A new species of Dixonius (Squamata: Gekkonidae) from the karst forest of Khammouane Province, central Laos Author Nguyen, Thuong Huyen Author Sitthivong, Saly Author Ngo, Hanh Thi Author Luu, Vinh Quang Author Nguyen, Truong Quang Author Le, Minh Duc Author Ziegler, Thomas text Zootaxa 2020 2020-04-06 4759 4 530 542 journal article 10.11646/zootaxa.4759.4.4 a056a6d5-d43d-475e-aa60-6a02fff9896b 1175-5326 3741047 A09D92BC-8048-45F1-A8AC-0ED70D3BC9B0 Dixonius lao sp. nov. ( Figs. 2–5 ) Holotype . Adult male, VNUF R .2016.2 (Field no. TK16.2) in Na Ngua village , Thakhek Town , Khammouane Province ( 17 o 32N , 104 o 51E , at an elevation of 145 m a.s.l. ), collected by V . Q. Luu and N. Schneider on 24 February 2016 . Paratypes . IEBR A.2019.5 (Field no. TK16.3), adult female ; IEBR A.2019.6 (Field no. TK16.1), subadult female; the same data as the holotype . FIGURE 1. Phylogram based on the single-model Bayesian analysis. Numbers above and below branches are MP/ML bootstrap values and Bayesian posterior probabilities, respectively. Dash represents unresolved node. FIGURE 2. Dorsal view of the adult male holotype of Dixonius lao sp. nov. (VNUF R.2016.2). Photo: V.Q. Luu. TABLE 2. Uncorrected pairwise p-distances between samples of Dixonius .

No.	Species with Genbank	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17
Accession numbers
1	Dixonius aaronbaueri	-
HM997152
2	Dixonius cf. siamensis	0.1905	-
KX379195
3	Dixonius cf.	0.1877	0.1249	-
vietnamensis
KX379201
4	Dixonius melanostictus	0.1528	0.1306	0.1300	-
HM997153
5	Dixonius minhlei	0.1791	0.1547	0.1392	0.1409	-
KX379194
6	Dixonius siamensis	0.1688	0.1560	0.1281	0.1233	0.1308	-
EU054299
7	Dixonius siamensis	0.1667	0.1556	0.1277	0.1219	0.1305	0.0030	-
EU054298
8	Dixonius sp EU054297	0.2090	0.2365	0.2040	0.1710	0.1299	0.1556	0.1565	-
9	Dixonius sp KX379196	0.1897	0.0632	0.1215	0.1337	0.1392	0.1421	0.1419	0.2300	-
10	Dixonius taoi	0.1712	0.1407	0.0872	0.1220	0.1468	0.1305	0.1291	0.1824	0.1251	-
KP979736
11	Dixonius taoi	0.1667	0.1354	0.0749	0.1138	0.1344	0.1231	0.1217	0.1735	0.1178	0.0118	-
KP979733
12	Dixonius vietnamensis	0.1931	0.1374	0.0257	0.1315	0.1413	0.1290	0.1287	0.2028	0.1215	0.0808	0.0674	-
KX379198
13	Dixonius lao sp. nov.	0.1703	0.0989	0.1177	0.1027	0.1368	0.1232	0.1233	0.1601	0.0898	0.1203	0.1135	0.1226	-
VNUF R. 2016.2
( MT024681 )
14	Dixonius lao sp.	0.1710	0.0961	0.1167	0.1048	0.1346	0.1231	0.1232	0.1600	0.0864	0.1217	0.1150	0.1225	0.0044	-
nov. IEBR A.2019.6
( MT024682 )
15	Dixonius lao sp.	0.1739	0.1001	0.1199	0.1069	0.1379	0.1248	0.1255	0.1621	0.0914	0.1248	0.1180	0.1257	0.0053	0.0030	-
nov. IEBR A.2019.5
( MT024683 )
16	Gekko gecko JN019051	0.3567	0.3657	0.3731	0.3223	0.3611	0.3457	0.3432	0.3402	0.3810	0.3431	0.3393	0.3763	0.3279	0.3277	0.3300	-
17	Heteronotia spelea	0.2535	0.2398	0.2521	0.2376	0.2509	0.2559	0.2536	0.2842	0.2511	0.2525	0.2477	0.2575	0.2421	0.2422	0.2441	0.3379
HQ840102

