Litoria pterodactyla, Oliver & Richards & Donnellan, 2019

Oliver, Paul M., Richards, Stephen J. & Donnellan, Stephen C., 2019, Two new species of treefrog (Pelodrydidae: Litoria) from southern New Guinea elucidated by DNA barcoding, Zootaxa 4609 (3), pp. 469-484 : 470-473

Litoria pterodactyla sp. nov.

Pale-eyed parachuting treefrog

Figs. 1–2

Holotype. SAMA R65030 (Field number SJR 10954), adult male, Muller Range , Gugusu Camp, Western Province, Papua New Guinea (5.729°S, 142.263°E; 515 m a.s.l.), collected by Stephen Richards and Chris Dahl on 7 September 2009.

Diagnosis. Distinguished from all other Litoria by the following combination of characters: moderately large size (SVL of male holotype 62 mm); plain green dorsum; no enlarged parotoid glands; finger webbing extending to at least base of penultimate phalanx on all fingers; toe webbing extending to base of discs on all toes; iris in life predominantly pale whitish grey with light brownish outer edge and faint brown vermiculations; dorsal portion of lower eyelid unpigmented except for thin band along dorsal-most edge; white labial stripe not extending beyond posterior edge of lower jaw; lateral surfaces of torso and ventral surfaces of limbs and webbing light purplish-blue in life; and undivided, elongate nuptial pads extending approximately half length of finger I, distal half broad (approximately equal in height to minimum width of phalanx of finger I), proximal half narrow (approximately one third height of minimum width of phalanx of finger I).

Description of holotype. Adult male with vocal slits and pale brown nuptial pads. Body moderately robust, limbs long (TL/SVL 0.55), head wide (HW/SVL 0.36) and approximately equal to width of body in dorsal aspect ( Fig. 1 ). Snout truncate with rounded edges in dorsal and lateral views; canthus rostralis rounded, curved; loreal region shallowly concave. Nares round, closer to tip of snout than to eye, oriented laterally, close to top of snout, barely visible in dorsal aspect. Eyes large (EYE/SVL 0.11), clearly protruding in both dorsal and lateral aspects; pupil horizontal. Upper jaw protruding beyond lower jaw. Tympanum moderately large (EAR/SVL 0.074), bordered dorsally by a fleshy supratympanic fold extending to superior edge of upper arm insertion. Choanae large, circular; vomeropalatines prominent, positioned between anterior edges of choanae; tongue fleshy and ovoid, not free posteriorly, with broad, shallow notch in posterior edge. Vocal slits long, located laterally on floor of mouth. Dorsally, skin on torso, head and limbs mostly smooth with limited shallow creasing on scapular region. Laterally, skin of torso coarsely granular. Ventrally, skin of torso and thigh more moderately granular, posterior half of throat wrinkled and granular, remaining ventral surfaces smooth. Prominent dermal ridges along posterior edge of forearms, and along shanks, ankles and extending to toe V.

Fingers with relative lengths III>IV>II>I; fleshy opaque webbing between all digits; extending to base of penultimate phalanx between I and II, to disc on distal edge of II and proximal edge of IV, and to penultimate phalanx on both sides of III. Terminal discs expanded (3FD/SVL 0.052) and with distinct marginal grooves. Nuptial excrescences brown distally, tending towards unpigmented proximally, extending in a continuous patch along approximately half length of finger I, with distal half approximately equal in height to minimum width of finger I and proximal half approximately one third as high as finger I. Single unpigmented subarticular tubercle present at base of each penultimate phalanx, rounded on fingers I–III, bifid on IV; a series of additional indistinct unpigmented subarticular tubercles present on fingers III–IV; single indistinct, oval, proximal metacarpal tubercle present at base of I and smaller and very indistinct metacarpal tubercle at base of IV.

Relative lengths of toes IV>V>III>II>I. All toes with extensive fleshy opaque webbing extending to base of ultimate phalanges (discs). Terminal discs expanded (4TD/SVL 0.061), with distinct marginal grooves. Unpigmented bifid subarticular tubercles at proximal edge of all discs, additional single rounded tubercles under interphalangeal joints on I and II, and numerous (7–9) rounded tubercles extending length of III–V but concentrated proximally. Small, indistinct, unpigmented metatarsal tubercle at base of I.

