Litoria skeliphros, Oliver & Mcdonald & Dahl & Nagombi & Richards, 2024

Oliver, Paul M., Mcdonald, Peter J., Dahl, George, Nagombi, Elizah & Richards, Stephen J., 2024, A new species of treefrog (Litoria: Pelodryadidae) from the karstic South-fold Mountains of New Guinea, Zootaxa 5514 (6), pp. 559-576 : 561-570

Litoria skeliphros sp. nov.

urn:lsid:zoobank.org:act:05A6213D-7B3C-4F1E-A535-C28C4F43285A

Gigira Ridge Treefrog

Figs. 1–4 , 8

Holotype. SAMA R71746 (SJR15432), adult male with nuptial pads and well-developed testes, Gigira Ridge, Hela Province, Papua New Guinea (5.9191°S, 142.6949°E; 2,702 m a.s.l.), collected by Stephen Richards, George Dahl and Elizah Nagombi on 13 August 2019.

Paratype (n=1). SAMA R71747 (SJR15430), subadult female, collected less than 100 m from holotype (5.9184°S, 142.6953°E; 2,695 m a.s.l.) by same collectors on 11 August 2019 .

Diagnosis. Litoria skeliphros sp. nov. can be diagnosed from all other species in the family Pelodryadidae by the following combination of characters: pupil horizontal; size moderately large (male SVL up to at least 52.4 mm, female SVL up to at least 58.8 mm); canthus rostralis weakly defined, rounded in dorsal view; snout broadly rounded in dorsal view and slightly acuminate in lateral view; hands partially webbed on all digits; forelimbs long (FA/SVL 0.23–024) and thin (FAW/FA 0.27–0.28) with distinct dermal fold at corner of upper and lower forelimb; hindlimbs long (TL/SVL 0.60–061), very thin (SHW/TL 0.16–0.17), lacking prominent enlarged lateral or heel tubercles; thighs with long, thin, continuous medial strip of tuberculate skin on ventral surface that contrasts strongly with bordering regions of smooth skin; feet with webbing between all digits; dorsal colouration mottled green and brown on dorsal surfaces with extensive yellow spotting on lateral regions of torso; hidden surfaces of thighs and groin orange.

Description of holotype. Adult male with enlarged testes and very finely granular, translucent nuptial pads. Vocal slits absent. Habitus very slender ( Fig. 2 ), limbs long (TL/SVL 0.61), head narrow (HW/SVL 0.32). Snout protruding distinctly beyond tip of lower jaw, slightly acuminate in lateral view, broadly rounded in dorsal view. Canthus rostralis rounded, gently curved in dorsal view, rounded when viewed from front of frog, loreal region steeply sloping, slightly concave. Nostrils near top of snout, oriented laterally, visible in dorsal view. Vomeropalatines forming two prominent ridges midway between choanae, ridge on right with 11, ridge on left with five, small but distinct teeth. Tongue narrow, partially distorted during preservation. Eyes moderately sized (EYE/SVL 0.10), not protruding in dorsal view; pupil horizontal, pigmentation on nictitating membrane restricted to densely pigmented narrow band along dorsal edge and few scattered maculations elsewhere on membrane. Tympanum small (TYM/ SVL 0.042), less than half diameter of eye (TYM/EYE 0.43), annulus clearly defined except dorsal edge obscured by thick, slightly curved supratympanic ridge.

Skin on dorsal surfaces of torso and head smooth ( Fig. 1 ), on throat with few wrinkles but otherwise smooth, and on abdomen coarsely granular with granulations trending coarser towards lateral and anterior regions and finer towards midpoint and posterior regions. Forelimbs smooth on all surfaces, except for series of ventrolateral tubercles on distal edge of lower arm; a small but distinct dermal fold present at anterior edge of joint between upper and lower arm. Hindlimbs with skin smooth on all dorsal and lateral surfaces, and most ventral surfaces, with exception of distinctive and sharply contrasting coarsely granular region covering area around vent, on approximately basal third of thigh and extending in thin, curved medial strip almost to knee ( Fig. 2 ).

