Microhyla sriwijaya Eprilurahman, Hamidy, Smith, Garg & Biju, 2021

Eprilurahman, Rury, Garg, Sonali, Atmaja, Vestidhia Y., Alhadi, Farits, Munir, Misbahul, Ubaidillah, Rosichon, Arisuryanti, Tuty, Biju, S. D., Smith, Eric N. & Hamidy, Amir, 2021, A tiny new species of Microhyla Tschudi, 1838 (Amphibia: Anura: Microhylidae) from Belitung Island and Southeastern Sumatra, Indonesia, Zootaxa 5027 (4), pp. 451-488 : 459-481

Microhyla sriwijaya Eprilurahman, Hamidy, Smith, Garg & Biju , sp. nov.

( Figs. 1–8 ; Tables 1–7 ) http://zoobank.org/ urn:lsid:zoobank.org:act:8C57B2A0-BAE4-4736-A62E-B380F2C72650

Holotype. MZB Amph 31752 (Field number FA 0026.2019), an adult male, from Desa Kembiri (03.05489° S, 107.77467° E, at 6 m a.s.l.), Kecamatan Membalong , Kabupaten Belitung , in the Province of Kepulauan Bangka Belitung, Indonesia, collected from open garden area between a settlement and oil palm plantation, by F. Alhadi and team, on 17 March 2019.

Paratypes. MZB Amph 31749 (Field number FA 0009.2019), MZB Amph 31750 (Field number FA 0010.2019), and MZB Amph 31753 (Field number FA 0027.2019), three adult male collected along with the holotype; MZB Amph 31747 (Field number FA 0010.2018), an adult male, from the holotype locality, collected by F. Alhadi and team on 15 March 2018; MZB Amph 31751 (Field number FA 0025.2019) and MZB Amph 31754 (Field number FA 0028.2019), two adult females collected along with the holotype.

Referred specimens. MZB Amph 31748, an adult male from Desa Batu Penyu , Kecamatan Gantung, Kabupaten Belitung Timur, Kepulauan Bangka Belitung (03.00097° S, 108.12649° E, at 19 m a.s.l.), collected by F. Alhadi and team on 19 March 2018; MZB Amph 22241 ( Field number ENS 13705), MZB Amph 22254 ( Field number ENS 13759), and UTA A-66215 (ENS13708), three adult males from south slope of Gunung Rajabasa , Desa Canti , Kabupaten Lampung Selatan, in the province of Lampung, Indonesia (05.80937° S, 105.59759° E, 70 m a.s.l.), collected by A. Hamidy, E. N. Smith, and others (G. Barraza, C. Franklin, M. B. Harvey, A. M. Kadafi, Rizky W. Mulyoto, K. I. Nawie, K. O’Connell, U. Smart, W. Trilaksomo, E. Wostl, and D. R. Wulandari) on 4–5 June 2003.

Etymology. This specific name sriwijaya refers to the first unified kingdom to dominate much of the Malay Archipelago. It was based in Sumatra and influenced Southeast Asia between 7th and 11th century. The species epithet sriwijaya is used as an invariable feminine noun in apposition to the generic name.

Suggested English common name. Sriwijaya narrow-mouth frog

Suggested Indonesian common name. Percil sriwijaya

Diagnosis. Microhyla sriwijaya sp. nov. can be diagnosed from other known congeners by having the following combination of morphological characters: smaller snout-vent size (male SVL 12–16 mm, female SVL 18–20 mm); snout rounded in dorsal view; absence of mid-dorsal line and skin fold extending from tip of snout to vent; first finger reduced (FL I less than ½ of FL II); dorsum with a prominent dark median mark extending posteriorly, narrow anteriorly near the level of the shoulder and expanding dorsolaterally up to the vent; margins of the dorsal marking concave with broad reddish-brown or orange colouration on either side; dorsal skin with prominent tubercles, especially in life; foot webbing rudimentary, reaching just up to the first subarticular tubercle on all toes; tibiotarsal articulation of adpressed limb reaching beyond the snout tip ( Figs. 3 , 4 ).

Phylogenetic relationship and genetic divergence. Microhyla sriwijaya sp. nov. is a member of the Microhyla achatina group and shows a well-supported sister group relationship with M. orientalis ( Fig. 2 ). It differs from all the genetically known members of the Microhyla achatina group and other congeners by uncorrected pairwise genetic distances of ≥ 3.8% for the 16S rRNA ( Table 2 ).

