Platymantis parilis, Brown, Rafe M. & Richards, Stephen J., 2008

Brown, Rafe M. & Richards, Stephen J., 2008, Two new frogs of the genus Platymantis (Anura: Ceratobatrachidae) from the Isabel Island group, Solomon Islands, Zootaxa 1888, pp. 47-68 : 56-62

Platymantis parilis sp. nov.

Figs 3 B, 4B, 6, 7

Holotype. SAMA R56911, adult male, collected by S. Richards near Kolopakisa Village, ~ 0–10 m above sea level (07° 36.008'S, 158° 39.092'E), north-western Isabel Isl., Isabel Province, Solomon Islands, on 16 May 2000.

Paratypes. SAMA R56908–10, three males, same data as holotype except SAMA R56910 collected on 17 May 2000.

Etymology. The specific epithet is chosen from the Latin parilis , meaning equivalent, like, or similar, in reference to the morphological similarity between the new species and the acoustically and genetically distinct Platymantis neckeri .

Diagnosis. Platymantis parilis is distinguished from congeners by (1) body size (39.5–41.5 mm for four adult males), (2) widely expanded terminal disks of the fingers and toes ( Fig. 6 ), (3) skin of dorsum entirely smooth or with only a few low tubercular ridges in the scapular region, (4) subarticular tubercles of fingers, toes, hands and feet low and flattened on their ventral surfaces, (5) fingers and toes with lateral dermal flange, (6) toes with basal vestiges of interdigital webbing, and (7) unique advertisement call.

Platymantis parilis is morphologically indistinguishable from P. neckeri but cannot be confused with any other species of Platymantis . Aside from genetic data indicating that P. parilis and P. neckeri consistently form monophyletic clusters of moderately genetically distinct haplotypes (3.7–4.2% uncorrected percent divergence in the 16S ribosomal RNA mitochondrial gene between four samples of P. parilis and 16 samples of P. neckeri ; RMB, unpublished data), the new species can be readily distinguished by its unique advertisement call ( Figs. 7 , 8 ).

Description of holotype. A mature male, in excellent condition; habitus slender; head slightly distinct, only slightly wider in dorsal aspect than body, length 40.2% of SVL; head length 102% of head width; snout moderately long, its tip sharply pointed, protruding well beyond lower jaw, pointed in lateral aspect; eyes protrude laterally only slightly beyond silhouette of head in dorsal aspect, and well beyond dorsal surface of head in lateral aspect; labial region flat and slanted, lips flared, protuberant, extending well beyond eyes in dorsal aspect; interorbital region flat; eye diameter 118% of interorbital distance; pupil horizontally ovoid, nearly subcircular; canthus rostralis nearly straight (slightly medially bowed); loreal region very slightly concave, continuous with flat slanting upper lip; eye diameter 50.9% of snout length; nostrils laterally protuberant; eyenarial distance 4–5 times the distance from nostril to tip of snout; internarial region flat; tympanum distinct, its diameter 63.7% of eye diameter; dorsal edge of tympanic annulus in contact with, but not concealed by supratympanic fold, the latter extending from dorsoposterior corner of eye, along dorsal edge of tympanum, and terminating nearly at supra-axillary region; a single weakly conical post-rictal tubercle present between posteroventral edge of tympanum and forearm insertion; tongue triangular, with deep posterior notch and narrow anterior attachment; choanae round, minute, at anterolateral edge of palate, separated by a distance 5–6 times their diameter, not obscured by palatal shelf; dentigerous process of vomer ovoid; vomerine teeth tiny, translucent, numbering 4 or 5; dentigerous process sharply anterolaterally angled, with closest (posterior) points separated by a distance two times the diameter of one choana, their most distant (anterior) ends separated by a distance equal to 4–5 times diameter of choanae; openings to vocal sac moderate slits, at the level of the angle of the jaw.