Forearms very long (FA/SVL 0.23), slender (FAW/SVL 0.61). Fingers very long; relative lengths 3>4>2>1, partially webbed ( Fig. 3A ): in vestigial strip between fingers 1–2; reaching just short of basal subarticular tubercle on fingers 2 and 3, then extending to base of disc as distinct flange along outer edge of finger 2; reaching midway between basal and distal subarticular tubercles on outside of finger 3, then continuing as narrow fold to base of disc; and to distal edge of distal subarticular tubercle on inside of finger 4 ( Fig. 3A ). Terminal discs prominently expanded (3FP/3FD 0.5) with circum-marginal grooves on all fingers. Subarticular tubercles on all digits moderately prominent, rounded; supernumerary tubercles present along basal phalanges; outer metacarpal tubercle nearly circular, indistinct, approximately same size as disc on finger 1, inner metacarpal tubercle more prominent, forming lunate lateral extension from base of finger 1 in both ventral and dorsal views. Nuptial rugosities on outer metacarpal tubercle nearly smooth, translucent ( Fig. 3C ).

Hindlimbs long (TL/SVL 0.61), very slender (SHW/SVL 0.10). Toes long; relative lengths 4>3=5>2>1, extensively webbed ( Fig. 3B ): web reaching approximately to basal subarticular tubercle on outside of toe 1 and inside of toe 2, to base of disc on outside of toe 2 and nearly to base of disc on both sides of toe 3; to distal edge of distal subarticular tubercle on both sides of toe 4 and to base of disc on inside of toe 5. Discs prominent (4TP/4TD 0.69) with circum-marginal grooves. Subarticular tubercles on all digits distinct, rounded; supernumerary tubercles present on basal phalanx of toes 3 and 4; inner metatarsal tubercle small, ovoid, outer metatarsal tubercle very small, round.

Colouration of holotype in preservative: Exposed dorsal surfaces of head, torso and limbs mottled with dark, medium and light blue, dark and light mottling more contrasting towards posterior regions of torso. Snout with prominent dark brown canthal blotch, with dorsal edge sharply defined along canthus rostralis, and ventral edge grading into mottled pattern along edge of upper jaw; prominent white patches present below eye and along posterior edge of upper jaw; supratympanic fold and nearby regions of tympanum dark brown. Lateral regions of torso dark brown with numerous white blotches. Ventral surfaces of head, torso and most of limbs, digits and webbing with buff base colouration, with dense areas of tiny brown maculations, giving an overall ‘dirty’ appearance especially on throat, torso posterior of forelimb insertion, lower limbs and digits. Right knee with prominent rounded off-white patch. Ventral surfaces of thighs with dense maculations restricted to rugose medial region that strongly contrasts against bordering plain buff regions along both anterior and posterior edges.

Colouration of holotype in life: Dorsal and upper lateral regions of head, torso and limbs light yellowish brown, densely mottled with dark brown and traces of green, especially towards lateral regions of body; canthal stripe dark-brown, upper lip with yellowish spotting along edge. Lower lateral surfaces of torso dark brown with extensive yellow mottling. Ventral surfaces of head, torso and portions of limbs buff with dense dark-brown maculations, giving an overall dirty appearance, overlain with small yellow spots or blotches scattered across lateral surfaces of anterior torso and posterior region of head. Hidden surfaces of thighs, groin, portions of upper arm and areas at base of webbing bright orange ( Figs. 3D–E ). Iris chestnut brown with extensive thin darker brown vermiculations, sclera blue.

Measurements of the holotype: SVL 52.4; HW 16.7; HL 17.2; FA 12.0, FAW3.2; TL 32.1; SHW 5.0; EYE 5.1; TYM 2.2; IN 6.2; EN 3.7; 3FD 3.4; 3FP 1.8; 4TD 2.8; 4TP 1.9.

Variation. Dimensions of the single subadult female paratype are as follows: SVL 58.8 ; HW 18.2; HL 17.2; FA 14.0, FAW3.9 ; TL 35.1; SHW 5.9 ; EYE 5.5 ; TYM 2.0; IN 6.5; EN 4.2; 3FD 3.8; 3FP 1.9; 4TD 3.2; 4TP 2.2.

In overall proportions the paratype is very similar to the holotype, sharing notably long, slender arms (FA/ SVL 0.24, FAW / SVL 0.65) and legs (TL/ SVL 0.60, TW / SVL 0.10). The tongue of the paratype is much larger and broader than that of the holotype.

The paratype has a dorsal pattern quite different to the holotype. In preservative dorsal surfaces of head, torso and limbs relatively plain dark blue, with no obvious areas of lighter patterning. In life dorsal regions of head, torso and upper limbs have dark-brown regions contrasting against areas mottled with green, brown and traces of yellow on snout, lateral and anterior regions of torso, and lower limbs ( Fig. 4A ). Ventral and lateral colouration and skin texture of paratype are very similar to holotype, including presence of contrasting smooth buff and rugose brown regions on ventral surfaces of femur, dark brown canthal stripe, yellowish spotting along edge of upper lip, and lateral surfaces of torso dark brown with extensive yellow spotting. Orange ventral colouration is more extensive than on holotype, extending across ventral surface of torso ( Fig. 4B ).

