Hylarana serendipi sp. nov.
Sri Lankan Golden-backed frog
Holotype. DZ 1247, an adult male, Kudawa, Sinharaja, Ratnapura dist., Sri Lanka, collected by MM and others, 25 June 2013.
Paratypes. DZ 1146, DZ 1233, DZ 1235, DZ 1248, four adult males, DZ 1144-1145, DZ 1234, three adult females, collected along with holotype.
Comparison. Hylarana serendipi sp. nov. could not be confused with Hylarana temporalis, the only other species in the Hylarana temporalis group, due to its smaller adult size. It differs from H. temporalis by its smaller snout-vent size, male SVL 30.1-36.9, N = 5; female SVL 42.5-43.6, N = 3 (vs. larger, male SVL 48.1-68.1, N = 13; female SVL 63.5-79.4, N = 8); body slender (vs. robust); absence of supertympanic ridge (vs. presence) (Figs 17c, f, i). Hylarana serendipi is not closely related to any of the Western Ghats species, however due to a long history of its misidentification with H. aurantiaca, we provide a comparison with the latter. Hylarana serendipi differs from H. aurantiaca by its relatively larger adult size (male, SVL 30.1-36.9, N = 5; female, SVL 42.5-43.6, N = 3) (vs. smaller, male, SVL 27.1-31.7 mm, N = 9; female, SVL 37.9, N = 1); dorsal skin granular with scattered spinules (vs. dorsal skin shagreened); subarticular tubercles prominent on toes (vs. weakly developed); third toe webbing extends up to the disc on the outside (vs. extends just beyond the first subarticular tubercle) (Figs 8b-c, 18b-c).
Genetic divergence. Intraspecific genetic variation within populations of Hylarana serendipi was 0.1 ± 0.1% (range 0-0.2%, N = 3) for 16S, 0.9 ± 0.5% (range 0.3-1.2%, N = 3) for COI and 1.8% (N = 2) for Cytb. Based on phylogenetic position, H. serendipi is closely related to H. temporalis (Fig. 4) from which it differs by an average genetic divergence of 10.5 ± 0.1% (range 10.4-10.6%, N = 14) for 16S, 18.1 ± 0.2% (range 17.8-18.5%, N = 18) for COI and 23.8 ± 0.6% (range 23.0-25.0%, N = 18) for Cytb. Since H. serendipi was long misidentified as H. aurantiaca from India, the present study compared the two species, and found a very high genetic divergence of 13.8 ± 0.2% (range 13.6-14.2%, N = 10) for 16S, 18.8 ± 0.1% (range 18.7-19%, N = 18) for COI and 23.3 ± 0.5% (range 22.8-23.9%, N = 10) for Cytb (Tables SI-S3).
Description of holotype (Figs 17a-c, 18a-c). Small-sized, moderately slender adult male (SVL 36.9). Head small (HW 11.5, HL 14.8, IFE 6.3, IBE 9.3), longer than wide, flat above; snout sub-elliptical in dorsal and ventral view, rounded in lateral view, protruding, its length (SL 6.7) longer than horizontal diameter of eye (EL 4.9); loreal region acute and concave with rounded canthus rostralis; interorbital space flat, equal (IUE 3.2) to upper eyelid (UEW 3.2) and subequal to internarial distance (IN 3.6); distance between back of eye (IBE 9.3) 1.5 times the distance between front of eye (IFE 6.3); nostril oval, closer to tip of snout (NS 2.0) than eye (EN 4.2); tympanum (TYD 3.5) 71% of eye diameter (EL 4.9); tympanum-eye distance (TYE 0.8); pineal ocellus present, between anterior border of eye; vomerine ridge present, bearing small teeth, with an angle of 40° to body axis, as close to choanae as to each other; tongue moderately large, emarginated. Forelimbs moderately short and thin; forelimb (FAL 7.1) shorter than hand length (HAL 11.1), finger length formula I<II<IV<III, finger tips dorsoventrally compressed with obtusely pointed discs and lateroventral groove, moderately wide compared to finger width (FDI 0.7, FWI 0.4; FDII 1.0, FWII 0.5; FDIII 1.2, FWIII 0.6; FDIV 1.0, FWIV 0.6); dermal fringe present; subarticular tubercles weakly developed, oval, single, all present; prepollex distinct, oval; two oval palmar tubercles weakly developed; a weakly developed supernumerary tubercle on base of each finger. Hindlimbs relatively long and thin; thigh length (TL 16.3) shorter than shank (SHL 19.1), and foot (FOL 18.2); relative digit lengths I<II<III<V<IV; toe tips dorsoventrally compressed with obtusely pointed discs and lateroventral grooves, rather wide compared to toe width (TDI 0.8, TWI 0.5; TDII 1.1, TWII 0.6; TDIII 1.5, TWIII 0.5; TDIV 1.3, TWIV 0.5; TDV 0.9, TWV 0.4); webbing present, rather medium: I11/5 -2+II1-2III1-2+IV2-1V; dermal ridge along toe V present, subarticular tubercles rather prominent, oval, all present; inner metatarsal tubercles distinct and rather short; outer metatarsal tubercles rounded, rather prominent.
