Litoria grinpela, Richards & Oliver, 2024

Richards, Stephen J. & Oliver, Paul M., 2024, Two new species of torrent-breeding treefrogs (Anura: Pelodryadidae: Litoria) from hill forests on the southern edge of New Guinea’s Central Cordillera, Vertebrate Zoology 74, pp. 417-433 : 417-433

Litoria grinpela sp. nov.

Figures 7 A, B , 8 , 9

Green torrent treefrog

Holotype.

SAMA R 72339 ( SJR 10513 ), adult male with vocal slits and nuptial pads, Liddell River , upper Strickland River basin, Western Province, Papua New Guinea (5.8078 ° S, 142.3083 ° E; 215 m a. s. l.), collected by Stephen Richards on 30 March 2008.

Paratype.

SAMA R 72340 ( SJR [ JCUNQ] 3249), adult male with vocal slits and nuptial pads, Libano Sok , Hegigio River, Southern Highlands Province, Papua New Guinea (6.3989 ° S, 142.9761 ° E; 250 m a. s. l.), collected by Stephen Richards on 7 August 2003 .

Diagnosis.

A species of torrent-breeding Litoria that can be distinguished from all congeners by the following unique combination of characters: size moderately small (male SVL 26.1–27.5 mm); snout rounded in both dorsal and lateral view; canthus rostralis strongly curved in dorsal view, rounded in lateral view; limbs long (TL / SVL 0.62–0.64); finger webbing moderate, web between fingers 3 and 4 extending to distal subarticular tubercle and, on finger 4, continuing as fringe to base of disc; toe webbing extensive, extending to base of disc on all toes except toe 4 where it reaches distal subarticular tubercle on both sides of digit; dorsal skin relatively smooth with no prominent tubercles; vocal slits present in males; dorsal colouration predominately mid-green with no or little pattern; thin brown canthal stripe or blotch present; hidden surfaces of thighs and groin orange; venter largely off-white with no pattern; and advertisement calls comprising 7–21 rapidly repeated unmusical tapping notes produced at a rate of 7.8–9.6 notes / s at a dominant frequency of 2707–3082 Hz.

Comparisons with other species.

The combination of moderately small size (adult male SVL between 25–30 mm), snout rounded in dorsal view, dorsal skin relatively smooth with no prominent tubercles, moderate webbing on the fingers and predominantly green dorsal colouration (Fig. 7 A, B ) readily distinguishes L. grinpela sp. nov. from the majority of other torrent-breeding Litoria from New Guinea.

Litoria grinpela sp. nov. differs from other small, green, torrent-breeding species as follows: from L. lakekamu Richards & Bickford, 2023 in its larger size (male SVL> 25 versus <25 mm), white labial patch restricted to below eye only (versus full labial stripe), brown canthal stripe or patch present (versus absent), canthus rostralis moderately well defined (versus very indistinct), tympanum distinct (versus indistinct), and call consisting of 7–21 rapid popping notes (vs. a series of short, distinctly pulsed rasping notes followed by an explosive chattering; Richards and Bickford 2023); from L. leucova ( Tyler, 1968) in its slightly larger size (adult male SVL> 25 versus <25 mm), in having longer hindlimbs (TL / SVL> 0.62 versus <0.57), a wider head (HW / SVL 0.36 versus 0.32–0.34), shorter snout (EN / SVL <0.084 versus> 0.095) and yellow patches in groin and on hidden surfaces of thighs (versus translucent pink with yellow spots) ( Johnston and Richards 1994); and from populations of the geographically overlapping L. longicrus (Boulenger, 1911) (Fig. 7 C, D ) by its slightly larger size (adult male SVL> 25 versus <25 mm), plain green dorsum (versus mottled brown and green), green (versus brown) tympanic membrane, white lateral patch restricted to posterior edge of lower jaw (versus white patches extending from lower jaw along side of body almost to groin), and more extensive webbing on fingers (extending beyond distal subarticular tubercle on finger 4 versus not extending beyond distal subarticular tubercle on finger 4).

Litoria grinpela sp. nov. can be distinguished from three other species of moderately small, green lentic-breeding Litoria that occur in the Kikori region as follows; from L. auae Menzies & Tyler, 2004 by having a brown canthal stripe or blotch on the snout only (versus a white or yellow canthal stripe, and supratympanic stripe), in lacking white or yellow flecks on the dorsum (versus typically present), and by its slightly smaller size (male SVL <28 mm versus typically greater than 30 mm); and from two species in the L. bicolor (Gray, 1842) group ( L. chloristona Menzies, Richards & Tyler, 2008 and L. viranula Menzies, Richards & Tyler, 2008 ) by its broader head and more broadly rounded snout, the presence of a brown canthal stripe or blotch restricted to the head (versus brown and white lateral stripes extending along sides of torso) and its medium-green dorsal colouration (versus typically yellowish green or brown).

Description of holotype.

