Litoria azuroscelis, Günther & Richards & Hamidy & Trilaksono & Sulaeman & Oliver, 2023

Günther, Rainer, Richards, Stephen J., Hamidy, Amir, Trilaksono, Wahyu, Sulaeman, Taufan N. & Oliver, Paul M., 2023, A new large green treefrog (Litoria: Pelodryadidae) from western New Guinea, with the description of a new diagnostic character for the Litoria graminea group, Raffles Bulletin of Zoology 71, pp. 417-429 : 419-425

Litoria azuroscelis , new species

Azure-thighed Treefrog Katak-pohon paha-biru ( Figs 2F , 3 , 4 )

Holotype. MZB Amph. 32893 (former ZMB 70521 ). Adult male, most likely calling when collected, Wondiwoi Mountains at the base of the Wandammen Peninsula, Papua Barat Province, Indonesia, approximately 2.9559°S, 134.6318°E, 550 m a.s.l., 23 June 2003, collected by Rainer Günther and Genus Mareku.

Paratype. ZMB 70522 . Adult male, most likely calling when collected, with same locality and collector data as holotype .

Diagnosis. A treefrog that differs from other New Guinean Litoria in the following unique combination of characters: body large (adult male SVL to at least 66.6 mm) and robust; vomero-palatines large, prominently raised, each with ~6 small teeth; labial stripe narrow, white, not extending beyond rictus of jaw; dorsum in life predominantly or entirely dark green; enlarged parotoid glands absent; scapular region lacking deep skin creases; webbing on hands extending slightly beyond distal edge of subarticular tubercles at base of penultimate phalanges on inside of Finger 4 and outside of Finger 3; webbing on feet extending to discs on all toes except Toe 4, where it reaches to midway between disc and subarticular tubercle at base of penultimate phalanx; discs very wide (3FD/SVL 0.073 –0.074; 4TD/SVL 0.067 –0.069); nuptial pads elongate, broader anteriorly than posteriorly, comprised of distinct almost conical asperities; hidden surfaces of limbs purplish blue in life; iris reddish brown; upper half of nictitating membrane largely clear except for dark dorsal margin; and advertisement call consisting of a harsh note (= call) produced singly or more often in series of 2–7 calls with a mean repetition rate of 2.02 calls/s.

Description of holotype. Habitus robust ( Fig. 3 ), limbs moderately long (TL/SVL 0.55); snout broadly rounded in dorsal aspect, blunt, steeply sloping in lateral aspect. Canthus rostralis long, poorly defined, nearly straight ( Fig. 4A ); loreal region sloping, distinctly concave; nostrils near tip of snout, oriented laterally. Eyes moderate sized (EYE/SVL 0.110) ( Fig. 4B ), pigmentation on upper half of nictitating membrane restricted to narrow strip along dorsal edge. Tongue broad, covering most of mouth floor, with marginally indented posterior notch; vocal slits moderately long, lateral, extending ~ 4 mm anteriorly from level of angle of jaw; vocal sac single and subgular. Vomero-palatine ridges long (2 mm) prominently raised, each with six small teeth; ridges located midway between, and abutting medial edges of, internal nares, oriented postero-medially. Tympanum moderately large (TYM/SVL 0.072), annulus distinct except postero-dorsal edge obscured by thick, curved, postocular fold that extends from posterior edge of eye to above axillary junction. Skin finely but distinctly granular dorsally; lateral surfaces with large, flat tubercles; throat and abdomen coarsely granular.

