Diagnosis

The new species is distinguished from all other Litoria by the following unique combination of characters: size very small (SVL of four males 20.0–22.8 mm, females unknown); dorsum in life predominantly green; vomerine teeth absent; tympanum indistinct; finger webbing extensive, reaching distal edge of subarticular tubercle at base of penultimate phalanx on outer edge of Finger 3 and inner edge of Finger 4; finger discs slightly larger than or same size as toe discs; webbing on toes extending nearly to base of all discs except Toe 4 where it reaches midway between subarticular tubercle at base of penultimate phalanx and disc on both sides of digit; dermal fringes on limbs and below vent absent; pigmentation on nictitating membrane restricted to scattered flecks at dorsal margin; advertisement call a series of short (0.017–0.053 s) distinctly pulsed rasping notes repeated at 2.1–6.5 s intervals, followed by a discrete group of rapidly repeated pulses with highly variable inter-pulse intervals.

Etymology

The specific name lakekamu is a noun in apposition referring to the type and only known locality of this species.

Holotype

SAMA R70113 (FN: Biol Survey Field Series 11623), adult male, Sapoi River adjacent to Ivimka Research Station (7.735° S, 146.496° E; 120 m asl), Lakekamu Basin, Gulf Province, Papua New Guinea, collected by Stephen Richards, David Bickford, and Geordie Torr on 3 December 1996.

Paratypes

SAMA R70114 (FN: Biol Survey Field Series 11624), R70115 (FN: USNM 209310), PNGNM (FN: Biol Survey Field Series 11625), three adult males, same data as holotype.

Description of holotype

Adult male with vocal slits and small pale brown nuptial pads. Body slender, limbs moderately long (TL/SVL 0.56); head broad (HW/SVL 0.36), snout broadly rounded in dorsal aspect (Fig. 1A), blunt, near vertical, protruding marginally beyond lower jaw in lateral aspect; canthus rostralis broadly rounded, slightly curved; loreal region steep, slightly concave; nares round, near top of snout and closer to tip of snout than to eye, oriented anterolaterally, visible in dorsal aspect (Fig. 1A). Eyes large (EYE/SVL 0.15), clearly protruding in both dorsal and lateral aspects; constricted pupil horizontal. Pigmentation on nictitating membrane restricted to scattered flecks along dorsal edge of left membrane. Tympanum small (TYM/SVL<0.05), annulus poorly defined, bordered dorsally by broad, poorly defined supratympanic fold. Vomeropalatines absent; tongue not free posteriorly, broad, heart shaped with distinct notch in posterior edge; vocal slits long, located laterally on floor of mouth, extending from behind angle of jaws to about halfway between angle of jaws and front of mouth. Nuptial excrescences very pale brown, elongate, extending 1.7 mm along proximal outer edge of first finger.

Fingers with relative lengths 3>4>2>1, webbing extending beyond distal edge of subarticular tubercle at base of penultimate phalanx on Finger 4 (distal subarticular tubercle), and to about distal subarticular tubercle on outer edge of Finger 3 before continuing as broad flange to base of disc. Distal subarticular tubercles low, that on Finger 3 partially bifid; remainder unilobed. Small narrow inner, and broad but low outer, metacarpal tubercles present (Fig. 1B). Toes with relative lengths 4>5=3>2>1, webbing extending nearly to base of discs on Toe 3 and Toe 5, and to midway between distal subarticular tubercle and disc on both sides of Toe 4. Subarticular tubercles low, poorly defined. Inner metatarsal tubercle small, elongate, poorly defined; outer metatarsal tubercle not detectable (Fig 1B). Tips of fingers and toes expanded into terminal discs, those of fingers slightly broader than those of toes (4TD/3FD 0.92), all with distinct marginal grooves. A small puncture wound present in centre of each hand.

Skin with orange-peel texture dorsally and laterally, including head; dorsal surfaces of limbs with numerous low tubercles; ventral surfaces granular. Limbs without dermal ornamentation, heels without tubercles or dermal spikes, surfaces around vent without raised tubercles.

Colour of holotype in preservative

Dorsal surfaces of body uniform grey with scattered darker grey flecks; lemon-yellow lateral line in life has faded to white, ventral surfaces to off-white. Green spots on limbs in life (see below) are no longer evident while dense brown peppering has become more intense across all surfaces of limbs.