Distribution and ecological notes. Litoria skeliphros sp. nov. is only known from two specimens collected at 2,700 m a.s.l on the southern versant of Papua New Guinea’s Central Cordillera in Hela Province ( Fig. 5 ).

The habitat at the type locality is very wet and mossy upper montane forest on limestone basement ( Fig. 6 ). There are no surface streams or ponds in the vicinity of the type locality but lower on Gigira Ridge (~ 2,200 m a.s.l.) a small subterranean stream emerges from the limestone and remains on the surface for several metres before disappearing again.

The two type specimens were collected two days apart on vegetation less than two metres above the ground. The species was not seen at the type locality, or in nearby areas on Gigira Ridge, during six previous nights of surveys spanning four years. Extensive use of automated call recorders at the type locality and at other elevations along Gigira Ridge also failed to detect any frog calls that could be attributed to this species (Richards, Dahl, Nagombi, unpublished data). The frog community at the type locality is relatively depauperate, as is typical for high elevation sites elsewhere in New Guinea ( Dahl et al. 2023). It includes three direct-developing microhylids ( Callulops wihelmanus (Loveridge, 1948) , Choerophryne brevicrus (Günther & Richards, 2012) and Oreophryne notata Zweifel, 2003 ) that are all relatively common, and a montane pelodryadid species that occurs widely across the highlands of Papua New Guinea but has only been seen twice at Gigira Ridge ( Litoria becki (Loveridge, 1945)) .

Suggested IUCN conservation status. Litoria skeliphros sp. nov. occurs in an area that is difficult to access and unsuitable for large scale agriculture. However, the only known locality is near the highest elevation on Gigira Ridge and failure to detect this species at lower elevations on the ridge suggests potential vulnerability to climate change. It is also in a lineage of frogs that are stream breeders, and the lack of such habitats in the area raises the possibility that it may be dependent on localised and distinctive habitats for reproduction. This confluence of factors suggest that the species may have a restricted distribution, however this remains a hypothesis at this stage. Until the distribution, ecology and breeding requirements of this species are better known we suggest an IUCN conservation status of Data Deficient. Given the small known range of the species in a montane habitat, if the frog pathogen Batrachochytrium dendrobatidis is introduced to New Guinea, its status would likely have to be upgraded to Endangered or Critically Endangered ( Bower et al. 2017).

Comparisons with other species. Litoria skeliphros sp. nov. differs from most other species in the torrent-breeding clade of Litoria from New Guinea in the combination of its moderately large size (adult male SVL up to 52.4 mm, female up to at least 58.8 mm), hands partially webbed on all digits, hindlimbs lacking prominent enlarged lateral or heel tubercles, and snout rounded in dorsal view, but slightly acuminate in lateral view.

Litoria skeliphros sp. nov. shares the above characters with its close relative Litoria angiana , but when compared against geographically proximate populations differs in many proportions ( Fig. 7 ), including its slightly longer (FA/ SVL 0.23–0.24 versus 0.17–0.22) and more slender (FA/FAW 0.27–0.28 versus 0.34–0.50) forearms, and in also tending to have a narrower head (HW/SVL 0.31–0.32 versus 0.31–0.36) and thinner hindlimbs (SHW/TL 0.16–0.17 versus 0.16–0.23). Litoria skeliphros sp. nov. further differs from L. angiana by having a small but distinct dermal fold in the anterior junction of the upper and lower arm (versus fold indistinct or absent), and by having ventral surface of thighs with a long, thin and continuous medial region of tuberculate skin which contrasts strongly with bordering regions of smooth skin on either side (versus variable degree of tuberculation, but never with distinct and strongly contrasting tuberculate and smooth regions) ( Fig. 8 ). The colouration of Litoria angiana is extremely variable ( Fig. 9 ) making identification of diagnostic colour characters challenging, however available images suggest the new species further differs in having prominent orange areas on the groin and hidden areas of thighs (versus light blue or grey). The male holotype of L. skeliphros sp. nov. also has unpigmented nuptial pads, while most male L. angiana have pigmented pads. Variation of this character in L. angiana requires further examination to determine whether it is a useful diagnostic character for the new species.

