Litoria aplini, Richards & Donnellan, 2020

Richards, Stephen J. & Donnellan, Stephen C., 2020, Litoria aplini sp. nov., a New Species of Treefrog (Pelodryadidae) from Papua New Guinea, Records of the Australian Museum 72 (5), pp. 325-337 : 327-336

Litoria aplini sp. nov.

urn:lsid:zoobank.org:pub:act:09663F46-325A-42B0-AB45-86517976962A

Figs 1–2

Holotype. SAMA R71463 (Field number SJR12829), upper Sepik River catchment, West Sepik Province, Papua New Guinea (4°38.637'S 141°40.747'E, 950 m a.s.l.), 10 xii 2009, S. Richards . Paratypes. (n = 3) SAMA R71464 (Field number SJR12832) , SAMA R71465 (Field number SJR12833) , PNGNM (Field number SJR12834), same data as for holotype except collected 11 xii 2009 .

Etymology. The species epithet is an honorific for Dr Ken Aplin, in recognition of his immense contributions to New Guinean herpetology and in gratitude for his friendship and selfless collaboration with the authors over many years. Ken’s tremendous intellect, boundless energy, and unfailing humour in the field are sorely missed. We recommend the common name “Aplin’s Treefrog” for this beautiful species.

Diagnosis. Litoria aplini sp. nov. is diagnosed morphologically from all congeners by the combination of body size moderately small (male SVL 31.9–35.1 mm); snout relatively broad (EN/IN = 0.79–0.84) ( Table 4); presence of crenulated folds on outer edge of tarsi; webbing on hands extending to slightly past penultimate tubercle on fourth finger; presence of prominent ivory conical tubercles below vent and on ventral surfaces of thighs; and in the following colour in life traits - belly golden-yellow posteriorly, hidden surfaces of limbs predominantly blue with dark brown mottling except for discrete golden-yellow patch on posteroventral surface of thighs. The advertisement call is a short buzz normally followed by 1–7 clicks, the latter most commonly comprising two pulses. From a genetic perspective, apomorphic nucleotide states at 12 sites in the mitochondrial ND4 gene reliably diagnose L. aplini from the eight most closely related species ( Table 2).

Comparisons with other species ( Table 3 and Fig. 3 ): Litoria aplini sp. nov. differs from other small (adult male SVL <40 mm), green or green and brown New Guinean Litoria as follows: from L. albolabris , L. longicrus , and L. mystax in having larger body size (male SVL = 31.9–35.1 vs <30.0 mm), having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs uniform green), and lacking pale bar below eye (vs present).

Litoria aplini sp. nov. differs from members of the L. bicolor group ( L. bibonius , L. chloristona , L. contrastens , L. eurynastes , L. lodesdema , L. viranula ) in its larger size (male SVL = <31.6 mm in L. bicolor group; Menzies et al., 2008), having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs predominantly green), and venter golden-yellow (vs white); from L. bulmeri in having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs uniform green with broad black lateral stripe), and shorter limbs (TL/ SVL = 0.59–0.66 in L. bulmeri vs 0.56–0.57 in L. aplini ); from L. christianbergmanni in its larger size (male SVL = 26.9–31.2 mm in L. christianbergmanni ), dorsum green and brown (vs uniform green with white, yellow or pale green spots), and lacking white bar below eye (vs present in L. christianbergmanni ); from L. chloronota in having larger body size (males 27–32 mm in L. chloronota ), narrower snout (EN/IN = 0.63–0.71 in L. chloronota vs 0.79–0.84 in L. aplini ), having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs mottled pale and darker green with or without yellow spots), and venter posteriorly golden-yellow (vs cream) ( Menzies, 1993); and from L. gasconi and L. multiplica by its smaller size (male SVL ≥ 36 mm in these species), and dorsum green and brown (vs uniform green with pale spots).

