Choerophryne bisyllaba, Guenther, Rainer & Richards, Stephen, 2017

Guenther, Rainer & Richards, Stephen, 2017, Three new species of the microhylid frog genus Choerophryne (Amphibia, Anura, Microhylidae) from Papua New Guinea, Zoosystematics and Evolution 93 (2), pp. 265-279 : 270-274

Choerophryne bisyllaba sp. n.

Holotype.

SAMA R70326 (FN SJR 2178), adult male, Dendawang Camp, Finisterre Range, Huon Peninsula, Morobe Province, Papua New Guinea (6°04.899'S, 146°34.335'E; 2,400 m asl) collected on 1-10-2001 by S.J. Richards.

Paratypes.

SAMA R70327 (FN SJR 2179), PNGNM unreg. (FN SJR 2186, 2187), ZMB 84339-84340 (FN SJR 2188, 2190), same data as holotype; SAMA R70328-70330 (FN SJR 5992-4), same data as holotype but collected 28-09-2001; SAMA R70331-70332 (FN SJR 5990-5991), adjacent Teptep Village, Finisterre Range, Huon Peninsula, Morobe Province, Papua New Guinea (5°57.00'S, 146°33.60'E; 2,200 m asl) collected on 27-09-2001 by S.J. Richards.

Diagnosis.

A species of the genus Choerophryne lacking an elongated snout. Snout-urostyle length in males (n=10) from 14.2-17.4 mm (mean 15.4 ± 0.94 mm). No webs between fingers or toes; fifth toe longer than third; finger discs wider than toe discs (ratio T4D/F3D 0.70-0.89); shanks short (TL/SUL 0.36-0.42). Eyes medium sized (ED/SUL 0.115-0.141), eye-naris distance about same as internarial distance (END/IND 0.86-1.25). A brown hour-glass mark present on dorsum, with anterior part of mark much smaller than posterior part. Dorsal surfaces covered with scattered tubercles in life but these become inconspicuous or are absent in preservative. Lower surfaces smooth with a mixture of small brown dots and larger brown spots on a yellow-grey background, throat more strongly pigmented than remaining ventral surfaces. Advertisement calls consist generally of two short but clearly pulsed notes produced in long series, a call structure that is unique for short-snouted species in the genus Choerophryne . Dominant frequency is at 3.5 kHz.

Description of the holotype.

Adult male with a SUL of 14.4 mm. Additional measurements and ratios are listed in Table 3. Head broader than long (HL/HW 0.82); tip of snout truncate with a small median protuberance in dorsal view and truncate in lateral view; nostrils near tip of snout, directed laterally and not visible from above, distance between nares greater than distance between eye and naris (END/IND 0.92); canthus rostralis in dorsal view rounded and slightly bent; loreal region nearly vertical; tongue strongly widened posteriorly with distinct indentation, posterior half and sides free; prepharyngeal ridge without denticles, fairly long vocal slits on both sides of mouth floor; tympanum half size of eye, its upper margin covered by tympanic fold. Shanks short (TL/SUL 0.40). Fingers unwebbed and with broad and grooved terminal discs, their relative lengths 3>4>2>1 (Fig. 11a, b); disc of third finger twice as wide as penultimate phalanx, no prominent metacarpal or subarticular tubercles. All toes with wide and grooved terminal discs, discs of fourth toe narrower than disc of third finger (T4D/F3D 0.89), no webs between toes, no metatarsal tubercles or subarticular tubercles; relative lengths of toes 4>5>3>2>1 (Fig. 11a, b). All dorsal surfaces in preservative smooth with only a few low tubercles, flanks with more tubercles; conspicuous are tubercles on distal tarsi and behind angle of jaw; ventral surfaces smooth except for throat and anterior chest that are coarsely textured.

Colour of the holotype in preservative

(Fig. 11a, b): Colour of holotype in life not known. In preservative ground colour of dorsal surfaces of head, body and extremities light-grey or light brown; some dark brown flecks on head, in the scapular region and on extremities, one dark brown fleck bordered anteriorly by a yellowish fleck in the lumbar region, discs of fingers and toes yellowish and markedly less pigmented than most other dorsal surfaces. Conspicuous is an off-white interocular stripe continuing on eye lids and extending dorsolaterally to the lumbar fleck. This off-white stripe broadening irregularly in the scapular region and in combination with the dark brown mid-dorsum giving the impression of an hour-glass mark with anterior part clearly shorter than its posterior one. A distinct short whitish stripe between eye and angle of jaws. Ground colour of ventral surfaces yellowish. Extremities, throat and anterior chest fairly uniform dark brown, the paler abdomen mottled with some small brown spots. Margin of lower lip unpigmented; anal region spotted with dark brown.

Morphological variation in the preserved type specimens.

Measurements and body ratios of the type specimens are presented in Table 3. Ten adult males have a SUL between 14.2 and 17.4 mm (mean 15.4 ± 0.94 mm) and one subadult (?) female (SAMA R70332) with very small eggs in its ovaries measured 15.2 mm. All specimens exhibit a lighter or darker brown mid-dorsal patch that shows a clear constriction in the scapular region. There is a tendency for the anterior part of this patch to be more strongly pigmented than the posterior one. This patch is bordered dorsolaterally by an irregularly shaped light grey stripe in all specimens. A light interocular stripe is present in all but one specimen. A large, pale semi-circular patch in the coccygeal region is present in a few specimens. Throat brown with small whitish spots in most specimens; abdomen in most specimens light grey or yellowish with brown spots, and inferior surfaces of legs brown with whitish spots. Nine of the types have a whitish longitudinal hairline in middle of abdomen; in some specimens this line continues on the throat or forms a cross in the pectoral region.

