Platymantis adiastola, Brown, Rafe M., Richards, Stephen J., Sukumaran, Jeet & Foufopoulos, Johannes, 2006

Brown, Rafe M., Richards, Stephen J., Sukumaran, Jeet & Foufopoulos, Johannes, 2006, A new morphologically cryptic species of forest frog (genus Platymantis) from New Britain Island, Bismarck Archipelago, Zootaxa 1334, pp. 45-68 : 50-63

Platymantis adiastola , new species

( Figs 4–6)

Holotype: SAMA R61906, adult male, collected by S. Richards at Wanui Camp, Wanui River Valley (near Wide Bay), 310 m above sea level (05 21.638’S, 152° 05.266’E), New Britain Isl., East New Britain Province, Papua New Guinea, 20 March 2000.

Paratypes: SAMA R57014–15, R57040–41, same data as holotype except collected 13 March 2000; R60257–8, 15 March 2000; R60259, 18 March 2000; SAMA R61907, 19 March; SAMA R61908, UPNG 9974-6, 20 March 2000; SAMA R61909, 22 March 2000.

Etymology: The specific epithet is chosen from the Greek adiastolos, meaning confused, mixed up, or not separated, in reference to past confusion surrounding the taxonomic status of the new species.

Diagnosis: Platymantis adiastola is distinguished from congeners by (1) body size (39.5–43.9 for 11 males; 71.7 for one female), (2) narrowly expanded terminal disks of the fingers and toes, (3) skin of dorsum with scattered longitudinal tubercular ridges, including two long (4–6 mm) medially bowed suprascapular dermal ridges, (4) upper eyelids devoid of conical tubercles, (5) subarticular tubercles of fingers, toes, hands and feet prominent and raised, (6) digits lacking all vestiges of lateral flange and interdigital webbing, and (7) unique advertisement call.

The new species is morphologically nearly identical to P. schmidti but differs from this species by slight differences in body size and proportions ( Table 1 ), an apparent tendency towards a more elevated calling perch preference, and a possible greater extent of sexual size dimorphism ( P. adiastola male/female SVL = 0.57; P. schmidti = 0.69). The main distinguishing feature between these two morphologically cryptic forms is the male advertisement call. Platymantis adiastola produces a call composed of a series of shrill, high frequency (mean peak dominant frequency 3.0–3.2 kHz), complex, tonal notes whereas P. schmidti calls with a simple train of twin-pulse lower frequency (2.4–2.6 kHz) notes lacking tonal elements. Platymantis adiastola has a lower mean note repetition rate (4.3 notes/s) than P. s c h m i d t i (12.8 notes/s) and produces fewer mean notes per call (mean = 16.6) than P. s c h m i d t i (mean = 23.9). Finally, the call of P. adiastola exhibits a progressively decreasing internote interval across the call, whereas P. s c h m i d t i has a uniform internote interval throughout the entire call.

Description of holotype: A mature, undissected male specimen, in excellent condition; habitus moderately stocky; head distinct, slightly wider in dorsal aspect than body, length 42.6% of SVL; head length 114.2% of head width; snout short, its tip bluntly rounded, protruding slightly beyond lower jaw; snout posteroventrally slanted in lateral aspect; eyes protrude laterally beyond silhouette of head in dorsal aspect, and strongly beyond dorsal surface of head in lateral aspect; labial region flat and smooth, not flared, lips not swollen, not extending past eyes when viewed in dorsal aspect; interorbital region flat; eye diameter 143.4% interorbital distance; pupil horizontally ovoid; canthus rostralis slightly concave; loreal region gently sloping, slightly concave; eye diameter 73.0% of snout length, 126.6% of eye–narial distance; nostrils slightly laterally protuberant; eye narial distance much longer than distance from nostril to tip of snout; internarial region flat; tympanum distinct, its diameter 56.9% of eye diameter; dorsal edge of tympanic annulus in contact with and slightly overlapped by supratympanic fold, the latter extending from dorsoposterior corner of eye, along dorsal edge of tympanum, and Platymantis adiastola Platymantis schmidti Platymantis schmidti n. sp. (original collections) (recent collections) terminating nearly at supraaxillary region; tongue subcircular, with deep posterior notch and narrow anterior attachment; choanae round, minute, at anterolateral edge of palate, widely separated by a distance eight to ten times greater than their diameter, not obscured by palatal shelf; dentigerous process of vomer oblong; vomerine teeth tiny, translucent, numbering four to six; dentigerous process very slightly angled anterolaterally, with closest (posterior) points separated by a distance two times the diameter of one choana, their most distant (anterior) ends separated by distance equal to three times diameter of choanae; openings to vocal sac short slits, slightly posterior to rictus; prominent postrictal tubercle cluster present at posteroventral edge of tympanum.

