Micryletta lineata ( Taylor, 1962 )

Miller, Aryeh H., Zug, George R., Wogan, Guinevere O. U., Lee, Justin L. & Mulcahy, Daniel G., 2021, Phylogeny, Diversity, and Distribution of Micryletta (Anura: Microhylidae) in Myanmar, Ichthyology & Herpetology 109 (1), pp. 245-257 : 249-251

Micryletta lineata ( Taylor, 1962)

Figures 4 , 5 ; Tables 5 , 6

Diagnosis.— Micryletta lineata is a diminutive member of the genus Micryletta with adult size SVL 22.1–23.5 mm in males (n ¼ 17), 21.6–28.3 mm in females (n ¼ 13); snout slightly truncate in dorsal view, obtuse in lateral view, head length 28–34% SVL; head width 95–114% head length; hindlimb length 145–203% SVL. Skin, dorsal trunk, and hindlimbs moderately shagreen; dorsally snout, canthus, and forelimb smooth; hand with numerous metacarpal tubercles, foot with modest oblong inner metatarsal tubercles and no outer metatarsal tubercles; no webbing between fingers and toes; digit tips rounded, not expanded; dorsal coloration variable, usually light brown, grayish brown or rufous brown ground color and dorsally three or four rows of scattered dark-brown marks (usually elongate) from middle of head to sacrum, often forming three or four longitudinal rows; laterally dark-brown stripe from snout through eye to midtrunk or inguinal region; dorsally fore- and hindlimbs lightly patterned with small irregular dark marks except unicolor upper arm; venter beige with light-brown mottling along throat. This diagnosis and following description are based on 17 males and 13 females from Tanintharyi Region, Myanmar .

Description.— Body measurements summarized (in mm) in Tables 5 and 6 . Proportions (%) for the sampled males (MM) and females (FF) are: HeadL/SVL 30–34 (3261) MM, 28–34 (3162) FF; HeadWP/HeadL 96–110 (10164) MM, 95–114 (10265) FF; SnEye/HeadL 34–45 (3963) MM, 29–44 (4064) FF; TrunkL/SVL 36–49 (4163) MM, 37–52 (4465) FF; ForarmL/SVL 24–29 (2662) MM, 23–28 (2661) FF; ForarmL/ThighL 51–64 (5864) MM, 52–65 (5864) FF; 3 rd FingL/ HandL 62–86 (7266) MM, 62–74 (6964) FF; HindlL/SVL 150–203 (172614) MM, 145–180 (16568) FF; CrusL/SVL 42– 52 (4762) MM, 43–50 (4662) FF; CrusL/ThighL 96–111 MM (10564), 97–110 (10264) FF; ThighL/SVL 40–50 (4463) MM, 41–48 (4562) FF; FootL/HindlL 23–32 (2962) MM, 29–33 (3061) FF; FootL/SVL 45–58 (5063) MM, 46–52 (4962) FF; 4 th ToeL/FootL 58–68 (6263) MM, 54–68 (6264) FF; EyeD/ SnEye 83–124 (95611) MM, 81–138 (95614) FF; IntNar/ SnEye 55–80 (7066) MM, 63–81 (6965) FF; NarEye/SnEye 48–80 (5967) MM, 45–67 (5665) FF.

Body oblong with truncate snout; limbs slender with somewhat elongate digits; forefoot digit lengths 3. 2 ¼ 4. 1, hindfoot 4. 3 ¼ 5. 2. 1. Head as broad, or broader than long; canthus rostralis rounded; naris closer to snout than eye and slightly protuberant; tympanum visible, horizontal diameter about two-thirds that of eye. Dorsal skin surface as described above, ventrally smoother with large flat abutting tubercles most evident on chest and abdomen.

Dorsal ground color as above; dark-brown markings variable in density from few to many and most somewhat elongate rather than round; bilateral dorsolateral series/rows usually present, middorsal ones from moderate to near absent. Ventrally light cream background overlain by diffuse dark speckling on chin and throat or more frequently black sublabial border; trunk either unicolor or diffuse dark variegation.

Distribution.— Presently, M. lineata is restricted to the Isthmus of Kra region in southern Myanmar (Tanintharyi Region) and adjacent western Thailand, reaching its apparent northern latitudinal limit at nearly 158N. Micryletta lineata likely has a larger distribution and possibly extends north into the Salween Basin of Myanmar and south into northern Peninsular Malaysia, although these areas have yet to be thoroughly investigated. Specimens of Micryletta from this area must be examined closely (optimally integrating both morphology, genetics, and bioacoustics) owing to demonstration of sympatry of M. inornata sensu stricto and M. lineata .

