing four dark brown bands between limb insertions. Each of the four bands on dorsum posteriorly limited by a discontinuous series of whitish tubercles, similarly to the band above shoulders, the one on the neck and the one above sacrum. Original part of the tail showing three dark brown bands. Regenerated part of the tail light brown. Undersurfaces of the head, throat, venter and members uniformly beige. Coloration of the holotype in life is shown in Figure 3A. In life its dorsal ground color is darker than in preservative. The tubercles posteriorly bordering the four bands on dorsum are lighter and more contrasting than after preservation. The yellow color of the outer extremities of the supraciliaries disappears in preservative.

Variation: Morphometric and meristic values for the type series are provided in Table 3. Morphological and coloration characters of the paratypes agree in most respects with those of the holotype, differing only in minor details (Table 3 and remarks hereafter). Rostral crease in paratypes like in holotype. One internasal in paratype ZISP 29731 like in holotype (Figure 4C), no internasal in paratype ZMMU R-15384 (hence supranasals in large contact) (Figure 5C). The female paratype ZISP 29731 shows a continuous row of 52 enlarged femoral-precloacal scales including, from left to right: 1 pitless scale + 9 scales with pits + 12 pitless scales + 10 precloacal scales with pits + 11 pitless scales + 9 scales with pits + 1 pitless scale (Figure 4E). The female paratype ZMMU R-15384 shows a continuous row of 55 enlarged femoral-precloacal scales including, from left to right: 10 scales with pits + 11 pitless scales + 12 enlarged precloacal scales with pits + 12 pitless scales + 8 scales with pits + 2 pitless scales (Figure 5E). General background dorsal color in preservative lighter in the female paratypes than in the male holotype. The paratypes’ tails, original and complete, show nine dark brown bands, and they are longer than SVL (TailL/SVL ratio 1.16–1.27; see Figure 4A– Figure 5A, Figure 6).

Comparison with congeneric species: Synoptic tables comparing the main morphological characters of Lao Cyrtodactylus with the species known from adjacent regions were provided by Teynié & David (2014: 471–472) and Luu et al. (2016a, 2016b, 2016c). Among these species, we are comparing hereafter Cyrtodactylus thathomensis sp. nov. with all congeneric species found within a 500-km radius from its type-locality (a radius far superior to any maximal distance between two localities known for any species in the Indochinese Region, Thailand and Myanmar, cf. maps provided by Ellis & Pauwels, 2012; Nazarov et al., 2014: Figure 1; Grismer et al., 2015: Figure 1 – considering that Cyrtodactylus intermedius is a species complex composed of at least six species, loc. cit.: 114; Nguyen et al., 2014, 2017: Figure 1).

By its possession of transversely enlarged subcaudals, the new species is readily distinguished from Cyrtodactylus angularis (Smith, 1921), C. buchardi David, Teynié & Ohler, 2004, C. cryptus Heidrich, Rösler, Vu, Böhme & Ziegler, 2007, C. jarujini, C. papilionoides Ulber & Grossmann, 1991, C. pseudoquadrivirgatus Rösler, Nguyen, Vu, Ngo & Ziegler, 2008, and C. vilaphongi Schneider, Nguyen, Le, Nophaseud, Bonkowski & Ziegler, 2014. The possession of enlarged femoral scales separates Cyrtodactylus thathomensis sp. nov. from C. bobrovi Nguyen, Le, Pham, Ngo, Hoang, Pham & Ziegler, 2015, C. buchardi, C. chauquangensis Hoang, Orlov, Ananjeva, Johns, Hoang & Dau, 2007, C. cryptus, C. otai Nguyen, Le, Pham, Ngo, Hoang, Pham & Ziegler, 2015, C. pageli, C. pseudoquadrivirgatus, C. spelaeus Nazarov, Poyarkov, Orlov, Nguyen, Milto, Martynov, Konstantinov & Chulisov, 2014, C. vilaphongi and C. wayakonei Nguyen, Kingsada, Rösler, Auer & Ziegler, 2010.

The presence of precloacal and femoral pores separated by a diastema in male Cyrtodactylus thathomensis sp. nov. distinguishes this species from C. angularis, C. bansocensis, C. bobrovi, C. buchardi, C. calamei, C. chanhomeae Bauer, Sumontha & Pauwels, 2003, C. chauquangensis, C. cryptus, C. cucphuongensis Ngo & Chan, 2011, C. darevskii, C. hinnamnoensis, C. jaegeri, C. jarujini, C. khammouanensis, C. lomyenensis, C. martini Ngo, 2011, C. multiporus, C. otai, C. pageli, C. papilionoides, C. phongnhakebangensis, C. pseudoquadrivirgatus, C. puhuensis Nguyen, Yang, Le, Nguyen, Orlov, Hoang, Nguyen, Jin, Rao, Hoang, Che, Murphy & Zhang, 2014, C. roesleri, C. rufford, C. sommerladi, C. soudthichaki, C. spelaeus, C. vilaphongi and C. wayakonei. Cyrtodactylus teyniei was described based on a single female holotype. Teynié & David (2014) reported the first known male; it showed precloacal and femoral pores, but they did not mention if the femoral and precloacal pored scales were separated by a diastema or not. It should be noted that, while in the male holotype of Cyrtodactylus bansocensis the precloacal and femoral pore-bearing scales are separated by a diastema, they are not in the male paratype (Luu et al., 2016c).