Skin of dorsal surfaces of body, head, and limbs smooth; a few low and indistinct short tubercular ridges in scapular region; suprascapular dermal folds and dorsolateral folds absent; dorsal surfaces of limbs textured as body; tubercles absent; ventral surfaces of head, throat and limbs smooth; trunk weakly granular; groin slightly more granular; manus length 58.9% of foot length; digits of manus ( Fig. 6 A) wide and ovoid in crosssection, owing to lateral dermal flange bordering fingers; lateral edges of all digits with wide fleshy dermal flanges; terminal disks widely expanded, exceeding twice the width of penultimate phalanges, with circummarginal folds wrapping around distal portions of digits; supraarticlar flaps present above penultimate-ultimate phalangeal articulation; decreasing digital length III, IV, II, I; subarticular tubercles low, not pointed, angled anteriorly towards tip of digits, flattened on ventral surfaces; one subarticular tubercle under digits I– II, two tubercles under digits III–IV; supernumerary tubercles flat and somewhat indistinct, present at the base of all digits; palmar surfaces basal to supernumerary tubercles entirely smooth; thenar (inner metacarpal), medial palmar and outer metacarpal tubercles flat, edges indistinct; thenal tubercle greatly moderate and elongate, situated on medial edge of digit I, connected to medial dermal flange; medial palmar (inner metacarpal) tubercle greatly enlarged, subtriangular, twice the size of thenar tubercle; outer metcarpal tubercles small, subcircular, half the size of thenar tubercle, not separated from medial metacarpal tubercle; nuptial pads absent, forearm musculature not hypertrophied.

Hindlimbs short; tibia length 50.1% of snout-vent length, foot length 95.6% of tibia length; tarsus without minute dermal flaps but with a few very low tubercles, continuous in line with postaxial dermal flange along Toe V and outer edge of pes (terminating after wrapping around ankle); small tubercles present on tibio-tarsal articulation; digits of toes widely expanded ( Fig. 6 B), twice the width of penultimate phanges; circummarginal grooves wrapping around distal ends of digits; supraarticular cutaneous folds present above penultimateultimate phalangeal articulation; plantar surfaces of pes smooth, with low subarticular tubercles but lacking supernumerary tubercles or texture on plantar surfaces; subarticular tubercles with flattened ventral surfaces, 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 low, flattened, indistinct and circular; inner metatarsal tubercle moderate, low, elongate, twice the size of outer metatarsal tubercle, with only a slightly sharpened venterolateral edge; digits of pes basally webed; web reaching first subarticular tubecles of digits all digits, except extending half way between the first and second subarticular tubercle on the outer edge of Toe III; supracloacaal tubercles and dermal flaps absent.

Measurements of holotype. SVL 39.5; ED 4.1; TD 2.7; HL 16.7; SNL 7.7; IOD 3.3; HW 15.5; FL 20.3; TBL 20.6; TSL 910; PL 19.3; ML 11.5; FA 8.8; Toe4L 13.3; Fin1L 4.3; Fin3L 8.1; Fin3DW 1.9; Fin3PPW 1.1; Toe4DW 1.8; Toe4PPW 1.0.

Color of holotype in preservative. Dorsal surfaces dark brown with pale yellow streaks and blotches irregularly scattered across the trunk and head; eyelids and interorbital region yellowish-tan; dark dorsal coloration fades laterally into light yellowish-tan flanks with irregular brown blotches; dorsal and lateral surfaces of snout colored as body, with brown background coloration and yellowish-tan loreal region, tympanum, and labial bars; tympanum and post-rictal tubercle streaked with pale yellow; snout brown with yellow nares and tip of snout; dorsal surfaces of forelimbs pale yellow, with blotches of gray-brown on wrists, lacking transverse bars; dorsal surfaces of hindlimbs tan with gray-brown blotches, transverse bars absent; concealed surfaces on posterior thighs orange; dorsal surfaces of hands and fingers pale yellow with few brown flecks, lacking differentiated coloration on phalangeal articulations; dorsal surfaces of toes medium gray-brown with black to gray terminal disks; venter pale yellowish cream; underside of throat heavily flecked with slight brown and with medium brown labial blotches wrapping on to the lower lips; ventral surfaces of forelimbs yellowish, with darker brown blotches on outer edges, wrapping around from lateral surfaces; ventral surfaces of hindlimbs slightly darker, orangeish-cream; ventral surfaces of hands pale cream with cream subarticular tubercles and terminal disks; ventral surfaces of pes medium tan and subarticular tubercles and terminal disks gray.