In preservative, most dorsal and upper lateral surfaces, including torso, head, forearms, shanks, finger IV and toes IV–V bluish-green mottled with smaller regions of blue ( Fig. 1 ); surfaces with different colouration are thighs (predominantly blue dorsally), fingers I–II and associated webbing (unpigmented dorsally), remaining digits and webbing (extensive and dense purplish-blue maculations) and tympanic membrane (with U-shaped sparsely pigmented region). Off-white stripes along edge of lower jaw and along posterior dermal ridge of forearms and ankles. Lower lateral surfaces of torso and thigh purplish-blue. Ventral surfaces largely off-white and unpatterned, with exception of purplish-blue webbing between all digits except fingers I–II ( Fig. 1 ).

Summary meristic data for holotype. All measurements in mm: SVL 62.0; TL 34.0; HW 22.3; HL 20.5; EYE 6.8 ; TYM 4.6 ; IN 5.1; EN 6.7; 3FD 3.2; 3FP 2.9; 4TD 3.3; 4TP 3.0.

Colour in life. Dorsal and upper-lateral surfaces of torso and head, and upper surfaces of limbs and outer digits plain leaf green without any pattern; tympanic membrane with a distinct unpigmented U-shaped region; mid-lateral surfaces of torso tending towards sky blue; lower-lateral surfaces of torso, inner surfaces of limbs, throat, webbing and inner digits purplish-blue; belly cream. Prominent dermal ridges on the lower lip and posterior edges of forearm and hindlimb off-white. Iris predominately off-white with faint brown vermiculations that become denser towards the outer edges, giving the appearance of brownish outer rim ( Fig. 2 A–B).

Comparisons. Litoria pterodactyla sp. nov. differs from the five other large (adult male SVL> 55 mm), predominantly green, tree frogs from the southern side of New Guinea’s Central Cordillera as follows: from L. infrafrenata by its smaller adult size (adult male SVL 62 mm vs 105 mm), webbing on fingers extending beyond the proximal edge of the penultimate phalanx on all digits (vs at most extending to the base on the penultimate phalanx), and white labial stripe not extending beyond the posterior edge of the lower jaw (vs extending posterior to the tympanum); from L. sanguinolenta by its larger size (male SVL 62 mm vs 55 mm), bluish latero-ventral pigmentation (vs white and orange) and webbing on fingers extending to at least the base of the penultimate phalanx on all digits (vs at most extending to the base on the penultimate phalanx); from L. pallidofemora ( Fig. 2C ) by its smaller size (male SVL up to 62 mm vs 80 mm), light purplish-blue lateral venter, undersurface of limbs and webbing (vs bright yellow), light brownish and thinly patterned outer rim of iris (vs largely black); and from L. sauroni ( Fig. 2D ) in having an iris without red pigmentation (vs red-and black-vermiculations), in lacking pigment flecks across the lower eyelid (vs present), and in having elongate nuptial pads (vs small and round) (see Fig. 2 ).

Litoria pterodactyla sp. nov. differs from the other three (allopatric) members of the Litoria graminea complex in New Guinea as follows; from L. graminea in its bluish ventral colouration (vs orange or yellow), absence of deep skin creases extending to the shoulder (vs often present), predominately white iris (vs white and reddish), and elongate nuptial pad (vs small and rounded); from L. huntorum by its predominantly white iris (vs white and reddish), slightly larger size (62 vs 53–60 mm), purplish-blue lateral edges of venter and webbing (vs orange) and white labial stripe not extending beyond the rictus (vs extending to below the tympanum); and from L. nullicedens by its smaller size (SVL 62 vs 75 mm), elongate nuptial pads (vs round and small); weak white labial stripe (vs absent); iris predominately white (vs reticulated black and dark brown); nictitating membrane with a dorsal pigment band only (vs with a dark marginal band and heavily reticulated with pigment); and sides, abdomen, and webbing of hands and feet purplish-blue (vs bright orange-red).