FIGURE 3. Head portraits: A) Dorsal view and B) Ventral view; C) Lateral view (right); and D) Lateral view (left) of Dixonius lao sp. nov. (VNUF R.2016.2). Photos: S. Sitthivong. FIGURE 4. A) Dorsal tubercles at midbody; B) Ventral scale rows and C) Cloacal region of the preserved holotype of Dixonius lao sp. nov. (VNUF R.2016.2). Photos: T.H. Nguyen. FIGURE 5 . Lateral aspect of A) the holotype and B) the paratype of Dixonius lao sp. nov. Photos: V. Q. Luu. Diagnosis. A species of the genus Dixonius that can be distinguished from its congeners by a combination of the following characters: maximum SVL 55.4 mm ; 20–23 longitudinal rows of dorsal tubercles at midbody; 23 or 24 longitudinal rows of ventrals across the abdomen; 8–10 supralabials, 7 or 8 in mid-orbital position; 7 or 8 infralabials; 8 precloacal pores in male; the male without femoral pores; precloacal and femoral pores absent in females; uniformly pebble brown dorsum. Description of the holotype . Adult male, SVL 50.1 mm with dorsolaterally flattened body, TaL 69.0 mm, trunk length 20.6 mm . Head longer than wide, depressed, distinct from neck. Head length 14.1 mm , head width 9.2 mm , eye of moderate size 3.6 mm , ear-opening oblique (EL 1.4 mm ), snout-eye length 5.6 mm , internarial distance 1.7 mm . Rostral very large, wider than high (width 2.2 mm , height 1.2 mm ), with distinct suture; supralabials 10/9 (8/ 7 in midorbital position); nostril in contact with rostral, first supralabial, supranasal, and two nasals posteriorly on each side; supranasals in broad contact; without intersupranasals; snout flat, covered with granular scales; pupil vertical; ear opening oblique, oval, approximately one third of the eye diameter, without bordering enlarged scales; infralabials 8/8, decreasing gradually in size; mental triangular, wider than high (width 2.5 mm , height 1.7 mm ); two pairs of enlarged postmentals, first pair very large and in contact with each other, second pair about one third to one half size of first, in contact with the first and second infralabials and separated from each other by four gular scales; dorsal tubercle rows at midbody 22, keeled and separated from each other by one smaller scale which is keeled or at least almost conical shaped; ventral scales larger than dorsal scales, in 23 rows at midbody; dorsal surface of fore- and hind limbs covered with shallowly keeled scales, area around limb insertions covered with small granular scales; 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 43; paravertebral scales in a row between limb insertions 25; lamellae on fourth toe 15; precloacal pores 8, in an angular series; tail covered with smooth scales, in different sizes; subcaudals 42, enlarged and undivided. Coloration in life. In life, dorsum of the holotype pebble brown ( Fig. 2 ); head with brownish olive spots; canthal stripe absent; ventral surface light beige to uniformly whitish as the belly and the throat; supralabials grey with dark grey spots; upper surface of fingers and toes uniformly light grey; dorsal surface of the tail light brownish grey, with uniformly distributed light spots along the tail tip. Sexual dimorphism. Morphologically, the female paratypes corresponded well with the holotype , except for the lack of precloacal pores. Comparisons. We compared the new species from Laos with all other known Dixonius species (see Table 4 for a comparison with most similar species). Morphologically, the new species is most similar to Dixonius minhlei from Vietnam in the number of precloacal pores and ventral scale rows. However, the new species can be distinguished from the latter by having more dorsal tubercle rows at midbody (20–23 versus 14 or 15), the absence of canthal stripe ( versus canthal stripe continuing behind orbit to back of head), and by a different color pattern (pebble brown dorsum versus olive grey ground color on dorsum, with more or less discernible brownish olive blotches in D. minhlei ); from D. siamensis , which is known from Laos , Cambodia , Thailand and Vietnam , by having more dorsal tubercle rows (20–23 versus 10–14), more precloacal pores (8 versus 6 or 7), and generally more supralabials (8–10 versus 7 or 8); from D. hangseesom from Thailand by having more dorsal tubercle rows (20–23 versus 12–14), more paravertebral scales in a row from first scale posterior to parietal scale to last scale at the level of vent opening (PV 40–43 versus 26), and coloration of tail almost the same as the dorsum ( versus orange tail); from D. kaweesaki from Thailand by its larger size (maximum SVL 55.4 mm versus 41.6 mm ), having more dorsal tubercle rows at midbody (20–23 versus 12 or 13), and in dorsal head and body pattern (back pebble brown and head with brownish olive spots versus dorsal surface of head gray in D. kaweesaki ); from D. melanostictus from Thailand and Vietnam by having more dorsal tubercle rows (20–23 versus 10 or 11), more paravertebral scales in a row between limb insertions (PV’ 24–25 versus 10 or 11), and the absence of canthal stripe ( versus canthal stripe extending along flanks in D. melanostictus ); from D. aaronbaueri from Vietnam by having more ventral scale rows at mid-body (23 or 24 versus 18 or 19), more dorsal tubercle rows at midbody (20–23 versus 11), more precloacal pores in males (8 versus 5), and different dorsal pattern (back pebble brown versus dorsal yellowish-orange to bright orange color from head to tail tip); from D. taoi from Vietnam by its larger size (maximum SVL 55.4 mm versus 43.9 mm ), having more dorsal tubercle rows (20–23 versus 11 or 12), more precloacal pores (8 versus 5 or 6) and different dorsal pattern (back pebble brown versus one or two irregular rows of yellowish marks running from head along flanks in D. taoi ); from D. vietnamensis from Vietnam and Cambodia in having more dorsal tubercle rows at mid-body (20–23 versus 16), more supralabials (8–10 versus 5 or 6), more ventral scale rows at midbody (23 or 24 versus 20), more lamellae under fourth toe (15 versus 13), and more precloacal pores (8 versus 5–7). TABLE 3. Measurements (in mm) and morphological characters of the type series of Dixonius lao sp. nov. (for abbreviations see material and methods). Measurements taken on right side; FA and T4 are given in the left side; SPL/IFL/MO given in right/ left order; —absence.

