Bioacoustics of Limnonectes sarawakensis

Description of holotype . Adult female; SVL 31.2 mm ; body moderately sturdy, widest at temporal region, slightly tapering to groin ( Fig. 3G ); head large (HL/SVL 0.36, HW/SVL 0.37), about as long as wide (HW/HL 1.03); snout long (SL/HL 0.45), subacuminate in dorsal view, rounded and slightly protruding in lateral profile, slightly wider than long (SL/EE 0.92); canthus rostralis moderately distinct between eye and nostril, slightly concave from eye to nostril in dorsal view; loreal region oblique; nostrils rounded, directed dorsolaterally; situated closer to tip of snout and to eye (EN/NS 1.14), separated from each other by distance larger than distance between eye and nostril (NN/EN 1.30); eye directed anterolaterally, moderately protruding, very large (ED/HL 0.35), its diameter shorter than snout (ED/SL 0.78); interorbital distance about as wide as upper eyelid (IO/EW 1.02) and smaller than internarial distance (IO/NN 0.73); pineal spot weakly discernible, anterior to level of anterior upper-eyelid edge; tympanum and its annulus visible, its posterodorsal edge in contact with supratympanic fold; tympanum separated from eye by one-third of its diameter (ET/TD 0.35); tympanum diameter smaller than eye diameter (TD/ED 0.59); upper jaw with dentition; odontoid processes in lower jaw low, inconspicuous; choanae small, subtriangular, located far anterolaterally at margins of roof of mouth, lateral third covered by palatal shelf of maxilla in ventral view; vomer processes bearing teeth, long, separated from choana and from each other by about half length of individual process ( Fig. 4G ); tongue short and broad, bilobed for about one-sixth of its length, free distally for about half its length; median lingual process absent. Dorsal surfaces of head, trunk and limbs and lateral surfaces of trunk rough; enlarged tubercles sparsely scattered on the upper eyelid and on the dorsum; low, horseshoe-shaped dermal ridge in middle of back just behind level of arms; seven longitudinal dermal ridges running more or less parallelly to each other along the back; dorsolateral ridge most prominent, from posterior end of upper eyelid to groin; postpalpebral ridge well developed, from upper eyelid to anterior level of pelvis; median ridge indistinct from level of posterior upper-eyelid edge to horseshoe-shaped ridge, continuing more conspicuous from horseshoe-shaped ridge to vent, interruptedly above pelvis; lumbar ridge well developed, running interrupted from horseshoe ridge to vent; supratympanic fold thick and conspicuous, extending from posterior end of orbit, strongly curved, initially directed posterodorsally then turning sharply to arm insertion ( Fig. 5G ); ventral side of head smooth; transverse chest fold between arm insertions weakly distinct; ventral side of trunk smooth, evenly scattered with enlarged tubercles; ventral side of limbs smooth; cloaca without dermal flap. Forelimbs moderately sturdy; hand relatively small (HND/SVL 0.23); tips of fingers rounded, slightly enlarged into disks; relative length of fingers: II = IV <I <III; subarticular tubercles rounded, well developed, numbering one on Fingers I and II, two on Fingers III and IV, proximal tubercles on Fingers III and IV larger and more prominent than distal ones; finger webbing absent; thenar tubercle oval, small, about two-fifth length of metacarpal of Finger I; inner and outer palmar tubercles fused proximally, forming roughly U-shaped, low tubercle on proximal third of Fingers II–IV. Hindlimbs sturdy, very long ( LEG /SVL 1.76); heel reaching slightly beyond tip of snout when legs adpressed forwardly to body; tibiofibula long (TFL/SVL 0.56), slightly longer than thigh (TFL/THL 1.09); heels overlapping each other considerably when knees flexed and thighs held perpendicularly to median plane; foot shorter than tibiofibula (FOT/TFL 0.88); relative length of toes: I <II <V <III <IV; toe tips rounded, enlarged into disks; subarticular tubercles numbering one on Toes I and II, two on Toes III and V, and three on Toe IV; pedal webbing formula I 1/2 II 1/2+ III 1+/2.25 IV 2.5/1+ V ( Fig. 6 ); narrow dermal ridge on preaxial side of Toe I and on postaxial side of Toe V from proximal end of metacarpus to disk; inner metatarsal tubercle prominent, elongated, about half length of metatarsus of Toe I; outer metatarsal tubercle absent. Colouration. In life ( Fig. 7G ), dorsum light brown; horseshoe-shaped tubercle coloured like dorsum with blackish brown posterior edge in centre and small spot at lateral ends; dorsolateral fold with very narrow creamish line along medial edge and