Raorchestes rezakhani, Al-Razi & Maria & Muzaffar, 2020

Al-Razi, Hassan, Maria, Marjan & Muzaffar, Sabir Bin, 2020, A new species of cryptic Bush frog (Anura, Rhacophoridae, Raorchestes) from northeastern Bangladesh, ZooKeys 927, pp. 127-151 : 127

Raorchestes rezakhani sp. nov. Figures 4 , 5 Suggested English name: Reza Khan’s bush frog

Type.

Holotype (Figs 4A, B , 5 ). JnUZool-A0419, an adult male from Lawachara National Park, Kamalgonj, Moulavibazar, Bangladesh (24°20.746'N, 91°47.945'E, ca. 59 m a.s.l., Fig. 1 ), collected on 26 April 2019 by Hassan Al-Razi and Marjan Maria.

Paratypes (Fig. 4C, D ). Three specimens: adult male (JnUZool-A0319) same locality as the holotype; two adult males (JnUZool-A0519, JnUZool-A0619) from the Adampur, Rajkandhi Reserved Forest, Kamalgonj, Moulavibazar (24°14.878'N, 91°54.002'E, ca. 64 m a.s.l., Fig. 1 ), on 10 May 2019 by Hassan Al-Razi.

Generic placement.

We assign this species to Raorchestes based on molecular characterization of the 16S rRNA gene.

Etymology.

We take great pleasure in naming the new species as a patronym for one of the pioneers in the field of wildlife research in Bangladesh, Dr. Mohammad Ali Reza Khan.

Diagnosis.

A species of Raorchestes having the following unique combination of characters: (1) relatively small size (adult males = 18.85-20.90 mm SVL); (2) head wider than long (HW/HL 1.55; range 1.53-1.56, N = 4); (3) dark brown, granular dorsum bearing small, horny spicules; (4) vomerine teeth absent; (5) single transparent vocal sac while calling; (6) snout projecting, sub-elliptical in ventral aspect, and subequal to or smaller than horizontal diameter of eye; (7) tympanum indistinct; (8) supratympanic fold weakly distinct; (9) finger and toe discs well developed and rounded; (FD IV 0.50-0.60, TD IV 0.56-0.65 mm); (10) both inner and outer metacarpal and metatarsal tubercles absent; (11) nostril is closer to tip of snout than to eye (NS 0.63-0.90, EN 1.10-1.25 mm); (12) Tongue without papilla (13) venter pale white, with minute dark gray flecks present in the vocal sac region. Details of these measurements are provided in Table 3 .

Description of holotype.

A small frog (SVL = 20.30, Fig. 5 , Table 3 , all measurements in mm); head wider than long (HW = 7.0; HL = 4.5); snout sub-elliptical in ventral aspect, shorter than eye diameter (ED = 2.45; SL = 2.24). Canthus rostralis sharply rounded; loreal region slightly concave. Interorbital region flat and larger (IOD = 2.20) than the upper eyelid (UEW = 1.45 mm) or internarial distance (IND = 1.70). Nostrils oval (dorsally compressed), without flap, directed laterally, closer to tip of snout than to eye (NS = 0.80; EN = 1.20). Tympanum indistinct, oval (TD = 1.10), close to eye, supratympanic fold weakly distinct, extends from eye to the end of the tympanum. Vocal sac single, sub-gular, translucent. Tongue bifid, lingual papilla absent. Eyes relatively large (ED = 2.45), protruding; pupil horizontal.

Forelimb length shorter than hand length (FLL = 4.70; HAL = 4.90). Relative lengths of fingers I <II <IV <III (FL I = 1.20; FL II = 1.75; FL III = 3.40; FL IV = 2.15). Fingertips with well-developed discs (FD I = 0.25, FD II = 0.45, FD III = 1.1, FD IV = 1.2) bearing circum-marginal grooves. Dermal fringe absent on fingers. Webbing between fingers absent. Subarticular tubercles weak, number of subarticular tubercles in fingers: I = 1, II = 1, III = 1, IV = 1, rounded. Supernumerary tubercles indistinct. Nuptial pad absent.

