Oedura nesos, Oliver & Jolly & Skipwith & Tedeschi & Gillespie, 2020

Oliver, Paul M., Jolly, Chris J., Skipwith, Phillip L., Tedeschi, Leonardo G. & Gillespie, Graeme R., 2020, A new velvet gecko (Oedura: Diplodactylidae) from Groote Eylandt, Northern Territory, Zootaxa 4779 (3), pp. 438-450 : 440-445

Oedura nesos sp. nov.

Groote Eylandt Marbled Velvet Gecko

Figs. 1–4

Oedura bella (in part) Oliver & Doughty, 2016

Oedura “Marmorata North 6” Rosauer et al. 2016

Holotype. NTM R 38578, adult female with original tail, and liver samples stored in ethanol, from Cave Paintings Recreation Area (13.97322°S, 136.50316°E) Groote Eylandt, Northern Territory, Australia, collected by Graeme Gillespie and Jaime Heiniger on 14 November 2016.

Paratypes. (n=12) All from Groote Eylandt , Northern Territory, Australia . NTM R 38576 & R 38582 same locality and date as holotype ; NTM R 38579 – R 38581 from sandstone outcrop 700 m north of Alyangula (13.8412°S, 136.42305°E) collected 16 November 2016; NTM R 38583 from sandstone outcrop adjacent to Umbakumba Rd (13.93050°S, 136.4945°E) collected 17 November 2016; NTM R 38577 from sandstone outcrop adjacent to Umbakumba Rd (13.8927°S, 136.5112°E) collected 17 November 2016; AMS R138727–8 , Groote Eylandt (13.8299°S, 136.4200°E) ; NTM R7494 & R7495 , Umbakumba Rd (13.8799°S, 136.5000°E) ; NTM R7541 , Ayakamindadina (13.97°S, 136.60°E) .

Referred material. Tissue samples, stored at the Australian National University, Canberra. CCM4191 , CCM4195 , sandstone escarpment, Central Groote Eylandt (13.9736°S, 136.6033°E) .

Diagnosis. Differs from all Oedura in the following combination of characters: moderate size (to 85 mm SVL); head moderately wide (HW/SVL 0.18–0.20) and flattened (HD/SVL 0.07–0.12); tail short (TL/SVL original 0.52–0.62, regrown 0.45–0.54), transversely flattened (shallower than body), much narrower than head (TW/HW 0.59–0.77) and tapering gradually to tip; rostral 50% or less divided; postcloacal spurs 2 or 1 on each side (mode 2); 16 precloacal pores in adult males; head colouration dark brown with pale whitish-yellow supraoculars and canthal stripe absent or indistinct; and dorsal colouration of adults including five moderately well-defined whitish bands (including nuchal band), usually with greyish central shading, alternating with wider regions of extensive yellow splotching on a dark brown background.

Description. A medium-sized (adult SVL 70.0–85.0 mm) and robust Oedura (Trk/SVL 0.37–0.48); head moderately wide (HW/SVL 0.18–0.20) and flat (HD/SVL 0.07–0.12), although some variation in head width and depth likely attributable to body condition and quality of preservation. Rostral 50–30% divided, bordered dorsally by two nasals, nasals bordered dorsally by two supranasals and 1–2 (mode 2) similar sized intervening scales. Supralabials 9–10 to midpoint of eye, 11–12 in total; infralabials 9–11.

Forelimbs and hindlimbs of moderate length (FA/SVL 0.12–0.14, TA/SVL 0.14–0.17). Subdigital lamellae moderately expanded and prominent, 7–8 under third finger, 8–9 under third toe. Distal lamellae divided on all digits, proximal lamellae undivided. Apical lamellae on terminal scansors separated from more proximal pairs. Subapical lamellae series on fingers 2–5 slightly flared and equal to or narrower than width of terminal scansors on fingers. Subapical lamellae series on toes 2–5 flared, equal to or wider than terminal scansors on toes. Postcloacal spurs present and relatively distinct, mode of 2 and 2 (7 out of 11 adults), more rarely 1 and 2 (4 out of 11 adults). Adult males (n=2) with 16 precloacal pores, in a broken series separated medially by 2 non-pore bearing scales.