Litoria aplini sp. nov. differs from members of the L. gracilenta group ( L. aruensis , L. auae , L. callista , L. elkeae , L. eschata , L. kumae , and L. robinsonae ) in having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs plain green with or without pale or dark spots), and pale canthal and postocular stripes absent (vs present: Menzies & Tyler, 2004; Kraus, 2013); from L. havina in having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs uniformly green or occasionally brown), and lacking a fleshy rostral spike in males (vs present); from L. nigropunctata in having prominent crenulated skin fold along outer margins of tarsi (vs absent), extensive golden-yellow on posterior of venter (vs absent in L. nigropunctata ), grey (vs yellow) iris and extensive blue and dark brown mottling posterolaterally (vs absent); from L. rubrops in its larger size (male SVL = 21.4–25.2 mm in L. rubrops ), having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs green, usually speckled with black or darker green), and iris grey with pale gold inner rim (vs iris red in L. rubrops ); and from L. wapogaensis in having prominent crenulated skin fold along outer margins of tarsi (vs absent), dorsum green and brown (vs uniform green with or without pale spots), and hidden surfaces of thighs and groin golden-yellow (vs dark brown in L. wapogaensis ).

In its moderate size (male SVL 30–35 mm), green and brown dorsal colour, extensively webbed fingers, and colourful ventrum and limbs in life, Litoria aplini most closely resembles the following six species: L. iris , L. majikthise , L. ollauro , L. richardsi , L. singadanae , and L. verae . It differs from all of these except L. singadanae and L. verae in having a prominent crenulated skin fold along outer margins of tarsi (vs a series of isolated pale tubercles along margins of tarsi). Litoria aplini can be further distinguished from L. iris by having posterior of belly and plantar surfaces golden-yellow (vs belly white and plantar surfaces without yellow), axilla without violet patch (vs present), posterior surfaces of thighs mottled blue and brown bordered ventrally by golden-yellow patch (vs posterior of thighs blue, red, or yellow, frequently blotched with white or purple); from L. majikthise by having posterior surfaces of thighs mottled blue and brown bordered ventrally by golden-yellow patch (vs uniform red), and by lacking a pearl-white post-ocular bar (vs present); from L. ollauro in having dorsum variably green and brown (vs uniform green or green with yellow spots), posterolateral surfaces of venter, ventral surfaces of tibiae, and hidden surfaces of thighs with extensive blue and dark-brown mottling (vs posterolateral surfaces of venter and hidden surfaces of thighs sky-blue without brown mottling, and ventral surfaces of thighs and tibiae uniform yellow); from L. richardsi in its larger size (males 31–35 mm vs <27 mm SVL); dorsum without irregular black lines, and throat and finger and toe webbing without extensive black markings (vs present), and periphery of tympanic membrane not transparent (vs transparent); from L. singadanae in its larger size (males 31–35 mm vs <30 mm SVL); in having posterolateral surfaces of belly and posterior surfaces of thighs with blue and brown mottling (vs posterior of venter and hidden surfaces of legs uniform orange), tympanum much smaller (TYM/EYE = 0.45–0.49 vs 0.69–0.81), and pigmented (vs tympanic membrane transparent); and from L. verae in having posterolateral surfaces of belly and posterior surfaces of thighs with blue and brown mottling (vs posterior of venter and hidden surfaces of legs uniform yellow), feet dorsally with extensive areas of yellow (vs yellow absent) and dorsum without small brown spots aligned transversely (vs present). A summary of the major characters useful for distinguishing among these seven most similar species is presented in Table 3.

Molecular genetic comparisons. The final alignment for the mitochondrial ND4 gene comprised 694 bp. In a phylogram of relationships among mitochondrial ND4 sequences, the two sequences from L. aplini were the well supported sister group to a clade comprising L. iris and L. majikthise ( Fig. 4 ). The net uncorrected sequence divergence (d A) for ND4 between L. aplini and the two species in its sister clade was 0.14 for L. iris and 0.15 for L. majikthise ( Table 1). d A between sister species pairs ranged from 0.11 to 0.22 ( Table 1).

