Nactus simakal, Hoskin & Davies & Aland, 2024

Hoskin, Conrad J., Davies, Alexander & Aland, Kieran, 2024, A new species of Nactus gecko from boulder-pile habitat on Dauan Island, Torres Strait, Australia, Zootaxa 5497 (4), pp. 577-590 : 583-586

publication ID	https://doi.org/ 10.11646/zootaxa.5497.4.7
publication LSID	lsid:zoobank.org:pub:AE09F1B9-870C-420E-958C-94C7CE0240CB
DOI	https://doi.org/10.5281/zenodo.13629525
persistent identifier	https://treatment.plazi.org/id/039A87A5-F933-EA1F-FF11-D794C864F823
treatment provided by	Plazi
scientific name	Nactus simakal
status	sp. nov.

Treatment

Nactus simakal sp. nov.

Dauan Island Gecko

( Figures 4–7 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 )

Material examined. Holotype. Female , QM J97603 ( Fig. 4 View FIGURE 4 ), Dauan Island (- 9.41337° S, 142.53781° E; 50 m above sea level), field collection code: conx5934, C. J. Hoskin, K. Aland, A. Davies & A. Zwar, 11/01/2021 GoogleMaps . Paratypes. QM J97602 (field collection code: conx5935) , QM J97604 (conx5943) , QM J97605 (conx5948), all collection details as for holotype .

Diagnosis. A slender, elongate Nactus gecko with strongly banded pattern and prominently keeled subcaudal scales.

Measurements and scale counts of type series. Table 1 View TABLE 1 .