Colour of the new species in life

All specimens near-uniform green dorsally, white laterally and ventrally, with narrow but distinct lemon-yellow lateral stripe. The following extra details on colour in life are based on images of SAMA R70114 and PNGNM (FN 11625) taken in life shortly after capture (Fig. 2). Green dorsum of PNGNM (FN 11625) overlain with scattered small but distinct brown flecks, these less evident in SAMA R70114. Narrow lemon-yellow lateral line extends posteriorly from tip of snout along upper lip, below eye and tympanum continuing mid-laterally to groin, separating green of dorsum from white ventrolateral and ventral surfaces (Fig. 2). Limbs, including hidden surfaces of thighs, translucent with dense purplish-brown peppering, overlain on upper surfaces by lime green spots, these mostly restricted to surfaces of low tubercles. Green colour on arms restricted predominantly to areas below elbow; fingers, toes, and webbing translucent with scattered tiny purplish-brown spots. Iris creamy-white with scattered short veins of brown pigment, most dense in narrow rim around edge of pupil.

Variation

The type series is extremely uniform morphologically (Table 1). Body size of adult males 20.0–22.8 mm, females unknown. Dorsal colour consistently near uniform green in life, all specimens with lemon-yellow mid-lateral line. In preservative all specimens grey with fine darker grey flecks, variation restricted to degree of concentration of flecks into small blotches (small blotches most evident in PNGNM (FN 11625). Tongue nearly round in SAMA R70115 (vs. heart-shaped in holotype), nuptial pads of R70114–70115 present but barely detectable.

Distribution and natural history

Litoria lakekamu is to date known only from the Lakekamu Basin on the southern fringe of Papua New Guinea's central cordillera (Fig. 3). The type series was collected from vegetation adjacent to or overhanging the Sapoi River which at the type locality is a large, clear, rocky stream (Fig. 4) flowing through primary lowland forest. Other individuals were heard calling from about 10–15 m high in the lower canopy over the same stream.

Advertisement call

We recorded two complete call series produced by SAMA R70115 at a height of 3 m above the stream, and one series produced by an unvouchered animal at least 10 m high in a tree adjacent to the stream, all at an air temperature of 25.5°C. Litoria lakekamu produces two call types. Call type 1 is a single short, distinctly pulsed note repeated slowly in long series. This call type is here referred to as a short call. Call type 2 is longer than short calls and comprises a sequence of pulses produced at highly variable inter-pulse intervals resulting in the acoustic impression of a ‘spluttering’ sound. These calls do not contain clearly defined notes and are here referred to as long calls. Long calls always followed a series of short calls and, although sample size is small, additional calls with a similar structure were heard at the type locality. Detailed analysis is restricted to the call series produced by SAMA R70115 due to the poor quality of the unvouchered call.

The three recorded call series consisted of seven, eight and 11 short calls produced at intervals of 2.1–6.5 s (0.28–0.48 calls/s, n=3) (Fig. 5). Each series of short calls was followed by a single long call. Total lengths of the three call series (including long calls) were 21.5, 29.4, and 45.2 s. Short calls (=notes) in the series analysed in more detail were 0.017–0.053 s long (mean=0.033, SD=0.010, n=18), and contained 4–8 pulses (mean=5.7, SD=1.3, n=18) produced at a rate of 100–312 pulses/s (mean=164.2, SD=47.01, n=18). The two long calls of sufficient quality for detailed analysis were much longer than short calls, lasting 1.6 and 1.7 s. They contained 34 and 32 pulses, respectively, uttered at a rate of 18.8 and 21.3 pulses/s. However, pulse interval in the two long calls was extremely variable, ranging from 0.0003 to 0.17 s resulting in the acoustic impression of a rapid series of spluttering clicks. Dominant frequency of short calls was 3560–3860 kHz (mean=3714.4, SD=85.76, n=18), and that of the two long calls fell within this range (3759.5 and 3595 kHz). Fig. 5A illustrates a full call series and Fig. 5B–C illustrates the final short call and the following long call in that series, produced by SAMA R70115.

