Dixonius muangfuangensis, Luu & Nguyen & Le & Grismer & Ha & Sitthivong & Hoang & Grismer, 2023

Luu, Vinh Quang, Nguyen, Thuong Huyen, Le, Minh Duc, Grismer, Jesse L., Ha, Hong Bich, Sitthivong, Saly, Hoang, Tuoi Thi & Grismer, L. Lee, 2023, Two new species of Dixonius from Vietnam and Laos with a discussion of the taxonomy of Dixonius (Squamata, Gekkonidae), ZooKeys 1163, pp. 143-176 : 143

Dixonius muangfuangensis sp. nov.

Fig. 10 Muangfuang leaf-toed gecko

Material examined.

Holotype. Adult male, VNUF R.2020.42 (Field no. MF.02) in Sinxay Temple , Nadan Village , Muangfuang District, Vientiane Province, Central Laos (18°32'52"N, 101°58'31"E; 276 m a.s.l.), collected by Saly Sitthivong and Thuong Huyen Nguyen on 05 December 2020 . Paratypes. NUOL R.2022.01 (Field no. MF. 01), juvenile male, and VNUF R.2020.52 (Field no. MF. 03), adult female; the same data as given for the holotype.

Diagnosis.

Dixonius muangfuangensis sp. nov. can be separated from all other species of Dixonius by possessing the unique combination of having a maximum SVL of 56.7 mm; 21-23 longitudinal rows of dorsal tubercles at midbody; 20 or 21 longitudinal rows of ventrals across the abdomen; 7 or 8 supralabials, sixth in at midorbital position; 6 or 7 infralabials; 7 interorbital scales; 7 or 8 precloacal pores in males, femoral pores lacking; precloacal and femoral pores absent in female; 15 lamellae on fourth toe; dorsum olive grey color with numerous small and irregular black blotches; head with brown spots; light spots irregularly arranged from the back of the head to base of tail; lips with dark bars; two regularly disposed whitish tubercles on each side on each side. These characters are scored across all Dixonius species from Vietnam and Laos in Tables 6 , 7 .

Description of the holotype.

Adult male, SVL 55.6 mm; head moderate in length (HL/SVL 0.28), wide (HW/HL 0.71), depressed (HD/HL 0.45), distinct from neck; prefrontal region concave; canthus rostralis rounded; snout elongate (ES/HL 0.39), rounded in dorsal profile; eye moderate size (ED/HL 0.20); ear opening oval, obliquely oriented, moderate in size; diameter of eye much smaller than eye to ear distance (ED/EE 0.59); rostral rectangular, partially divided dorsally by straight rostral groove, bordered posteriorly by large left and right supranasals, bordered laterally by first supralabials; external nares bordered anteriorly by rostral, dorsally by large supranasal, posteriorly by two smaller postnasals, bordered ventrally by first supralabial; 8,8 (R,L) rectangular supralabials extending to below midpoint of eye, sixth in midorbital position; 7,7 (R,L), infralabials tapering smoothly to be just slightly past posterior below midpoint of eye, decreasing gradually in size; scales of rostrum and lores flat to domed, larger than granular scales on top of head and occiput; scales of occiput intermixed with distinct, small, conical tubercles; superciliaries elongate, largest anteriorly; mental triangular, bordered laterally by first infralabials and posteriorly by large left and right parallelogram postmentals contacting medially for 60% of their length posterior to mental; gular and throat scales small, granular, grading anteriorly into slightly smaller, flatter, smooth, imbricate, pectoral and ventral scales.

Body relatively short (AG/SVL 0.42) with well-defined ventrolateral folds; dorsal scales small, granular interspersed with moderate, conical, regularly arranged, keeled tubercles; tubercles extend from top of head onto interior haft of tail forming longitudinal rows, terminating at regenerated portion of tail; smaller tubercles extend anteriorly onto nape and occiput, diminishing in size and distinction on top of head; 23 longitudinal rows of tubercles at midbody; 45 paravertebral scales, number of scales in a paravertebral row from first scale posterior to parietal scale to last scale at the level of vent opening; 24 paravertebral scales in a row between limb insertions; 20 flat, imbricate, ventral scales much larger than dorsal scales; 8 enlarge, pore-bearing, precloacal scales in an angular series; and no deep precloacal groove or depression.

Forelimbs moderate in stature, relatively short (FA/SVL 0.12); granular scales of forearm slightly larger than those on body, interspersed with small tubercles; hind limbs more robust than forelimbs, moderate in length (TBL/SVL 0.13), covered dorsally by granular scales interspersed with large, and small conical tubercles; ventral scales of thigh flat, imbricate, larger than dorsals; subtibial scales flat, imbricate; proximal femoral scales smaller than distal femorals; femoral pores absent; digits relatively long with 15 lamellae on fourth toe; and claws well developed.