Hind limbs long, shank shorter than thigh (ShL = 10.03; TL = 10.10), longer than foot (FOL = 7.95). Relative toe length I <II <V <III <IV (ToL I = 1.15; ToL II = 2.10, ToL III = 3.20; ToL IV = 4.25; ToL V = 3.05). Toes with well-developed discs (TD I = 0.30, TD II = 0.35, TD III = 0.50, TD IV = 0.65, TD V = 0.60). Webbing moderate, webbing formula (fingers: I2-2+II 1¾-2+III1½-3IV2¾ -2-V) (Fig. 5D, E ). Inner and outer metatarsal tubercles absent, subarticular tubercle present (toe: I = 1, II = 1, III = 2, IV = 3, V = 2). Supernumerary tubercles absent.

In preservative, dorsum dark gray; loreal and tympanic regions lighter; forelimbs and hind limbs with black bands. Venter uniform cream white, vocal sac with dark gray flecks. Webbing cream; ventral side of feet and hands light gray with small black spots.

In life, dorsum grayish brown with dark brown specks; “)-(“ or “)(“ shaped blackish mark present on the mid dorsum; blackish line between upper eyelids; snout much darker, loreal and tympanic region blackish; iris dark golden brown. Dorsal side of hind limbs with several black bands; forelimbs with single band these bands are also present in the other members of this genus. Fingers and toes discs reddish or whitish. Abdomen brownish, with few black spots. Vocal sac translucent whitish, with a few black flecks. A few dark spots present near fore limbs. Foot webbing grayish.

Variation.

Because all specimens were males, sexual dimorphism could not be determined. Details of morphometric variation observed in four individuals are provided in Table 3 . All of the specimens are almost similar except the size and the coloration. One of the four specimens (JnUZool-A0619) is smaller than others. For two specimens (JnUZool-A0619, JnUZool- A0519) the ventral dark gray flecks are more than others. The) (shape is present on the dorsum of three specimens where for one specimen (JnUZool- A0519) it is shaped “)-(“. Some individuals have a greater proportion of dark gray spots on the ventral surface. Detailed comparisons between R. rezakhani sp. nov. and other species of Raorchestes are provided below.

Bioacoustics analyses.

An advertisement call of the paratype (JnUZool-A0519) from the Lawachara National Park were recorded at an ambient air temperature of 27.8 °C, 97% relative humidity. Advertisement calls occurred without call groups (Fig. 3 ). The duration of the analyzed call was 16 s. The number of notes within this call was 25, and number of pulses within a note varied from 5-11 (8.84 ± 1.70 SD). Note duration was 0.183 - 0.379 s. The interval between notes was 0.222 - 0.592 s (0.323 ± 0.098 SD, N = 24). These intervals increase gradually within a call (mean interval for first five notes = 0.2422, mid five notes = 0.2784, last five notes = 0.4754). Pulse duration was 0.003-0.029 s (0.013 ± 0.007 SD, N = 205 pulses), duration of intervals between pulses was 0.005-0.127 s (0.027 ± 0.017 SD, N = 179 intervals). Pulse rate was 10-19/s (14.27 ± 2.49 SD, N = 15 seconds interval). The advertisement call had a dominant frequency at 4.32-4.77 kHz (4.55 ± 0.12 SD, N = 25). To the human ear, the calls sounded similar to cricket calls.

Distribution and natural history.

Raorchestes rezakhani sp. nov. was recorded from the semi-evergreen forests of northeastern Bangladesh. They were active with the onset of the rainy season in the month of April. We did not hear calls of this species after August. Frogs were found inside the primary and secondary forest mainly on the edge of streams and near man-made trails. They often use the hilly slopes during calling. Individuals perch on leaves and branches of small trees and on bamboo trunks (with diameters of 1.5-4 cm). Vocalizing individuals were perched 1-1.5 m above the forest floor. We usually heard the calls immediately after the sunset (ca. 1815 h in April) although calling activity started a little earlier when it was raining.

Comparisons.

