Bioacoustics of Hylophorbus lengguru

Diagnosis: A Hylophorbus species recognizable by the following unique combination of characters: (i) medium size (male SV = 24.0–29.0 mm; female SV = 27.3–30.4 mm ); (ii) poorly developed, sometimes indistinct, basal subarticular tubercle on T4 and T5 (male 4st =.35–. 60 mm ; female 4st =. 60 mm ; male 5st =.49–. 59 mm ; female 5st =. 46 mm ); (iii) a thenar tubercle and two palmar tubercles, ovoid, at proximal edge of hand; (iv) absence of lateral stripe ( Figs 5C–F , 6F ); (v) dark brown or black lumbar ocellus, with reddish anterior margin fading towards a ‘crescent’-shaped blackish brown blotch on anterior flank; (vi) yellow and red pigmentation of various intensity around lumbar ocellus and acromial region; (vii) bright yellow groin, axilla, and yellow flecks on rear of thigh; (viii) overall drab whitish yellow coloration on abdomen and ventral surfaces of legs; (ix) well-defined black spot of variable size on superior edge of eye, aligned with vertical dark pigmentation of iris; and (x) calls of one to six single-pulse notes (mean = 3) with an upward frequency modulation (dominant frequency ~1.13 kHz) and up to five harmonics ( Fig. 6D ).

Description of the holotype : Adult male (for measurements, see Supporting Information, Table S7). Head as wide as long (HL/ HW =.98); nares directed laterally, closer to tip of snout than to eye, internarial distance larger than distance from nostril to anterior edge of eye (EN/IN =.63); snout acute in lateral view, rounded in dorsal view, slightly pointed. Eye moderately large (EY/SV =.13). Tympanum large (TY/SV =.08, TY/ EY =.65), supratympanic fold inconspicuous, outlined by a black line overlaid by a triangular black–brown coloration, pointing ventrally. Skin finely granular with sparse flat tubercles on dorsal surfaces, smooth on ventral surfaces. Fingers unwebbed, relative lengths 3> 4> 2> 1, nearly the same for F1, F2, and F4; fingers with slightly expanded truncate discs, all with circum-marginal grooves. Subarticular tubercles on all fingers, well developed; thenar tubercle and two palmar tubercles present, ovoid, well developed, at proximal edge of palm, with inner palmar tubercle located slightly more anteriorly. Toes unwebbed, relative lengths 4> 3> 5> 2> 1; discs on T1 and T5 slightly expanded, ~1.5 times wider than penultimate phalanges, discs much larger on T2–T4, ~3 times wider than penultimate phalanges, all with circum-marginal grooves. Subarticular tubercles mostly developed on T1–T3, basal subarticular tubercles indistinct on T4–T5, inner metatarsal tubercle ovoid, well developed, others lacking. Posterior dorsum to inter-orbital region brown, anterodorsal head with scattered dark brown spots; very thin vertebral skin ridge extending from tip of snout to urostyle. Ventral half of flank overall pale grey, sharply contrasted with dorsum. Small speckles of black, yellow, grey, and white extend from anterior flank to anterior abdomen. Large anterolateral ‘crescent’-shaped blotch and lumbar ocellus both black, middle flank region red, with scattered black spots ( Fig. 6F ). Posterodorsal forelimb and posteroventral and anterodorsal edge of eye reddish, upper arm with strong red pigmentation; lateral snout and under eye both blackish brown. Chin, throat, chest, and anterior portion of abdomen drab white heavily mottled with brown, with scattered light grey flecks; distinct dark brown blotch on each side of posterior submandibular region ( Fig. 6B, H ). Anteroventral forelimbs, axilla, abdomen, and ventral thigh greyish yellow, almost transparent. Ventral shank, groin, and flecks on posterior dorsal thigh bright yellow. Hands and feet reddish brown, with dark brown blotches. Ventral surface of hands and feet light brown. Red blotch above tip of urostyle, margined in black posterolaterally. Iris silver, with dark brown vertical line crossing pupil; pupil margined with bright orange. Variation: Eleven specimens are available to assess variation within the samples ( Supporting Information , Table S 7). The longest basal subarticular tubercle on the hand is either 1sf or 2sf, and always 2st on the foot. There is extensive variation in the relative size of 3st (3st/SV =.40–.60; male 3st =.61–. 79 mm ) compared with the other basal subarticular tubercles, and 4st and 5st are either indistinct or at least less developed than other tubercles ( Supporting Information , Fig. S6B ). The relative size and shape of the palmar tubercles varies greatly between specimens (e.g. palmar tubercles seemingly fused on MZB . Amph. 24 341 and MZB . Amph. 24 342; palmar tubercles thin and elongated on MZB . Amph. 24 333 and MZB . Amph. 24 335), but their positioning relative to the palm remains the same (proximal; Supporting Information , Fig. S 10). Dorsal and lateral colour patterns of preserved specimens are remarkably similar, except for paratype MZB . Amph. 24 241, which displays striking blackish-brown ‘wavy’ stripes on the dorsum, top of head, and top of thigh ( Fig. 5F ). Mottling on the chin and throat varies in density between all specimens, such that it is nearly solid dark brown with very few unpigmented areas on MZB . Amph. 24 333 and MZB . Amph. 24 345. Nevertheless , the dark brown blotch on both sides of the posterior submandibular region is still distinguishable. Information on colour in life is available only for MZB . Amph. 24 333, MZB . Amph. 24 335, MZB . Amph. 24 336, and MZB . Amph. 24 341; only those are discussed ( Fig. 5C–F ). Overall , the colour pattern in life is as described for the holotype , with the exception of MZB .Amph.24 341, which displays striking blackish-brown motifs in dorsal view, as discussed above. Variation in pigmentation intensity in the margin of the lumbar ocellus and acromial region is observed between all specimens. Call: We analysed a total of 53 calls from two males , one from each locality ( Table 1 ; Supporting Information, Table S3). The analysed files are deposited in the sound collection of ‘La Sonothèque du Muséum National d’Histoire Naturelle’ (Supporting Information, Table S3; Guilbert and Loret 2018 ). The advertisement call consists of one to six single-pulse notes (mean = 3), and mean note duration is 107 ms (range 89.0–138 ms) ( Table 1 ; Fig. 6D ). Mean inter-note duration is 163 ms (range 132–208 ms). Mean dominant frequency is 1.13 kHz (range 1.10–1.14 kHz). Notes can exhibit up to five harmonics, between 1.5 and 3.5 kHz ( Fig. 6D ; Supporting Information, Fig. S5D ). Notes within a call are remarkably similar in their durations, frequency, and amplitude modulations ( Table 1 ). Frequency modulation never exceeds an increase of.20 kHz.

