Gehyra rohan, Oliver, Paul M., Clegg, Jonathan R., Fisher, Robert N., Richards, Stephen J., Taylor, Peter N. & Jocque, Merlijn M. T., 2016

Oliver, Paul M., Clegg, Jonathan R., Fisher, Robert N., Richards, Stephen J., Taylor, Peter N. & Jocque, Merlijn M. T., 2016, A new biogeographically disjunct giant gecko (Gehyra: Gekkonidae: Reptilia) from the East Melanesian Islands, Zootaxa 4208 (1), pp. 61-76 : 65-71

Gehyra rohan sp. nov.

Figs 2–5

Holotype. RBINS 2684 (Field No. PNG 14-88 ), adult male, near Lorengau , Manus Island, Papua New Guinea (2.0388S, 147.2371E), collected 3 December 2014 by J. R. Clegg, P. N.Taylor and M. M. T. Jocque.

Paratypes. AMS R129497 – 129498, adult females, Lombrum, Los Negros Island, Admiralty Islands , Papua New Guinea (2.01S, 147. 42E), collected 15 December 1951 by N. C. Goddard ; CAS 252881 , adult female, south bank of Lorengau River, 2.5 km southwest of Lorengau , Manus Island , Papua New Guinea (2.0415S, 147.2594E), collected 30 May 2010 by R. Fisher ; PNGNM 25220 ( PNG 14-158 ), adult female, Yiringou Village , Manus Island , Papua New Guinea (2.0833S, 147.1167E), collected 9 December 2014 by J. R. Clegg, P. N. Taylor and M. M. T. Jocque) ; RBINS 2685 ( PNG 14-157 ), adult male, Yiringou Village , Manus Island , Papua New Guinea (2.0833S, 147.1167E), collected 9 December 2014 by J. R. Clegg, P. N. Taylor and M. M. T. Jocque ; SAMA R69881 (SJR15105), adult male, near Nae , Mussau Island , Papua New Guinea (1.524S, 149.739E), collected 18 October 2015 by K. Aplin.

Diagnosis. Gehyra rohan sp. nov. is distinguished from other Gehyra species by the following suite of characters: very large size (adult SVL 130–150 mm), large head (HW/SVL 0.18–0.22, HD/SVL 0.11–0.14), prominent skinfolds on the anterior forelimbs and posterior hind limbs, weak lateral fold, heterogeneous dorsal scalation consisting of large rounded scales bordered by numerous much smaller rounded or triangular scales, massive digital discs with high number of wide undivided subdigital lamellae (finger IV 23–25, toe IV 22–26) that are not deeply notched or divided, rostral with near horizontal dorsal edge and not deeply notched, precloacal and femoral pores in a moderately long single continuous chevron of up to at least 40 pores, original tail without lateral serrations, slightly compressed and with a prominent medial row of enlarged subcaudals, and a prominent ring of orange scales around the eye in life.

Description of holotype. Adult male. Habitus, large (SVL 140.3 mm) and robust ( Fig. 2 ). Head triangular, robust (HW/HL 0.87), moderately long (HL/SVL = 0.23) and deep (HD/HL = 0.47). Snout long and robust (EN/ HL = 0.35). Rostral large, broadly rectangular with rounded corners, rostral groove descends approximately 35% of rostral height, bifurcates, and extends to almost contact both nares ( Fig. 3 ). Supranasals ovoid but with distinct points at ventrolateral edges, separated by three much smaller asymmetrical (becoming smaller from right to left) squarish internasals in a transverse series. Nares bordered by rostral, first supralabial, one large supranasal and three or four postnasals. Supralabials large and squarish with rounded dorsal edges, total number to inflexion of mouth 14 (left) and 13 (right), and total number to midpoint of eye 11 (both sides). Supralabials bordered dorsally by 2–3 rows of enlarged scales. Infralabials large and squarish, total number to rictus of jaw 14 on both sides. Mental triangular, bordered by two infralabials and two large rounded postmentals ( Fig. 3 ). Scales on dorsal surface of head tiny, irregular and slightly conical, becoming larger and flatter laterally and anteriorly. Superciliaries forming a brillar fold of small spiniform scales extending along the dorsal border of the orbit from anteroventral to posterodorsal corners. Pupil partially dilated, somewhat elliptical with limited crenulations.