Natural history.— Micryletta lineata is a diurnal terrestrial frog usually found among leaf litter and often near forest streams. Tadpole morphology, diet, advertisement calls, and various other crucial facets of the ecology and biology of M. lineata have yet to be characterized.

Comparison to other Myanmar Micryletta . — Our sample of Tanintharyi M. inornata is small (single adult female [ Fig. 6 ] and single immature female). Morphometrically, all its measurements lie within the range of the sample of M. lineata ( Table 5 ). Its distinguishing attributes are a combination of coloration features: dorsal nape with a single median narrow dark nape bar vs. few scattered small dark spots or smudge; upper lip uniformly white vs. mottled or narrow white stripe with dark ventral border; side of trunk with broad dark, irregular-edged stripe vs. narrow, smooth-edged stripe of series of spots and bars as continuation of postocular stripe; ventrally chin unicolor vs. dark bordered lower lip; and unicolor chest vs. diffuse reticulate chest pattern.

We have 14 specimens representing northern Myanmar M. aishani ( Tables 5 , 6 ). Morphometrically, M. aishani and M. lineata share most traits, although the former has a larger head in both length and width even though they share similar SVLs. It is important to note that both sexes of the Kachin M. aishani are significantly smaller than the topotypic M. aishani with no overlap of body lengths (Das et al., 2019: table 3). Furthermore, coloration differs between Kachin M. aishani and Tanintharyi M. lineata : dorsally snout usually with faint marks or reticulation vs. often unicolor; lateral trunk stripe continuous for third or more of length vs. series of spots and bars; dorsal surface of femur light and dark variegated vs. distinctly longitudinally striped, median light stripe bordered anteriorly and posterior by dark color; upper lip with longitudinal white stripe irregular vs. mottled or narrow white stripe with dark ventral border; dark postorbital strip crosses tympanum vs. dark postorbital strip not on tympanum.

Conservation status.— Specific threats imposing substantial risk to populations of M. lineata in southern Myanmar are largely unknown, but presumably include those endangering other anurans in Southeast Asia—primarily rapid rates of deforestation ( Rowley et al., 2010). In the Tanintharyi Region, Connette et al. (2017) reported extensive deforestation of critical lowland wet evergreen forest which hosts a wide array of endemic or seriously threatened species (e.g., Cyrtodactylus , Panthera , Elephas ). Indeed, between 2002 to 2014, the Tanintharyi Region lost 185,952 ha of forest (Bhagwat et al., 2017), largely owing to expanding oil palm plantations (which, in Myanmar, are specific to the Tanintharyi Region). Despite the increasing loss of forest throughout southern Myanmar, the Tanintharyi Region, along with Kachin State in the north, remain the country’s major strongholds for remaining intact forest tracts (Bhagwat et al., 2017).

Presently, the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species (IUCN, 2020) contains classifications for three Paddy Frog species: M. inornata (Least Concern) , M. steinegeri (Vulnerable) , and M. erythropoda (Data Deficient [DD]). In Myanmar, M. lineata occurs at an approximate extent of occurrence (EOO) of 21,054 km 2, whereas its distribution in adjacent Thailand is largely uncharacterized. Given the uncertainty surrounding the distribution of this species, and a lack of population density estimates in this region, we recommend classifying M. lineata as DD under the IUCN Red List, although substantial concerns exist regarding accelerating rates of deforestation of lowland evergreen wet forests in the Tanintharyi Region.

Figures

FIG. 4. Micryletta lineata (USNM 587907) from Tanintharyi Region, Myanmar. Scale for each perspective given in parenthesis. (A) Ventral view (10 mm); (B) dorsal view (10 mm); (C) lateral view (1 mm); (D) volar view of right hand (1 mm); (E) plantar view of left foot (1 mm). Note that gold dots are heads of pins that were used to hold the specimen in place.

FIG. 5. Micryletta lineata (USNM 587923) from the Tanintharyi Region, Myanmar. Dorsal views of in-life (A) and subsequent to preservation (B). Scale bar is 10 mm.

FIG. 6. Micryletta inornata sensu stricto (USNM 587901) from Tanintharyi Region, Myanmar. Scale for each perspective given in parentheses. (A) Ventral view (10 mm); (B) dorsal view (10 mm); (C) lateral view (1 mm); (D) volar view of right hand (1 mm); (E) plantar view of left foot (1 mm). Note that gold dots are heads of pins that were used to the hold the specimen in place.