Description of type series. A medium-sized (SVL 44.4–53.6 mm, mean 49.1 mm) Nactus with slender body and limbs, a long, slender tail, and a banded pattern. Body. Moderate length (AG/SVL 0.33–0.41, mean 0.38); slightly flattened; slender (BW/SVL 0.18–0.22, mean 0.20); dorsal scales minute, with longitudinal rows of enlarged tubercles (12–14 rows, mean 13.0, counted at the mid body; 7–8 rows, mean 7.8, counted at the hips), with the rows starting on the back of the head, ‘funnelling’ through the neck, then extending generally unbroken down the back and flanks and converging above the hips and base of tail (enlarged tubercle count for second parasagittal: 30–35 tubercles, mean 32.3); scales on ventral surfaces of head and body moderate-sized, finely keeled, and increasing in size from throat to subcaudals; typically 2 spurs (post-cloacal tubercles) positioned laterally on either side of the cloaca in both sexes (except holotype, which has 3 on left side, 2 on right side), rounded rather than pointed, more well-defined in males; row of 9 (N = 2) pre-cloacal pores in mature males, aligned in a V-shape, not divided medially, not extending to underside of legs; pre-cloacal pores not evident in females (N = 2); neck long (NL/SVL = 0.17–0.22, mean 0.18). Head. Distinct from neck; moderately long (HL/SVL = 0.25–0.28, mean 0.26), narrow (HW/SVL = 0.18–0.19, mean 0.18) and flattened (HD/SVL = 0.091 –0.104, mean 0.096); snout moderately long (SL/HL = 0.40–0.47, mean 0.44), relatively wide (SW/HW = 0.22–0.22, mean 0.22) and slightly up-turned to give a ‘beaky’ appearance; snout covered in small granular scales, with some larger tubercles interspersed across the crown; scales diamond-shaped on snout and temporal areas; scales highly variable in shape across crown; rostral scale approximately twice as wide as deep, divided 50–70% (mean 58%) vertically by a medial groove; rostral contacting nostril, scales bordering posterior margin of supra-nasals 13–14 (mean 13.3); scales contacting nostril 6– 7 (mean 6.3), counted as all scales contacting the nasal (including the rostral and first supralabial); supralabials, total count 7–8 (mean 7.8); supralabials, count to below middle of eye 3; supralabials all similar shape, but decreasing in size posteriorly; infralabials, total count 7–8 (mean 7.5); infralabials, count to below middle of eye 3; first two infralabials obviously deeper than wide; two large scales contact posterior margin of mental scale and first infralabials, typically contacting each other to exclude granular scales from contacting mental; scales contacting other infralabials then minute and rounded, except for those along the infralabials, which are moderate-sized (but quickly grade ventrally to minute rounded scales on throat); ear opening small and rounded or slightly horizontally or diagonally elongate; eye large (ED/SVL = 0.059 –0.072, mean 0.063). Limbs. Long (FL/SVL = 0.14–0.16, mean 0.15; L1/SVL 0.35–0.38, mean 0.36; LHL/SVL = 0.19–0.20, mean 0.20; L2/SVL 0.47–0.53, mean 0.50); scales on dorsal surface of forelimbs evenly small; scattered large tubercles on posterior thigh and lower hindleg (crus); scales under limbs evenly very small; digits laterally compressed, with small subdigital lamellae, all undivided, with the lamellae being relatively large for the first half of the series and then small to the tip of the digit, with the apical lamellae forming a sheath on the claw; lamellae shape and size progression similar on all digits; finger subdigital lamellae counts (including apical pair): F1 9–10 (mean 9.5), F2 12–14 (mean 13.0), F3 14–15 (mean 14.5), F4 14–16 (mean 14.8), F5 12–13 (mean 12.8); toe subdigital lamellae counts (including apical pair): T1 10–11 (mean 10.3), T2 13–15 (mean 14.0), T3 16–19 (mean 17.5), T4 17–19 (mean 18.0), T5 17–18 (mean 17.8); large scales along the inner and outer edge of the palm and foot, the rest smaller and even-sized. Original tail. Long (TL/SVL = 1.13–1.39, mean 1.28, N = 3), narrow (TW/SVL = 0.068 –0.080, mean 0.074, N = 4), rounded to slightly depressed (TW/TD = 1.02–1.25, mean 1.15, N = 4; TD/SVL = 0.054 –0.079, mean 0.065, N = 4), and evenly tapering to a very fine tip; enlarged, longitudinal tubercle rows extend about 10% along base of tail; remaining dorsal scales on tail moderate-sized and pointed; scales on underside of tail large, with angular posterior edge, and obviously keeled; Regrown tail. No regrown tails in type series. Colouration in spirit (e.g., Figs 4B View FIGURE 4 , 6 View FIGURE 6 ). Dorsal pattern consists of prominent dark and pale bands. A thin, dark vertebral line typically connects the dark bands and breaks the pale bands. Dark bands are black or dark brown; each pale band has a white anterior edge and then grades to dark grey. All individuals share the same number of bands on the body, consisting of a pale nape band, then five pale bands from the shoulders to above the vent (i.e., just posterior to the hips), and five dark bands from the neck to the hips. Dark and pale bands are approximately even width on body. Bands extend along tail, but as unbroken dark and white bands, with the dark bands getting relatively broader along the length. Bands on body and tail fade out abruptly on lower lateral surfaces. Forelimbs faintly banded; hind limbs prominently banded with two or three dark bands on a grey background. Top of head grey or light brown with brown blotches or mottling; dark band extends from snout, above supralabials, through the ear opening, and then in an irregular way around back of crown; pale grey band along canthal ridge; infralabials white, and white markings extending along lower sides of head (and as pale spots along lower flank in some individuals). Ventral surface of head, body and limbs cream or grey/light brown; darker pigment starts posterior to cloaca and underside of tail dark brown to black, with white tail bands not quite connecting initially ( Fig. 2A View FIGURE 2 ) but then connecting ventrally towards end of tail. Palms and feet dark grey. Colour pattern in life ( Figs 4A View FIGURE 4 , 5 View FIGURE 5 , 7A View FIGURE 7 ). As described above but all markings more contrasting dark and light. A subadult photographed in life (but not collected) had a similar pattern to the adults but most aspects were more contrasting dark and white, including bright white spots extending from the lower jaw, along the neck and flanks, and down the lower lateral surfaces of the tail ( Fig. 5D View FIGURE 5 ).