Va r i a t i o n. The paratypes all exhibit dorsal coloration darker than that of the holotype. The three specimens are nearly homogeneously dark brown, with slightly lighter interorbital regions and snouts. All have indistinct transverse bars on limbs, numbering two on forearm, two on tibial segment, and a single bar on the tarsus. In these more darkly-colored specimens, there is a distinct demarcation on the flanks between dark dorsal coloration and yellowish-tan ventral color. In one paratype (SAMA R56908) this stratification occurs more dorsally, and the flanks are predominantly yellow with distinct dark blotches; in SAMA R56906, the dark-light demarcation occurs ventrally, and the flanks are dark brown with bright yellow blotches.

In paratype SAMA R56909 the loreal region is distinctly lighter than the rest of the lateral surfaces of the head and in all paratypes the post-rictal tubercles are bright white. In all specimens, the cartilaginous protrusion at the tip of the snout is pale cream. In the three paratypes, the throats are distinctly darker than the holotype, owing to infusion of small, scattered flecks; in these same specimens, ventral trunk coloration is pale cream with brown flecks and ventral surfaces of hindlimbs are darker brown. In all paratypes, the ventral surfaces of the hands are darker than that of the holotype, with dark brown to gray palmar coloration and light cream subarticular tubercles and terminal disks; ventral surfaces of the feet are dark brown with dark gray tubercles and terminal disks.

Color in life. Based on color images of paratype SAMA R 56908 in life, before preservation ( Fig. 3 B). Dorsal surfaces homogeneous light brown with light interorbital bar and slightly lighter snout. Lateral head color similar to dorsum, but with darker streak across tympanum and a few dark blotches on the upper lips. The iris was silvery above and blue below the pupil and post-rictal tubercles were distinctly white-tipped. The upper arm was distinctly purple in life and remaining dorsal surfaces of the limbs were colored as body, but with indistinct slightly darker brown transverse bars. The dorsal surfaces of the digits were tan with dark brown.

Advertisement call of P. parilis (and comparison to the call of P. n e c k e r i). The following call descriptions are based on two approximately 1 min recording segments per species (all recorded by SJR, within 2°C of each other; P. parilis SAMA R 56911 and P. neckeri SAMA R56792).

Platymantis parilis calls (defined here as sounds produced per single expiration) with a simple, fast train of low frequency (dominant frequency = 1.3–1.5 kHz), dull sounding, dual frequency component notes, lacking any tonal elements ( Fig. 7 ). The impression on the human ear is the sound of wood blocks striking together very rapidly with a constant rate of note delivery.

Calls of individual males of P. parilis contained 11–14 (mean 12.6 ± 2.7 SD) notes per call. Each note contains two distinct frequency components ( Fig. 7 A, B) with a simple, amplitude modulated structure within each call ( Fig. 7 B–F). The lower dominant frequency component of each note peaked at 1.3 kHz and 1.5 kHz. The higher frequency component varied from 2.7 kHz for one specimen and 3.0 kHz for the other. In all calls, the fundamental (lower) frequency component was the dominant (= emphasized) frequency at the start of each call. Towards the end of many calls, the two frequency components were approximately equivalent in relative intensity, suggesting a slight change in call energy from the fundamental to the first multiple of the fundamental (the higher frequency component of the call). However, the dominant call frequency never shifted markedly away from the fundamental ( Fig. 7 B, D).

The calls of P. parilis appeared stereotyped and nearly invariant. Some variation was detected in dominant frequency between males (1.3–1.5 kHz) but we found little or no within-male or within-call frequency modulation, except for the aforementioned slight shifts in call energy towards the higher frequency component.

Although P. neckeri also produces an amplitude-modulated call ( Fig. 8 ), the structure and overall impression on the human ear is unlike that of P. p a r i l i s. The call of P. n e c k e r i sounds to humans like a rapid, clanging “chi-keng…..chi-keng …chi-keng …chi-keng–chi-keng–chi-keng–chikeng!” with an increasing rate of note delivery, often terminating at a rapid burst of notes. Platymantis neckeri has a lower mean note repetition rate (4.7–9.6–notes/s) than P. parilis (11.8–12.1 notes/s) and produces fewer notes per call (5–7) than P. parilis (11–14). The call of P. neckeri exhibits a progressively decreasing internote interval across the call, whereas P. parilis has a uniform internote interval throughout the entire call.