Dermal ridges along posterior edge of forearms and along shanks and ankles prominent ( Fig. 3 ). Fingers short, terminal discs wide (3FD/SVL 0.074), with circum-marginal grooves; webbing reaches to slightly beyond distal edge of subarticular tubercles at base of penultimate phalanges on inside of Finger 4 and outside of Finger 3, to halfway between subarticular tubercles at base of penultimate and ultipenultimate phalanges on inside of Finger 3, to base of disc on outside of Finger 2, restricted to thin basal strip between Fingers 1 and 2 ( Fig. 4C ). Subarticular tubercles prominent, undivided. Relative lengths of fingers 3>4>2>1. Nuptial excrescences comprising dark-brown granules in an unbroken patch 3.5 and 3.7 mm long on each Finger 1, wider distally (2.0 mm) than proximally (1.1 mm) ( Fig. 2F ).

Toes moderately short, terminal discs wide (4TD/SVL 0.069) with circum-marginal grooves; webbing reaches discs on Toes 1–3 and 5, and to half-way between subarticular tubercle at base of penultimate tubercle and disc on Toe 4. Inner metatarsal tubercle and subarticular tubercles prominent. Relative lengths of toes 4>5>3>2>1.

In life, dorsal and upper-lateral surfaces of torso and head uniformly dark green; tympanic membrane with distinct unpigmented U-shaped region ( Fig. 3A ); exposed midlateral surfaces of torso fawn with green reticulations along skin creases; hidden surfaces of torso and inner surfaces of limbs purplish blue ( Fig. 3B ). Dorsal surfaces of digits and webbing fawn. Dermal ridges on posterior edges of forearm and hindlimb white. Labial stripe white, moderately distinct, extending to approximately level with posterior edge of eye. Iris reddish-brown. Skin above eye with very thin white band.

In preservative, most dorsal and upper lateral surfaces medium blue, including torso, head, outer forearms, shanks, and Toe 5 ( Fig. 4D ); tympanic membrane with broad U-shaped unpigmented mark; inner edge of forearm, digits and webbing buff. Lower lateral and ventral surfaces buff.

Summary meristic data. SVL 66.6; TL 36.8; HW 24.4; HL 21.7; EYE 7.0; TYM 4.8; IN 5.7; EN 6.7; 3FD 4.9; 3FP 3.4; 4TD 4.6; 4TP 3.6.

Variation. The sole paratype (ZMB70522) is an adult male with the following measurements: SVL 65.5; TL 35.1; HW 23.8; HL 21.5; EYE 7.3; TYM 4.8; IN 5.8; EN 6.6; 3FD 4.8; 3FP 3.3; 4TD 4.4; 4TP 3.7. It closely resembles the holotype in all pertinent respects, except that the vomerine teeth are in two prominent circular clumps (rather than two elongate ridges), and the tongue is narrower with a more distinct posterior notch. It is also a predominantly green frog but there are several small, irregular patches of pale cream (in preservative) colour on the head and anterior dorsal surfaces of the torso.

Advertisement call. The advertisement call is a loud, harsh “tonk….tonk…tonk” sound uttered from the forest canopy. Of the 51 calls recorded, two were produced singly and the remainder were produced in 16 call series each containing 2–7 calls (mean 3.19 ± 1.28). A total of 18 calls that were most likely produced by the holotype were of sufficient quality for detailed analysis. They were uttered in five short series, each containing 3–4 calls (mean = 3.6 ± 0.55) produced at a rate of 1.93–2.16 calls/s (mean = 2.02 ± 0.11 calls/s). Calls start abruptly with high sound amplitude which decreases quickly to a very low level. This low-amplitude sound component is relatively long but its terminal point is difficult to determine precisely due to loud background noise ( Fig. 5 ). Call duration is approximately 100–150 ms and intercall intervals within a call series are around 450–550 ms. Six harmonics, all with a weak frequency modulation from higher to lower frequencies, are apparent: the basal one is the weakest with a peak at 0.45 kHz, followed by three strongly pronounced bands with peaks at 0.9 kHz, 1.35 kHz and 1.8 kHz (the latter is the dominant frequency); the last bands, with peaks at 2.25 kHz and 2.70 kHz are again weakly expressed ( Fig. 5 ). An additional 33 calls were audible on recordings but were of insufficient quality for detailed analysis. They were uttered singly (n = 2) or in short series similar to those produced by the holotype. These series (n = 11) contained 2–7 calls (mean = 3.0 ± 1.48).