Its banded dorsal pattern separates Cyrtodactylus thathomensis sp. nov. from C. buchardi, C. jarujini, C. multiporus, C. pseudoquadrivirgatus, C. spelaeus and C. teyniei, which show blotched patterns. Additional differences distinguishing the new species from Cyrtodactylus jarujini include its smaller SVL (75.5 vs. 90 mm in C. jarujini) and a lower total number of pores in males (47 vs. 52–54). Additional differences with Cyrtodactylus multiporus include the new species’ much smaller SVL (75.5 vs. 98 mm in C. multiporus) and a much lower total number of pores in males (47 vs. 58–60). From Cyrtodactylus teyniei the new species differs also by its smaller SVL (75.5 vs. 89.9 mm in C. teyniei), generally lower number of midbody scale rows across belly between ventrolateral folds (30–36 vs. 36–38), and a much lower total number of pores in males (47 vs. 58).

Among the remaining species living within the 500-km radius of its type-locality, Cyrtodactylus thathomensis sp. nov. can be differentiated from C. auribalteatus Sumontha, Panitvong & Deein, 2010 by its much smaller SVL (75.5 vs. 98.1 mm), lower DorTub (14–18 vs. 22–24), lower Ven (30–36 vs. 38–40), and higher FemPo on each side (18 or 19 vs. 4 or 5) and PreclPo (10 vs. 6) in males; from C. bichnganae Ngo & Grismer, 2010 by its much smaller SVL (75.5 vs. 99.9 mm), much higher EnlFemSc on each side (20–22 vs. 11–13), and much higher FemPo on each side in males (18 or 19 vs. 9); from C. doisuthep Kunya, Panmongkol, Pauwels, Sumontha, Meewasana, Bunkhwamdi & Dangsri, 2014 by its smaller SVL (75.5 vs. 90.5 mm), lower DorTub (14–18 vs. 19 or 20), presence of femoral pores (vs. pits) in males, higher PreclPo (10 vs. 6), and 4 (vs. 5 or 6) dark bands between limb insertions; from C. dumnuii Bauer, Kunya, Sumontha, Niyomwan, Pauwels, Chanhome & Kunya, 2010 by its generally lower DorTub (14–18 vs. 18–22), its lower Ven (30–36 vs. 40), and much higher FemPo on each side (18 or 19 vs. 6 or 7) and PreclPo (10 vs. 5 or 6) in males; from C. huongsonensis Luu, Nguyen, Do & Ziegler, 2011 by its by its smaller SVL (75.5 vs. 89.8 mm), lower Ven (30–36 vs. 41–48), higher PreclPo (10 vs. 6) and much higher FemPo on each side (18 or 19 vs. 7–10) in males, and its discontinuous (vs. continuous) nuchal loop; from C. interdigitalis Ulber, 1993 by its generally lower DorTub (14–18 vs. 18–22), its lower Ven (30–36 vs. 37–42), much higher FemPo on each side (18 or 19 vs. 9) and lower PreclPo (10 vs. 14) in males, and absence (vs. presence) of webbing; from C. intermedius ( Smith, 1917) by its lower Ven (30–36 vs. 40–50) and much higher EnlFemSc on each side (20–22 vs. 6–10); from C. inthanon Kunya, Sumontha, Panitvong, Dongkumfu, Sirisamphan & Pauwels, 2015 by its generally lower DorTub (14–18 vs. 18–20), and much higher FemPo on each side (18 or 19 vs. 6) and PreclPo (10 vs. 5) in males; from C. khelangensis Pauwels, Sumontha, Panitvong & Varaguttanonda, 2014 by its much smaller SVL (75.5 vs. 95.3 mm), and much higher FemPo on each side (18 or 19 Po vs. 6 or 7 Po or Pi) and PreclPo (10 vs. 2–5) in males; from C. kunyai Pauwels, Sumontha, Keeratikiat & Phanamphon, 2014 by its much higher FemPo on each side (18 or 19 vs. 5 or 6) and PreclPo (10 vs. 3) in males; and from C. soni Le, Nguyen, Le & Ziegler, 2016 by its much smaller SVL (75.5 vs. 103.0 mm), higher DorTub (14–18 vs. 10–13), lower Ven (30–36 vs. 41–45), and much higher FemPo on each side (18 or 19 vs. 6–8) and PreclPo (10 vs. 6 or 7) in males.

Besides differentiating Cyrtodactylus thathomensis sp. nov. from all congeneric species found within a 500-km radius, its combination of characters presented in the Diagnosis allows to unambiguously separate it from all species found in Bangladesh, Cambodia, Myanmar, Thailand and Vietnam (see, among other references in the literature cited, Bauer, 2003; Connette et al., 2017; Grismer et al., 2012; Le et al., 2016; Mahony et al., 2009; Mahony, 2009; Panitvong et al., 2014; Pauwels & Sumontha, 2014; Pauwels et al., 2014, 2016; Sumontha et al., 2014, 2015).

Distribution and natural history: Cyrtodactylus thathomensis sp. nov. is so far known only from its type-locality. The types were collected on karst boulders on a steep forested limestone hill (Figure 7).

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Figure 7

Habitat of Cyrtodactylus thathomensis sp. nov. at the type-locality

A: General view of karst massif at Ban Thathom in Xiangkhoang Province, northeastern Laos; B: Microhabitat of Cyrtodactylus thathomensis sp. nov.. Photos by E.L. Konstantinov.

Phylogenetic position: The new species is a member of the C. phongnhakebangensis species group sensu Luu et al. (2016a) within which it is most closely related to C. multiporus, C. teyniei and C. cf. jarujini (see Results).

Etymology: The specific epithet “thathomensis” is a Latinized toponymic adjective, referring to the type locality of the new species, Ban Thathom. We suggest the following common names: Ki Chiem Thathom (Lao), Tuk Khai Thathom (Thai), Thathom Bent-toed Gecko (English), Tatomskiy Krivopalyi Gekkon (Russian), Thathomkromvingergekko (Dutch), and Cyrtodactyle de Thathom (French).