Mantophryne insignis, Guenther, Rainer & Richards, Stephen, 2016

Guenther, Rainer & Richards, Stephen, 2016, Description of a striking new Mantophryne species (Amphibia, Anura, Microhylidae) from Woodlark Island, Papua New Guinea, Zoosystematics and Evolution 92 (1), pp. 111-118 : 112-115

Taxon classification Animalia Anura Microhylidae

Mantophryne insignis sp. n.

Holotype.

SAMA R69237 (field number = FN SJR 13920); adult male, collected on the slopes of Talpos Mountain, Woodlark Island (Fig. 1), Milne Bay Province, Papua New Guinea (9°09.364'S, 152°46.495'E, 180 m a.s.l.) on 15.IV.2011 by S.J. Richards.

Paratypes.

ZMB 83181 (FN SJR 13923), same data as for holotype, and FN SJR 13932 (to be deposited in the PNG National Museum), Upper Muniai Creek, Woodlark Island, Milne Bay Province, Papua New Guinea (9°07.502'S, 152°44.902'E, 30 m a.s.l.).

Diagnosis.

The new species is assigned to the genus Mantophryne on the basis of the following characters: body slender, circum-marginal grooves on all finger and toe discs, those on the toes wider than those of fingers; symphygnathine condition of the maxillary bones (anterior processes of the maxillary bones not fused but almost in contact and joined by a ligament); and two protuberances on chin. It differs from all hitherto known congeners by its 1) relatively long legs (TL/SUL 0.55-0.57 vs. <0.51 in males of all congeners; Menzies 2006, Kraus and Allison 2009), 2) more expanded terminal discs on the toes, 3) smooth dorsum, 4) advertisement calls consisting of 38-52 notes and lasting 4.6-6.5 s, and 5) distinct colouration normally comprising a uniformly golden tan dorsum, broad blackish dorsolateral bands edged below with a narrow, slightly undulating white stripe and large, distinct dark brown blotches each encircled by a white border, on the abdomen.

Description of the holotype.

In life mid-dorsal band and dorsal surfaces of thighs uniform golden tan, dorsal surfaces of shanks yellow, posterior of thighs, extending partly to dorsal surfaces, orange-red; supra-canthal stripe, extending onto upper eyelids, yellowish; dorsolateral band blackish, ventral boundary of this band delineated by narrow white stripe; axillary region yellowish and inguinal region orange-red. Lateral surfaces of shanks and dorsal surfaces of tarsi dark brown, their ventral parts mottled with dark brown. Iris silvery with a few irregular dark lines; anterior and posterior portions of iris more strongly pigmented by dark lines and with an orange hue (Fig. 2). Ground colour of all ventral surfaces whitish. Throat and chest covered by variably intense brown pigmentation and scattered large dark-brown spots especially along the chin and on the bases of the forelegs. Abdomen and lower areas of flanks are covered by a pattern of very conspicuous dark-brown blotches, each encircled by a narrow white line; areas between the spots are less densely pigmented than the throat and chest; brown spots on inferior thighs are smaller than on abdomen and not encircled by white lines (Fig. 3).

Colouration of the preserved holotype: Dorsal surfaces of head, shanks and mid-dorsum uniform light grey; dorsal surfaces of thighs with faint brown mottling; those of upper arm more strongly mottled with brown; anterior of lower arm and dorsal surfaces of hands, tarsi and metatarsi irregularly brown; conspicuous large dark brown spots edged with a white line extend to posterior of lower arm and anterior tarsus and metatarsus; a relatively wide whitish supra-canthal stripe extends from snout tip to middle of eyelid. The broad dorsolateral bands begin at the posterior edge of the orbital opening, are widest on middle of flanks, and end with a small tip at cloacal opening. Ground colour of all ventral surfaces is off-white. Mottling is same colour as in life.