Skin of dorsal surfaces of body, head, and limbs generally smooth, except for fine longitudinal ridges of variable length on dorsum; a faint pair of medially bowed suprascapular dermal folds present; several other short glandular folds present along dorsolateral edge of trunk and in temporal region; ventral surfaces of trunk, head, throat, and limbs smooth; manus length 45.9% of foot length; digits of manus narrow in appearance and round in cross-section; lateral edges of digits without fleshy dermal flanges; terminal disks moderately expanded and protuberant, with short circumarginal folds on distal tips of digits; minute supraarticlar flaps present above penultimate-ultimate phalangeal articulation; decreasing digital length III, I, II=IV; subarticular tubercles extremely prominent and protuberant, rounded on ventral surfaces; one subarticular tubercle on digits I–II, two tubercles under digits III–IV; supernumerary tubercles very prominent and rounded, present at the base of all digits; minute palmar tubercles preset basal to supernumary tubercles; thenar (inner metacarpal), medial palmar and outer metacarpal tubercle prominent, ovoid, highly convex, and nearly equal in size; slightly raised dermal tubercles present on ventral surfaces of wrists; nuptial pads absent, forearm musculature not hypertrophied.

Hindlimbs moderately well developed; foot length 91.9% of tibia length; tibia length 60.3% of snout-vent length; tarsus smooth, lacking folds, flaps, or tubercles; digits of toes moderately expanded and ovoid; slight, narrow lateral dermal flanges present along distal phalanges; circummarginal grooves limited to distal ends of digits; supraarticular cutaneous folds slight; plantar surfaces of pes smooth, with prominently protuberant subarticular tubercles but lacking supernumerary tubercles; subarticular tubercles numbering three under Toe IV, two under Toes III and V, and one each under Toes I and II; decreasing digit length IV, III, V, II, I; outer metatarsal tubercle prominent and subcircular, pointed; inner metatarsal tubercle prominent and elongate, with a sharp venterolateral edge; digits of pes completely free of web; cloacal region smooth and devoid of supracloacaal tubercles or dermal flaps.

Measurements of holotype: SVL 40.6; ED 5.6; TD 3.2; HL 17.3; SNL 7.7; IOD 3.9; HW 15.1; FA 8.6; TBL 24.5; TSL 13.5; PL 22.5; ML 10.3; Toe4L 15.0; Fin1L 5.9; Fin3L 7.2; Fin3DW 1.5; Fin3PPW 0.8; Toe4DW=1.5; Toe4PPW=0.6.

Color of holotype in preservative: Dorsum homogeneous dark brown, blending laterally into light and dark brown marbled flanks with scattered enlarged distinct white spots; dorsal surfaces of head grayish; lateral surfaces of snout and head darker, nearly black with light brown tympanum and distinct white spots on lips; postrictal region heterogeneous, with black and brown blotches and white-tipped postrectal tubercles; dorsal surfaces of limbs brown with darker transverse bars (two on forearm, three on humerus, three on tibia, two on tarsus); dorsal surfaces of hands, feet, and digits dark brown with white bars on phalangeal articulations; inner two digits of hands and feet distinctly lighter than outer digital surfaces; venter pale cream; underside of throat speckled with brown, coalescing into nearly solid brown ventrolateral margins of throat; ventral surfaces of hands dark brown with prominent white subarticular tubercles; ventral surfaces of feet solid dark gray with light gray, velvety digital disks. Holotype color in life unrecorded.