Description of holotype (measurements in mm) ( Fig. 4 ). A small-sized adult male (SVL 13.5), rather slender. Head characters: head wider than long (HW 4.5, HL 3.7); snout obtusely rounded in dorsal and ventral view, rounded in lateral view, its length (SL 1.5) longer than horizontal diameter of eye (ED 1.2); loreal region acute, rounded canthus rostralis; interorbital space flat; interorbital distance wider (IOD 1.8) than upper eyelid width (UEW 0.7) and internarial distance (IND 1.2); nostrils oval, placed more towards lateral side of snout, closer to snout (S–NL 0.5) than eye (N–EL 0.8); tympanum hidden; supratympanic fold extending from posterior corner of eye to the shoulder weakly-developed; vomerine teeth absent; tongue small, oval, without papillae. Forelimb characters: Arms short, forearm length (FAL 2.4) shorter than hand length (HAL 3.5); relative length of fingers I<IV<II<III (FL I 0.3, FL II 0.8, FL III 2.2, FL IV 0.6); tips of all fingers with dorso-terminal grooves, cover bifurcate distally, finger tips slightly wider compared to finger width (FD I 0.4; FW I 0.3, FD II 0.5; FW II 0.4, FD III 0.5; FW III 0.4, FD IV 0.4, FW IV 0.4); dermal fringes weakly-developed, webbing absent between fingers; subarticular tubercles rather prominent; outer and inner palmar tubercles weakly developed; supernumerary tubercles absent; nuptial pad absent. Hindlimb characters: Hind limbs short, thigh (TL 7.6) shorter than shank (SHL 8.2) and nearly equal to foot (FOL 7.5); distance from base of tarsus to tip of toe IV (TFOL 11.1); relative length of toes I<II<III<V<IV; toe tips rounded, slightly enlarged into discs (TD I 0.4; TW I 0.5, TD II 0.6; TW II 0.5, TD III 0.6; TW III 0.5, TD IV 0.7, TW IV 0.5,TD V 0.5, TW V 0.3); toe discs with prominent dorso-terminal grooves, cover bifurcate distally; dermal fringes weakly-developed; foot webbing rudimentary: I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V; subarticular tubercles prominent, all present, circular; inner metatarsal tubercle prominent (IMTL 0.4), oval-shaped; outer metatarsal tubercle, small (OMTL 0.2), rounded; supernumerary tubercles absent.

Skin. Skin of snout shagreened, upper eyelids shagreened to sparsely granular; supratympanic skin fold extending from postorbital area to shoulder weakly developed; anterior and posterior parts of dorsum shagreened with prominent tubercles (more conspicuous in life and inconspicuous in preservation); and upper and lower parts of flank shagreened; dorsal surfaces of forelimb, thigh, and shank shagreened with granular tubercular projections; posterior parts of thigh and cloacal region sparsely granular. Ventral surfaces of throat, chest, belly, and limbs smooth ( Figs. 3 , 4 ).

Colour in life. Dorsum dark brown with scattered light and dark brown to orangish minute spots; dorsum with a prominent dark median mark extending posteriorly up to the vent, narrow anteriorly from the level of the shoulder and expanding dorsolaterally towards flanks and groin; margins of the dorsal marking concave with broad reddishbrown or orange colouration on either side; iris golden brown; tip of tubercular projections on the dorsum reddishorange; a narrow brown stripe between the eye; snout and lateral surface of head lighter than dorsal colouration, with scattered contrasting patches and spots; a faint yellowish-grey streak extending from posterior corner of eye to arm insertion; flank dark brownish-black with scattered light brown or white patches and spots spread from postorbital region towards groin ( Fig. 3 ); groin greyish-brown; anterior parts of thigh light brown with faint grey spots; a dark blackish-brown crescent-shaped marking above the cloacal opening; forelimbs and hind limbs (including toes) light greyish-brown with dark brown transverse bands. Ventral surface of throat dark bluish-black; belly light grey with blue tinge and scattered white spots; limbs flesh coloured; ventral surfaces of foot and hand dark greyish-brown. In preservation. Dorsum greyish-brown; brick red margins of the dorsal marking turn light reddish-grey after preservation (40 days); forelimbs and hind limbs grey with greyish-brown transverse bands. Ventral surface of throat blackish with grey mottling; belly light grey; limbs light grey with dark grey mottling on the margins ( Fig. 4 ).