Measurements of the holotype are listed in Table 1. There is a longitudinal incision in the abdomen. Head longer than broad (HL/HW 1.06). Snout truncate, with only a slight narrowing at the tip in dorsal view and protruding in lateral view. Canthus rostralis rounded, straight anterior to eyes before bending laterally above the nares; loreal region flat, nares directed laterally, close to end of snout and not visible from above; distance between nares greater than distance between eye and naris (END/IND 0.86). Supratympanic skin fold scarcely pronounced, tympanic annulus clearly visible; horizontal diameter of tympanum more than half that of eye (TyD/ED 0.55). Pupil horizontally oval. Tongue very broad, long and free laterally and posteriorly, its posterior margin not notched. Anterior prepharyngeal ridge with three lobes and posterior ridge with ten denticles. Vocal slits small and near angle of jaws. No webbing between fingers; one well developed subarticular tubercle on finger I and II and two well developed tubercles on fingers III and IV; three less prominent metacarpal tubercles; no other palmar tubercles; all fingers bear small but distinct, grooved discs; disc of third finger clearly smaller than that of fourth toe (F3D/T4D 0.63); relative length of fingers III>IV>II>I (Fig. 4). Legs long and slender (TL/SUL 0.57). Toe discs clearly broader than those of fingers and all with distinct circum-marginal grooves; no webbing between toes; one well-developed subarticular tubercle on toe I and toe II, two prominent subarticular tubercles on toes III, V and three on toe IV; clearly expressed inner metatarsal tubercle, no outer one; relative length of toes IV>III>V>II>I (Fig. 5). All dorsal and ventral surfaces of legs, body and head smooth except two inconspicuous)(-shaped longitudinal ridges beginning between eyes and reaching to occiput. Two small chin protuberances, clearly visible in the living specimen, disappeared in preservative. There are 3 faint, whitish tubercles on the upper edge of the eyelid.

Variation in the type series.

Body size (SUL) of three adult males (including the holotype) varied only slightly, from 35.0 mm to 36.2 mm, mean 35.5 mm, SD (standard deviation) 0.61. Measurements of all types are listed in Table 1. Deviations in colouration of the paratypes from the holotype are insignificant; all share the striking colour pattern of a golden tan dorsum with broad, blackish dorsolateral bands and a heavily spotted venter.

Additional variation.

Three additional adult male specimens of this species (BPBM 40135-7) collected on Woodlark Island by F. Kraus are 34.1-35.3 mm SUL and agree closely with the description of the type series in all features except that the dorsal colouration of one of the three specimens (BPBM 40135), including the mid-dorsal band, is creamy tan rather than golden tan.

Vocalisation.

The advertisement call of Mantophryne insignis sp. n., recorded at an air temperature of 25 °C, is a rattle of several seconds duration (Fig. 6).

Two complete calls of the holotype and two calls of SJR 13932 were analysed. Call duration varied from 4.6 to 6.5 s, mean 5.9 s. Number of notes per call was 38-52, mean 47.5. Note repetition rate was from 8.0 to 8.3/s, mean 8.1 notes/s. Mean note duration of two calls from the holotype was 53.1 ms, SD 15.4, range 30-78 ms, n=104; mean internote interval duration was 72.9 ms, SD 12.7, range 41-153 ms, n=102. For technical reasons note and internote length from the calls of the second specimen could not be measured exactly and therefore are not considered here. Note and internote interval length and amplitude of notes clearly increased during the course of the call (compare Figs 7 and 8).

In three of the four calls the last internote interval is clearly the longest and in one call the last but one interval was the longest. All notes are composed of pulses, and these mostly cluster into pulse-groups. The first pulse of almost all notes is clearly separated from the following (clustered) pulses. Frequencies scatter mainly from 1.0 to 3.5 kHz with dominant frequency at 2.0 kHz (Fig. 9). There are no harmonics evident and no modulation of frequencies.

Distribution and ecological remarks.