Character	VNUF R.2016.2	IEBR A.2019.5	IEBR A.2019.6
(Holotype)	(Paratype)	(Paratype)
Sex	Adult male	Adult female	Subadult female
SVL	50.1	55.4	35.8
TaL	69.0	52.1	46.9
TrunkL	20.6	22.2	15.2
TW	5.3	5.5	4.0
BW	9.7	11.5	7.2
HL	14.1	14.3	9.9
HW	9.2	9.7	7.0
HD	5.3	6.2	4.0
EL	1.4	1.7	1.1
CrusL	7.6	8.5	5.9
FA	6.9	7.1	4.6
ED	3.6	3.6	2.7
EN	4.4	4.0	2.8
ES	5.6	5.5	3.6
EE	4.1	4.4	2.6
IN	1.7	1.8	1.1
IO	1.7	1.5	1.1
V	23	23	24
DTR	22	23	20
PV	43	43	40
PV’	25	24	25
T4	15	15	15
IOS	9	8	8
ICS	26	27	26
SPL	10/9	8/9	9/9
IFL	8/8	8/8	7/8
MO	8/7	7	8
PP	8	-	-

TABLE 4. Comparison of selected morphometric and morphological characters of Dixonius lao sp. nov. with morphologically most similar congeners. For abbreviations see Table 1. Measurements in mm; - = data unavailable.

Character	Dixonius lao sp. nov.	D. minhlei	D. hangseesom	D. vietnamensis	D. siamensis
SVL	50.1–55.4	40.6–47.5	36.6–42.1	25.9–40.8	57
TaL	52.1–69.0	51.0–53.2	33.5–51.5	2.5–37.8	58
TW	5.3–5.5	3.7–4.4	3.3–4.4	2.3–5.2	-
BW	9.7–11.5	8.5–9.7	-	4.0–9.1	-
TrunkL	20.6–22.2	-	14.9–18.4	11.8–21.0	-
HL	14.1–14.3	6.7–7.7	10.2–11.3	5.2–7.5	-
HW	9.2–9.7	6.0–7.7	6.2–7.6	5.1–7.9	-
HD	5.3–6.2	4.3–5.2	4.2–4.7	3.3–6.0	-
EL	1.4–1.7	1.2–1.5	0.8–0.9	0.6–1.1	-
CrusL	7.6–8.5	-	5.7–6.3	-	-
FA	6.9–7.1	5.9–6.7	4.9–5.6	4.0–6.2	-
ED	3.6	2.2–3.3	2.6–3.0	1.8–2.9	-
EN	4.0–4.4	3.2–3.8	2.6–3.0	2.2–3.7	-
ES	5.5–5.6	4.4–5.2	4.0–4.4	3.0–4.6	-
EE	4.1–4.4	3.4–3.9	2.6–3.2	2.2–4.0	-
IN	1.7–1.8	1.3–1.6	1.0–1.3	0.9–2.1	-
IO	1.5–1.7	3.4–4.0	3.2–3.9	2.1–3.6	-
V	23–24	20–23	22–26	20	18–25
DTR	20–23	14–15	12–14	16	10–14
PV	40–43	38–44	26	-	-
PV’	24–25	23–26	-	-	-
T4	15	13–15	-	13	12–16
IOS	8–9	7–10	10	8–10	-
ICS	26–27	25–29	-	-	-
SPL	8–10	7–9	8	5–6	7–8
IFL	7–8	6–7	8	6–7	6–7
MO	7–8	5–6	6	-	-
PP	8	7–8	7–8	5–7	6–7

Natural history notes. The type series was found between 20:00 and 21:00h on the forest floor or on karst cliffs, about 0.3 m above the ground. The surrounding habitat was secondary karst forest on the mountain ( Fig. 6 ). The relative humidity ranged from 58% to 70%, and air temperature was 25–26 oC . Distribution. Dixonius lao sp. nov. is currently known only from the type locality in Khammouane Province , central Laos ( Fig. 7 ). Etymology. The specific epithet “ lao ” is derived from both the official name of Laos , the Lao People’s Democratic Republic in which the species was discovered, and the Lao, the main group of people inhabiting Laos .