Morphological variations ( Figs. 3 , 5 ). Morphometric data from five adult males and two adult females is given in Table 3 . The overall morphology of the paratypes is similar to the holotype with slight variations in skin texture, colour, and markings. Paratype (MZB Amph 31747, male): Dorsum greyish-brown with brownish-orange patches on either side of dorsum, flanks light grey with scattered blackish-brown blotches; ventral surface with a reddish tinge. Paratype (MZB Amph 31753, male): dorsum brown with a reddish tinge and the dorsolateral concave stripes light brown. Referred specimen (MZB Amph 31748, male): dorsum reddish-brown. Paratype (MZB Amph 31754, female): dorsal skin granulation relatively less compared to the male samples, and dorsum light brown with dark median marking, with lesser reddish tinge compared to the males; flanks blackish-brown with a bluish tinge; ventral surfaces greyish-brown with a bluish tinge and light grey spots. In general, the Belitung specimens were relatively more colourful and boldly patterned dorsally and laterally, flank blotches orange to cream, as compared to Sumatran individuals.

Secondary sexual characters. Males with single median vocal sac. Female (MZB Amph 31754): ova pigmented on poles (diameter 0.9–1.1 mm, N = 9).

Morphological comparison. With members of Microhyla achatina species group ( Table 4 ): Microhyla sriwijaya sp. nov. is included genetically and morphologically as a member of the M. achatina group ( M. achatina , M. borneensis , M. daklakensis , M. fodiens , M. gadjahmadai , M. heymonsi , M. irrawady , M. kodial , M. malang , M. mantheyi , M. minuta , M. neglecta , M. nepenthicola , M. ninhthuanensis , M. orientalis , and M. pineticola ) and can be distinguished by its small adult size, nostril located towards lateral side of snout; finger and toe discs with dorsoterminal grooves, cover bifurcate distally, except in M. fodiens ; terminal phalanges of toes T-shaped, and a light yellowish-grey streak extending from posterior corner of eye to arm insertion (Garg et al., 2019). A morphological comparison of the new species with all other members of the Microhyla achatina group are summarized in Table 4 , and an illustrated comparison specifically with the Indonesian members is depicted in Figure 6 .

Microhyla sriwijaya sp. nov. differs from its sister taxon, M. orientalis from Indonesia by its stocky body (vs. slender), eye diameter nearly equal to internarial distance, ED/IND ratio 0.9–1.1 (vs. eye diameter larger than internarial distance, ED/IND ratio 1.3–1.6), thigh length nearly equal to foot length, TL/FOL ratio 1 (vs. thigh shorter than foot, TL/FOL ratio 0.8–0.9); absence of a mid-dorsal line or skin fold from the tip of snout to the vent (vs. present); comparatively longer hindlimbs, with tibiotarsal articulation of straightened limb projecting up to or beyond snout tip (vs. up to the level of eye); rudimentary foot webbing, reaching just above the first subarticular tubercles on all toes, I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V (vs. up to the base first subarticular tubercles: I2–2 + II2–3III3–4IV4–3V); and reddish-brown or orangish colouration along concave margins on either side of the dorsum (vs. absent). Furthermore, a PCA of 40 morphometric characters of the two species revealed that Microhyla sriwijaya sp. nov. differs significantly from M. orientalis with respect to size-corrected characters such as HW, FAL, TL, SHL, TFOL, FL IV, FW II, and FW IV. A total of 76.9% percent variance was accounted by the first three principal components, with the first principal component accounting for 54.5% of the variance, followed by 13.3% and 9.09% of the variance covered by the second and third principal components, respectively. Graphical plotting of the first two principal components recovered the two taxa as separate clusters along PC1 ( Fig. 7 , Table 5 ).