Body robust (TrK/SVL 0.50). Dorsal and lateral scales distinctly heterogeneous in both shape and size, generally consisting of irregularly arranged large rounded scales, bordered by numerous much smaller rounded or triangular scales, often forming a ‘Star of David’ pattern; scales on nape much smaller than those on snout and torso. Ventral scales imbricate, arranged more regularly than those on dorsum, larger towards middle and posterior of venter, and tiny and granular on throat. Skin along ventrolateral edge of body loose and forming a weak fold along axilla-groin interval ( Fig. 4 ). Precloacal and femoral pores (n = 40) arranged in a single recurved series terminating halfway along each femur. Hemipenal bulge present, moderately pronounced.

Limbs robust and fleshy, with prominent lateral folds along anterior and posterior edge of forelimb, posterior edge of hindlimb, and less prominently on anterior edge of hindlimb ( Fig. 4 ). Digits on both the fore- and hind limbs with prominent and expanded pads; terminal phalanges free and with well developed claws on all digits except finger I and toe I. Subdigital lamellae undivided, wide under expanded portion of disk, tapering and becoming narrower than toe proximal to the expanded disc ( Fig. 3 ); total lamellar counts for all digits as follows (left/right): fingers I = 23/23, II = 24/25, III = 26/26, IV = 30/31, V = 27/26; toes I = 21/19, II = 24/26, III = 28/28, IV = 32/27, V = 24/22; total number of lamellae under expanded portion of the disk (left/right): fingers I = 22/21, II = 18/21, III = 19/19, IV = 21/24, V = 21/22; toes I = 21/19, II = 20/21, III = 22/23, IV = 23/23, V = 23/22. Webbing extending to base of disc on all digits, folded in preservative.

Tail original, thin and short (107.8 mm in length) with blunt tip, much narrower than body at base; dorsal and lateral caudal scales granular and arranged irregularly, similar to dorsal scales on body; subcaudal scales distinctly enlarged, rounded, with a single medial row of 54 dilated (0.35–0.50 width of tail) ovoid scales extending full length of tail.

Coloration in preservative. Dorsal and lateral surfaces grey with an indistinct chestnut wash and scattered darker grey maculations, generally corresponding to a single scale. Dorsal surfaces of limbs with coloration similar to dorsum of body, becoming distinctly darker distally and on posterior skinfolds of hindlimbs. Ventral surfaces of body, limbs and tail predominantly plain light tan. Paired pinkish-brown regions on anterior lateral edges of throat, and also forming two series of faint bars extending along lateral edges of venter, from posterior edge of insertion of the forelimbs to anterior edge of insertion of hindlimbs. Subdigital lamellae under expanded discs of all digits beige proximally, tending distinctly darker greyish-brown distally. Tail coloration as for body, but with more dense dark grey maculations on dorsal surfaces.

Coloration in life. When initially captured: dorsal and lateral surfaces of head, body, limbs and tail dark chestnut brown mottled with patches of orange, light brown and off white, and with extensive black maculations, especially towards posterior region of dorsum and tail ( Fig. 4 ). After capture: base dorsal color faded towards greyish but with same basic pattern ( Fig. 4 ). Ventral surfaces of torso and limbs yellow, brightest anteriorly, undersurface of head brownish and digits white, transition between white of digits and yellow coloration of limbs relatively sharply defined, throat and torso both with regions of diffuse brown barring. Ventral surface of tail yellowish white with extensive dark-brown flecks. Scales around orbit forming a distinct orange ring, larger spiniform superciliary scales around dorsal edge bright reddish orange, grading to paler orange on smaller scales around ventral edge of eye.

Details of holotype. Measurements (in mm): SVL 140.3; TL 107.8; TrK 69.8; HW 27.5; HL 31.6; HD 14.8; EN 11; EYE 6.5; IORB 12.4; POM 3.4; FA 16.9; CS 18.8. Meristic data: IN 3; SUPR 14; INFR 14; LAMF4 23; LAMT4 25; POR 40.

