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Taxonomy

Diagnosis. A small sized frog, described as Philautus(Male: 23.2–29.9 mm SVL) based on small size,all digits with well-differentiated disks, predominantly inhabiting in shrubs, and presumably having direct development, is distinguishedfrom all known congeners in the Western Ghats by the combination of absence of tympanum and supratympanic fold, both dorsal and ventral surfaces granular, unpigmented vocal sac (Fig. 2a, e), yellow to cream body coloration with minute brown dots and larger brown patches on the back, and a complete blue ring on the outer margins of the golden pupil.

Etymology.The species name neelanethrus is derived from Sanskrit meaning ‘blue eye’, and is a nominative singular noun standing in apposition to the generic name.

Description of the holotype (Male, BNHS-4510).A small-sized bush frog (SVL=29.9 mm), width of head broader than head length (HW=10.8 mm; HL=9.0 mm), flat dorsally, snout pointed in total profile, protruded slightly beyond mouth. Snout length is equal or subequal to diameter of eye (SL=4.1 mm; EL=4.1 mm). Canthus rostralis angular, loreal region slightly concave. Inter orbital distance (IUE=3.8 mm) flat and broader than upper eyelid (UEW=2.2 mm), wider than internarial distance (IN=2.4 mm). Internal distance between posterior margins of the eyes 1.64 times that of anterior margins (IFE=6.1 mm, IBE=10.0 mm). Nostrils oval, nearer tip of snout (NS=1.4 mm) than eye (EN=2.8 mm). Pineal ocellus absent. Vomerine ridge absent. Eyes protruding, prominent, pupil rounded, horizontal, with blue ring on the outer margin. Tympanum indistinct. Tongue bifid, without papilla, Supratympanic fold obscure/absent (intense brown dots indicate the fold), unpigmented single vocal sac present. In alcohol-preserved specimens, the blue ring on the eye turns dark blue in color.

Forearm (FLL=7.1 mm) less than hand (HAL=8.2 mm). Relativelength of fingers I less than II less than IV less than III. Finger tips with well-developed disks (fd1=1.0 mm; fd2=1.3 mm; fd3=1.8 mm; fd4=1.7 mm; fw1=0.7 mm; fw2=0.7 mm; fw3=0.7 mm; fw4=0.8 mm), with distinct circum-marginal grooves, fingers with dermal fringes on both edges. Webbing in hand absent, sub-articular tubercles prominent, rounded and single, pre-pollex tubercle oval, distinct (Fig. 2c).

Hindlimbs long, heels do not overlap when folded at right angles to the body, tibia 4.6 times longer than wide (TL=14.3 mm, TW=3.1 mm). Tibia shorter than femur (FL=15.2 mm). Tibia longer than foot (FOL=12.0 mm). Heel to tip of fourth toe (TFOL=19.8 mm) 2.8 times length of fourth toe (LT4=7.0 mm). Relative toe lengths I less than II less than III less than V less than IV. Toe disk width and toe width are: td1=1.0 mm, td2=1.0 mm, td3=1.1 mm, td4=1.7 mm, td5=1.5 mm, tw1=0.7 mm, tw2=0.7 mm, tw3=0.9 mm, tw4=1.0 mm, tw5=1.0 mm. Webbing distinct and medium (MTTF=6.4 mm, MTFF=6.7 mm, TFTF=5.3 mm, FFTF=5.2 mm). Tibiotarsal articulation reaches anterior border of eye. Inner metatarsal tubercle present (IMT=0.9 mm), nearly 2.6 times length of first toe (ITL=2.0 mm) (Fig. 2d).

Overall coloration of the male of P. neelanethrus sp. nov. (live specimen) yellowish (during breeding season) to creamish white (non-breeding season). Abdominal region turned pink during and after advertisement-call bouts. Dorsum with varied intensity of brown granulation. Skin on dorsal as well as on ventral surface granular. Granulation on ventral surface round and white, on dorsum brownish. Feeble cross bars present on forelimbs and hindlimbs. Circular brown patches (region with more brown granules) on head (4–5 in a line) and nearer to vent (1–2). In alcohol-preserved specimens, the overall yellow coloration turned to cream and the blue-colored ring around the eye turned to dark blue/black, but there were no changes in the brown pigmentation.The morphological measurements were based on nine specimens, with ranges, means, and standard deviations detailed in Table 2.

During one of the field surveys, an amplected pair was spotted wherein the female was larger than the male (Fig. 2b). The female was cream colored with brownish black granulation on the body. We observed this pair for more than 9 hours (from 21:30 to 6:30 h), during which time the amplected pair descended from a shrub and entered a leaf-litter heap, making their way into a cavity inside the wet foliar litter.

Advertisement calls. The mating call of P. neelanethrus sp. nov. starts with a shrill ‘treeek’ note followed by repeated ‘tink’ notes (treeek – tink-tink-tink-tink-……………….-tink). Variation was observed in the duration and pattern of calling, even though call notes and peak frequencies remained same. Calls were in the region of 2.35–2.41 kHz, and peak frequency was 2.35 kHz. The spectrogram of a call lasting for 6.6 sec, generated from a single call of a 29 mm P. neelanethrus sp. nov. male at 20:30 h on 18 June 2004, at 26.8°C (97% relative humidity), within 50 cm from the species and approximately 2 m above the ground, is shown in Fig. 3. Calling patterns analyzed using 16 calls (total duration of each call [mean±SD] 3.86±0.312 sec, range 1.93-14.35 sec) revealed two types of calls, one with repeated short-duration calls (call duration 0.33±0.04 sec, range 0.27–0.42; number of pulses 10.88±1.654, range 9–15) and another with long-duration calls (call duration 3.34±3.029 sec, range 1.42–13.84; number of pulses 13.6±13.3, range 6–60). Two exceptionally long-duration calls examined (not included in the analysis) were 39.77 sec and 71.92 sec in duration, with 101–191 tinking notes.