In general morphology, Microhyla sriwijaya sp. nov. also morphologically resembles M. kodial (endemic to India) and M. minuta (endemic to Vietnam) due to comparable snout-vent size, absence of a mid-dorsal line or skin fold from the tip of snout to the vent, and rudimentary webbing between toes. However, M. sriwijaya sp. nov. differs from M. kodial by its first finger shorter than one half of the second finger, F I <½F II (vs. longer, F I> ½F II); comparatively longer hindlimbs, with tibiotarsal articulation of straightened limb projecting up to or beyond snout tip (vs. up to the level of eye); rudimentary webbing between toes, reaching just above the first subarticular tubercles on all the toes, I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V (vs. absent or a trace of webbing below the first subarticular tubercles, I2–2 + II2–3III3–4IV4–3V); and reddish-brown or orangish colouration along concave margins on either side of the dorsum (vs. greyish-brown with olive-green markings). Further, M. sriwijaya sp. nov. differs from M. minuta by its stocky body (vs. slender); first finger shorter than one half of the second finger, F I <½ F II (vs. first finger long, almost equal, or slightly shorter than one half the length of the second finger); comparatively well-developed finger discs (vs. very weakly developed discs on the three outer fingers); comparatively longer hindlimbs, with tibiotarsal articulation of straightened limb projecting up to or beyond snout tip (vs. up to or just above the level of eye); and reddish-brown or orangish colouration along concave margins on either side of the dorsum (vs. bright yellow).

Microhyla sriwijaya sp. nov. differs from M. achatina , M. fodiens , and M. gadjahmadai by its stocky body (vs. stout in all species), and smaller male snout vent size, SVL 12–15 mm (vs. larger, SVL 21–24 mm, SVL 20–29 mm, and SVL 18–22 mm, respectively). Specifically it also differs from M. achatina and M. gadjahmadai by the absence of a mid-dorsal line or skin fold (vs. present), and postorbital area and flank light brown with scattered spots or patches (vs. prominently blackish-brown). Individually, it further differs from M. achatina by snout obtusely rounded in dorsal view (vs. obtusely pointed); differs from M. gadjahmadai by its F I <½F II (FL I 0.5 mm, FL II 1.1 mm, vs. F I> ½F II, FL I 0.9 mm, FL II 1.3 mm) ( Table 4 ). Microhyla sriwijaya sp. nov. specifically also differs from M. fodiens by the presence of finger and toe discs (vs. absent), and with dorso-terminal grooves, cover bifurcate distally (vs. absent).

Microhyla sriwijaya sp. nov. differs from M. borneensis , M. malang , and M. mantheyi by its rudimentary foot webbing, reaching just above the first subarticular tubercles on all toes, I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V (vs. moderate foot webbing, above the second subarticular tubercles on either side of toe IV in all the three species: I1–2II1–3III2½–3⅓IV3½–2V, I1–1⅔II1–1⅔III1–2½IV2½–1V, and I1–2II1–2III2–3IV3–1½V, respectively), and snout obtusely rounded in dorsal view (vs. obtusely pointed in all three species). Specifically it also differs from M. borneensis by well-developed first finger, FI <½FII (vs. greatly reduced to a nub), and absence of a mid-dorsal line or skin fold (vs. present); differs from M. malang by F I <½ F II (vs. F I> ½F II), and absence of light or dark brown spots on margins of thigh and shank, and lateral surfaces of the head and lips (vs. present); differs from M. mantheyi by the absence of a mid-dorsal line or skin fold (vs. present).

