Limnonectes sarawakensis, Dehling & Neokleous & Das & Grafe & Min & Hertwig, 2025

Dehling, Maximilian, Neokleous, Dario N., Das, Indraneil, Grafe, Ulmar, Min, Pui Yong & Hertwig, Stefan T., 2025, Cryptic radiation within the tadpole-carrying Guardian Frogs from Borneo, Limnonectes palavanensis and L. finchi (Anura: Dicroglossidae), with the description of eight new species, Zootaxa 5650 (1), pp. 1-80 : 34-37

Limnonectes sarawakensis sp. nov.

Rana microdisca palavanensis (nec Rana palavanensis Boulenger, 1894 ): Inger 1966: 222 (partim); Inger et al. 1986: 523. Rana palavanensis (nec Rana palavanensis Boulenger, 1894 ): Inger 1985: 52 (partim); Inger & Voris 1988: 1060 (partim). Limnonectes palavanensis (nec Rana palavanensis Boulenger, 1894 )— Das et al. 2016: 19 (partim); Dehling & Dehling 2021:

Table A2.

Holotype. NMBE 1057455 , adult female, from Lambir Hills National Park (4.2°, 114.0°; 100–400 m), Sarawak, Malaysia, collected in September 2010 by A. Haas, S. T. Hertwig and A. Jankowski ( Fig. 3G ).

Paratypes. NMBE 1057451 , adult male, collected on 8 September 2010 by A. Haas , S . T. Hertwig, A. Jankowski , NMBE 1069412 , adult male, collected on 14 March 2014 by S . T. Hertwig et al., both from Lambir Hills National Park , Sarawak, Malaysia . NMBE 1101233–1101234 , two adult males , NMBE 1101235 , juvenile; all from Camp Koyan (3.342366°, 114.177573°; 822 m), High Plateau , Gunung Dulit, Sarawak, Malaysia , collected on 8 February 2019 by L. Etter , S . T. Hertwig and F. Heussler . NMBE 1101236 , adult male, from Summit Trail (2.655489, 112.903817; 185 m), Bukit Kana National Park , Sarawak, Malaysia , collected on 15 March 2019 by L. Etter , S . T. Hertwig and F. Heussler . NMBE 1101217–1101219 , three adults of undetermined sex, from unnamed stream at 537 m (3.096895°, 114.2673°; 537 m), Camp Balah , Gunung Dulit, Sarawak, Malaysia , collected on 24 February 2019 by L. Etter, L. Fehland, S. T. Hertwig and F. Heussler . NMBE 1101238–1101240 , three adults of undetermined sex, from sidestreams and ponds near camp (1.960155°, 114.783815°; 495 m), Long Unai , Sarawak, Malaysia , collected on 13 March 2018 by S. Cilloni, L. Etter, L. Fehland, S. T. Hertwig, B. Minder and Y. M. Pui .

Referred specimens. NMBE 1065274 , tadpole, from alluvial forest near headquarters, Gunung Mulu National Park , Sarawak, Malaysia, collected on 24 March 2009 by A. Haas . ZRC 12728 , adult male, from Nanga Tekalit (1.63°, 113.58°), Sarawak, Malaysia, collected on 28 March 1984 by R. F. Inger and P. Walker .

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.

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 ).

Distribution. The species is distributed in lowland and submontane rainforest in central and eastern Sarawak (Lambir Hills National Park, Gunung Mulu National Park, Gunung Dulit National Park, Bukit Kana National Park, Long Unai, Nanga Tekalit; Fig. 8 ), between 50 and 1,000 m ( Fig. 9 ). The species occurs sympatrically with L. gunungensis sp. nov. on the High Plateau on Gunung Dulit, Sarawak, and parapatrically with L. phylax sp. nov. in the lowland forests of Gunung Mulu National Park, Sarawak ( Fig. 9 ).