The Bartlett test of homogeneity of variances revealed significant differences in many call characteristics of P. neelanethrus sp. nov. from P. luteolus, as evident from the ?2 values for peak frequency, total duration, slow-phase duration, and number of pulses.

Comparison with congeners. As many as 118 valid species names are recognized in Philautus (Manamendra-Arachchi and Pethiyagoda, 2005), and we examined the nomenclature of all of them. For morphometric comparisons, data from 14 congeners (Supplemental Table 2) among the 20 available names (Supplemental Table 3) endemic to the Western Ghats, and P. longicrus (a species described from Borneo and Philippines, but included in the Indian frog fauna by some workers; Rao, 1937), were included in an unweighted pair-group average cluster analysis. The data on 19 morphometric and three meristic characters for the 15 reference taxa used for the cluster analysis are shown in Supplemental Table 4. As systematic morphometric information was not available for six congeneric species (Supplemental Table 3), these were not included in the cluster analysis; nonetheless, their known morphological features such as pointed snout, supratympanic fold, tympanum, granulation on dorsum and belly, and dorsum coloration, were used for comparisons to distinguish Philautus neelanethrus sp. nov. from each of them. Philautus taxa from Sri Lanka were not used for comparisons, as advocated by Manamendra-Arachchi and Pethiyagoda (2005).

With relatively small size (21.4–29.9 mm), yellow to cream coloration on the body, lack of tympanum, indistinct supratympanic fold, granular dorsum and ventral region, blue-colored outer margins of the eye, and distinct calling pattern, the new species clearly differs from all congeners. Philautus neelanethrus sp. nov is distinct from P. beddomi, P. bombayensis, P. chalazodes, P. femoralis, and P. travancoricus in having a pointed snout. It is distinct from P. temporalis in the absence of a tympanum and a distinct supratympanic fold. Apart from these, the dorsal coloration in P. beddomi, P. chalazodes, P. femoralis, and P. temporalis varies from green to brown, whereas in P. neelanethrus sp. nov. it is yellowish. Moreover, while the dorsum is smooth in P. beddomi, P. chalazodes, P. femoralis, P. travancoricus, and P. temporalis, whereas it is distinctly granular in P. neelanethrus sp. nov.

The UPGMA cluster analysis, based on 19 morphometric and three meristic characters for the other 15 congeners and reference species, revealed P. neelanethrus sp. nov. as a distinct species and closest to P. luteolus (Fig. 4). The distinction of P. neelanethrus sp. nov. from P. luteolus was even clearer when the clustering was done using only morphometric characters and excluding meristic characters, which are constrained by being subjective in their comparative weighting (data not shown). The relationship observed between P. neelanethrus sp. nov. and P. luteolus is also apparent in morphological features, many of which distinguish between them, though many others are similar between them. Distinctive features of P. neelanethrus sp. nov. include lack (indistinct) of tympanum and supratympanic fold, snout length equal/subequal to eye diameter, and a distinct blue ring on the outer margin of the eye. In contrast, P. luteolus has a distinct supratympanic fold seen as a strong, arch-shaped skin fold extending from behind eyes to the shoulder, and a longer snout compared to eye diameter (Kuramoto and Joshy, 2003). In their description of P. luteolus, Kuramoto and Joshy (2003) did not mention a distinct blue ring around the iris, which is also not visible in the preserved type specimen. The two species also differ in advertisement call pattern, and emerged as distinct in the phylogentic analysis. Advertisement call characteristics differed significantly, with a peak frequency of 2.39 kHz (range 2.35–2.41 kHz) in P. neelanethrus sp. nov. compared to 2.70 kHz (range 2.45–2.87 kHz) in P. luteolus. There were significant differences in peak frequency, total call duration, slow-phase duration, and number of pulses.

rDNA phylogenetic analysis

The sequenced rDNA fragments were identical for individuals of the new taxon collected from different localities. Phylogenetic analysis of the 12S and 16S sequences with a large number (>100) of reference amphibian taxa representing families Nyctibatrachidae, Dicroglossidae, and Ranidae revealed the new taxon to be a member of the family Rhacophoridae of Rhacophoroidea, and closest to the Philautusspecies (data not shown). A subsequent analysis done to resolve the exact taxonomic status of the new taxon, using a reduced number of reference taxa belonging mainly to the Rhacophoridae and including three taxa from the related families Ranidae and Nyctibatrachidae (Table 2) as outgroup species, revealed P. neelanethrus to be a new, distinct Philautus species most closely related to P. luteolus(Fig. 5). Moreover, P. neelanethrus sp. nov. was revealed to be a distinct and relatively early member of the sub-clade/lineage including other Philautus species described from the Western Ghats, and overall as a member of a broader clade distributed in the Western Ghats and Sri Lanka.

Distribution

Philautus neelanethrus sp. nov. was widespread across the study area (Fig. 1, Table 1), though its abundance varied. There were 6–8 individuals/mhs (man-hours of search) in the Myristica swamps, where densities were relatively high compared to the densities of 2–4 individuals/mhs observed in other locations in the Western Ghats (Table 1). Moreover, different localities where the frog was spotted were far from each other, with long stretches of the Ghats without any sign of the frog. Importantly, these stretches were characterized by various ecological (e.g., rock outcrops, forest fires) and/or anthropogenic disturbances (e.g., open/barren lands, agricultural fields, plantations, and built-up areas).

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