Microhyla sriwijaya sp. nov. differs from M. daklakensis , M. heymonsi , and M. ninhthuanensis by the absence of a mid-dorsal line or skin fold (vs. present); absence of a ‘()’-shaped dark marking at the centre of its dorsum (vs. present); and absence of blackish-brown lateral band (vs. absent). Microhyla sriwijaya sp. nov. differs from M. irrawaddy by having a stocky body (vs. slender); snout obtusely rounded in dorsal view (vs. acuminate); F I <½F II (vs. F I> ½F II); and finger and toe discs with dorso-terminal groove, cover bifurcate distally (vs. absent). Microhyla sriwijaya sp. nov. differs from M. neglecta by its stocky body (vs. slender); snout obtusely rounded in dorsal view (vs. acuminate); first finger shorter than one half of the second finger, F I <½F II (vs. first finger longer than one half of the second finger, F I> ½F II); absence of a mid-dorsal line or skin fold and a black spot at mid-dorsum (vs. present); and absence of dark lateral stripe from posterior margin of the eye to groin (vs. present). Microhyla sriwijaya sp. nov. differs from M. pineticola by its stocky body (vs. stocky, triangular); comparatively longer hindlimbs, with tibiotarsal articulation of straightened limb projecting up to or beyond snout tip (vs. below the snout tip); and absence of a mid-dorsal line or skin fold (vs. present). Microhyla sriwijaya sp. nov. differs from M. nepenthicola by its relatively larger adult male size, SVL 12–15 mm (vs. SVL 10–13 mm); snout obtusely rounded in dorsal view (vs. obtusely pointed); relatively well-developed first finger, FI <½FII (vs. greatly reduced to a nub); absence of a mid-dorsal line or skin fold (vs. mid-vertebral ridge present); and rudimentary foot webbing, reaching just above the first subarticular tubercles on all toes, I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V (vs. relatively more webbing, up to or slightly below the second subarticular tubercle on either side of toe IV).

Comparison with Indonesian species outside the Microhyla achatina group. The new species cannot be confused with any other known Microhyla members from Indonesia, outside the Microhyla achatina species group ( M. palmipes , M. superciliaris , M. berdmorei , and M. fissipes ). It differs from all these four species in having reddishbrown or orangish colouration along concave margins on either side of the dorsum (vs. absent); and irregular light or dark spots on the flanks (vs. bold or diffused dark stripe extending from the snout, behind the eye, or mid-body, through the flank or groin). Microhyla sriwijaya sp. nov. also specifically differs from the species with having an overlapping sie range, as discussed below.

Comparison with similar-sized members (SVL 12–20 mm) outside the Microhyla achatina group. Microhyla sriwijaya sp. nov. (SVL 12–20 mm) can be differentiated from other congeners outside the Microhyla achatina group, which have with the following overlapping size ranges: M. beilunensis (male 19–24 mm, female 26–29 mm), M. butleri (male 20–25 mm, female 21–26 mm), M. chakrapani (male 17–22 mm, female 23–24 mm), M. darreli (male 15–16 mm, female 17 mm), M. fanjingshanensis (male 19–23 mm, female 22–23 mm), M. fissipes , (male 18–28 mm, female 20–28 mm), M. karunaratnei (male 13–19 mm, female 19–21 mm), M. kuramotoi (male 23–28 mm, female 28–35 mm), M. laterite (male 14–16 mm, female 18–19 mm), M. maculifera (male 12–14, female 11.8 mm), M. mixture (male 17–25 mm, female 25–27 mm), M. mukhlesuri (male 16–24 mm, female 17–26 mm), M. mymensinghensis (male 14–24 mm, female 20–25 mm), M. nilphamariensis (male 17–24, female 20–25 mm), M. ornata (male 15–23 mm, female 22–25 mm), M. palmipes (male 13–16 mm, female 17–19 mm), M. sholigari (male 16–18 mm, female 17–19 mm), M. superciliaris (male 12.7 mm, female 12 mm), M. taraiensis (male 20–22 mm, female 24 mm), M. tetrix (male 10–14 mm, female 15–18 mm), and M. zeylanica (male 15–19, female 16–22 mm). It differs from M. butleri , M. darreli , M. karunaratnei , M. laterite , M. sholigari , M. superciliaris , M. tetrix , and M. zeylanica by nostrils placed towards the lateral side of the snout (vs. towards the dorsal side of the snout); rudimentary foot webbing, reaching just above the first subarticular tubercles on all toes, I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V (vs. relatively more webbing in all these species, well above the first subarticular tubercle and maximum up to the second subarticular tubercle on either side of toe IV); and absence of a mid-dorsal line or skin fold (vs. present). Microhyla sriwijaya sp. nov. differs from M. beilunensis , fanjingshanensis , M. fissipes , M. kuramotoi , M. chakrapani , M. mixtura , M. mukhlesuri , and M. mymensinghensis by its finger and toe discs with dorso-terminal groove, cover bifurcate distally (vs. absent, except in M. kuramotoi and M. mixtura ); inner metatarsal tubercle rounded (vs. elongate); absence of a mid-dorsal line or skin fold (vs. present); and irregular light or dark spots on the flanks (vs. a prominent dark lateral band extending from the posterior corner of eye to flank). Microhyla sriwijaya sp. nov. differs from M. nilphamariensis , M. ornata , and M. taraiensis by its finger and toe discs with dorso-terminal grooves, cover bifurcate distally (vs. absent); weakly developed inner and outer metatarsal tubercles (vs. distinct); irregular light or dark spots on the flanks (vs. a prominent dark lateral band behind the posterior corner of eye to flank). Microhyla sriwijaya sp. nov. differs from M. palmipes by its nostrils placed towards the lateral sides of the snout (vs. towards the dorsal side of the snout); finger and toe discs with dorso-terminal groove, cover bifurcate distally (vs. circum-marginal grooves); and absence of a mid-dorsal line or skin fold (vs. present). Microhyla sriwijaya sp. nov. differs from M. maculifera by its finger and toe discs with dorso-terminal grooves, cover bifurcate distally (vs. absent); and two metatarsal tubercles (vs. one metatarsal tubercle).

