Choerophryne crucifer, 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 : 265-268

Choerophryne crucifer sp. n.

Holotype.

SAMA R69448 (Field number: FN SJR 8623), adult male, Iagifu Ridge near Moro, Southern Highlands Province, Papua New Guinea (06°22.099'S, 143°13.374'E; 900 m asl) collected on 21-11-2004 by S.J. Richards.

Paratypes.

ZMB 84336 (FN SJR 8622), same data as holotype; SAMA R69440-69442 (FN SJR 3147-3148, 3151), Darai Plateau, Gulf Province, Papua New Guinea (07°07.771'S, 143°36.806'E; 400 m asl) collected on 23-07-2003 by S.J. Richards.

Diagnosis.

A species of the genus Choerophryne lacking an elongated snout. Snout-urostyle length in males (n=5) from 13.4-17.3 mm (mean 14.7 ± 1.58 mm). No webs between fingers or toes; fifth toe longer than third; finger discs wider than toe discs (ratio T4D/F3D 0.78-0.88); shanks short (TL/SUL 0.38-0.44). Eyes medium sized (ED/SUL 0.110-0.127), eye-naris distance greater than internarial distance (END/IND 1.00-1.25). Dorsum with a brown hour-glass mark that has an approximately median constriction; and a pale cross with a definite posterior ‘extension’ on head. Dorsal surfaces covered with tubercles in life, lower surface smooth and brown with numerous whitish dots, inguinal region yellowish. Advertisement call a series of musical clicks sounding like ‘tink-tink-tink…’ lasting 1.01-4.75 s and containing 5-22 clicks (notes) per call at a repetition rate of 4.39-5.18 notes/s. Dominant frequency is at 5.5 kHz.

Description of the holotype.

Adult male with a SUL of 14.9 mm. Additional measurements and ratios are listed in Table 1. Head broader than long (HL/HW 0.73); tip of snout rounded in dorsal view and truncate in lateral view; nostrils near tip of snout, directed laterally and not visible from above, distance between nares less than distance between eye and naris (END/IND 1.25); canthus rostralis in dorsal view straight and rounded; loreal region slightly sloped; tongue oval, narrower anteriorly than posteriorly, posterior margin without indentation; anterior prepharyngeal ridge well developed and smooth, posterior “ridge” a plaque with many longitudinal furrows; fairly long vocal slits on both sides of mouth floor; tympanum small (about one-third of eye diameter) and hardly visible; no supratympanic fold. Shanks of medium length (TL/SUL 0.44). Fingers unwebbed with broad, grooved terminal discs, their relative lengths 3>4>2>1 (Fig. 1a, b); disc of third finger slightly more than twice width of penultimate phalanx, no prominent metacarpal or subarticular tubercles. All toes with wide, grooved terminal discs, those of fourth toe slightly narrower than those of third finger; no webs between toes, no metatarsal tubercles, subarticular tubercles weakly developed; relative lengths of toes 4>5>3>2>1 (Fig. 1a, b). Skin smooth with small but distinct tubercles dorsally in life, less conspicuous in preservative. No distinct tubercles on ventral surfaces in preservative.

Colour of the holotype in preservative

(Fig. 1a, b). Colour of holotype in life unknown. In preservative ground colour of dorsal surfaces of head, body and hind limbs light-grey, that of fore limbs yellowish; a dun hour-glass shaped patch from eyes to inguinal region, this patch constricted at mid-dorsum and “split” anteriorly by posterior arm of pale cross on head; some diffuse smaller brownish spots on head and dorsal surfaces of extremities. Inguinal region with conspicuous dark brown areas bordered anteriorly by yellow flecks; dark brown inguinal spots merge ventrally into brown colour of abdomen. Underside of thighs, chest and throat also brown and interspersed with small whitish spots. An irregularly shaped dark brown band across anal region.

Colour in life.

Based on paratype SAMA R69440, mid-dorsum covered by a large brown patch, dorsolaterally bordered by an irregular off-white longitudinal stripe. Flanks reddish-brown with a dark grey reticulum, inguinal region with a yellowish area, dorsal surfaces of extremities grey-yellowish with irregular dark grey, brownish and reddish spots; ventral surfaces grey with whitish mottles (Fig. 2).

Morphological variation.

Measurements and body ratios of the type specimens are presented in Table 1. While four males had a SUL between 13.8 and 14.9 mm, one male measured 17.3 mm. This difference of 3.5 mm between adult males is fairly large for frogs of this small size. All five specimens exhibit a dark brown mid-dorsal patch with a pair of anterior and a pair of posterior “wings”, the posterior ones in almost all cases more strongly expanded than the anterior ones. This patch is bordered dorsolaterally by an irregular whitish stripe in four specimens and by a light brown stripe in one specimen. A complete cross-shaped figure on the head is evident in four specimens; it is incomplete in ZMB 84336 where only the posterior section is pronounced. All specimens exhibit the large, pale semicircular patch on the posterior end of the body and pale spots or bands proximally on posterior thighs and distally on dorsal shanks. Throat, chest, abdomen and inferior surface of thighs are brown and more or less densely speckled with whitish spots in all specimens. Ventral surfaces of extremities are off-white and mottled with brownish and/or whitish spots.