Based on morphology, we compared Raorchestes rezakhani sp. nov. with some other member of this genus. This new species is differs from R. amboli (Biju & Bossuyt, 2009), R. anili (Biju & Bossuyt, 2006), R. charius (Rao, 1937), R. chlorosomma (Biju & Bossuyt, 2009), R. flaviventris (Boulenger, 1882), R. glandulosus (Jerdon, 1853), R. jayarami (Biju & Bossuyt, 2009), R. kaikatti (Biju & Bossuyt, 2009), R. luteolus (Kuramoto & Joshy, 2003), R. munnarensis (Biju & Bossuyt, 2009), R. nerostagona (Biju & Bossuyt, 2005), R. ochlandrae (Gururaj et al., 2007), R. ponmudi (Biju & Bossuyt, 2005), R. signatus (Boulenger, 1882), R. sushili (Biju & Bossuyt, 2009), R. wynaadensis (Jerdon, 1853), R. kakachi Seshadri et al., 2012, R. crustai Zachariah et al., 2011, R. johnceei Zachariah et al., 2011, R. theuerkaufi Zachariah et al., 2011, R. thodai Zachariah et al., 2011, R. gryllus ( Smith 1924) by its smaller size. SVL of male individuals of these species ranged from 24.9-36.8 mm whereas Raorchestes rezakhani sp. nov. is 20.06 mm. Raorchestes rezakhani sp. nov. is quite similar to R. longchuanensis Yang et al. 1979 but differs for the following characters: tympanum indistinct in males (vs. distinct); snout sub-elliptical (vs. pointed); thigh shorter than the tibia/shank, TL/ShL = 93% (vs. Thigh slightly longer than the tibia/shank, TL/ShL = 97%); inner metatarsal tubercles absent (vs. present) [ Yang et al. 1979; Al-Razi et al. 2020]. Raorchestes rezakhani sp. nov. differs from R. tuberohumerus in: snout sub-elliptical (vs. slightly pointed); relative lengths of fingers I <II <IV <III (vs. I <IV <II <III); thigh shorter than the tibia/shank, TL/ShL = 93% (vs. thigh longer than the tibia/shank, ShL/TL = 96%); inner metatarsal tubercles absent (vs. present); supernumerary tubercles feebly distinct (vs. distinct) [ Kuramoto and Joshy 2003; Padhye et al. 2015]. Raorchestes rezakhani sp. nov. differs from R. gryllus in: snout sub-elliptical (vs. pointed); tympanum indistinct in males (vs. large and rounded); relative toe lengths I <II <V <III <IV (vs. I <II <III <V <IV); subarticular tubercles in finger weakly distinct I = 1, II = 1, III = 1, IV = 1 (vs. distinct I = 1, II = 1, III = 2, IV = 1) [ Smith 1924; Orlov et al. 2012]. Raorchestes rezakhani sp. nov. is also similar to R. shillongensis (Pillai & Chanda, 1973) but differs in: SVL of male 20.06 ± 0.87 (vs. 16.51 ± 1.29); head wider than long, HL/HW = 61% (vs. length slightly greater than the width, HW/HL = 98%); snout length shorter than the eye diameter (vs. slightly longer than eye diameter); subarticular tubercles in finger weakly distinct, I = 1, II = 1, III = 1, IV = 1 (vs. distinct, I = 1, II = 1, III = 2, IV = 1) [ Pillai and Chanda 1973; Boruah et al. 2018]. Raorchestes rezakhani sp. nov. is very similar to R. parvulus but differs in: forearm and hand length (9.05-9.95 mm) generally shorter than half body size (vs. longer than the half body size); relative toe length I <II <V <III <IV (vs. I <II <III <V <IV); toe subarticular tubercle: I = 1, II = 1, III = 2, IV = 3, V = 2 (vs. I = 1, II = 1, III = 2, IV = 2, V = 1); inner metatarsal tubercles absent (vs. present) [ Boulenger 1893; Yu et al. 2019]. Raorchestes rezakhani sp. nov. differs from R. sahai (Sarkar & Ray, 2006) in: smaller SVL (18.85-20.90 vs. 25-26 mm); nostril closer to tip of snout than to eye, NS/EN = 67% (vs. equidistance from the tip of the snout and the eye NS/EN = 100%); snout length shorter than the eye diameter, SL/ED = 87% (vs. slightly longer than eye diameter, ED/SL = 81%); interorbital distance larger than the upper eyelid UEW/IOD= 65% (vs. equal to the upper eyelid, UEW/IOD = 100%) [ Sarkar and Ray 2006]. Raorchestes rezakhani sp. nov. differs from R. annandalii in: snout sub-elliptical (vs. pointed); nostril closer to tip of snout than to eye, NS/EN = 67% (vs. equidistant from the tip of the snout and the eye, NS/EN = 100%); inner metatarsal tubercles absent (vs. feebly distinct); ShL longer than TL, TL/ShL = 93% (vs. ShL shorter than TL) [ Boulenger 1906; Chanda 1994]. Raorchestes rezakhani sp. nov. differs from R. menglaensis ( Kou 1990) in: male with external single subgular vocal sac (vs. internal single subgular vocal sac); outer metatarsal tubercle absent (vs. present); [ Padhye et al. 2013; Kou 1990]. This new species differs from R. garo ( Boulenger 1919) in: SVL 18.85-20.90 (vs. 13-16 mm); eye diameter larger than the interorbital distance, IOD/ED = 88% (vs. less than interorbital distance, ED/IOD = 92%); dark line present between eyelids (vs. absent); nostril closer to tip of snout than to eye, NS/EN = 67% (vs. equidistance from the tip of the snout and the eye or slightly closer to the tip of snout); tympanum indistinct (vs. distinct); inner metatarsal tubercles absent (vs. present) [ Boulenger 1919; Chanda 2002]. Raorchestes rezakhani sp. nov. differs from R. kempiae ( Boulenger 1919) in: SVL 18.85-20.90 (vs. 13-17.5 mm); nostril closer to tip of snout than to eye (vs. equidistant from the tip of the snout and the eye); tympanic fold indistinct (vs. distinct) [ Boulenger 1919, Chanda 1994, 2002].