Description of holotype. An adult male with right-lateral incision in abdomen. Vomero-palatines with two patches of small, poorly-defined teeth between internal nares. Vocal slits lateral, very long, extending from well behind angle of jaws to approximately 1/3 distance between angle of jaws and front of mouth. Tongue oval with distinct posterior notch. Head moderately wide (HW/SVL = 0.30), slightly less than length (HL/SV = 0.35, HL/HW = 1.15); loreal region steep, slightly concave; canthus rostralis rounded, distinctly curved; nostrils closer to tip of snout than to eyes; internarial distance greater than distance from external naris to eye (EN/IN = 0.79, IN/SVL = 0.12, EN/SVL = 0.09); snout truncate when viewed from above, with slightly angular tip; steeply sloping when viewed from side; eyes large (EYE/ SVL = 0.13), prominent, protruding in dorsal and ventral views; tympanum prominent, raised above surrounding skin; tympanic ring distinct but top margin covered by thick supratympanic skin fold, horizontal diameter slightly less than half width of eye (TYM/EYE = 0.45).

Skin of dorsal and lateral surfaces including limbs, finely granular; ventral surfaces including limbs coarsely granular; patches of large ivory tubercles on ventral surface of thighs and around vent—largest around vent; a series of low tubercles along outer margin of tibiae and crenulated white skin fold on outer margin of F4 from proximal edge of disc extending along forearm to elbow, and prominent on outer margin of T5 from proximal edge of disc along tarsus to heel ( Fig. 2F ), patch of low ivory tubercles on heel.

Fingers moderately short with distinct lateral fringes, extensively webbed, webbing reaching slightly past penultimate tubercle on F4, to slightly below penultimate tubercle on outside of F3, and to level of penultimate tubercle on outside of F2; webbing between F1 and F2 greatly reduced; finger relative lengths 3> 4> 2> 1; tips of all fingers expanded into discs bearing circum-marginal grooves; disc on F3 approximately 1.4 times width of penultimate phalanx; palmar surfaces with numerous prominent tubercles ( Fig. 1 ), subarticular tubercles at base of penultimate phalanx on F3–4 bilobed; first finger with elongate, brown nuptial pad with narrow “handle” proximally, broadening distally at approximately mid-length (1.7 mm long, 0.9 mm at widest point and 0.5 mm at narrowest point). Toes nearly fully webbed, web reaching to base of disc on T5, and on outside of T2 and T3, to base of penultimate phalanx on both sides of T4, and slightly beyond penultimate tubercle on T1 ( Fig. 1 ); relative lengths 4> 5 = 3> 2> 1; tips of all toes expanded into discs with circum-marginal grooves; disc of T4 approximately 1.4 times wider than penultimate phalanx; subarticular tubercles at base of penultimate phalanx on T2–5 partially or completely bilobed; inner metatarsal tubercle elongate, bean shaped; outer absent. Hind legs moderately long (TL/SV = 0.56), with patch of small but prominent tubercles at heel.

Colour in life: body and limbs rufous brown dorsally and laterally, with small flecks of dark brown and large patches of green mottling posterolaterally and on arms, and pale green blotches on dorsum and limbs, most prominent being five blotches aligned anteroposteriorly on posterior half of mid-dorsum ( Fig. 2A ). Head predominantly pale green, mottled with flecks of dark green, green colouration extending laterally across tympanum to dorsal edge of axilla and on to forearms, blotch of green on dorsal surface of hand isolated from green on forearm. Iris pale grey with moderately dense dark-brown reticulations and pale gold inner rim without reticulations. Intensity and shade of dorsal green and brown colouration in life varied from beige to rufous brown depending on time of day, being darker (rufous brown, as shown in Fig. 2A ) at night.