Colour in life.

Colour images taken in life are available for three individuals from the type series, but we are unable to assign them to specific vouchered specimens. Two of these individuals are shown in Figs 12 and 13. In the first specimen the snout, dorsolateral stripe, lumbar spots, distal tarsi and heel region are light grey; anterior part of dorsal hourglass mark is blackish, its posterior (much larger) part more brownish; all dorsal surfaces with a few reddish sections even on basal parts of finger and toe discs; stripe between eye and angle of jaws striking white; iris silvery with blackish venation, its inner margin an orange oval; all dorsal surfaces and throat with small white dots (Fig. 12). The second specimen has grey lateral surfaces, the anterior part of the hourglass mark on dorsum is blackish, its posterior part a mixture of dark brown and reddish spots; reddish spots also occur around the elbows and heels, in the inter-ocular and the dorsolateral stripe; throat, lateral sides of head and lower flanks grey with dark grey and white dots (Fig. 13). The third specimen is coloured much as is illustrated in Fig. 13 with most of its dorsal surfaces dark brown or blackish, but conspicuous is a dark red diagonal stripe above insertion of forearm and a large dark red fleck on the coccygeal region.

Distribution and ecological notes.

Choerophryne bisyllaba is currently known only from two locations at elevations between 2,200 and 2,400 m asl in the mountains of the Huon Peninsula, Morobe Province, north-eastern Papua New Guinea (Fig. 14). Males called from semi-concealed or exposed positions on low foliage, normally between 1-2.5 m above the forest floor at night. At Teptep males were calling from leaves in remnant and severely disturbed forest patches, while at Dendawang the species was common in undisturbed, wet mossy forest.

Vocalisation.

The advertisement call of C. bisyllaba normally consists of two notes that are uttered in long series lasting up to several minutes (Fig. 15). A few calls were recorded that consist of only one note, and these were normally (but not always) early in a sequence. Those calls were not considered further. Two-note calls recorded at air temperatures of 14.8 °C to 16.4 °C were analysed from SAMA R70327 (n=50), SAMA R70329 (n=13) and SAMA R70329 (n=32). Because characteristics of all two-note calls are similar, they were combined for analysis here. Mean call duration was 0.39 ± 0.034 s, range 0.25-0.52 s, n=95. Mean duration of intervals between successive calls 1.01 ± 0.20 s, range 0.78-2.03 s, n=94. Mean duration of the first note 34.2 ± 7.21 ms, range 25-52 ms, n=46. Notes are clearly pulsed and most notes start with pulses of maximum sound amplitude that drops relatively quickly; this amplitude decrease is more pronounced in the second note than in the first (Fig. 16). Mean number of pulses in the first note 4.6 ± 0.99, range 2 -8, n=46. Mean duration of the second note with 47.7 ± 3.79 ms is longer than that of the first note, range 39-54 ms, n=46. Mean number of pulses in the second note 7.35 ± 0.77, range 6-8, n=46. Mean duration of intervals between both notes 0.30 ± 0.039 s, range 0.15-0.35 s, n=46. Mean note repetition rate is 5.18 ± 0.57 notes/s, range 4.65-8.33 notes/s, n=95. Frequencies scatter mostly between 2.50 and 3.75 kHz; the dominant frequency is at 3.50 kHz (Fig. 17), a second (lower), peak is pronounced at 2.9 kHz.

Etymology.

The specific epithet bisyllaba is a feminine Latin adjective (in accordance with the feminine genus name) and means disyllabic. It refers to the advertisement call of the species which consists predominantly of two notes (or syllables).

Comparisons with other species.

With its short snout Choerophryne bisyllaba differs from all Choerophryne with an elongated snout. According to Frost (2016) 18 species of short-snouted Choerophryne are recognized at present. All of these have buzzing, squeaking, clicking or bell-like ( ‘peeping’) advertisement calls except C. multisyllaba with rattling calls. Choerophryne bisyllaba is the only species in the genus known so far which utters disyllabic calls with discretely pulsed notes. Menzies (1999) mentioned, but did not formally describe, a population of Choerophryne (then Albericus ) from Teptep with a ‘double-note’ call. However he described that species’ call as ‘bell-like’ with notes lasting <10 ms, and these clearly differ from calls of C. bisyllaba which are distinctly pulsed and notes last>25 ms. Resolution of the taxonomic status of the Choerophryne population from Teptep reported by Menzies (1999) is not possible with the information currently available.

Choerophryne variegata is known from a single specimen, and its advertisement call is unknown. According to measurements by Menzies (1999) the holotype of this species differs from C. bisyllaba by the ratios TL/SVL (0.47 vs. 0.36-0.42), F3D/SVL (0.071 vs. 0.053-0.065) and END/IND (1.38 vs. 0.86-1.25). Moreover, toes 4 and 5 are connected by webbing in C. variegata and not so in C. bisyllaba .