Original tail short (TL/SVL 0.52–0.62), moderately narrow (TW/HW 0.59–0.77) and strongly depressed in cross section, tapering relatively gradually to tip and with no obvious ventral groove, some variation in width and depth likely attributable to body condition and quality of preservation. Caudal scales on original tail arranged in regular transverse rows of irregularly shaped and sized scales. Dorsal and ventral caudal scales of similar size. Regrown tails short (TL/SVL 0.45–0.54), narrow (TW/HW 0.64–0.73) and strongly depressed in cross section, tapering relatively gradually to tip and with no obvious ventral groove. Some variation in width and depth likely attributable body condition and quality of preservation. Caudal scales on regrown tail arranged in irregular transverse rows of variable sized scales, ventral scales tending to be larger than caudal scales.

In preservative, base coloration of dorsum on adults is purplish brown, with five distinct whitish to buff transverse dorsal bands extending from nape to groin. Extensive further light buff blotching and flecking usually present between the light bands and elsewhere on the dorsal and lateral surfaces of the head, torso and limbs, with blotches tending to be quite large, usually more than four scales wide. Light and brown pigmentation on head usually broken and never forming a distinct continuous canthal stripe. Venter plain light buff, with variable amounts of tiny brown maculations on the terminal lamellae, around the infralabials, and sometimes extending onto the lateral regions of the throat. Original tails with four light buff dorsal bands, separated by slightly wider purplish-brown regions with moderate to very extensive areas of buff blotching and flecking. Subcaudal surfaces mostly light buff, with varying amounts of light brown, esepecially around edges, and sometimes forming indistinct light transverse sudcaudal bands. Regrown tails dark brown with extensive and variable light buff splotching and spotting but no regular pattern.

Hatchlings and small juveniles lack light buff flecking and generally have a very simple pattern of five sharplydefined light bands on the nape and body, and 4–5 light bands on the tail, separated by broad plain dark brown regions. As specimens grow, the sharp definition of light and dark bands decreases, and the amount of light flecking and blotching across the body increases.

In life, the basic adult pattern and coloration consists of three clear and contrasting colouration elements ( Fig. 2 A–D, F): background dorsal colouration of dark purplish brown; extensive yellow blotching and spotting overlaying dark-brown regions; and whitish transverse bands with small areas of underlying dark purplish brown visible.

Summary measurements of the adults in type series (n=11). Quantitative measurements (mean and range) in mm: SVL 80 (70–85); HW 16.4 (14.5–17.7); HD 7.6 (5.4–9.7); HL 20.9 (19.3–22.0); EN 7.1 (6.6–7.5); IN 3.1 (2.8–3.4); IO 7.2 (6.6–7.9); EYE 5.3 (4.6–5.8); TrK 34.7 (28.0–40.6); Crus 10.4 (8.1–11.4); Tibia 11.8 (9.7–13.5); 3FW 1.8 (1.5–1.9); 3TW 2.1 (1.8–2.4); TL (original) 41.4 (36.0–44.8); TW (original) 10.2 (8.6–11.5); TD (original) 5.3 (3.2–6.9); TL (regrown) 41.4 (36.0–44.8); TW (regrown) 11.6 (9.8–12.7); and TD (regrown) 4.0 (3.5–5.3). Scale counts: SuL 9.5 (9–10); InF 10.6 (9–11); CS 1.8 (1–2); FLAM3 7.7 (7–8); and TLAM3 8.1 (8–9).

Particulars of the holotype. Adult female with original tail. Quantitative measurements in mm: SVL 85.0; HW 11.7; HD 7.8; HL 22.0; EN 7.5; IN 3.2; IO 7.5; EYE 5.4; TrK 33.7; Crus 10.6; Tibia 11.6; TL 43.0; TW 12.6; TD 3.8; 3FW 1.9; and 3TW 2.2. Scale counts: SuL 10 (12 to rictus of jaw); InF 10; CS 2/2; FLAM3 7; and TLAM3 8.