Distribution and natural history. Litoria azuroscelis , new species, is only known from a single locality on the Wandammen Peninsula in the Bird’s Neck region of Indonesian New Guinea ( Fig. 6 ) The habitat where it was collected is primary hill rain forest in the Wondiwoi Mountains , near a waterfall on a mountain stream called Sungai Maja at about 550 m a.s.l ( Fig. 7 ). The type specimens were calling from elevated positions in trees; although several additional specimens were heard in the vicinity, they were not collected. Based on repeated observations that they call from high in trees in areas where there is no obvious standing water on the ground, we speculate that this species, and other related taxa in the L. graminea group, breed in tree hollows. The new species is sympatric with two other large green Litoria species, L. infrafrenata (Günther) and L. pallidofemora Kraus. Litoria multicolor Günther , a similarly large arboreal Litoria , was collected a few kilometres from the type locality on the main ridge of the Wondiwoi Mountains at around 900 m a.s.l. ( Günther, 2004).

Suggested IUCN Conservation Status. This large hill forest species is known only from a single locality, but it is probably more widespread given that large areas of similar habitat remain intact on the Wandammen Peninsula and in nearby areas adjacent to Cenderawasih Bay. However, at the time the specimens were collected, a logging road was being constructed at the foot of the Wondiwoi Mountains , and in the years thereafter numerous large trees in the vicinity of this road were felled (R. Günther, personal observations). If our speculation that this species breeds in tree-hollows is correct (see above), it could make these frogs particularly vulnerable to the loss of large trees. Until its distribution and potential threats are better documented, we suggest that the new species be considered Data Deficient.

Etymology. Named after the colouration on the hidden surfaces of the hindlimbs, from the combination of the Greek azur (deep blue) and scelis, latinised version of Greek skelos (leg).

Comparisons. Litoria azuroscelis , new species, differs from all other Litoria except taxa in the L. infrafrenata group and L graminea group in the following combination of characters; adult size large (> 55 mm SVL), dorsal colouration uniform green, parotoid glands not evident, and interdigital webbing extensive.

Litoria azuroscelis , new species, is similar in size and build to members of the L. graminea group but differs from all known species in that group by having webbing on the hands not extending beyond the penultimate tubercle on the inside of Finger 3 (versus extending beyond penultimate tubercle). Litoria azuroscelis , new species, further differs from L. dux in having nuptial pads elongate and longer than terminal disc on Finger 1 (versus rounded and half size of disc) and iris reddish brown (versus white and reddish) (Richards & Oliver, 2006); from L. graminea by having nuptial pads elongate, longer than disc on Finger 1 (versus rounded and half size of disc), iris reddish brown (versus “tan/pale gray with red margin, finely stippled with black”; Kraus, 2018) and lacking deep skin creases extending to shoulder (versus usually present); from L. huntorum by lateral edges of venter and limbs purplish-blue (versus yellow or orange ( Fig. 1A ), larger size (male SVL 66 mm versus 53–60 mm; n = 5) and indistinct labial stripe ending before rictus (versus extending to below tympanum); from L. nullicedens by nuptial pads elongate (versus round and small), white labial stripe present (versus absent), iris predominately reddish brown (versus reticulated black and dark brown), nictitating membrane without flecking (versus present) and lateral surfaces of torso and limbs purple (versus bright orange-red; Kraus, 2018); from L. pallidofemora Kraus by having lateral edges of venter and limbs purplish-blue (versus yellow or orange ( Fig. 1B ), and iris predominately reddish-brown (versus tan or reddish with a wide black outer margin); from L. pterodactyla by iris predominately reddish brown (versus light grey with light-brown vermiculations) and its more prominently expanded finger discs (3FD/SVL 0.073 –0.074 versus 0.052) and toe discs (4TD/SVL 0.067 –0.069 versus 0.053); and from L. sauroni in having iris reddish-brown (versus with red and black vermiculations), pigment flecks across lower eyelid absent (versus present) and nuptial pads elongate (versus small and round) (Richards & Oliver, 2006).