Variation. Summary meristic values for all adults (2 males, 4 females) in the type series are as follows (mean, with the range in parentheses): SVL 138.4 (131.1–150.0); TL 107.2 (93.0–141.0); TrK 64.9 (58.0–72.6); HW 26.9 (24.5–29.8); HL 32.0 (30.2–35.0); HD 16.3 (14.8–18.80); EN 11.5 (10.9–13.2); EYE 7.6 (6.5–9.6); IORB 12.5 (11.4 –13.7); POM 3.4 (3.0–3.8); FA 16.5 (15.5 –17.3); CS 20.0 (17.7 –22.7). Summary scalation information for these same 6 individuals are as follows: SUPR (to midpoint of eye) 10.5 (9–11); SUPR (rictus of mouth) 13.9 (12– 14); INFR 12.7(11–14); LAMF4 22.9 (21–25); LAMT4 24.1 (22–26); POR 36.5 (33–40).

The single male paratype SAMA R69881 (SJR15105) ( Fig. 5 ) has a presumed developmental anomaly in which the pore-bearing and surrounding large scales have been shifted to the left, such that the right end of the pore series starts in the precloacal region, and extends almost fully along the left tibia, while the ventral scales on the right tibia are heterogeneous and do not appear to have formed properly. This specimen has two large, welldeveloped testes and in other respects appears to be a normal adult male.

All adult specimens are similar to the holotype and share the key diagnostic traits including a bright orange ring extending around the eye, wide subcaudals under the original tail and prominent skinfolds on the arms and legs, although the prominence of the latter character varies with the angle of limb preservation. Smaller specimens tend to have a plainer ventral coloration and less obvious brown barring and mottling on the throat and ventrum in preservative, suggesting that this pattern is most pronounced in adult specimens. The largest specimens in the type series are all female (max SVL 150 versus maximum of 140 mm for the males), raising the possibility that the species is sexually dimorphic like several other Pacific Gehyra ( Zug 2013) , but given the very small number of males, more material is needed to confirm this.

Based on photographs and field notes the dorsal coloration in life varies from quite dark chestnut brown to light grey, and the pattern of extensive but indistinct orange, greyish and brown mottling also varies in intensity. However much of this variation appears to be temporal, and single specimens vary extensively in appearance over short timescales (several hours) ( Fig. 4 ).

Comparisons. Only four other species of Gehyra approach the large size (adult SVL consistently> 120 mm) of Gehyra rohan sp. nov.: G. georgepottshaasti ( Vanuatu) , Gehyra marginata Boulenger, 1887 (Maluku) , G. membranacruralis ( Papua New Guinea) and G. vorax ( Fiji) . Based on published descriptions ( Flecks et al. 2012) and field observations (RNF, SJR and Fred Kraus pers. com.) these taxa all lack a complete, bright orange ring around the eye in life, although occasional specimens of Gehyra vorax do have a yellow contour (as opposed to orange) around the dorsal edge of the eye (RNF pers. obs., for an example see page 172 in Ryan 1998). Gehyra rohan sp. nov. further differs from Gehyra marginata in having enlarged subcaudals under the original tail (versus absent), in having a chestnut brown iris (versus light green), and in having a less prominent ventrolateral dermal fringe on the body; from G. georgepottshaasti in having rounded postmentals (versus distinctly elongate) ( Flecks et al. 2012); from Gehyra vorax in having a lower number of femoral pores in adult males (up to 40 versus 58–90) ( Beckon 1992); and from Gehyra membranacruralis by its heterogeneous dorsal scalation consisting of large rounded scales separated by numerous much smaller rounded or triangular scales (versus large rounded scales only), and by having larger enlarged subcaudals (maximum anteroposterior length on adults> 2.5 mm versus <2.5 mm).

All other Gehyra are consistently smaller than Gehyra rohan sp. nov. Gehyra baliola ( Duméril, 1851) and Gehyra barea Kopstein, 1926 from New Guinea and surrounding islands are moderately large (max SVL up to at least 105 mm), but Gehyra rohan sp. nov. can be readily distinguished from these taxa by the presence of prominent popliteal folds on the forelimbs (versus not prominent), a rostral that is not or barely notched, and low number of large internasals (versus rostral deeply notched (u-shaped) with a moderate to high number of very small granular internasals). Gehyra serraticauda Skipwith & Oliver 2014 is also large (potentially up to 120 mm SVL), but can be distinguished by the same characters as the preceding two species, in addition to having well-developed tail serrations (Skipwith & Oliver 2014).