blackish brown lateral edge, black edge wider in posterior part; interorbital bar black with narrow light grey anterior edge, continued onto posterior part of upper eyelids; dorsal face of head anterior to interorbital bar greyish light brown with black speckling; sides of head and tympanic area light brown with large black supralabial flecks and few small white dots; supratympanic fold black with white dots; area above tympanum and anterior part of flanks light brown with small and larger dark spots; posterior part of flanks greyish brown with off-white mottling; arms orange brown with few dark brown irregularly shaped spots; fingers I and II bright yellow, fingers II and IV pale yellow, all with dark brown spots; legs reddish light brown with greyish light brown crossbars; crossbars narrower and more frequent on thigh than on crus; ventral side of head, arms, and legs dark yellow; dark brown spots along mandibular edge; chest and abdomen bright yellow; greyish brown speckling along postaxial side of lower arm and tarsus, and on preaxial and postaxial sides of thigh and crus; palmar side of hand and plantar side of foot dark brown. In preserved state, dorsum of holotype brownish grey overall with more distinct light brown colour along dorsal dermal ridges and on postaxial half of thigh Black dorsal pattern elements lightened to dark brown; orange colouration on arm, yellow colouration on hands, and reddish colouration on legs faded to brownish grey; crossbars on legs changed to mid-brown; upper eyelids with bluish tinge ( Fig. 3G ); ventral side of head, chest, arms and legs pale reddish cream; spots along mandibular edge light brown; abdomen hardly pigmented, mottled bluish and yellowish; palmar side of hand and plantar side of feet light brown. Variation. The paratypes match the holotype in general appearance. Males lack nuptial pads and have weak dermal folds parallel to posterior part of mandible on ventral side of head. The vocal sac aperture is slit-like, directed posterolaterally, situated at corner of mouth. SVL of adult males is 25.2–29.7 mm , of the adult female 31.2 mm ( Table 2 ). Inger & Voris (1988) recorded 26.8–31.6 mm SVL for males and 26.1–34.4 mm for females from Nanga Tekalit. Pedal webbing variation is I 1 [71] ,1+ [29] /2 [57] ,2+ [43] II 1 [71] ,1+ [29] /2 [43] ,2+ III 1 +/2 [14] ,2+ [29] ,2.25 [14] ,2.5 [14] ,2.75 [29] IV 2 [14] ,2+ [14] ,2.5 [29] ,2.75 [14] ,3- [29] /1+ V ( Fig. 6 ) . Bioacoustics. The advertisement call of males (n=1) is a long rising trill, consisting of 26–32 notes and lasting 1.6– 2.0 s . Individual notes last 33–47 ms and are repeated at a rate of 15 notes/s ( Table 3 ). Frequency is weakly modulated and continuously increases from the beginning to the end of the call, with the dominant frequency constantly rising from 1.4 to 1.8 Hz ( Fig. 11C ). The amplitude increases continuously from the beginning, reaching its maximum at the end of the call ( Fig. 11C ).

Diagnosis. Limnonectes sarawakensis sp. nov. belongs to the L. palavanensis species group, showing the typical characters of the group, including small size (SVL < 40 mm ); odontoid processes in lower jaw low and inconspicuous in both males and females; dorsum finely shagreened, with prominent longitudinal dorsolateral glandular ridges; interorbital distance equal to or larger than upper eyelid width; toes not fully webbed; and horseshoe-shaped dermal ridge in middle of dorsum posterior to arm insertion. The species differs from all other species of the group by a unique combination of morphological characters, including toe webbing extensive; supratympanic fold strongly curved; pineal spot weakly discernible, anterior to level of anterior upper-eyelid edge; vomer processes long, separated from choana and from each other by about half length of individual process; postpalpebral ridge well developed, from upper eyelid to anterior level of pelvis; median ridge indistinct from level of posterior upper-eyelid edge to horseshoe-shaped ridge, more conspicuous from horseshoe-shaped ridge to vent; lumbar ridge well developed, interrupted; size relatively small with SVL of adult males 25.2–29.7 mm , of adult females 30.1–34.4 mm . The species differs from all other species of the group by at least 5.8% in the sequence of the 16S barcoding gene. The advertisement call is a long rising trill, consisting of 26–32 notes, lasting 1.6– 2.0 s , at a dominant frequency of 1.4–1.8 kHz with a weak frequency modulation and an amplitude maximum at the end of the call. The species is distributed in lowland and submontane rainforests of central and northern Sarawak , between 60 and 1,000 m .