Comparisons with other species: Hylophorbus lengguru can be distinguished immediately from H. nigrinus , H. picoides , H. atrifasciatus, H. infulatus , and H. sigridae by the absence of a lateral stripe; from H. extimus and H. myopicus by its smaller size ( 23.9–30.4 mm in H. lengguru vs. 40.0–49.0 mm). It can be distinguished from H. proekes and H. sextus by its greyish-yellow ventral coloration and its single-pulsed notes. It is further distinguished from H. richardsi by its yellowish ventral coloration; from H. rainerguentheri by its greyish flanks and the presence of a lateral ‘crescent’-shaped blotch; and from H. monophonus by the absence of a bright yellow coloration on the posteroventral flanks. Hylophorbus lengguru is also distinguished from H. richardsi , H. rainerguentheri , and H. monophonus by having multi-note calls. Hylophorbus lengguru can be distinguished from H. wondiwoi by its light-brown flanks more contrasting with the dorsum, and by its notes being twice as long (100 ms for H. lengguru vs. ~50 ms). Colour patterns of H. lengguru resemble those of H. tetraphonus (Bird’s Neck species, West Papua province , Indonesia ), but it can be distinguished by its call: H. lengguru notes are lower (dominant frequency 1.13 kHz vs. ~1.75 kHz) and have lower frequency modulation, reaching an increase of <.20 kHz (vs..50 kHz). Finally, because of the ambiguity surrounding H. rufescens sensu Macleay (1878) , we cannot compare their morphology explicitly. However, their habitat type differs (lowland rainforest at 300–400 m a.s.l. for H. lengguru vs. seasonal woodland and mangroves for H. rufescens ), and their type localities are> 1000 km apart, making their conspecificity highly unlikely.