Litoria azuroscelis , new species, differs from the five species in the L. infrafrenata group by having nuptial pads consisting of relatively large and widely spaced conical asperities (versus numerous densely packed minute low asperities) ( Fig. 2 ). It further differs from L. infrafrenata and L. tenuigranulata by having hidden lateral surfaces of limbs and torso purplish blue (versus plain light yellow or off white) and pale labial stripe ending before posterior edge of lower jaw (versus distinct and extending to tympanum ( Fig. 1C )); from L. lubisi in having hidden lateral surfaces of torso and limbs purplish blue (versus largely yellow ( Fig. 1D )) and a slightly narrower head (HW/SVL 0.36 versus 0.38); from L. multicolor in its larger size (adult male SVL 66.0 mm versus SVL of 49.1–55.4 mm, n = 14; Günther 2004), dorsal colouration uniformly green (versus green, grey, brown or yellow, and often patterned with black spots ( Fig. 1E )), red spots on venter and thighs absent (versus present), webbing extending to just beyond penultimate subarticular tubercle between Fingers 3 and 4 (versus ending at subarticular tubercle on Finger 4 and before subarticular tubercle on Finger 3); from L. purpureolata in having discs wider (3FD/SVL 0.073 –0.074 versus 0.054 –0.066; n = 10); and from L. sanguinolenta by its larger size (male SVL 66 mm versus maximum male SVL 55 mm; n = 10) and latero-ventral regions of torso yellow with light purple reticulations (versus white).

Figures

Fig 1. Selected frogs in the Litoria graminea (A–B) and Litoria infrafrenata (C–F) groups that occur in the western (Indonesian) half of New Guinea. A, Litoria huntorum from the foothills of the Foja Mountains, B, L. pallidofemora from Batanta Island, C, Litoria infrafrenata from Batanta Island, D, Litoria lubisi from Timika region, E, Litoria multicolor from the Wondowoi Mountains, and F, Litoria purpureolata from Biak Island. Note the typically less extensive webbing on the fingers and toes of species in the Litoria infrafrenata group. Photographs: A–D, Stephen Richards, E–F, Rainer Günther.

Fig 3. Litoria azuroscelis, new species, holotype MZB Amph. 32893 in life. A, lateral view, B, more dorsal view highlighting blue wash on groin and hidden surfaces of hindlimbs. Photographs: Rainer Günther.

Fig. 2. Details of nuptial excrescences in frogs from the Litoria infrafrenata (A–B) and Litoria graminea groups (C–F). A, Litoria purpureolata, B, Litoria lubisi, C, L. pallidofemora, D, L. pterodactyla, E, L. huntorum, and F, L. azuroscelis, new species. Note very fine excrescences in the two species from the Litoria infrafrenata group (A and B).

Fig. 4. Details of Litoria azuroscelis, new species, holotype MZB Amph. 32893 in preservative. A, Details of eye showing largely unpigmented nictitating membranes, B, dorsal view of head, C, details of hand show moderately extensive webbing, and D, whole animal showing colouration in preservative.

Fig. 5. A, Spectrogram of male Litoria azuroscelis, new species, and B, amplitude spectrum for calls in 5A. Calls recorded at 25°C.

Fig. 6. Map of New Guinea with the type locality of Litoria azuroscelis, new species, at the base of the Wandammen Peninsula indicated by a red star.

Fig. 7. Forest interior at Maja Waterfall, Papua Barat Province, Indonesia, the type locality of Litoria azuroscelis, new species. Photograph: Rainer Günther.