Principle Components Analysis showed that the specimens of R. rezakhani sp. nov. did not overlap with R. longchuanensis , R. tuberohumerus , or R. gryllus (Fig. 6 ). Eigenvalues indicated that PC1 accounted for more than 91% of the variation in the data while PC2 contributed another 5% (Table 4 ). Thus, the inclusion of further principle components would not add substantially to the characterization of these species based on these variables. Loading of individual morphological variables indicated that SVL, HL, HW, THL and TL strongly influenced PC1, ED, SL, UEW and THL strongly influenced PC2, while HL and TL strongly influenced PC3, that helped to segregate the R. rezakhani sp. nov. from the remaining three species (Table 5 ).

Figures

Figure 1. Map showing the type location of Raorchestes rezakhani sp. nov. in northeastern Bangladesh as well as adjoining areas.

Figure 3. Advertisement call of Raorchestes rezakhani sp. nov. showing 25 notes that vary in amplitude A waveform of 25 notes B shows variation in frequency C shows waveform of first six notes of the call; and D shows a spectrogram of the six notes E shows a pulse of fourth note and F shows the spectrogram of pulse of fourth note.

Figure 4. Color variation in R. rezakhani sp. nov. A holotype, showing single transparent vocal sac during advertisement call (B holotype with brown dorsum and ") - (" mark; C dorsolateral view of paratype (JnUZool- A 0519) D ventral view of paratype (JnUZool- A 0519), showing small dark brown spots.

Figure 5. Holotype of R. rezakhani sp. nov. A dorsal view B ventral view C ventral view of right hand D ventral view of right foot E web pattern in foot.

Figure 6. A Scatterplot of principle component axes 1 and 2 and B principle component axes 2 and 3. R. tuberohumerus (light blue), R. gryllus (green), R. longchuanensis (black), and R. rezakhani sp. nov. (purple).