Ecology. Males of the species are known to transport up to about 30 tadpoles on their backs to water bodies ( Inger et al. 1986). Tadpoles were found in pools of small intermittent streams, in low shallow buttress tank, in a water-filled hole in a log, in small isolated rain pools on forest floor ( Inger et al. 1986, Inger & Voris 1988) and in a shallow puddle with silky bottom and scattered leaves together with tadpoles of Occidozyga in alluvial forest in Gunung Mulu National Park (A. Haas, pers. comm.). Total clutch size of females was estimated at 35–50 ( Inger et al. 1986), later corrected to half this number ( Inger & Voris 1988). Tadpole of the species were described by Inger (1966, 1985). Like in other species of the group, we expect the species to deposit eggs in moist leaf litter which are subsequently guarded by the males until the hatched tadpoles are transported to water bodies.

Etymology. The species epithet is composed of the name of the Malaysian State of Sarawak and the Latin suffix -ensis (“from”); meaning “the one from Sarawak ”, in allusion to the distribution of the new species.

Suggested English name. Sarawak Guardian Frog.

Figures

FIGURE 3. Holotypes, lectotypes, and paratypes of the species of the Limnonectes palavanensis group (A–H) and L. finchi group (I & J): (A) Limnonectes palavanensis, lectotype (BMNH 1947.2.1.96, adult female); (B) L. gunungensis sp. nov., holotype (NMBE 1061576, adult female); (C) L. kinabaluensis sp. nov., holotype (NMBE 1075310, adult female); (D) L. nephophilus sp. nov., holotype (NMBE 1056394, adult male); (E) L. oreibates sp. nov., holotype (NMBE 1061519, adult female); (F) L. phylax sp. nov., holotype (NMBE 1072362, adult female); (G) L. sarawakensis sp. nov., holotype (NMBE 1057455, adult female); (H) L. suboliferus sp. nov., holotype (NMBE 1059945, adult female); (I) L. finchi, paratype (NMW 16961, adult male); (J) L. gyrinophorus sp. nov., holotype (NMBE 1075255, adult female). Scale bar represents 10 mm.

FIGURE 4. Relative size and position of teeth-bearing vomer ridges in (A) Limnonectes palavanensis—lectotype, BMNH 1947.2.1.96, adult female; (B) L. gunungensis sp. nov.—adult female, NMBE 1061576, holotype; (C) L. kinabaluensis sp. nov.—adult female, SP 1355; (D) L. nephophilus sp. nov.—adult male, NMBE 1073581, paratype; (E) L. oreibates sp. nov.— adult female, NMBE 1061519, holotype; (F) L. phylax sp. nov.—adult male, UBDM-GG012; (G) L. sarawakensis sp. nov.— adult female, NMBE 1057455, holotype; (H) L. suboliferus sp. nov.—adult male, NMBE 1059943, paratype; (I) L. finchi—adult female, NMBE 1072469; (J) L. gyrinophorus sp. nov.—adult female, NMBE 1075255, holotype.

FIGURE 5. Schematic drawings illustrating the shape of the supratympanic fold and the relative size and the position of the tympanum in the eight species of the L. palavanensis group: (A) Limnonectes palavanensis, (B) L. gunungensis sp. nov., (C) L. kinabaluensis sp. nov., (D) L. nephophilus sp. nov., (E) L. oreibates sp. nov., (F) L. phylax sp. nov., (G) L. sarawakensis sp. nov., (H) L. suboliferus sp. nov. (Drawings by J. M. Dehling).

FIGURE 6. Schematic drawings illustrating the extent of toe webbing in the eight species of the Limnonectes palavanensis group and the two species of the L. finchi group.Toes I to V are arranged from right to left in each drawing. Open circles represent terminal disks, filled circles represent subarticular tubercles. Solid lines represent the most common outline of webbing between toes, dotted lines represent the maximum or minimum extent due to variation between specimens.