Ventrally white anteriorly with patches of grey laterally on throat, and small flecks and short reticulations of dark brown concentrated in a broad band around ventral edge of lower jaw; posterior half of venter and patch around axilla that extends on to base of arm golden-yellow; laterally dark-brown flecks extend from axilla to groin, these small and scattered anteriorly, becoming large interconnected blotches near groin. Anterior surfaces of thighs and tibiae pale blue, extensively mottled with deep brown; blue colouration extends anteriorly onto ventrolateral surfaces of belly but barely intrudes onto ventral golden-yellow patch. Posterior surfaces of thighs extensively mottled with blue and brown, bordered ventrally by broad band of golden yellow that narrows towards heel and incorporates patch of prominent tubercles of same colour. Ventral surfaces of tibiae pale iridescent blue with large dark-brown blotches; of tarsus suffused with golden-yellow, with peppering of fine dark-brown specks ( Fig. 2E ); plantar surfaces golden-yellow, except disc of T3, distal half of T4, and entirety of T5; these areas with, at most, light peppering of fine, dark-brown specks. Outer margins of limbs with pale crenulated skin folds, vent surrounded by patch of prominent pale tubercles, heel with cluster of small, ivory tubercles ( Fig. 2F ).

Colour in preservative: green markings have become shades of blue, large green dorsal blotches palest; background beige-brown has become mottled grey; dark-brown patches and flecks remain dark brown, but blue on limbs is darker and without iridescence; ivory of crenulated skin folds, and prominent tubercles around vent, have become more cream. Ventral surfaces predominantly cream, golden-yellow patches have disappeared except for slight suffusion on plantar surfaces and posterior of thighs.

Variation. The three paratypes are adult males; morphometric variation in the type series is limited ( Table 4). The extent of green markings on the dorsum is variable ( Fig. 2 ). All of the types have predominantly green heads and limbs, but in SAMA R71465 ( Fig. 2B ) brown on dorsum extends further anteriorly than in the other types, reaching to mid-way between eyes, and there are more extensive patches of mottled green, with more numerous pale green blotches dorsally; SAMA R71464 ( Fig. 2C ) is predominantly brown dorsally, with green restricted to dorsal surfaces of arms and legs, a large patch of mottled green posterolaterally, small, scattered patches of mottled green on dorsum and small green spot on each hand. SJR12834 ( PNGNM) ( Fig. 2D ) is more uniformly green than the other specimens, lacking pale green spots and mottling. In life the three paratypes shared with the holotype a large golden-yellow patch posteriorly on the venter that was bordered by dark brown blotches; a large golden-yellow patch on the posteroventral surfaces of the thighs; and blue with dark brown blotches on the other hidden surfaces of the limbs. However, there is variation in the size, distribution, and connectivity of the brown blotches that border the ventral golden-yellow patch. In SAMA R71465 and SJR12834 ( PNGNM) these are similar to the holotype, being interconnected to form a single large, irregular blotch, though the size of the blotch is variable; in SAMA R71464 the dark markings in the groin are not interconnected, instead forming a cluster of smaller, discrete blotches. Brown spotting on the anterior half of the venter is barely detectable in the holotype and two of the paratypes, but extensive in SAMA R71465 .

Advertisement call. The advertisement call of L. aplini is a finely pulsed note (a “buzz”) normally followed by one or more shorter clicking notes (“clicks”) ( Fig. 5 ). Twenty-two calls of the holotype recorded at an air temperature of 23.7°C were produced at a rate of 1.26 calls/s, lasted 0.16– 1.21 s (mean = 0.34, SD = 0.24, n = 20), and had a dominant frequency of 2150–3336 hz (mean = 2550, SD = 360, n = 18; however in most calls dominant frequency was between 2300 and 2400 hz). Most calls (20 of 22; 91%) comprised a single buzz note lasting 0.026 – 0.062 s (mean = 0.046, SD = 0.010), followed by one (13 of 22; 60%) or up to seven, sharp multi-pulsed clicking notes lasting 0.005 – 0.020 s (mean = 0.014, SD = 0.004, n = 29). Note rate for multi-note calls was 3.98–6.99 notes/s (mean = 5.40, SD = 0.81, n = 17). Pulses in buzz notes were produced too rapidly to count in all but one call, in which 15 pulses were produced at a rate of 272 pulses/s. Clicks consisted predominantly of two, but occasionally 1 or 4, discrete pulses each lasting c. 0.005 s. Pulse rate in click notes was much slower than in buzz notes, at around 166 pulses/s. The distribution of energy in the two types of notes also differed, with amplitude in buzzes increasing gradually from the start of the call, and reaching maximum intensity near the end of the call before rapidly declining ( Fig. 5 ); in contrast amplitude in the clicks was at or near maximum from the start of the call and then distributed uniformly until the end ( Fig. 5 ). Although only one recorded buzz was not followed by one or more clicks, and only one recorded call was represented solely by a click, a number of additional calls comprising buzz and click calls produced in isolation were heard at the type locality.