Var i at io n: There are three basic color patterns evident in our sample of P. adiastola from the type locality. The majority (9 of 11 specimens) exhibit solid gray dorsal coloration, with faint brown interoribital bars and only scattered flecks of black associated with dorsal tubercular ridges. This largely pigment-free pattern continues on to dorsal surfaces of limbs in a few specimens (SAMA R61907, 61909) but all remaining specimens have distinct transverse brown bars on limbs. The other two major color patterns include a specimen with a single, thick, vertebral yellow stripe (SAMA R61908) and one with two dorsolateral pale lines (SAMA R60259). Lateral surfaces of head with dark bar from tip of snout, through loreal region, encircling orbit, and following supratympanic fold posteroventrally to rictus of jaw. In most specimens (8/11), this dark coloration covers the majority of the lateral portions of the head. In three specimens (SAMA R61907, 61909, 60259), lateral portions of the head are distinctly lighter and darker pigmentation is limited to the canthus rostralis and supratympanic fold. Flank coloration varies from a simple dark (dorsally) to light (ventrally) fade (SAMA R60257, 60259) to a more distinct stratification between dark (above) and pale (below), with numerous moderately distinct pale round spots scattered across flanks.

Ventral surfaces of the body are uniform pale cream with throat similarly colored or with a diffuse dark gray ventral surface of the entire head and throat (SAMA R61906, 61908, UPNG 9974-5). In these specimens, the chin and lower lips are distinctly lighter than surrounding throat. Palmar surfaces of the hands vary from very dark gray with white subarticular tubercles (e.g., UPNG 9974) to pale cream throughout their ventral surfaces (SAMA R60257). Plantar surfaces of the feet are uniform light gray (SAMA R60258) to dark gray with lighter subarticular tubercles (SAMA R61906, R61908, UPNG 9974).

Color in life: Based on color images of paratype SAMA R61907 before preservation. Dorsal surfaces are khaki to dark tan or brown (e.g. Fig. 5). The dark canthal and supratympanic bars are dark brown, tympanum is light brown, the loreal region is dark brown with gold flecks and the labial region grayish pink with gold bars. The iris is gold above and dark below below pupil and postrictal tubercles are tan with white tips. Bars on limbs are varying shades of brown on a lighter tan or brown background. The dorsal surfaces of the digits are brown with white on spots on digital articulations and the inner two digits on hands and feet and bright white. The throat is white and the venter is white anteriorly, fading to cream or yellow ventrally by groin. Ventral surfaces of limbs are yellow or pink.

Size dimorphism: The single available female specimen of P. adiastola has a snoutvent length of 71.7 mm which is considerably larger than all of the nine available P. schmidti specimens examined by us (Talasea population: SVL 41.1–57.6; Table 1 ). This suggests to us the possibility that P. adiastola may have a greater extent of sexual size dimorphism than P. schmidti (P. a d i a s t o l a male/female SVL = 0.57; P. schmidti = 0.69) but larger sample sizes will be required to address this question in the future.

Ecology and natural history: Platymantis adiastola was observed, collected, and recorded at Wanui Camp in primary forest (two hours walking distance from Sampun Village; 0 5o 21.638'S, 152o 05.266'E), 300–500 m above sea level. This site was sampled for 14 days (14–28 March 2000). At Wanui the new species was subjectively characterized as 8–10 times more abundant than P. schmidti . In contrast, P. schmidti is clearly the most common form at lower elevations. Vocalizations confirming the sole presence of P. schmidti have been recorded or noted at numerous coastal localities, e.g. Kokopo and the vicinity of Rabaul, (Gazelle Peninsula), Sulu and Silali (foothills of the Nakanai Mountains) and, most significantly, at Talasea, the type locality of P. schmidti (SJR and JF pers. obs.). It was also abundant near Sampun Village (~ 50 m above sea level) and no P. adiastola were confirmed from this lowland site.