Comparison with larger-sized members (SVL 21–33 mm) outside the Microhyla achatina group. Microhyla sriwijaya sp. nov. can be differentiated from all other congeners outside the Microhyla achatina group, which have a comparatively larger snout-vent length (SVL) as follows. It differs from the following species in having a small snout-vent size, SVL male 12–15, female 17–18 mm (vs. larger: M. aurantiventris : male 25–27 mm, female 30 mm; M. okinavensis : male 22–29, female 26–31 mm; M. berdmorei : male 23−33 mm, female 26−45 mm; M. picta : male 25–30 mm, female 27–34 mm; M. pulchra : male 22–29 mm, female 26–34 mm; M. eos : male 21 mm, female 26–28 mm; M. mihintalei : male 21–27 mm, female 24–25 mm; M. rubra : male 24–29, female 30–31 mm). Microhyla sriwijaya sp. nov. specifically also differs from M. aurantiventris by the tibiotarsal articulation of its adpressed limb reaching beyond snout tip (vs. tibiotarsal articulation up to eye); absence of a mid-dorsal line or skin fold (vs. present); and belly yellowish-grey or with blue tinge (vs. orange-yellow). It differs from M. okinavensis by its finger and toe discs with dorso-terminal groove, cover bifurcate distally (vs. absent); absence of a mid-dorsal line or skin fold (vs. present); and inner metatarsal tubercle rounded (vs. elongated). It differs from M. berdmorei by rudimentary foot webbing (vs. fully webbed); and differs from M. mihintalei , M. picta , and M. rubra by finger and toe tips dorsoterminal groove, cover bifurcate distally (vs. finger and toe tips without grooves); and inner and outer metatarsal tubercles not shovel-shaped (vs. shovel-shaped). It differs from M. eos by its finger and toe tips with dorso-terminal groove, cover bifurcate distally (vs. finger and toe discs with dorso-terminal grooves, cover rounded distally); and by rudimentary foot webbing, I2 –– 2II2 –– 3 – III3 –– 4 – IV4 –– 3 – V (vs. more, I1½–2 + II1⅔–3 – III2½–4 – IV4 –– 1½V). It further differs from M. pulchra by the presence of discs on finger and toe tips (vs. absent); and finger and toe tips dorso-terminal groove, cover bifurcate distally (vs. absent).

Call characteristics and acoustic comparison. The measures of central tendency and dispersion for 13 studied acoustic properties from 100 advertisement calls recorded from five individuals of Microhyla sriwijaya sp. nov. and M. orientalis are shown in Table 6 . In both species, typical advertisement calls were relatively short with a pulsatile temporal structure ( Fig. 8 ). The call and pulse characteristics of both the species are described below.

Microhyla sriwijaya sp. nov. Advertisement calls typically ranged between 31.8–62.8 ms in duration. On an average, the interval between two calls was 1.3 ± 5.1 s. The call rise time was short (= 12.2 ms ± 14.7 ms) and call fall time was relatively longer (= 34.8 ms ± 13.2ms). The advertisement calls had a pulsatile temporal structure and consisted of about 2 to 3 pulses. Pulses were typically produced at a rate of 32.2 to 36.0 pulses/second with a mean pulse period of 28.7 ms. The individual pulses of a call were about 4.4 ms in duration. Pulses had a short rise time (= 0.8 ms) and reached 50% of the maximum amplitude in 0.5 ms. The pulse fall time (= 3.7 ms) was nearly 10 times longer than the rise time. The pulse decreased to 50% of its maximum amplitude in nearly 3.1 ms before the end of the pulse. The spectrum was characterized by a single broad peak with mean dominant frequency of 4.3 kHz ( Fig. 8 ; Table 6 ).