Comparisons

Litoria lakekamu sp. nov. is compared here with small (male SVL 20–30 mm), predominantly green New Guinean Litoria that are known or presumed to breed in lentic water bodies as follows: It differs from L. albolabris (Wandolleck, 1911) and L. mystax (Van Kampen, 1906), both from the northern lowlands of New Guinea, in having longer limbs (TL/SVL 0.56–0.59 vs. 0.50–0.55 in L. albolabris and 0.54 in L. mystax; Tyler, 1968), and in lacking (vs. having) a prominent, short white bar below the eye; from New Guinean members of the L. bicolor (Gray, 1842) group (L. bibonius Kraus & Allison, 2004, L. chloristona Menzies, Richards & Tyler, 2008, L. contrastens (Tyler, 1968), L. eurynastes Menzies, Richards & Tyler, 2008, L. lodesdema Menzies, Richards & Tyler, 2008, and L. viranula Menzies, Richards & Tyler, 2008) (Tyler 1968; Kraus and Allison, 2004; Menzies et al. 2008), in having a moderately robust (vs. slender) body (Fig. 2D), with snout not projecting and near-vertical in lateral view (vs. projecting, distinctly rounded in lateral view) (Kraus and Allison, 2004; Menzies et al., 2008), and having (vs. lacking) a distinct lemon yellow mid-lateral line in life (Fig. 2D); from L. christianbergmanni Günther, 2008 in its smaller size (male SVL 20.0–22.8 mm vs. 26.9–31.2 mm in L. christianbergmanni), and white bar below eye lacking (vs. present in L. christianbergmanni) (Günther, 2008); from L. chloronota (Boulenger, 1911) by its smaller body size (males 27–32 mm in L. chloronota), and broader snout (EN/IN 0.74–0.80 vs. 0.63–0.71 in L. chloronota; Menzies, 1993); from members of the L. gracilenta (Peters, 1869) group (L. aruensis (Horst, 1883), L. auae Menzies & Tyler, 2004, L. callista Kraus, 2013, L. elkeae Günther & Richards, 2000, L. eschata Kraus & Allison, 2009, L. kumae Menzies & Tyler, 2004, and L. robinsonae Oliver, Stuart-Fox and Richards, 2008) in its smaller size (male SVL<23 mm vs. >25 mm) and lacking pale canthal and postocular stripes (vs. present: Menzies and Tyler, 2004; Oliver et al., 2008; Kraus and Allison, 2009; Kraus, 2013); from L. havina Menzies, 1993 in lacking (vs. having) a fleshy rostral spike in males; from L. rubrops Kraus & Allison, 2004 in having dorsum without (vs. with) black or darker green speckling, and iris predominantly creamy white (vs. iris red in L. rubrops; Kraus and Allison, 2004); from L. nigropunctata (Meyer, 1875), L. iris (Tyler, 1962), L. majikthise Johnston & Richards, 1994, and L. ollauro Menzies, 1993, in its smaller size (male SVL<23 mm vs. >25 mm) and further from these species in having posterior surfaces of thighs translucent with purplish-grey spotting (vs. posterior of thighs blue, red, or yellow, sometimes blotched with white or purple) (Menzies, 1993); from L. richardsi Dennis & Cunningham, 2006 and L. singadanae Richards, 2005 in having a pigmented (vs. transparent) tympanic membrane (Dennis and Cunningham, 2006; Richards, 2005); and from L. verae Günther, 2004 in lacking (vs. having) crenulated skin folds along outer margins of tarsi (Günther, 2004).

Among small, green, stream-dwelling Litoria the new species differs from L. bulmeri (Tyler, 1968) by its smaller size (males 20.0–22.8 mm vs. 29–34 mm SVL), and black lateral stripe absent (vs. present); from L. longicrus (Boulenger, 1911) in having dorsum slightly granular (vs. smooth), and in lacking (vs. having) a distinct white bar beneath the tympanum (Tyler, 1968), and from L. wapogaensis Richards & Iskandar, 2001 in its smaller size (males 20.0–22.8 mm vs. 30.5–33 mm SVL), lacking (vs. having) vomerine teeth and having (vs. lacking) a distinct lemon yellow mid-lateral line (Tyler, 1968; Richards and Iskandar, 2001). The new species is morphologically most similar to L. leucova (Tyler, 1968), a small (males 21.7–24 mm SVL; S. Richards, personal observation) green treefrog known from the northern slopes of New Guinea's central cordillera and from the Hun-stein Mountains (Tyler, 1968; Johnston and Richards, 1994; Kraus and Allison, 2006; S. Richards, personal observation). It differs from that species by having longer limbs (TL/SVL 0.56–0.60 vs. 0.53–0.55; Johnston and Richards, 1994), a poorly defined (vs. prominent) tympanum, in having (vs. lacking) a distinct lemon yellow mid-lateral line (Figs. 2A–C), and in its unique advertisement call (Fig. 5). Litoria lakekamu and L. leucova both produce short and long calls but the short call of L. lakekamu is a distinctly pulsed note containing 4–8 pulses (vs. a single pulse in L. leucova) and two long calls of L. lakekamu contained 32 and 34 pulses and lasted 1.6–1.7 s (vs. 10 pulses in L. leucova and lasting 0.09 s); Johnston and Richards, 1994; S. Richards, personal observation).

IUCN Status.

Litoria lakekamu is known from a single location in primary lowland forest in southern Papua New Guinea. Although extensive areas of apparently suitable habitat remain in the region, this species was not detected during numerous fauna surveys in the Kikori and Purari basins to the west between 2001 and 2017 (S. Richards, personal observations). Until this species' distribution, habitat requirements and potential threats have been better documented we recommend that it be listed as Data Deficient.