Where the two species have been observed together, we have noted slight but clear microhabitat differences between the two forms (e.g. Foufopoulos & Richards in press): P. adiastola has been consistently observed calling from elevated perches (leaves and branches) as high as 2 m above the ground. In contrast, P. schmidti called predominantly from the ground, from low, herbaceous vegetation, or from stumps or fallen logs, consistently less than 1 m above the ground ( Menzies 1982a, SJR and JF pers. obs.).

Distribution: Confirmed only at two localities ( Fig. 1): near Sulu and Silali Villages, foothills of the Nakanai Mountains, West New Britain ( Foufopoulos & Brown 2004) and Wanui, East New Britain (Foufopoulos & Richards in press).

Advertisement calls: The advertisement call of P. adiastola is markedly distinct from that of P. s c h m i d t i in both temporal and spectral characteristics. It is, however, similar in general call structure (a rapidly amplitude-modulated train of notes) and so its impression on the human ear is similar. Because the call of the new species is one of the primary characteristics distinguishing the new species, we describe its vocalizations and compare them to those of P. s c h m i d t i in some detail, below. The following descriptions are based on 4 vouchered recordings of P. adiastola (2 from the Nakanai Mountains; 2 from Wanui) and 11 of P. s c h m i d t i (9 from the Nakanai Mountains; 2 from Wanui).

The call of P. adiastola is a series of shrill, high-frequency tonal notes, delivered in a train of variable total duration and note repetition rate. One very distinctive characteristic of the call is the progressive shortening of inter-note intervals throughout the call, such that calls start slowly and gradually shift towards a more rapid note delivery rate towards the end of the note train. The effect on the human ear is a sound akin to that of a marble being dropped and bouncing, faster and faster, until it comes to rest after a final burst of rapid strikes ( Fig. 7 A). In contrast, the calls of P. s c h m i d t i consist of a much more rapid, evenly-spaced train of dull, lower frequency, stridulating, vibrational notes, like the sound produced by slowly running a finger over the teeth of a comb or running a stick down a length of wood fence ( Fig. 7 B). Menzies stated that the call of P. s c h m i d t i “lacks musical quality and merely sounds like a stick being rubbed against wooden railings” ( Menzies 1982a: 2).

Individual male mean note repetition rate ([total number of notes – 1]/time from beginning of first note to beginning of last) was 4.0–4.5 (= 4.3 ± 0.4 SD; n = 4) notes/s for P. adiastola and 9.7–15.3 (= 12.8 ± 3.7 SD; n = 9) notes/s for P. s c h m i d t i.

Calls of individual males of P. adiastola contained as few as 9–15 (mean 11.6 ± 3.6 SD) to as many as 11–38 (17.1 ± 8.9 SD) notes per call. The average number of notes per call for our sample of four males was 16.6 ± 3.4 (11.6–17.1; n = 5). Calls of individual male P. s c h m i d t i contained as few as 8–15 (mean 13.6 ± 5.2 SD) to as many as 42–55 (45.2 ± 8.1 SD) notes per call. The average number of notes per call for our sample of 13 P. schmidti recordings was 23.9 ± 8.8 SD (13.6–45.2).

Individual note structure between the two species was quite different. The shrill, high frequency tonal notes of the call of P. a d i a s t o l a have a relatively complex internal temporal and spectral structure ( Fig 8). Each note contains three distinct frequency components ( Fig. 8 A, C) and a complex, amplitude modulated internal note structure with pronounced differences in call energy contained in the different amplitude modulated within-note pulses ( Fig. 8 B). The dull, lower frequency twin-pulse notes of the call of P. schmidti ( Fig. 9) are quite different in that each note contains a tightly-spaced twin-pulse structure ( Fig. 9 B–D), with pulses only slightly differentiated in amplitude ( Fig. 9 B, D) and both very similar to one another in spectral structure ( Fig. 9 C). Menzies referred to the call of P. schmidti as "little more than a succession of double clicks” ( Menzies 1982a: 2).