Distribution and ecology. Known only from the southern slopes of the Muller Range in Western Province, Papua New Guinea ( Fig. 3 ). Most species of frog in the Litoria graminea complex are very rarely collected, and apparently similar hill forest occurs over large areas of southern New Guinea, so it seems probable that this species ranges more widely. The holotype was collected in undisturbed primary hill forest at 515 m a.s.l. ( Fig. 4 ), from high in a tree where it was calling at night. Nothing further is known about its ecology. Based on its extensive finger and toe webbing and canopy habitat we predict that, like at least some other members of the Litoria graminea complex, it is capable of parachuting (Tyler 1978, Kraus 2018).

IUCN Status. Although Litoria pterodactyla sp. nov. is known only from a single specimen, the type locality is located in a region where extensive suitable habitat occurs and, given the absence of major biogeographic barriers, it probably has a broad distribution in southern Papua New Guinea. However until this species’ distribution has been better documented we recommend that it be listed as Data Deficient .

Molecular differentiation. Genetic divergences (p-distances) between Litoria pterodactyla sp. nov. and three other recognised species of the Litoria graminea complex ( L. graminea , L. huntorum , and L. sauroni ) were between 0.23–0.24 (based on comparisons of approximately 700bp of mitochondrial ND4 gene data). Our molecular data also revealed a divergence of 0.21 between L. graminea (as defined by Kraus (2018)) and topotypic L. dux , suggesting that the Huon Peninsula population of large green treefrogs synonymised with L. graminea by Kraus (2018) represents a valid species which can be distinguished from L. pterodactyla most easily by its red and white iris colouration and round nuptial pad. The status of other populations of large green Litoria from northern New Guinea that were synonymised with graminea by Kraus (2018) requires further study.

Etymology. Pterodactyla: Latin, meaning winged-finger, in reference to the extensive finger webbing of this species.

Remarks. The Litoria graminea complex has proven to be a taxonomically challenging lineage. They call from high in the canopy so they are relatively difficult to collect and specimens are rare in collections. There are few morphological characters to distinguish among species, information about calls is scarce, and some key characters are most clearly apparent in live specimens ( Kraus 2018). With the description of Litoria pterodactyla sp. nov. the number of species in this group reaches seven (we consider L. dux to be valid – see above), of which three occur south of the Central Cordillera between Gulf and Western Provinces of Papua New Guinea. At least two of these species ( L. pallidofemora and L. sauroni ) occur in sympatry ( Kraus 2018, SJR pers. obs.), and there are no obvious geographic barriers between these two species and Litoria pterodactyla sp. nov., so it is reasonable to hypothesise that all three species may occur in sympatry. If this is the case it will further complicate identification of these species in the field because they are most commonly heard calling from the canopy, their calls are poorly documented, and frogs are rarely sighted. A better understanding of call structure and variation within and between species in the Litoria graminea complex will be crucial for improving our knowledge about the distributions of species in this complex of frogs.

Figures

FIGURE 1. Holotype of Litoria pterodactyla sp. nov. SAMA R65030 in preservative. Scale bar 10 mm.

FIGURE 2. Images in life of three species in the Litoria graminea complex occurring along the southern side of the New Guinean Central Cordillera; a–b) Litoria pterodactyla sp. nov. holotype SAMA R65030, Muller Range, Western Province, c) Litoria pallidofemora SAMA R71201 upper Fly River region, Western Province, and d) Litoria sauroni SAMA R60727 (holotype), Darai Plateau, Gulf Province. Note differences in eye and lateral colouration. All photographs by S. Richards.

FIGURE 3. Distribution of Litoria pterodactyla sp. nov. and other species in the Litoria graminea species group in Papua New Guinea. On the basis of genetic distinctiveness (see text) topotypic Litoria dux is here considered to represent a distinct species; however, correct assignation of some specimens from across northeastern New Guinea will require further work.

FIGURE 4. Hill-forest habitat of Litoria pterodactyla sp. nov. at Gugusu Camp, 515 m a.s.l., Muller Range, Western Province, Papua New Guinea. Photograph by S. Richards.