Tail 37.8 mm in length, first 17.1 mm original, 6.1 mm in width at base, tapering to a point; dorsal scales of flat, square with conical, keeled tubercles, regenerated portion covered with small, smooth subcircular scales; median row of transversely expanded subcaudal scales, significantly larger than dorsal caudal scales on original portion; base of tail bearing hemipenal swellings; and postcloacal scales flat, imbricate.

Coloration in life

(Fig. 10 ). Ground color of dorsal head and dorsum dark grey with numerous small and irregular black blotches; lips with dark bars; two regularly disposed whitish tubercles on each side on each side running from postorbital along the flanks to tail, terminating at regenerated portion of tail; upper surface of fore and hind limbs uniformly dark brown with round black-brown spots; dorsum of tail covered with some large black-brown blotches; ventral surface beige uniformly as the belly and the throat.

Variation

(Fig. 10 ). The female paratype (VNUF R.2020.52) generally matches that of the holotype in all characteristics. The juvenile male paratype (NUOL R.2022.01) has fewer black blotches on head and dorsum and two regularly disposed whitish tubercles on each side on each side of the head extending from the postorbital region, along the flanks, to the tail tip. Further measurements are summarized in Tables 2 - 4 and Suppl. material 1: table S2.

Distribution.

Dixonius muangfuangensis sp. nov. currently is only known from the type locality of Nadan Village, Muangfuang District, Vientiane Province, Central Laos (Fig. 1 ).

Etymology.

The specific epithet of the new species refers to the type locality of the new species in Muangfuang District, Vientiane Province, Central Laos.

Natural history.

The type series was collected between 19:10 and 19:30 h, on the ground inside Sinxay Temple, at an elevation of 276 m a.s.l. The surrounding habitat was disturbed lowland karst forest (Fig. 11 ).

Comparisons.

Dixonius muangfuangensis sp. nov. is the sister species to D. lao (Fig. 2 ) from which it differs by an uncorrected pairwise sequence divergence of 3.10% (Table 4 ). It is differentiated morphologically by having a significantly higher mean number of head length (HL), infralabials (IFL), and numbers of supralabial at midorbital position (MO). In addition, it differs from D. lao in dorsal pattern (dorsal pebble brown versus dorsal dark gray with black blotches). Statistically significant and discrete categorical differences between Dixonius muangfuangensis sp. nov. and all other species and populations are presented in Tables 5 - 7 .

Figures

Figure 1. Location of the type localities of all known species of Dixonius. The inset delimits the study area. 1 Dixonius aaronbaueri from Ninh Thuan Province, Vietnam; 2 D. dulayaphitakorum from Ranong Province, Thailand; 3 D. mekongensis from Ubon Ratchathani Province, Thailand; 4 D. hangseesom from Kanchanaburi Province, Thailand; 5 D. kaweesaki from Prachuap Khiri Khan Province, Thailand; 6 D. pawangkhananti from Phetchaburi Province, Thailand; 7 D. lao from Khammouane Province, Laos; 8 D. melanostictus from Nakhon Ratchasima Province, Thailand; 9 D. minhlei from Dong Nai Province, Vietnam; 10 D. siamensis from SaraBuri and Nakhon Ratchasima provinces, Thailand; 11 D. somchanhae from Vientiane Capital, Laos; 12 D. taoi from Binh Thuan Province, Vietnam; 13 D. vietnamensis from Khanh Hoa Province, Vietnam; 14 D. muangfuangensis sp. nov. from Vientiane Province, Laos; 15 D. gialaiensis sp. nov. from Gia Lai Province, Vietnam.

Figure 2. Maximum likelihood topology of the Dixonius species from Vietnam and Laos with ultrafast bootstrap values (UFB) and Bayesian posterior probabilities (BPP) at the nodes, respectively.

Figure 10. View of Dixonius muangfuangensis sp. nov. A adult male holotype VNUF R. 2020.42 (Field no. MF. 02) B adult female paratype VNUF R. 2020.52 (Field no. MF. 03) C juvenile male paratype NUOL R. 2022.01 (Field no. MF. 01) in Nadan Village, Muangfuang District, Vientiane Province, Central Laos.

Figure 11. Habitat of Dixonius muangfuangensis sp. nov. Nadan Village, Muangfuang District, Vientiane Province, Central Laos.