Skin of snout, between eyes, side of head and anterior part of dorsum granular, more prominently granular on upper eyelids; posterior part of back and upper part of flanks granular; lower part of flanks rather smooth; dorsolateral folds that extend from the posterior corner of the eye to the entire body length on both sides, moderately developed (Figs 5, 17a, c); dorsal part of forelimb smooth, thigh, tibia and tarsus with glandular warts in longitudinal lines bearing horny spinules; distinct rictal gland posterior to corner of mouth; flat indistinct humeral glands; ventral part of throat smooth, anterior part of belly shagreened, posterior part of belly and thigh shagreened.
Colour in preservation (Figs 17a-c). Dorsum light brown in colour; lower flanks dark grey with black speckles; tympanic area dark grey; upper lip with white stripe continuing through rictal gland to above arm insertion; dorsolateral folds light brown; forelimbs, dorsal parts of thigh, tibia and foot light brown coloured; throat and margin of throat greyish-white; chest and belly greyish-white; ventral parts of thigh, tibia and foot light brownish-white; webbing dark grey with minute specks. Colour in life (Figs 19a-b). Dorsum uniform reddish-brown with black specks; tympanum and surrounding area dark brown; upper lip with white stripe continuing through yellowish-white rictal gland to above arm insertion; iris reddish-brown with golden specks and dark patches on either side; flanks light yellowish-grey; limbs dorsally light brown with light grey cross-bands; ventral side white, throat and limbs light grey, feet and webbing dark grey.
Variation. See Table 2 for morphometric data from five adult males and three adult females. DZ 1235: dorsum dark brown in life, turned dark grey in preservation with prominent cross-bands on both hind and forelimbs; throat and chest dark grey in life, turns light grey in preservation.
Secondary sexual characters. Males: Single oval shaped nuptial pad on finger I present, cream-coloured; two vocal sacs faintly visible externally on the posterior lateral side of the throat; humeral gland weakly developed, positioned laterally on the preaxial side of the upper forelimb. Females (DZ 1145): ova white, pigmented on pole (diameter 0.7-0.9 mm, N = 10).
Etymology. The species is named after an ancient name for Sri Lanka, the country of its type locality. The English word serendipity, for which the contemporary meaning is ‘a fortunate discovery or an event by chance’, has its earliest roots in Sanskrit, where Sri Lanka was referred to as Swavarnadveepa, and later modified by Persian merchants as Serendip. The species epithet serendipi is a noun in the genitive case.
Fig. 20. Geographic distribution of two species of the Hylarana temporalis group in Sri Lanka. Open square = Hylarana serendipi; closed square = Hylarana temporalis. Coordinates are provided in Table 1.
Habitat and natural history. The primary habitat type in Sinharaja World Heritage Site is broadly regarded as tropical lowland evergreen forest (Gunatilleke and Gunatilleke, 1985). The species was found on the banks of streams and in marshy areas, which were under forest cover, where it was relatively abundant during the breeding season (May-August). These marshy areas are covered with a thick layer of leaf litter. All of the type series was collected between 19:00-23:30 h.
Remarks. This species was historically considered to be conspecific with the Indian species Hylarana aurantiaca (Dutta and Manamendra-Arachchi, 1996). For more about taxonomic history see ‘Remarks’ under H. aurantiaca.