Comparisons. Readily distinguished from all other Nactus (except N. galgajuga and N. kunan ) by obviously banded colour pattern (versus all other species light or medium grey/brown dorsal ground colour, with variable dark brown bars/blotches/flecks and white spots/flecks; Zug & Fisher 2012; Zug 2020). Distinguished from N. kunan by pale bands being white/grey (vs yellow), smaller size (SVL 44.4–53.6 vs 56.6 mm), and longer snout–forelimb length (SF/SVL 0.41–0.47 vs 0.40) ( N. kunan data from a single adult female; Zug & Fisher 2012). Nactus simakal sp. nov. is distinguished from N. galgajuga by keeled subcaudal scales (vs smooth). In terms of other Nactus recorded on Torres Strait islands, N. simakal sp. nov. is readily distinguished from N. eboracensis by keeled subcaudal scales (vs smooth), and from N. c.f. papua by banded body pattern (vs brown or grey with dark brown bars or blotches, and white flecks), slender and elongate form (e.g., Fig. 6 View FIGURE 6 ), and shape differences including longer hindlimbs (LHL/SVL, L2/SVL), longer neck (NL/SVL) and snout–forelimb (SF/SVL), flatter head (HD/SVL), and longer (TL/SVL), thinner (TW/SVL) and flatter (TD/SVL) tail ( Table 1 View TABLE 1 ).

Genetic data. Two ND 2 sequences were deposited on GenBank: OM523359 (specimen: QM J97603 ; holotype; genetic sample code: conx5934) and OM523360 (specimen: QM J97602 ; paratype; genetic sample code: conx5935).

Etymology. The species name ‘ simakal ’ is in reference to Simakal Pad, the local language name for Mt Cornwallis (the mountain that dominates Dauan Island). The local language name was provided by Laurie Elisala, Torenzo Elisala, Abi Mooka, Tenny Elisala, and Thomas Mooka.

Distribution. Known only from Dauan Island, in the northern Torres Strait ( Fig. 1 View FIGURE 1 ). The island is only 10.5 km from the mainland of New Guinea but is situated within the boundaries of the state of Queensland, Australia. Nactus simakal sp. nov. is probably restricted to Dauan Island due to occurrence on deeply piled granite boulder habitat, which is not present to any significant degree on nearby islands or the adjacent New Guinea mainland.

Natural history. Habitat consists of piled granite rock. All observations were made in areas of boulders under a rainforest canopy (e.g., Fig. 8 View FIGURE 8 ). Observed at night on rock surfaces or in crevices among rocks. Moves quickly across rock surfaces and into deep crevices when disturbed. No information on diet but assumed to feed on invertebrates. No information on breeding biology. Neither of the two females collected in January were carrying eggs.

Conservation. Given restriction to a single island and a very small known area of occurrence on the island, N. simakal sp. nov. requires conservation assessment. Assuming N. simakal sp. nov. is found in all piled rock areas across the island, the extent of potential habitat is approximately 1.3 km 2 (or 1.4 km 2 as a minimum convex polygon). Density appears to be low, but this may reflect low detection rather than actual low density. Invasive Asian house geckos, Hemidactylus frenatus Duméril and Bibron, 1836 , could pose a risk to N. simakal sp. nov.. Hemidactylus frenatus was observed on Dauan Island during the survey but was only seen on buildings and in coastal forests. The species was not detected in the piled boulder habitat occupied by N. simakal sp. nov.; however, this should be monitored through time given invasion of various natural habitats by H. frenatus in other parts of north-east Queensland ( Hoskin 2011; Barnett et al. 2017, 2018). This invasive species should be recognised as a significant potential threat to N. simakal sp. nov. given the severe declines documented in several Nactus species in the Mascarene Islands due to H. frenatus invasion of natural habitats ( Cole et al. 2005). Other invasive species also pose a potential threat, including invasive ants. Yellow crazy ant ( Anoplolepis gracilipes ) infestations have been shown to impact small lizards in north-east Queensland ( Lach et al. 2022) and have been implicated in reptile declines on Christmas Island ( Smith et al. 2012). Nactus simakal sp. nov. is best considered Data Deficient until further data on distribution, abundance and threats are obtained.