Distribution and habitat. Litoria aplini is known from one location on the northern slopes of Papua New Guinea’s central cordillera ( Fig. 6 ), where it was collected from primary hill forest ( Fig. 7A ) at an altitude of 940 m a.s.l. The substrate at the type locality is limestone, and free-standing water was limited. The type series was collected from trees adjacent to a narrow, mostly dry gully where males called from perches up to five metres high over small (<1 m 2), isolated pools of water in the base of the gully ( Fig. 7B ). However, no eggs or larvae were observed so the breeding strategy of this species remains unknown.

It is not known whether this species is endemic to forest on karst substrates, but there is increasing evidence for a suite of karst associated herpetofauna on the southern slopes of Papua New Guinea’s central cordillera ( Oliver et al., 2019a) so it is possible that a similar assemblage occurs in the much more poorly surveyed northern karst habitats.

ACKNOWLEDGEMENTS. Fieldwork in Papua New Guinea by SJR was approved by the PNG National Research Institute, and the PNG Department of Environment and Conservation (now the Conservation and Environment Protection Authority). Fieldwork in the Sepik River basin was supported by Frieda River Limited and SJR is particularly grateful to Michael Hawkins of FRL for his support. An ABRS Research and Capacity-Building grant (205-54) supported the nucleotide sequencing which was carried out by Luke Price and Leanne Wheaton. We thank Mark Hutchinson and Carolyn Kovach (South Australian Museum) for access to specimens in their care, Rainer Günther (Museum für Naturkunde Berlin) for providing valuable comparative tissue samples and Fred Kraus (University of Michigan) for providing images of Litoria ollauro . Lisa Capon kindly produced figures 1–3 and 5–7 and Paul Oliver and Rainer Günther provided useful comments that greatly improved the manuscript.

Figures

Figure 1. Views of Litoria aplini holotype (SAMA R71463) in preservative. (A) dorsal; (B) ventral (scale bar = 10 mm); (C) palmar; and (D) plantar surfaces (scale bar = 5 mm).

Figure 2. Type series of Litoria aplini in life: (A) SAMA R71463; (B) SAMA R71465; (C) SAMA R71464; (D) SJR12834 (PNGNM); (E) SAMA R71463, in ventral view; and (F) SAMA R71463, ventral surfaces of hind limb.

Figure 3. Closely related species that could beconfused with Litoria aplini:(A) Litoria iris(SAMA R71615), adult male inlife (Hindenburg Range,Western Province); (B) Litoria iris showing bright colours on hidden surfaces of the hind legs (unvouchered animal, Hela Province); (C) Litoria majikthise (SAMA R65042), in life, Muller Range, Western Province); (D, E) Litoria majikthise (SAMA R65042), showing colour ventrally and on hidden surfaces of hind limbs; and (F) Litoria ollauro, Milne Bay Province, photo courtesy of Fred Kraus.

Figure 4. Maximum likelihood (ML) phylogram of relationships between mitochondrial ND4 nucleotide sequences of Litoria. Numbers at nodes are: left—Bayesian posterior probabilities, right—ML bootstrap proportions.

Figure 5.Advertisement call of the holotype of Litoria aplini(SAMA R71463), showing (top) wave form and (bottom) audiospectrogram of a four-note call recorded at 23.7°C.

Figure 6. Map of Papua New Guinea showing the type locality of Litoria aplini.

Figure 7. Habitat of Litoria aplini: (A) forest interior at the type locality; and (B) males were calling from trees over small pools (arrow) in the bed of a steep, narrow limestone gully.