Distribution and ecological notes.

All records of Choerophryne crucifer are from lowland and foothill forest in south-central Papua New Guinea, at altitudes ranging from ~100 m in the lowlands and foothills of Gulf Province to nearly 1,000 m asl on Iagifu Ridge in Southern Highlands Province. Males called at night from the upper surfaces of leaves, generally between 2-10 m above the forest floor.

Vocalisation.

The advertisement call of the new species, recorded at air temperatures of 23.2-24.0 °C, consists of a series, or ‘train’ of rather musical clicks (Fig. 3). Calls follow one another at variable intervals (a few seconds to half a minute and more). Eleven calls were analysed from ZMB 84336 and 16 from SAMA R69442. Because characteristics of both call trains are similar, they are treated together here. 27 calls had a mean duration of 2.75 ± 0.82 s, range 1.01-4.75 s. Mean number of clicks (notes) per call 13.2 ± 3.81, range 5-22. Notes had a mean duration of 20.6 ± 2.91 ms, range 13-25 ms, n=93. Inter-note intervals lasted 200.6 ± 13.4 ms, range 176-238 ms, n=92. Mean note repetition rate 4.82 ± 0.21, range 4.39-5.18 notes/s, n=27. Frequencies scatter mostly between 5 and 6 kHz; the dominant frequency is at 5.5 kHz (Fig. 4). Notes start at maximum sound amplitude and, after a short time at this level, amplitude drops quickly. All notes have a similar maximum amplitude.

Etymology.

The specific epithet crucifer is a Latin substantive in apposition and means carrier (porter) of a cross. It refers to the conspicuous yellowish cross on the head of most specimens.

Comparisons with other species.

With its short snout Choerophryne crucifer differs from all twelve Choerophryne with an elongated snout and would have been placed in the genus Albericus in the former sense. According to Frost (2016) 18 species of short-snouted Choerophryne are recognized at present. The advertisement call of most short-snouted species is described as a buzz. Apart from C. crucifer , calls consisting of clicking notes are produced only by C. gudrunae , C. gunnari , C. sanguinopicta and C. valkuriarum .

Choerophryne gudrunae has longer legs (TL/SVL 0.44-0.46 vs. 0.38-0.44) and a higher ratio of END/IND (1.20-1.50 vs. 1.00-1.25) than C. crucifer . The advertisement calls of the former consist of about 10 clicks, those of C. crucifer of 13 on average. Dominant frequency of gudrunae -calls is at 3.5 kHz, of crucifer -calls at 5.5 kHz.

Choerophryne gunnari has longer legs (TL/SVL 0.44-0.51), a higher ratio END/IND (1.25-1.45) and conspicuous blue pigmentation on the belly and hind limbs (absent in C. crucifer ). Note repetition rate of the advertisement call of C. gunnari is, according to the spectrograms published by Menzies (1999, 2006), about two clicks/s (erroneously reported as about 4 clicks/s in the 1999 paper) vs. 4.4-5.2 clicks/s in C. crucifer . Figure 17 in Menzies (1999) shows a dominant frequency of about 3.3 kHz for this species, which is much lower than in calls from C. crucifer (5.5 kHz). Menzies (1999) also reports that the clicks uttered by C. gunnari have 'no musical quality’ whereas those produced by C. crucifer are distinctly musical, sounding to the ear like ‘tink..tink..tink’.

Choerophryne sanguinopicta occurs at elevations of>1,400 m asl (vs. lowlands and foothills <1000 m asl) and exhibits an extraordinary polychromatic colouration (absent in C. crucifer ). Moreover its advertisement calls are very long series (several minutes) of clicks with a note (= call) repetition rate of less than three calls/s and a dominant frequency of around 4.0 kHz (vs. shorter series of clicks, each series lasting less than 4 seconds and with a repetition rate of more than 4.4 per second and a higher dominant frequency (at 5.5 kHz) in C. crucifer ).

Choerophryne valkuriarum generally occurs at elevations over 2000 m asl (vs. <1000 m asl in C. crucifer ). According to Kraus and Allison (2005a) HW/SVL in C. valkuriarum is 0.37-0.43 and F3D/SVL is 0.067-0.088, we found values of 0.33-0.35 and 0.054-0.064 in C. crucifer . There are also differences in the advertisement calls. Menzies (1999) notes a maximum repetition rate for C. valkuriarum of two notes/s and reports that notes are uttered "once or in irregular series". In C. crucifer clicks are uttered at regular intervals and at a rate of 4.4-5.2 per s.

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 the new species described here by the ratios TL/SVL (0.47 vs. 0.38-0.44), F3D/SVL (0.071 vs. 0.054-0.065), END/IND (1.38 vs. 1.00-1.25) and ED/SVL (0.133 vs. 0.110-0.127). Moreover, toes 4 and 5 are connected by webbing in C. variegata and not so in C. crucifer .