Hylarana aurantiaca (Boulenger, 1904)
Boulenger's Golden-backed frog
Original name and description. Rana aurantiaca Boulenger 1904. Description of three new frogs from southern India and Ceylon, Journal of Bombay Natural History Society, 15: 430. Holotype. By monotypy, NHM 1918.104.22.168 (ex BMNH 1903.9.26.1), an adult female, collected by K.S. Ferguson. Type locality. ‘near Trivandrum, Travancore [Kerala]’, Thiruvananthapuram dist., Kerala state, India. Current status of specific name. Valid name, as Hylarana aurantiaca (Boulenger, 1904).
Referred specimens. BNHS 5809 and SDBDU 2011.520, two adult males, Chathankod, Thekal, Thiruvananthapuram dist., collected by SDB and Systematics Lab team, 10 August 2011; BNHS 5810-5811 and SDBDU 2001.795, three adult males, Chathankod, Thiruvananthapuram dist., collected by SDB, 23 October 2001; BNHS 5812, an adult male, Chathankod, Thiruvananthapuram dist., collected by SDB, 23 May 2006; SDBDU 2006.4776, an adult male, Karamana, Thiruvananthapuram dist., collected by SDB, 8 July 2006; BNHS 5813 and SDBDU 2012.1894, two adult males, Vellayani, Thiruvananthapuram dist., collected by SDB and SG, 30 January 2012; SDBDU 2006.309, a sub-adult, Kallar, Ponmudi, Thiruvananthapuram dist., collected by SDB, 24 May 2006; SDBDU 2011.277, a sub-adult, Kattilappara, Shendurney WLS, Kollam dist., collected by SDB and Systematics Lab team, 12 September 2011.
Comments. Holotype is moderately dehydrated (Fig. 7a-b) and many of the measurements of hand and feet cannot be reliably made to provide a comprehensive description. The present collection from ‘Trivandrum’ (= Thiruvananthapuram) is comparable to the holotype and hence, for a more accurate description of this species, we provide a complete description based on a topotype BNHS 5809.
Comparison. Hylarana aurantiaca could be confused with Hylarana doni sp. nov., Hylarana intermedius and Hylarana urbis sp. nov. in the Hylarana aurantiaca group, due to its small adult size. However, H. aurantiaca differs from H. doni and H. intermedius by its smaller adult male snout-vent size, SVL 27.1-31.7 mm, N = 9 (vs. SVL 38.0-43.1 mm, N = 12, H. doni; SVL 33.0-41.6 mm, N = 14, H. intermedius), toes thin (Figs 8b, e, h) with weakly developed subarticular tubercles (vs. thick with well developed subarticular tubercles in both species), third toe webbing not extending up to the disc on the outside (vs. up to the disc in both species). Furthermore, H. aurantiaca differs from H. doni by its dorsal skin shagreened (vs. granular), dorsolateral folds weakly developed (vs. moderately developed), forearm without granular projections (vs. ventral side of forearm, having a straight line of granular projections from the base of finger IV to the elbow); differs from H. urbis by its interorbital space equal to the upper eyelid width, IUE 2.5 ± 0.2 mm, UEW 2.5 ± 0.2 mm, N = 9 (vs. wider IUE 2.9 ± 0.2 mm, UEW 1.9 ± 0.1 mm, N = 5), relatively more webbing between toes I1⅓-2II1+-2+III1½-3IV2½-1¼V (vs. less I2--2+II1¾-2¾III2--3IV3-1¾V ) (Figs 8b-c, k-l).
Genetic divergence. Intraspecific genetic variation within populations of Hylarana aurantiaca was 0.2 ± 0.1% (range 0-0.4%, N = 5) for 16S, 0.1 ± 0.1% (range 0-0.4%, N = 6) for COI, and zero (N = 7) for Cytb. Based on phylogenetic position, H. aurantiaca is closely related to the members of Hylarana aurantiaca group (Fig. 4); differs from H. doni by mean genetic divergence of 4.2 ± 0.1% (range 4.1-4.6%, N = 40) for 16S, 8.5 ± 0.3% (range 7.9-9.2%, N = 63) for COI, and 9.8 ± 0.3% (range 9.4-10.4%, N = 50) for Cytb; from H. intermedius by mean genetic divergence of 3.3 ± 0.2% (range 3.0-3.6%, N = 45) for 16S, 8.9 ± 0.2% (range 8.6-9.4%, N = 63) for COI, and 9.6 ± 0.9% (range 8.9-12.4%, N = 45) for Cytb; from H. urbis by mean genetic divergence of 4.1 ± 0.2% (range 3.9-4.4%, N = 15) for 16S, 7.4 ± 0.2% (range 7.3-7.8%, N = 21) for COI, and 8.7 ± 0.4% (range 8.2-9.3%, N = 15) for Cytb (Tables S2-S3).