Microhyla orientalis . Advertisement calls typically ranged between 51.9–63.0 ms in duration. On an average, the interval between two calls was 0.6 ± 0.3 s. The call typically reached its full amplitude in about 18 ms (rise time) and decreased in amplitude over the last 39.2 ms (fall time). The call comprised of 3 to 5 pulses produced at a rate of 48.3–63.1 pulses/second. The pulse period of the call was 28.1 ms. The individual pulses of a call were about 5.3 ms in duration. Pulses had a short rise time (= 0.9 ms), with pulse reaching 50% of the maximum amplitude in 0.6 ms. The pulse fall time (= 4.3 ms) was nearly 5 times longer than the rise time. The pulse decreased to 50% of its maximum amplitude in nearly 3.7 ms before the end of the pulse. The spectrum was characterized by a single broad peak with mean dominant frequency of 3.7 kHz ( Fig. 8 ; Table 6 ).

Call comparison between Microhyla sriwijaya sp. nov. and M. orientalis . The calls of Microhyla sriwijaya sp. nov. differed from those of M. orientalis by their relatively shorter call duration, 46.9 ms (vs. longer, 57.8 ms); relatively less number of pulses, 2.0 (vs. more number of pulses, 4.0), delivered at slower rate, 34.7 pulses/s (vs. faster rate, 53.5 pulses/s); and a higher overall dominant frequency of 4.3 kHz (vs. lower 3.7 kHz) ( Fig. 8 ; Table 6 ). The calls of M. sriwijaya sp. nov. and M. orientalis were also well differentiated based on statistical analyses of their acoustic properties. The first three PCA factors with eigenvalues> 1.0 explained 87.9% of the variation between the two species ( Table 7 ). The two species also formed considerably distinct clusters on factor planes recovered using the first two PCA factors, supporting distinction of the new species based on acoustic properties ( Fig. 7 ). Discriminant function analysis using the first three PCA factors as input resulted in 100% individuals (five male specimens each) being classified into their respective species. The DFA generated a single discriminant function (root) that had an eigenvalue> 1.0, and explained 100% of the variation among the species.

Distribution and natural history. The new species is known from Belitung Island and the province of Lampung in southeastern Sumatra ( Fig. 1 ). The type specimens come from rural areas with oil palm plantations Kembiri village of Belitung. The holotype was collected while calling on the ground covered with grass and leaf litter, between a settlement and an oil palm plantation. During the day time animals were observed to be hiding under the litter or fallen logs, and emerged out by 18:30 h and started calling on leaf litter or soil close to small ponds. This new species of Microhyla is common and locally abundant on the island of Belitung, from west (Kembiri village, Mamblong district) to east (Batu Penyu village, Gantung district) and north (Tanjung Pandan, Tanjung Pandan district), in the urban, semi-urban, and rural areas. This species is always spotted close to water, either in small sewers with running water, small ponds for fish, or grass patches adjacent to beaches. The population from Canti, south slope of Gunung Rajabasa in Sumatra was found at coffee plantations and secondary forests. Due to vast development in both Belitung Island and Gunung Rajabasa of South Sumatra, habitat loss mainly due to plantations and associated anthropogenic activities is likely to be the main threat to this new species.

Figures

FIGURE 1. A. Map showing known localities of Microhyla sriwijaya sp. nov. and its closest relative, M. orientalis, in Indonesia; B. Sampling localities of Microhyla sriwijaya sp. nov. on the island of Belitung, where the type series was collected. Red circles indicate the sampling localities for the type series and black circles represent localities of the referred specimens.

