Amolops gerutu, Onn & Abraham & Grismer & Grismer, 2018

Onn, Chan Kin, Abraham, Robin Kurian, Grismer, Jesse L. & Grismer, L. Lee, 2018, EleVational size Variation and two new species of torrent frogs from Peninsular Malaysia (Anura: Ranidae: Amolops Cope), Zootaxa 4434 (2), pp. 250-264 : 256-260

Amolops gerutu sp. nov.

Tuberculated Torrent Frog

Figs. 6 , 7B, D

Amolops larutensis, Sumarli, Grismer, Anuar, Muin & Quah, 2015 , pp 4,9,12.

Holotype. LSUHC 11178 , adult female, collected 2 September 2012 by Lee Grismer , Chan Kin Onn , Alexandra Sumarli , Evan Quah , Mohd. Abdul Muin, Shahrul Anuar , Ariel Loredo , and Anthony Cobos from Gunung Tebu, Terengganu, Malaysia (05°35′35.47″ N, 102°36′45.63″ E; 1039 m asl).

Paratopotypes. LSUHC 11179, adult male and 11176–77, 11187–88, adult females bear the same collection data as the holotype.

Description of holotype ( Fig. 6 ). Adult female; habitus moderately robust; head slightly longer than wide; snout sharply angular, obtusely pointed in dorsal profile, slightly projecting beyond lower jaw in lateral profile; nostrils located laterally, closer to tip of snout than to eye; canthus rostralis sharp, constricted anteriorly; lores vertical, distinctly concave; eye diameter less than snout length; pineal body visible, located level to the anterior margin of orbits; tympanum distinct, tympanic rim slightly elevated; vomerine teeth well-developed, on two oblique, oval ridges almost contacting each other; tongue cordiform.

Forelimbs moderately robust; relative length of fingers, II=IV<I<III; fingers without web; tips of fingers expanded into large discs bearing circummarginal and transverse dorsal and ventral grooves, discs of third and fourth fingers distinctly larger than discs of first and second fingers; fringe of skin along lateral edges of all fingers; subarticular tubercles slightly raised, proximal subarticular tubercle on fourth finger oval, others round; inner metacarpal tubercle elongate, medial and outer metacarpal tubercle oval, in contact, outer slightly smaller than medial; one supernumerary tubercle posterior to proximal subarticular tubercle on second, third and fourth fingers, that on second finger barely visible.

Hind limbs robust; tips of toes expanded into round discs bearing circummarginal and transverse dorsal and ventral grooves, width of fourth toe disc less than width of third finger disc; toes fully webbed; wide, movable flap of skin on inner side of first toe and a narrower flap of skin on outer side of fifth toe from the level of the proximal subarticular tubercle to toe disc; subarticular tubercles distinct, oval; inner metatarsal tubercle elongate, outer round, approximately one third size of inner.

Skin on dorsum and dorsal surfaces of forelimbs densely covered with irregularly-sized, raised tubercles; tubercles on dorsolateral region slightly enlarged, elongated, ridge-like; tubercles on flanks larger than those on dorsum; tubercles on dorsal surfaces of hind limbs sparser; supratympanic fold absent; skin on gular region and chest smooth, belly slightly granular; anterior half of ventral surface of thigh smooth, posterior half granular; large pectoral glands present.

Measurements of holotype (mm): SVL=58.2; HL=21.4; HW=20.2; IND=6.2; SNL=9.1; FAL=13; FL=31.3; TBL=33.6; Fin3DW=3.8. Additional measurements: horizontal diameter of orbit=6.6; interorbital distance=5.3; largest diameter of tympanum=2.6; distance between anterior margin of tympanum and posterior margin of orbit=2.7

Diagnosis. Amolops gerutu sp. nov. is placed in the genus Amolops based on its overall morphological similarity with A. larutensis and phylogenetic placement as its sister lineage ( Chan et al. 2017). It can be distinguished from other congeners by the following combination of characters: adult females large (SVL 45.0– 58.2 mm), males moderate in size (SVL 34.0– 37.2 mm); dorsum densely covered with irregularly-sized, raised tubercles; tubercles on dorsolateral region slightly enlarged, elongated, ridge-like; tubercles on flanks larger than those on dorsum; tubercles on dorsal surfaces of hind limbs sparser; posterodorsal surface of thighs with dense, dark stippling.