The only congener recorded from Manus and Mussau is the widespread taxon Gehyra oceanica , from which Gehyra rohan sp. nov. is readily differentiated by its much larger adult size (> 100 mm versus <100 mm), having enlarged subcaudals (versus absent), prominent popliteal skinfolds (versus absent), and distinctive orange ring around the eye in life (versus absent). The Gehyra insulensis / mutilata complex is also widespread in the Pacific, but Gehyra rohan sp. nov. is easily distinguished from this species complex by its much larger size (max SVL> 100 versus <65 mm), and the absence of minute serrations along the lateral edges of the original tail (versus present).

Distribution and ecology. Gehyra rohan sp. nov. is recorded from several localities across Manus Island. While most type material is from the east, one author (SJR) observed a very large Gehyra that is most likely this species at in lowland rainforest at Yeri River (2.001S, 146.819E) in north-western Manus ( Fig. 6 ). Older material has also been collected from nearby Los Negros Island (see paratypes). This species has also been recorded from a single site on Mussau Island. The extent of its distribution, if any, beyond these islands remains unknown. Beckon (1992) reported a large Gehyra supposedly from Nauna Island near Manus (UPNG 5772), but noted that as it was collected from a banana box so its ultimate provenance was uncertain. Based on morphology, especially its high number of pores (62) Beckon further suggested that this animal is consistent with specimens from Fiji. Given uncertainty about provenance and morphology at this stage do not consider this a confirmed record of Gehyra rohan sp. nov.

Gehyra rohan sp. nov. appears to be largely arboreal and is generally found in primary or disturbed lowland tropical rainforest ( Fig. 6 ) on the trunks of large trees. It is also found on around human habitation in forested areas. Three of the authors (MJ, JRC, PT) found it to be reasonably common around Yiringou village in the interior of Manus, and two specimens were found on the same night on wooden beams below houses. The holotype was found running across a road in forest at night. The specimen from Mussau was found in a cave in disturbed forest close to the coast.

One paratype (CAS 252881), from forest on the bluffs above the Lorengau River, that was initially ~6 meters high on the trunk of a tree, “glided” approximately 3 meters to an adjacent tree trunk when disturbed. Similar gliding or parachuting behavior has been observed in Gehyra mutilata ( Heyer & Pongsapipatana 1970) , and in numerous other genera of arboreal lizards, including many that lack obvious adaptations for gliding ( McGuire & Dudley 2011).

Eytmology. Rohan is the Sohoniliu Village (Nali language) ‘tok ples’ (local language) name for this gecko. The community of Sohoniliu Village requested that this name be used for the formal description of this species, and we thank them for their support of this work.

Figures

FIGURE 2. Preserved holotype of Gehyra rohan sp. nov. (RBINS 2684): A) dorsal view; and B) ventral view. Scale bar = 20 mm. Note diagnostic skin folds on the fore and hindlimbs, and widened subcudal scale row.

FIGURE 3. Details of holotype of Gehyra rohan sp. nov. (RBINS 2684): A) rostral configuration, scale = 5 mm; B) mental configuration, scale = 5 mm; C) subdigital lamellae hand, scale = 10 mm; and D) subdigital lamellae feet, scale = 10 mm.

FIGURE 4. Details of coloration on holotype Gehyra rohan sp. nov. (RBINS 2684): A) dorsum; B) venter; C) lateral view of head at time of capture; and D) lateral view of head after capture. All photographs by M. M. T. Jocque.

FIGURE 5. Gehyra rohan sp. nov. in life: A) holotype, RBINS 2684, near Lorengau Village, Manus Island, Papua New Guinea; and B) SAMA R 69881 (SJR 15105) near Nae, Mussau Island, Papua New Guinea. Photographs by M. M. T. Jocque and S. Venter.

FIGURE 6. Lowland Tropical Rainforest around the Yeri River in north-west Manus Island. A single specimen of Gehyra rohan sp. nov. was observed, but not collected on the trunk of a large tree partially obscured by vegetation on the left hand side of this photo. Photograph S. Richards.