Comparisons. Oedura nesos sp. nov. differs from its three closest relatives in the Oedura marmorata complex from northern Australia in aspects of tail morphology (both original and regrown) and colour pattern ( Figs. 2–4 ). Oedura nesos sp. nov. was formerly confounded with Oedura bella , from which it differs in having a dorsal pattern including alternating transverse bands of white then regions of brown heavily blotched with yellow (versus yellow dots coalescing into distinct to indistinct yellow bands; Figs. 3–4 ), and in having no or a very indistinct and wavy canthal stripe (versus clearly defined, narrow, straight and continuous or near continuous canthal stripe; Figs. 3–4 ). Oedura nesos sp. nov. differs from Oedura gemmata in its smaller size (SVL 70–85 mm versus 84–103 mm), in having a tail (original or regrown) much narrower than the head (TW/HW 0.59–0.77 versus 0.75–1.08), and in having prominent white bands and large yellow splotches on the dorsum (versus smaller yellow or white spots only). Oedura nesos sp. nov. differs from Oedura marmorata in its smaller size (SVL 70–85 mm versus 77–97 mm), and in having a tail (original or regrown) that is much narrower than the head in dorsal perspective versus nearly as wide to wider than head (TW/HW 0.59–0.77 versus 0.76–1.2) and gradually tapering to the tip (versus sharply tapering to attenuated tip; Fig. 2–4 ). It can be further differentiated from geographically proximate populations of Oedura marmorata in eastern Arnhem Land by having yellowish-white supraoculars in life versus bright yellow supraoculars in life ( Fig. 2 ), and tending to have a tail that is highly depressed in cross-section and shallower than body versus a tail that is comparatively rounded in cross-section and as deep or deeper than the body ( Fig. 3–4 ). Hatchling and small juvenile Oedura nesos sp. nov. are easily distinguished from juveniles of its two relatives in the Oedura marmorata complex with a similar colour pattern ( Oedura bella and Oedura marmorata ) from northern Australia by having white bands (versus yellow; Fig. 3 ).

Of the other species that are more phylogenetically divergent and geographically distant, Oedura nesos sp. nov. differs from Oedura cincta De Vis, 1888 , Oedura fimbria Oliver & Doughty, 2016 , and Oedura luritja Oliver & McDonald, 2016 (three arid-zone taxa also formerly included in Oedura marmorata ) in its smaller size (SVL 70–85 mm versus 78–108 mm O. cincta , 71–104 mm O. fimbria , 85–99 mm O. luritja ), and shorter tail (original tail TL/ SVL 0.52–0.62 versus 0.61–0.87) which is also distinctly flattened in cross section (versus rounded).

Oedura nesos sp. nov. differs from the three Oedura endemic to the Kimberley region of north-western Australia as follows: from Oedura gracilis King, 1984 by its short and transversely flattened tail (versus very long tail that approaches length of body) and higher number of paired lamellae on the digits (more than 4 versus less than 4) arranged in slightly flared series (versus tapering); and from both Oedura filicipoda King, 1984 and Oedura murrumanu Oliver, Laver, Melville & Doughty, 2014 in its smaller size (max SVL 85 mm versus 100–110 mm), in having narrower proximal subapical lamellae on fingers 3–4 (not wider than the apical lamellae versus distinctly wider), and further differs from the former species in having a tail that is not wider than the head (versus wider).

Oedura nesos sp. nov. is distinguished from all nine remaining Oedura in eastern Australia by having 2 postcloacal spurs on at least one, and usually both sides, of the tail base (versus usually 1) and having a tail that is deeply depressed in cross-section (versus subcircular). Oedura nesos sp. nov. further differs from a subset of these nine eastern Australia Oedura species by having a dorsal colour pattern consisting of five distinct relatively straight edged whitish bands (versus pale v-shaped transverse bands in Oedura castelnaui Thominot, 1889 , distinct darkedged ocelli or transverse blotches of varying size in Oedura coggeri Bustard, 1966 , Oedura elegans Hoskin, 2019 , Oedura lineata Hoskin, 2019 , Oedura monilis De Vis, 1888 , Oedura picta Hoskin, 2019 , and Oedura tryoni De Vis, 1884 , or two pale bands across the nape and base of tail in Oedura jowalbinna Hoskin & Higgie, 2008 ). Oedura nesos sp. nov. further differs from the remaining eastern Australian taxon Oedura argentea Hoskin, Vanderduys & Zozaya, 2018 in having a dark blackish-brown iris in life (versus silvery).

Genetic differentiation. Estimates of pairwise interclade genetic distances between O. nesos sp. nov. and other members of the Oedura marmorata group from the Top End and Gulf regions range from 15–19% for mtDNA and 7–14% for UCEs, with both datasets finding the highest distances between this lineage and O. bella , and lower divergences with populations of Oedura marmorata . Phylogenetic analyses of the UCE dataset suggest that it is the sister lineage to Oedura marmorata from across the Top End region ( Fig. 1A ).