FIGURE 7. Photographs of the species of the Limnonectes palavanensis group in life.A) Limnonectes palavanensis, adult male, Mt. Mantalingahan, Barangay Samarinana, Municipality of Brooke’s Point, Palawan Province, Palawan Island, Philippines (photo: R. Brown). (B) L. gunungensis sp. nov., paratype, adult male, Gunung Dulit, Sarawak, Malaysia (photo: S. T. Hertwig). (C) L. kinabaluensis sp. nov., holotype (NMBE 1075310), adult female, Silau-Silau Trail, Kinabalu National Park, Sabah, Malaysia (photo: S. Hertwig). (D) L. nephophilus sp. nov., holotype (NMBE 1056394), adult male, Camp 3, Gunung Mulu National Park, Sarawak, Malaysia (photo: J. M. Dehling). (E) L. oreibates sp. nov., paratype (UNIMAS P1186), adult male, Gunung Penrissen, Sarawak, Malaysia (photo: I. Das). (F) L. phylax sp. nov., adult male (not collected), Camp 5, Gunung Mulu National Park, Sarawak, Malaysia (photo: J. M. Dehling). (G) L. sarawakensis sp. nov., adult female (not collected), Headquarters, Gunung Mulu National Park, Sarawak, Malaysia (photo: J. M. Dehling). (H) L. suboliferus sp. nov., paratype (NMBE 1056615), adult male, Kubah National Park, Sarawak, Malaysia (photo: J. M. Dehling).

FIGURE 8. Collection localities of vouchers examined in the study of the different species of the L. palavanensis group and the L. finchi group in northern Borneo (Sarawak, Brunei, Sabah; main frame) and Palawan (inset). Respective localities are marked with a star (the exact type locality of L. palavanensis s. str. on Palawan is unknown). BK: Bukit Kana National Park, Sarawak; BP: Mt. Mantalingaha, Brooke’s Point, Palawan; DK: Deramakot, Sabah; DU: Gunung Dulit National Park, Sarawak; DV: Danum Valley Conservation Area, Sabah; GG: Gunung Gading National Park, Sarawak; GM: Gunung Mulu National Park, Sarawak; GT: Gunung Trusmadi, Sabah; KA: Kalabakan, Tawau District, Sabah; KB: Kuala Belalong Field Studies Centre, Ulu Temburong National Park, Brunei; KI: Kinabalu National Park, Headquarters, Sabah; KS: Kampung Sebako, Sarawak; KU: Kubah National Park, Matang Range, Sarawak; LH: Lambir Hills National Park, Sarawak; LP: Long Pasia, Sipitang, Sabah; LU: Long Unai, Sarawak; ME: Merarap Hot Spring Lodge, Sarawak; ML: Mendolong, Sipitang, Sabah; MR: Gunung Murud, Pulong Tau National Park, Sarawak; NT: Nanga Tekalit, Sarawak; PE: Gunung Penrissen, Sarawak; PM: Payeh Maga, Sarawak; PO: Kinabalu National Park, Poring, Sabah; PP: Barangay Irawan, Puerto Princesa, Palawan; PT: Pulong Tau National Park, Sarawak; PU: Purolon Camp, Crocker Range, Sabah; SP: Sepilok Forest Reserve, Sabah; SY: Kinabalu National Park, Sayap, Sabah; TW: Tawau Hills National Park. Map data © OpenStreetMap contributors.

FIGURE 9. Elevational distribution of the different species of Guardian Frogs, i.e. the L. finchi group, the L. palavanensis group and L. parvus.

FIGURE 11. Sound spectrograms (left) and corresponding waveforms (right) of typical advertisement calls or call series of (A) Limnonectes finchi, Danum Valley Conservation Area, Sabah, 400 m; (B) Limnonectes phylax sp. nov., Gunung Mulu National Park, Sarawak, 150 m; (C) L. sarawakensis sp. nov., Gunung Mulu National Park, Sarawak, 50 m; (D) L. nephophilus sp. nov., Gunung Mulu National Park, Sarawak, 1,300 m, (E) L. oreibates sp. nov., Gunung Penrissen, Sarawak, 1,000 m; (F) L. suboliferus sp. nov., Kubah National Park, Sarawak, 300 m; See Table 3 and respective species accounts for details.