Redescription of holotype (Figs 7a-b). Small-sized, slender adult female (SVL 37.9). Head small (HW 10.4, HL 13.2, IFE 5.9, IBE 7.8), longer than wide, slightly concave above; snout rounded (due to poor preservation) in lateral view, its length (SL 5.6) longer than horizontal diameter of eye (EL 4.2); loreal region acute and concave with rounded canthus rostralis; interorbital space slightly concave, wider (IUE 3.7) than upper eyelid (UEW 2.0) and internarial distance (IN 3.3); nostril oval with flap of skin laterally, closer to tip of snout (NS 2.0) than eye (EN 4.1); tympanum (TYD 2.3) 54% of eye diameter (EL 4.2); vomerine ridge present but weak, bearing numerous small teeth, with an angle of 45° to body axis, closer to choanae than each other, shorter than the distance between them; tongue moderately large, emarginated, bearing no medium lingual process. Forelimbs moderately long and thin; forelimb (FAL 7.9) shorter than hand length (HAL 9.3); fingers long and rounded with lateral fringes, finger lengths not obtainable due to damage, tip of all intact fingers with discs, with lateroventral groove, slightly wider than finger width (not measured due to specimen desiccation); subarticular tubercles prominent, oval, single, all present; palmar and supernumerary tubercles all indistinct. Hindlimbs relatively long and thin, thigh length (TL 16.9) shorter than shank (SHL 20.0); relative digit lengths I<II<III=V<IV; tips of all toes obtusely pointed with small discs possessing lateroventral grooves (not measured due to specimen desiccation); webbing present (not measured due to specimen desiccation and damage); dermal ridge along toe V present; subarticular tubercles prominent, oval, all present; inner and outer metatarsal tubercles and supernumerary tubercles indistinct (due to desiccated state of specimen).
None of the skin characters can be reliably determined due to poor preservation of the specimen.
Description of topotype, male, BNHS 5809 (Figs 7c, 8a-c). Small-sized, moderately slender adult male (SVL 31.7). Head small (HW 9.2, HL 12.9, IFE 5.6, IBE 7.6), longer than wide, flat above; snout subovoid in dorsal and ventral view, rounded in lateral view, protruding, its length (SL 5.9) longer than horizontal diameter of eye (EL 4.0); loreal region vertical and concave with rounded canthus rostralis; interorbital space flat, equal (IUE 3.0) to upper eyelid (UEW 3.0) and narrower than internarial distance (IN 3.1); distance between back of eyes (IBE 7.6) slightly more than 1.3 times the distance between front of eyes (IFE 5.6); nostril closer to tip of snout (NS 2.0) than eye (EN 2.8); tympanum (TYD 2.8) 70% of eye diameter (EL 4.0); tympanum-eye distance (TYE 0.6); pineal ocellus present, between anterior border of eyes; vomerine ridge present, bearing small teeth, with an angle of 45° to body axis, as close to choanae as to each other, tongue moderately large, emarginated. Forelimbs short and thin; forelimb (FAL 5.5) shorter than hand length (HAL 8.6); fingers short, finger length formula I=II<IV<III, tip of all fingers with obtusely pointed discs, with lateroventral groove, moderately expanded relative to finger width (FDI 0.7, FWI 0.5; FDII 0.8, FWII 0.6; FDIII 1.0, FWIII 0.4; FDIV 1.1, FWIV 0.5); dermal fringe present; subarticular tubercles not prominent, oval, single, all present; two oval distinct palmar tubercles weakly developed; a distinct supernumerary tubercle on base of each finger. Hindlimbs relatively long and thin, thigh length (TL 13.0) shorter than shank (SHL 15.0), and foot (FOL 14.4); relative digit lengths I<II<III<V<IV; tips of all toes with small obtusely pointed discs possessing lateroventral grooves, moderately expanded relative to toe width (TDI 0.8, TWI 0.6; TDII 0.8, TWII 0.5; TDIII 0.9, TWIII 0.5; TDIV 0.7, TWIV 0.5; TDV 0.8, TWV 0.5); webbing present, moderate: I11/3 -2II1+-2+III11/2 -3IV21/2 -11/4 V; dermal ridge along toe V present, subarticular tubercles prominent, oval, all present; inner metatarsal tubercle distinct and rather short, outer metatarsal tubercle rounded, prominent; supernumerary tubercles absent, tarsal tubercle absent.