In P. adiastola calls, each note contains a clear fundamental frequency component at 1.0 to 2.2 kHz (mean peak frequency = 1.1–1.3 kHz for four males), an emphasized (=dominant) frequency between 2.5 and 3.6 kHz (mean peak frequency = 3.0–3.2 kHz), and then an additional frequency component between 4.2 and 5.0 kHz (mean peak frequency 4.3–4.8 kHz). The three frequency components are stereotyped, with variation in frequency between males present (and apparently varying inversely proportionately with body size; correlations not shown) but with little or no within-male or within-call frequency modulation or energy shifts. In P. s c h m i d t i, the emphasized (= dominant) frequency lies between 2.2 and 2.9 kHz (peak frequency = 2.4–2.6 kHz for 11 males), and then minor frequency components include a fundamental between 1.1–1.9 kHz (= 1.5kHz) and weak harmonics between 7.4 and 8.6 kHz. Unlike the new species, P. schmidti males exhibit a shift in emphasized frequency across the duration of long calls. Thus, calls typically start with the first 6–10 notes at a lower dominant frequency (2.4–2.6 kHz) and males shift the calling energy of subsequent notes to higher dominant frequencies (2.8–2.9 kHz) towards the end of the call.

Individual notes of P. adiastola begin with 2–4 internal amplitude modulated pulses of 5–10 ms ( Fig. 8 B), followed by the intense tonal note ( Fig. 8 B–D) of 18–25 ms. Average relative intensity (in dB) of each of the preceding pulses is approximately 45–55% of the subsequent tonal portion of each note. Total note duration for individual males ranged from 42.2–46.5 ms (= 44.8 ± 3.8; n=13 notes) to 47.4–53.5 ms (= 50.8 ± 3.1; n=17 notes); mean note duration for our entire sample of recordings was 47.3 ± 4.4 (42.3–56.7; n=4). Inter-note intervals for the same males ranged from 232–255 ms to 245–267 ms; mean inter-note interval for the entire sample was 252.2 ± 26.3 SD ms (242.3–254.7; n=4).

Individual notes of P. schmidti are paired pulses ( Fig. 8 B–D) of similar amplitude ( Fig. 9 D). Both pulses begin with a rapid rise to peak amplitude (2–5 ms), followed by a more gradual decline to ambient levels ( Fig. 9 B); in the second pulse, time for amplitude to fall to ambient levels is 2–3 times that of the first pulse. The average relative intensity (in dB) of the first pulses is approximately 75–90% of the second pulse ( Fig. 9 B, D). Total note duration for individual males ranged from 44.0–47.8 ms (= 45.8 ± 2.9; n=27 notes) to 48.9–61.7 ms (= 56.1 ± 4.7; n=34 notes); mean note duration for our entire sample of recordings was 47.3 ± 4.4 SD (45.8–56.1; n= 11 males). Duration of the first pulse was consistently briefer (approximately 10–20 ms) than that of the second (25–33 ms). Individual male interpulse intervals ranged from 11.2–14.3 (= 12.4 ± 1.2 SD) to 17.8–22.5 (20.6 ± 2.6 SD and internote intervals varied from 26.3–37.4 (= 32.2 ± 4.6 SD) to 53.2–64.8 (= 58.2 ± 8.3). Mean interpulse interval for the entire sample was 16.7 ± 5.4 SD (12.4–20.6; n=11) and mean internote interval was 46.3 ± 12.9 SD (32.2–58.2; n=11).

Tables

TABLE 1. Morphometric variation (in mm) in adult Platymantis adiastola n. sp. and P. s c h m i d t i (original collections, holotype and paratypes, as well as recent collections). Table entries include mean ± 1 standard deviation (with range shown below), and sample size (n). See text for character abbreviations.