Coloration in preservative. Dorsum dark-brown, overlain with irregular light-gray patches; flanks yellowish white with dark-brown blotches; lips yellowish white, mottled with dark-brown; dorsal surface of fore and hind limbs light-brown with distinct, wide, dark-brown crossbars; dorsal surface of third and fourth fingers brown with dark-brown crossbars, second finger yellowish white, mottled with dark-brown, first finger yellowish white with minute brown speckling; posterodorsal surface of thighs with dense, dark stippling; toe webbing light-brown with fine, dense, dark-brown veins; venter yellowish white; ventral surface of hands speckled with dark-brown; darkbrown stripe on outer side of forearm; gular with irregular, dark-brown streaks; anterior half of ventral surface of thighs orange, posterior half dark-brown with light-colored spots; ventral surface of feet and outer half of tarsus dark-brown; pectoral glands orangish.

Variation. Males differ from females in being smaller; having paired vocal sacs; distinct nuptial pads on base of first finger; lacking humeral glands; and having indistinct pectoral glands.

Comparisons. Because the new species forms a clade with A. larutensis and is substantially distant genetically from all other congeners, we restrict our comparisons to A. larutensis and the other undescribed species. Amolops gerutu sp. nov. differs from A. larutensis by having denser and more pronounced dorsal tubercles and posterodorsal side of thighs having dense, dark stippling as opposed to vermiculations ( Fig. 7E, F ). After correcting for body size, males of A. gerutu sp. nov. have larger heads (HL and HW) and longer hind limbs (FL and TBL; Fig. 3 ), whereas females have smaller SVL, HL, and larger IND, TBL, and Fin3DW ( Table 3; Fig. 4 ). See the Discussion section for the use of continuous morphological characters to diagnose this species.

Distribution. Besides the type locality, Amolops gerutu sp. nov. has been documented from a number of other

localities east of the Titiwangsa mountain range including Gunung Stong Forest Reserve, in the state of Kelantan; Lata Tembakah, Lata Belatan, and Sekayu Recreational Forest in the state of Terengganu ( Dring 1979; Sumarli et al. 2015); and Sungai Lembing, Sungai Pandan Waterfall, and Chemerong Amenity Forest in the state of Pahang. At Gunung Stong, A. gerutu sp. nov. occurs in syntopy with A. larutensis ( Fig. 1 ).

Natural history. Like most congeners, Amolops gerutu sp. nov. is a strict torrent specialist that only occurs within or along torrential zones of rocky streams from lowland to montane forests. During the day, frogs dwell in rock cracks and sheltered areas among boulder stacks along streams and are rarely seen out in the open. They can be seen in abundance at night, most frequently on boulders by splash zones and occasionally on adjacent low vegetation. When disturbed, frogs dive into the rapids and float downstream. Like other congeners, tadpoles of this species are gastromyzophorous ( Pham et al. 2015) and can be seen clinging onto boulders in the splash zone. On such boulders, tadpoles are usually observed above or just below the water line.

Etymology. The specific epithet “ gerutu ” (English pronunciation “gir-roo-too”) refers to the Malay word of the same construct, meaning “tubercle”, in reference to the pronounced dorsal tubercles that are diagnostic of this species.

Figures

FIGURE 1. Distribution of sampled populations and an ultrametric maximum-likelihood phylogeny inferred from 1,466 bp of the 16S rRNA-encoding mitochondrial gene. All major nodes were highly supported with>90% bootstrap. Populations represented by circles belong to the western clade, triangles represent populations from the eastern clade, and star denotes the type locality of Amolops larutensis at Bukit Larut, Perak. The red box indicates a contact zone between the eastern and western clades. This figure is adapted from Chan et al. (2017).

FIGURE 3. Boxplots representing the log-transformed and body-size corrected morphological characters in males. Clusters with the same letter code are not significantly different (Tukey HSD test at p<0.05). Blue=E2; purple=E1; orange=Amolops larutensis.

FIGURE 4. Boxplots representing the log-transformed and body-size adjusted morphological characters in females. Clusters with the same letter code are not significantly different (Tukey HSD test at p<0.05). Blue=E2; purple=E1; orange=Amolops larutensis.

FIGURE 6. Holotype (LSUHC 11178) of Amolops gerutu from Gunung Tebu, Terengganu.

FIGURE 7. Top row: (A) female Amolops larutensis from Fraser’s Hill, Pahang; (B) female A. gerutu from Chemerong, Pahang; Middle row: (C) male A. larutensis from Fraser’s Hill; (D) male A. gerutu from Sekayu, Terengganu; Bottom row: (E) color-pattern comparisons of the posterodorsal portion of the thigh that diffentiates A. larutensis from (F) A. gerutu and (G) A. australis.