Two other moderate-sized species in the torrent breeding clade of Litoria with somewhat rounded snouts also occur at high elevations (> 1,000 m. a.s.l.) in the Central Cordillera. L. skeliphros sp. nov. can be distinguished from them as follows: from Litoria bulmeri ( Tyler, 1968) by its larger size (male SVL 52.4 mm versus 34 mm), presence of webbing between fingers 3 and 4 (versus absent), and ventral surfaces of thighs with contrasting regions of smooth skin with sparse brown maculations and tuberculate skin with dense maculations (versus overall smooth and buff with brown mottling), and in lacking a prominent black lateral band extending from behind the eye to the thighs (versus present); and from Litoria micromembrana (Tyler, 1963) by its larger size (male SVL 52.4 mm versus 36 mm), possession of extensive webbing between the fingers (versus absent), lateral regions of torso with prominent yellow spotting in life (versus mottled with varying shades of brown), and ventral surfaces of thighs with contrasting regions of smooth skin with sparse brown maculations and tuberculate skin with dense brown maculations (versus smooth, with base buff colouration and darker brown mottling).

Etymology. Skeliphros is ancient Greek for skeleton and is an allusion to the slender build and limbs of the new species. Used as a noun in apposition.

Molecular differentiation. Genetic divergences (p-distances) between Litoria skeliphros sp. nov. and L. angiana were between 0.10–0.11 (based on comparisons of 786bp of mitochondrial ND4 gene data) and maximum likelihood analyses strongly support a sister taxon relationship between these two species ( Fig. 10 ). Samples ascribed to L. angiana from as far west as the Hindenburg Range and east to the Huon Peninsula formed a more shallowly divergent and strongly supported clade exclusive of L. skeliphros sp. nov. (maximum p-distances 0.074).

Figures

FIGURE 1. Holotype of Litoria skeliphros sp. nov. (SAMA R71746) from Gigira Ridge, Hela Province, Papua New Guinea in A) lateral and B) frontal views. Photographs by S. Richards.

FIGURE 2. Dorsal (A) and ventral (B) views of preserved holotype of Litoria skeliphros sp. nov. (SAMA R71746). Scale bar = 10 mm. Note long slender limbs and contrasting smooth and tuberculate regions on ventral surfaces of upper hindlimbs.

FIGURE 3. Details of holotype of Litoria skeliphros sp. nov. (SAMA R71746) in life:A) ventral view of right hand; B) ventral view of right foot; C) details of unpigmented nuptial pad; D) hidden surfaces of anterior thighs and groin showing distinctive orange colouration; and E) posterior surfaces of thighs showing same orange colouration. Photographs by S. Richards.

FIGURE 4. Female paratype of Litoria skeliphros sp. nov. in life showing: A) dorsolateral colouration; and B) ventral colouration. Photographs by S. Richards.

FIGURE 5. Distribution of Litoria skeliphros sp. nov. (red star) and its sister taxon L. angiana (black circles). Distributional records for L. angiana compiled from Vertnet, iNaturalist and S. Richards personal records.

FIGURE 6. Upper montane forest habitat of Litoria skeliphros sp. nov. on Gigira Ridge at around 2,700 m a.s.l. in Hela Province, Papua New Guinea: A) view of canopy from above; and B) internal view of very wet mossy forest. Photographs by S. Richards.

FIGURE 7. Summary boxplots of meristic ratios for Litoria skeliphros sp.nov. and its sister taxon L.angiana.Key abbreviations are as follows: SVL—Snout to vent length; TL—tibia length; SHW—shank width; FA—forearm length; FAW—forearm width; HW—head width; HL—head length; and eye—eye diameter. Note that the hindlimbs and especially forearms of Litoria skeliphros sp. nov. are consistently longer and narrower than those of Litoria angiana.

FIGURE 8. Dorsal (A) and ventral (B) comparisons of preserved paratype of Litoria skeliphros sp. nov. and specimens of Litoria angiana. Note much more slender build of the new species and presence of contrasting smooth and tuberculate areas on the thighs.

FIGURE 9. Colour variation in Litoria angiana, the sister taxon to Litoria skeliphros sp. nov.Litoria angiana is highly variable, but lacks orange in the groin and hidden areas of thighs and has a much more robust build. All photographs by S. Richards.

FIGURE 10. Maximum-Likelihood phylogeny for the torrent-breeding Litoria of New Guinea and selected outgroups estimated from a ~700 base pair region the ND4 gene. Note that samples of Litoria angiana from both east (Chimbu and Madang Provinces) and west (Western Province) of the type locality of L. skeliphros sp. nov. are closely related to each other and genetically divergent from L. skeliphros sp. nov.