	Holotype	Male (n=10)	Female (n=1)	Holotype	Male (n=8)	Female (n=8)	Male (n=7)
SVL	41.9	41 ± 1.4 39.4–43.9	71.7	55.9	34.4 ± 2.1 30.5–36.4	50.2 ± 5.8 41.1–57.6	39.7 ± 2.3 35.6–42.6
ED	6.0	5.6 ± 0.4 5–6.3	7.5	4.8	3.7 ± 0.4 3.1–4.3	5.1 ± 0.5 4.3–5.7	3.7 ± 0.5 3.1–4.6
TD	3.7	3.9 ± 0.3 3.2–4.5	5.7	3.8	3.2 ± 0.2 2.9–3.5	4 ± 0.3 3.6–4.4	2.9 ± 0.2 2.7–3.2
HL	17.6	16.9 ± 0.6 16–17.8	27.7	20.6	14.3 ± 0.8 13–15.4	20 ± 2 16.4–23	15.9 ± 1.3 14.2–18.1
SNL	6.9	7.5 ± 0.4 6.9–8.2	12.5	8.9	6.6 ± 0.5 5.9–7.5	9.1 ± 1.1 7.4–10.4	7.0 ± 0.7 6.0–7.9
IOD	4.7	4.1 ± 0.2 3.9–4.7	7.4	4.1	3.3 ± 0.2 3.0–3.5	4.6 ± 0.6 3.8–5.4	3.1 ± 0.1 3.0–3.2
HW	16.4	15.4 ± 1.0 14.2–17.5	24.7	19.1	12.2 ± 0.7 11.4–13.5	18.5 ± 2.5 14–22.1	13.9 ± 1 12.3–15.1
FA	10.4	10.1 ± 0.7 8.6–10.8	16.3	10.2	7.3 ± 0.9 6.0–8.8	11.1 ± 1.9 8.9–14.2	7.3 ± 0.9 6.4–8.8
TBL	22.5	23.8 ± 0.8 22.5–24.9	38.8	33.6	19.4 ± 0.7 18.6–20.5	28.6 ± 3 25.1–33.6	23.2 ± 1.2 21.3–24.3
TSL	13.0	13.4 ± 0.5 12.6–14	21.8	16.4	10.5 ± 0.4 10.0–11.0	15.4 ± 1.4 13.3–17.6	11.2 ± 0.8 10.3–12.4
PL	22.2	22.8 ± 0.6 22–23.9	36.5	29.2	17.9 ± 0.6 17.1–19.1	25.8 ± 2.2 22.7–29.2	20.8 ± 1.5 18.1–22.3
ML	11.0	10.7 ± 0.5 10.0–11.7	17.3	13.9	8.6 ± 0.3 8.1–9.1	12.5 ± 1.2 10.6–13.9	9.9 ± 1.3 8.1–11.2
TL	14.8	16 ± 0.9 14.8–17.3	30.0	22.6	13.6 ± 1.0 12.5–15.4	19.8 ± 2.5 15.8–23.4	15.6 ± 2.2 12.4–17.7
Fin1L	6.1	6 ± 0.5 5.3–6.6	10.4	7.4	4.6 ± 0.3 4.2–5.1	7.4 ± 0.7 6.5–8.5	5.7 ± 0.7 4.4–6.2
Fin3L	7.6	7.4 ± 0.4 6.9–8.3	11.4	9.4	5.9 ± 0.3 5.7–6.4	8.5 ± 0.9 7.2–9.9	7.1 ± 0.9 5.9–8.1
Fin3DW	1.5	1.5 ± 0.1 1.3–1.8	1.9	1.4	1.0 ± 0.1 0.9–1.1	1.2 ± 0.1 1.1–1.4	1.1 ± 0.1 1.0–1.3
Fin3PPW	0.73	0.6 ± 0.1 0.6–0.8	1.07	1.01	0.7 ± 0.1 0.6–0.9	0.9 ± 0.1 0.8–1	0.9 ± 0.1 0.7–1.0
Toe4DW	1.46	1.6 ± 0.2 1.3–1.8	2.27	1.53	1.1 ± 0.1 1–1.2	1.3 ± 0.2 1.1–1.5	1.2 ± 0.2 1.0–1.5
Toe4PPW	0.63	0.6 ± 0.1 0.5–0.7	1.21	0.91	0.7 ± 0.1 0.6–0.9	0.8 ± 0.1 0.7–1	0.9 ± 0.1 0.7–1.0