Adult male with vocal slits and pale-brown nuptial pads made up of fine asperities. Habitus moderately robust, limbs long (TL / SVL 0.64), head wide (HW / SVL 0.48). Snout protruding beyond lower jaw, slightly rounded (nearly truncate) in lateral view, rounded in dorsal view (Fig. 8 A, B ). Canthus rostralis clearly defined, strongly curved in dorsal view, rounded in lateral view; loreal region steeply sloping, slightly concave. Nostrils near top of snout, oriented laterally, not visible in dorsal view. Vomeropalatines poorly developed, detectable but teeth insufficiently developed to count. Tongue rounded with prominent posterior notch; vocal slits laterally in floor of mouth, extending from near angle of jaws about one third distance to front of jaw. Eyes large (EYE / SVL 0.12), prominent, protruding in dorsal and ventral views; pupil horizontal, nictitating membrane unpigmented. Tympanum moderately small (TYM / SVL 0.047), less than half diameter of eye (TYM / EYE 0.39), tympanic annulus clearly defined except dorsal edge obscured by moderately thick, slightly curved supratympanic ridge.

Skin on dorsum finely rugose, on dorsal surfaces of limbs largely smooth except for scattered indistinct tubercles on forearms; skin on throat finely granular, on abdomen coarsely granular. Ventral surfaces of forelimbs smooth with scattered tubercles; ventral surfaces of thighs coarsely rugose along posterior edge, becoming less so on adjacent surfaces, with scattered large pale off-white tubercles below vent; tarsi and tibiae smooth ventrally.

Fingers moderately long with expanded terminal discs (3 FD / 3 FP 1.6; 3 FD / SVL 0.058) with distinct circum-marginal grooves; relative lengths of fingers 3> 4> 2> 1, subarticular tubercles unilobed or weakly bifid. Webbing moderate (Fig. 8 C ), reaching distal edge of distal subarticular tubercle and continuing to disc as narrow fringe on inside of finger 4; to base of distal subarticular tubercle on outside of finger 3; to base of penultimate subarticular tubercle on inside of finger 3; to base of distal subarticular tubercle on outside of finger 2; and in a narrow basal flange between fingers 1 and 2. Hands with long (1.3 mm) prominent ovoid inner metacarpal tubercles and shorter (0.5 mm), rounded and lower, but still distinct, outer metacarpal tubercle. Nuptial pads pale brown, comprising fine asperities, extending across base of finger 1, elongate, much longer that high, with distinct constriction demarcating short distal portion from much longer proximal portion.

Toes with expanded terminal discs with terminal grooves, some discs slightly shrivelled in preservative; disc on toe 4 distinctly narrower than disc on finger 3 (3 FD / 4 TD 1.2). Relative lengths of toes 4> 5> 3> 2> 1. Webbing between toes extensive (Fig. 8 D ) reaching to distal subarticular tubercle on both sides of toe 4, to base of disc on inside of toe 5 and outside of toes 1–3, and to distal subarticular tubercle on inside of toes 2–3. Inner metatarsal tubercle oval, short (1.1 mm long) but prominent; outer metatarsal tubercle absent.

Colouration in preservative.

Dorsum predominately blue with few indistinct small brown blotches just behind eyes. Lateral surfaces of snout densely spotted with blue and brown, brown maculations coalesce to form canthal stripe that extends from eye, across nostril and down to edge of jaw; white patch below eye; upper lip with thin margin lacking maculations giving appearance of an off-white labial stripe. Exposed dorsal surfaces of limbs blue, hidden surfaces of limbs buff with scattered dark-brown or green maculations, dorsal surfaces of digits buff, with scattered dark-brown flecking. Ventral surfaces largely off-white, with scattered regions of brown maculations along edges of lower jaw, extremities of limbs, and posterior edge of thighs.

Summary meristic data. These data were determined for the holotype (all measurement in mm):

SVL 27.5; TL 17.6; HW 13.4; HL 10.3; EYE 3.3; TYM 1.3; IN 3.5; EN 2.3; 3 FD 1.6; 3 FP 1.0; 4 TD 1.3; 4 TP 1.0.

Variation.

The paratype ( SAMA R 72339 ) is an adult male with the following measurements: SVL 26.1; TL 16.2; HW 9.3; HL 9.9; EYE 4.5; TYM 1.3; IN 3.8; EN 2.0; 3 FD 1.2; 3 FP 0.8; 4 TD 0.9; 4 TP 0.8. It is broadly similar in colouration, nuptial pad form, and extent of webbing to holotype, but differs in having a mauve dorsal colouration in preservative (likely a preservation artefact), much more prominent white patch laterally on head extending from below eye, across tympanic membrane to insertion point of forelimb, and exposed dorsal surfaces of limbs largely cream with extensive very fine mauve maculations. The vomeropalatines are more prominent than those of the holotype, each supporting 3–4 sharp teeth medial to the choanae (vs. vomeropalatines small, poorly developed in the holotype).

Colouration in life.