Individual note structure between the two species was also quite different. In contrast to Platymantis parilis , which exhibits 11–14 invariant dual-frequency note structure across the call, the call of P. n e c k e r i typically delivers 12 notes of a mean peak dominant frequency of 3.2–3.4 kHz that alternate back and forth between two structurally different syllables ( Fig 8 B). Menzies (1982b) described the calls as an invariant 6-note call, with each note divided into two or three syllables (depending on the presence of the brief suffix added to the tonal note in some calls).

The first note is a dual-frequency pulse with two distinct frequency components. This is followed by a second note consisting of a simple tone or shallow declining tonal frequency sweep. This two-note sequence is repeated 5–7 times ( Menzies, 1982b, reported this repeated sequence as invariably six).

Unlike P. parilis , which exhibits a two-frequency note structure wherein the fundamental was usually the dominant frequency (but occasionally calls in which the two frequencies were equivalent), P. n e c k e r i invariably possessed calls in which the dominant frequency corresponds to the higher frequency component of the call. Additionally, unlike P. p a r i l i s, which produces a harmonically simple call, the calls of P. neckeri have a rich harmonic structure, with clear multiples of the dominant frequency occurring at 6.7–6.9 and 10.1–10.3 kHz (not shown).

Ecology and Natural History. The new species called exclusively from elevated sites (typically leaves), normally between 2 and 6 meters above the ground in dense rainforest. At least one specimen appeared to be calling from within an epiphyte; others were perched on leaves in dense foliage. Other species occurring in sympatry with P. parilis included Ceratobatrachus guentheri , Discodeles guppyi , Palmatorappia solomonis , Platymantis aculeodactylus , P. guppyi , P. neckeri , P. solomonis and P. w e b e r i. In sympatry, the advertisement calls of P. parilis and P. neckeri were remarkably invariant and consistently different. Our impression at the type locality was that P. p a r i l i s is much more abundant than P. neckeri .

Distribution. Known only from the vicinity of Kolopakisa village, north-western Isabel Island.

Figures

FIGURE 3. Photographs of the holotype of P. d e s t i c a n s (A: SAMA R 56849) and a paratype of P. parilis (B: SAMA R 56908) in life.

FIGURE 6. The advertisement call of P. desticans (holotype SAMA R 56849) recorded at ambient temperature of 24.7 ° C Barora Faa Island, by SJR. A power spectrum (A: Fast Fourier Transformation; relative amplitude vs. frequency in kHz), a 200 ms audiospectrogram (B: frequency in kHz vs. time in ms), and an expanded waveform (C: relative amplitude vs. time in ms) of a single call. A 2.0 s audiospectrogram (D: frequency in kHz vs. time in ms) and oscillogram (E: relative amplitude vs. time in ms) of a typical pair of calls from the 35 s recording segment waveform depicted in F (showing paired call groups during peak calling activity).

FIGURE 7. The advertisement call of P. parilis (holotype SAMA R 56911) recorded at ambient temperature of 22.1 ° C, Kolopakisa Village, Isabel Island, by SJR. (A) a power spectrum (Fast Fourier Transformation; relative amplitude vs. frequency in kHz); a 1.2 s audiospectrogram (B: frequency in kHz vs. time in ms) and an expanded waveform (C: relative amplitude vs. time in ms) of a single call. A 10 s audiospectrogram (D) and oscillogram (E) of a typical pair of calls from the 35 s recording segment waveform depicted in F (showing calls during peak calling activity).

FIGURE 8. Comparisons of complete calls of sympatric P. parilis (A: 22.1 ° C) and P. neckeri (B: 22.3 ° C). Included are 1250 – 1500 ms audiospectrograms (top panels: frequency in kHz vs. time in ms) and oscillograms (bottom panels: relative amplitude vs. time in ms). Note invariant structure and internote interval in P. parlis (A) versus complex, alternating note structure and declining internote interval across the call of P. neckeri (B).