FIGURE 2. Maximum Likelihood tree showing the phylogenetic position and relationship of the new species within the genus Microhyla, based on a 470 bp fragment of the mitochondrial 16S rRNA gene. Values above and below the branches indicate Ultrafast Bootstrap Support (UFB)> 50% and Bayesian Posterior Probabilities (BPP)> 0.50, respectively. Orange circles on the nodes denote species groups. Putative species delimited in the Microhyla achatina group using bPTP analysis are indicated with grey vertical bars (support>0.90) or open vertical bars (support <0.70); black bars represent the currently recognized species identities. GenBank accession numbers and other sample details are referenced in Table 1. Photographs of frogs in life represent Microhyla species known to occur in Indonesia. (Photo credits: M. achatina, M. berdmorei, M. orientalis, M. palmipes, M. sriwijaya sp. nov. and M. mukhlesuri by S.D. Biju; M. gadjahmadai by E. Smith; M. heymonsi by F. Alhadi; M. malang by A. Sorokin).

FIGURE 3. Type and referred specimens of Microhyla sriwijaya sp. nov. from Belitung, in life. A–F. Holotype (MZB Amph 31752, male): A, B. Dorsolateral view, C. dorsal view, D. ventral view, E. ventral view of hand, F. ventral view of foot; G–M. Paratype (MZB Amph 31747, male): G. dorsolateral view, H. dorsal view, I. ventral view, J. lateral view, K. posterior view of thighs, L. ventral view of hand, M. ventral view of foot; N. Paratype (MZB Amph 31753, male) photographed on an Indonesian 1000-rupiah coin (24.1 mm in diameter); O. referred specimen (MZB Amph 31748, male). Photographs by S. D. Biju and F. Alhadi.

FIGURE 4. Type specimens of Microhyla sriwijaya sp. nov. in preservation. A–F. Holotype (MZB Amph 31752, male): A. dorsal view, B. ventral view, C. lateral view of head, D. ventral view of hand, E. magnified view of the third finger tip showing dorso-terminal groove, F. ventral view of foot, G. magnified view of the fourth toe tip showing dorso-terminal groove, H. schematic illustration of webbing on foot; I–J. Patatype (MZB Amph 31751, female): I. ventral view of hand, J. ventral view of foot. Photographs and illustrations by S. D. Biju.

FIGURE 5. Colour variation among paratypic and referred specimens of Microhyla sriwijaya sp. nov. from Belitung Island and Lampung. MZB Amph 31747, paratype; MZB Amph 31750, paratype; MZB Amph 31748, referred specimen; UTAA-66215, referred specimen. All specimens are males. Star indicates the type locality; circles indicate other collection localities. Photographs by F. Alhadi and E. N. Smith.

FIGURE 6. Schematic comparison of Microhyla sriwijaya sp. nov. with all the known members of the Microhyla achatina group from Indonesia. A. Dorsolateral colouration and markings in life; B. dorsal markings; C. lateral markings; D. schematic illustration of structure and shape of digit tip on third finger (left) and fourth toe (right); E. schematic illustration of webbing on foot. Microhyla achatina, UIMZ 0031 (Photographs by S. D. Biju); M. gadjahmadai, MZB Amph 26081 (Photograph in life by E. N. Smith); M. heymonsi, voucher not preserved (Photographs by F. Alhadi); M. malang, voucher not preserved (Photographs by A. Sorokin); M. orientalis, UIMZ 0037 (Photographs by S. D. Biju); M. sriwijaya sp. nov., MZB Amph 31752 (Photographs by S. D. Biju).

FIGURE 7. Morphometric and acoustic differentiation between Microhyla sriwijaya sp. nov. and M. orientalis. A. Plot of the first two principal components (PC1 and PC2) derived from a principal component analysis based on morphometric data (Tables 3, 5); B. Plot of the first two factor planes (PC1 and PC2) derived from a principal component analysis based on acoustic data (Tables 6, 7).

FIGURE 8. Comparison between the male advertisement calls of Microhyla sriwijaya sp. nov. and the closely related species, M. orientalis. A–D. M. orientalis: A. ten-second oscillogram with multiple calls, B. 1-second oscillogram showing two pulsatile calls, C. 0.1-second oscillogram with four pulses in a single call, D. 0.1-second spectrogram for a call. E–H. M. sriwijaya sp. nov.: E. ten-second oscillogram with multiple calls, F. 1-second oscillogram showing two pulsatile calls, G. 0.1-second with three pulses in a single call, H. 0.1-second spectrogram for a call.