The following description is based on photographs of the holotype and paratype (Figs 7 A, B , 8 C – E ,). Dorsum green with small number of darker-brown flecks. Lateral surface of snout with brown patch bordered sharply dorsally by canthus rostralis, this brown patch forming thin canthal stripe in holotype but covering most lateral surfaces of snout in paratype. Supratympanic fold light brown. Small white patch on upper lip and below eye present in both specimens but more prominent and extensive in paratype. Lateral surfaces of torso ranging from green, yellowish green to translucent with extensive buff flecks, also overlain with sparse brown flecks in paratype. Exposed surfaces of limbs green, sometimes edged by indistinct brown regions. Hidden surfaces of groin and posterior surface of thighs orange (Fig. 8 E ). Iris pale grey with extensive darker-brown vermiculation, pupil with very thin orange margin.

Vocalisation.

We analysed 14 calls from the holotype (n = 4) and paratype (n = 10) at 23.6 and 24.5 ° C respectively. Calls of both animals were extremely similar and were combined for analysis. The call of L. grinpela sp. nov. is a series of 7–21 (mean = 15.0, SD = 5.03) unmusical tapping or popping notes uttered in quick succession (Fig. 9 ). Calls are produced at intervals of 4.3–132.0 seconds (mean = 24.1, SD = 39.4). Call length is 0.67–2.56 seconds (mean = 1.62, SD = 0.62), and notes within calls are produced at a rate of 7.8–9.6 notes / s (mean = 8.74, SD = 0.44). Dominant frequency is 2707–3082 Hz (mean = 2910, SD = 131.08). An exemplar call from the holotype has been uploaded to iNaturalist (https://www.inaturalist.org/observations/218063820).

Molecular differentiation.

Genetic divergences (p-distances) indicate that L. grinpela sp. nov. is most genetically similar to the clade comprising L. kikori sp. nov. and L. spartacus (p-distances from 0.144 –0.161).

Etymology.

The name combines the New Guinea pidgin word for green (grin) with its adjectival ending (- pela).

Distribution and ecological notes.

Litoria grinpela sp. nov. is known from two locations along the southern slopes of Papua New Guinea’s Central Cordillera: the type locality in the upper Strickland River basin in Western Province, and Libano Sok, on the Hegigio River in the Kikori River basin in Southern Highlands Province, 100 km to the east of the type locality (Fig. 5 ).

Both animals were calling from foliage 3–4 m above the ground in low-elevation hill forest (Fig. 6 B ) adjacent to swiftly flowing rivers. Four other torrent-breeding pelodryadids were documented at the type locality, one of which ( L. longicrus ) occurred in microsympatry with the new species, while three others ( L. arfakiana , L. spartacus and Nyctimystes pulcher Wandolleck, 1911 ) were found slightly upstream where a waterfall emerges from the side of a karst hill slope (Fig. 6 C ). At just 215 m a. s. l. this location appears to be the lowest known elevation for L. arfakiana , L. spartacus and N. pulcher ( Menzies 2006; Richards and Oliver 2006). At Libano Sok L. grinpela sp. nov. occurred in sympatry with only one other stream-breeding pelodryadid, L. kikori (described above).

Suggested IUCN status.

The two Litoria grinpela sp. nov. records span approximately 100 kilometres of extensively forested terrain with relatively low human population density. It also occurs at elevations (<500 m a. s. l.) at which populations of torrent-breeding Litoria in the Australian wet tropics have been able to persist in the face of the frog pathogen B. dendrobatidis . If this pathogen colonises New Guinea, this species may therefore be less vulnerable than most other Melanesian torrent-breeding Litoria , which are restricted to higher and cooler areas. For these reasons we suggest an IUCN status of Least Concern.

Figures

Figure 5. Distributions of Litoria kikori sp. nov. (white circle), L. spartacus (blue squares) and L. grinpela sp. nov. (black circle, type locality). The black and white circle is Libano Sok where both new species occur in sympatry. Libano Sok is the type locality of Litoria kikori sp. nov.

Figure 6. A Streamside habitat of Litoria kikori sp. nov. in foothill forest at Bifo Creek, Southern Highlands Province, Papua New Guinea; B habitat of L. grinpela sp. nov at the type locality along the Liddell River, Western Province, Papua New Guinea; C a waterfall emerging out of the ground just upstream from image B. This is the lowest known locality (215 m a. s. l.) for three other stream-breeding pelodrydadid treefrog species: L. arfakiana, L. spartacus and Nyctimystes pulcher.

Figure 7. In-life images of: A holotype (SAMA R 72339); B paratype (SAMA R 72340) of Litoria grinpela sp. nov.; C, D specimens of the ecologically and morphologically similar and geographically overlapping torrent-breeding Litoria longicrus from the foothills of the Muller Range. Note the brown tympanic membrane and extensive white lateral markings in L. longicrus. All photographs by Stephen Richards.

Figure 8. Details of holotype (SAMA R 72339) of Litoria grinpela sp. nov.: A dorsal view of head; B lateral view of head; C hand webbing in life; D foot webbing in preservative; E colouration of hidden surfaces of groin and thighs in life. All photographs by Stephen Richards. Scale bars = 5 mm.

Figure 9. A wave form; B power spectrum; C spectrogram of a single call of Litoria grinpela sp. nov. (SAMA R 72340) recorded at an air temperature of 24.5 ° C. The lower-frequency peak evident in (B) is an artefact of the loud stream noise.