Skin of snout, between eyes, side of head and anterior part of dorsum finely shagreened; posterior part of back and upper part of flank finely glandular; dorsolateral folds that extend from the posterior corner of the eye to the entire body length on both sides, weakly developed (Figs 5, 7c); dorsal part of forelimb without glandular warts; thigh, tibia and tarsus with weakly developed glandular warts; distinct rictal gland posterior to corner of mouth; flat weakly developed humeral glands.
Colour in preservation (Figs 7c, 8a-b). Dorsal parts greyish-brown, lower flank light grey with black speckles; tympanic area dark grey; upper lip with white stripe continuing through rictal gland to above arm insertion; dorsolateral folds light grey; forelimbs, dorsal parts of thigh, shank and foot light greyish-brown with grey spots, and weakly formed cross-bands; throat and margin of throat greyish-white with black flecks; chest and belly greyish-white; ventral parts of thigh, tibia and foot greyish-white with black spots; webbing dark grey with minute specks. Colour in life (SDBDU 2006.4776) (Fig. 9a). Dorsal parts light brown, lower flank greyish-brown with black specks, tympanic area reddish-grey; upper lip with white stripe continuing through rictal gland to above arm insertion; dorsolateral folds light brown; forelimbs, dorsal parts of thigh, shank and foot light brown with grey spots; margin of throat white with black flecks; chest and belly off-white, ventral parts of thigh, tibia and foot greyish-white with black spots; webbing dark grey with minute specks; iris reddish-brown.
Variation. See Table 2 for morphometric data from nine adult males and an adult female (holotype). SDBDU 2012.1894: dorsum finely granular; SDBDU 2011.520, SDBDU 2006.4776, SDBDU 2001.795 and BNHS 5810: dorsum light brown with minute dark spots and without scattered granular projections; BNHS 5811-5812: dorsum with scattered granular projections; SDBDU 2001.795: tympanic region light grey.
Secondary sexual characters. Males: Single oval-shaped nuptial pad on finger I present, cream-coloured; vocal sac not visible externally on lower jaw (internal vocal slits present); humeral gland weakly developed, positioned laterally on the preaxial side of the upper forelimb.
Fig. 10. Geographic distribution of four species of the Hylarana aurantiaca group in the Western Ghats. Open circle = Hylarana aurantiaca, closed circle = Hylarana intermedius, closed square = Hylarana doni, open square = Hylarana urbis. Coordinates are provided in Table 1.
Habitat and natural history. This species was collected either from disturbed habitats adjacent to secondary forests (BNHS 5809), or wayside temporary ponds surrounded by vegetation (SDBDU 2006.4776) below 180 m asl. Animals were found both in temporary (SDBDU 2006.4776) and permanent water bodies (BNHS 5809-5811, SDBDU 2011.520, SDBDU 2001. 795), but none were found in fast flowing streams. BNHS 5810-5811 were collected from leaves about one meter above the ground close to a water body, whereas BNHS 5809 was collected along a stream, where over 30 aggressively calling males were observed. During the dry season this species was not found at any of these sites, however, immediately after a few monsoon showers, aggregating males called continuously just after sunset to approximately 22:00 h.
Remarks. Small-sized Hylarana species from Sri Lanka have long been misidentified as H. aurantiaca (e.g. Grandison and Senanayake, 1966; Dutta and Manamendra-Arachchi, 1996; Dutta, 1997; Pethiyagoda et al., 2006; De Silva, 2009; Ukuwela, 2009; Bopage et al., 2011). Biju (2001) first raised doubts about the occurrence of this taxon in Sri Lanka and suggested careful comparison of Sri Lankan and south Indian populations. Subsequently, Biju et al. (2004a) suggested that the Sri Lankan populations belong to an undescribed species that requires further scientific validation.
We sampled some commonly misidentified small-sized ‘Hylarana aurantiaca’ populations from the wet zone of Sri Lanka, and reveal that these are either variants of H. gracilis or populations belonging to an altogether new species, described herein as Hylarana serendipi sp. nov. Populations from Galle and Udawatta Kele (Ampitya), which include earlier records of Hylarana aurantiaca (Dutta and Manamendra-Arachchi, 1996; Dutta, 1997; Ukuwela, 2009; Bopage et al. 2011) belong to H. gracilis, whereas populations from Kudawa in Sinharaja forest (Dutta and Manamendra-Arachchi, 1996) and the adjacent Kanneliya forest reserve (Grandison and Senanayake, 1966) belong to the new species H. serendipi. Furthermore, the size of ‘H. aurantiaca’ reported by previous authors (14.6-62.6 mm) is far too variable, and clearly includes misidentifications of adults and/or immature specimens of other species (i.e., adult male H. aurantiaca sensu stricto have SVL 27.1-31.7 mm).