Distribution and habitat. Only known from Groote Eylandt, off the eastern coast of the Top End region of the Northern Territory ( Fig. 1B ). All specimens with associated data have been collected from sandstone and it appears to be endemic to these habitats ( Fig. 5 ). Despite significant survey effort across the island, it has not been observed or collected in open woodland habitats away from sandstone escarpment, nor observed on trees or woody debris in the vicinity of sandstone outcrops. When encountered, most geckoes were observed peering out from within crevices, potentially in ambush. Typically, shelter crevices were horizontal cracks in small boulders on bedrock. A number of geckoes were also observed foraging on open, vertical boulder faces on large, dissected sandstone pillars and outcrops. Foraging geckoes were not observed any higher than about two metres from the bedrock. Gecko species observed in sympatry include an undescribed Gehyra and Amalosia rhombifer (Gray) .

Suggested IUCN status. Oedura nesos sp. nov. appears to be restricted to sandstone outcrop habitats on Groote Eylandt. These habitats are only approximately 43, 919 ha (439 km 2) in extent; however, they are not under any foreseeable threat. Currently, manganese mining operations on Groote Eylandt do not pose a threat to Oedura nesos sp. nov. because manganese deposits are mostly found beneath flat, lateritic soils away from the sandstone escarpment. Where the species has been found it appears to be locally common. We therefore tentatively recommend that it be listed as Least Concern.

Etymology. Nesos (Greek) meaning island, in reference to the insular distribution of this species. Used as a noun in apposition.

Figures

FIGURE 1. A) Summary tree for species in the Oedura marmorata group from the Australian Monsoonal Tropics. Maximum likelihood tree derived from analyses of genomic dataset presented in Skipwith et al. (2019). B) Distribution data of the four recognised species in the Oedura marmorata complex in northern Australia. Species dots correspond to museum records.

FIGURE 2. Colour pattern variability and diagnostic features of O. nesos sp. nov., Groote Eylandt, Northern Territory in life: A) O. nesos sp. nov. paratype, adult with regenerated tail, NTM R38576, Groote Eylandt, Northern Territory; B) O. nesos sp. nov. paratype, subadult with original tail, NTM R38582, Groote Eylandt, Northern Territory; C) O. nesos sp. nov. uncollected specimen, subadult with original tail, Groote Eylandt, Northern Territory; D) O. nesos sp. nov. uncollected specimen, adult with regenerated tail, Groote Eylandt, Northern Territory; E) O. nesos sp. nov. uncollected specimen, showing yellowish-white supraoculars and incomplete canthal stripe, Groote Eylandt, Northern Territory; F) O. nesos sp. nov. uncollected specimen, dorsal view showing tail narrower than head, Groote Eylandt, Northern Territory. Photographs: A–B) G. Gillespie; C–F) C. Jolly.

FIGURE 3. Comparison of adult and juvenile species in the Oedura marmorata complex from the Top End, Northern Territory in life:A) adult O. nesos sp. nov. uncollected specimen, Groote Eylandt, Northern Territory; B) juvenile O. nesos sp. nov. uncollected specimen, Groote Eylandt, Northern Territory; C) adult O. bella sp. nov. uncollected specimen, Caranbirini Conservation Reserve, Northern Territory; D) juvenile O. bella sp. nov. uncollected specimen, Caranbirini Conservation Reserve, Northern Territory; E) adult O. marmorata, uncollected specimen, Wongalara Station, Northern Territory; F) juvenile uncollected specimen, Litchfield National Park, Northern Territory. Photographs: A–B) C. Jolly; C) J. Mulder; D) S. Nielsen; E) S. Zozaya; F) M. Clancy.

FIGURE 4. Comparison of genetically and geographically proximate species in the Oedura marmorata complex from eastern Northern Territory in preservation. All specimens held in the Museum andArt Gallery of the Northern Territory:A–D preserved material of Oedura nesos sp. nov., from Groote Eylandt, Northern Territory: A) NTM R38578 (holotype); B) NTM R7494 (paratype); C) NTM R7495 (paratype); D) NTM R7541 (paratype). E–H preserved material of Oedura bella from the Gulf Country, Northern Territory: E) NTM R37304; F) NTM R21288; G) NTM R37947; H) NTM R37983. I–L preserved material of geographically proximate Oedura marmorata from eastern and southern Arnhem Land, Northern Territory. I) NTM R36746; J) NTM R36801; K) NTM R19029; L) NTM R37370. Scale bar = 1 cm.

FIGURE 5. Sandstone escarpment habitat of Oedura nesos sp. nov. on Groote Eylandt, Northern Territory. Photograph: S. Cameron.