The three type specimens of Mantophryne insignis were detected by their calls, which were uttered at night from hidden perches 50-80 cm high in a limestone block, a tree buttress and a fallen log, all in lowland rainforest (30-180 m asl) in south-central Woodlark Island. However two of three additional specimens found calling on Woodlark Island by F. Kraus (pers. comm.) were approximately 4 m above the ground, in climbing pandanus ( Freycinetia sp.) plants. The third specimen was calling from under a leaf on the forest floor. The slender body form, long legs and expanded toe discs (relative to congeners) reflect the unusually arboreal habits of this Mantophryne species. Given the uniformity of habitat across the island, and the lack of major topographic relief, it is likely that the species is widespread in lowland rainforest on Woodlark Island. This species has not been reported from any other islands in the region and may be endemic to Woodlark.

Etymology.

The name insignis is derived from the Latin ‘insignis’ meaning remarkable or conspicuous, and refers to the species’ distinctive colour pattern and unusual (for the genus) ecology.

Comparison with other species.

Mantophryne lateralis , which is mainly distributed throughout the lowlands of eastern New Guinea ( Oliver et al. 2013), is most similar to the new species in having black lateral bands and distinct spotting on the abdomen. Some specimens of this species also have extremely smooth skin, approaching the state in the new species. However it is larger than the new species (males more than 40 mm SUL vs. less than 40 mm SUL in Mantophryne insignis ), has shorter legs (SUL/TL <0.51 vs. 0.55-0.57), smaller toe discs (T4D/SUL <0.034-0.042 vs. 0.042-0.044), lacks the conspicuous golden tan dorsum, and has very long advertisement calls (up to 30 s) at 22-24 °C with a note duration of about 200 ms vs. calls of about 6 s and a mean note length of about 50 ms in the new species ( Zweifel 1972, Menzies 2006).

With a snout-vent length up to 82 mm Mantophryne louisiadensis is substantially larger than the new species; it also has a broader head, a more robust habitus, lacks dark lateral bands and does not exhibit the striking golden tan middorsal area or clearly delimited brown spots on the abdomen ( Zweifel 1972, Kraus and Allison 2009).

Mantophryne axanthogaster male is also larger (> 40 mm SVL) than Mantophryne insignis and further differs from the new species by its flecked (vs. uniform golden tan) dorsum, lack of dark lateral bands, and uniform grey venter (vs. strongly spotted). Moreover, its advertisement call contains 13-18 notes (vs. 38-52 notes) with a mean note duration of 126 ms (vs. about 50 ms) and a mean note repetition rate of 1.8 notes/s (vs. 8.1 notes/s) at 26.5 °C ( Kraus and Allison 2009).

With a snout-vent length of 25-31 mm Mantophryne menziesi is smaller than the new species, lacks dark lateral bands and a blotched venter, and has a grey- brown (vs. golden tan) dorsum. Its advertisement call is also different, with notes having a length of about 200 ms (temperature not available) (vs. 50 ms). Moreover in Mantophryne menziesi the squamosal and frontoparietal bones meet to form an arch over the prootic region, a character which is unique for asterophryine microhylid frogs.

Hylophorbus infulatus (until recently Mantophryne infulata ) is similar to Mantophryne insignis sp. n. in many body proportions. The species differ, however, in their internarial spacing. The ratio END/IND of 20 specimens of Hylophorbus infulatus ranges from 0.73-0.84 ( Zweifel 1972) whereas three specimens of the new species have values of 0.86-0.91. Moreover, the species differ in their colouration. Hylophorbus infulatus has an inconspicuous brown mid-dorsum with some darker markings (vs. uniform golden tan mid-dorsum in most Mantophryne insignis ), the upper margin of its blackish dorsolateral band is poorly defined (vs. well defined in Mantophryne insignis ) and its ventral surfaces are mottled with diffuse flecks (vs. covered with well-defined dark brown blotches) ( Zweifel 1972).