Megastomatohyla pellita (Duellman, 1968)
Oaxacan Yellow Treefrog
© 2010 Division of Herpetology, University of Kansas (1 of 1)
The moderately long and slender arms have a small axillary membrane. There is also a weak tubercular fold located at the ventrolateral edge of the forearm. There is no distinct transverse dermal fold on the wrist. There is a low, flattened, and diffuse palmar tubercle. The moderately short and stout fingers have relative lengths of 1 < 4 < 2 < 3 and end in small discs. A barely enlarged pre-pollex that lacks nuptial excrescences is present. The subarticular tubercles are large, round, and flattened with the exception of the distal tubercles on the third and fourth fingers, which are bifid. Large, round supernumerary tubercles can be found on the proximal finger segments. Webbing is absent on the first and second fingers but is present on the second, third, and fourth fingers (Duellman 1968, 2001).
When the moderately long and stout hindlimbs are held at right angles to the body, the heels overlap by one-fourth to one-fifth the length of the shank. When adpressed along the body, the tibiotarsal articulation reaches the middle of the eye. A tarsal fold can be found along the entire length of the tarsus. The flat inner metatarsal tubercle is oval and partly visible from above. There is no outer metatarsal tubercle. The relative toe lengths are 1 < 2 < 3 < 5 < 4 with the toes ending in discs that are smaller than the fingers discs. The subarticular tubercles are small and round. Like the fingers, the supernumerary tubercles are small, flattened, and found irregularly on the proximal segments of the toes. The toes are three-fourths webbed (Duellman 1968, 2001)
The skin is smooth on the dorsum and the ventral surfaces of the arms and shanks. The throat, chest, and belly are very granular. The anal opening is directed posteriorly and found at the level with the dorsal side of the thighs. It is bordered on the posterior side by vertical dermal folds and a few small tubercles. There is a short anal sheath with a membranous connection to the posterodorsal surfaces of the thighs (Duellman 1968, 2001).
At Gosner stage 28 and 30, tadpoles had total lengths of 38.22 mm and 38.45 mm respectively, body lengths of 13.45 and 13.94, and tail lengths of 24.60 mm and 24.25 mm. The bodies are globular with an oval shape in the dorsal view. The bodies are wider than high, giving them a compressed appearance in the lateral view. In the dorsal view, the snout is oval, while in the lateral view, it is tapered. The oval nostrils are slightly elevated, located dorsolaterally, and directed anterodorsally. The internarial distances are smaller than the interorbital distance. The small eyes are located and directed laterally. The distinct oral disc of the tadpoles located and directed ventrally. The disc has a boarder of continuous marginal papillae positioned in a single alternating row anteriorly and laterally, and in two alternating rows posteriorly. The outer papillae are long, conical, and smaller than the triangular inner papillae. The marginal papillae row formula is 1 - 2/1 - 2/2 - 3. At the lateral ends of the lower labium there are submarginal lateral papillae. The labial keratodont row formula is usually 7(7)/10. The first three anterior rows are fragmented, shorter than the latter four, and have smaller keratodonts than the latter four. The seventh anterior row has a distinct medial gap. The first six posterior rows are about equal in length while the ninth and tenth rows are shorter and fragmented. The first three posterior rows have large keratodonts, but the keradont size decreases for the latter rows. The low spiracle is sinistrally positioned, ending with a posterolaterally directed, free tube opening that is narrower than the base. The cloacal tube is longer than wide and located medially with a tapered dextral opening that is attached to the ventral fin. The dorsal fin raises slightly beyond the height of the body and has a convex shape. The ventral fin is lower than the dorsal fin but also extends slightly beyond the border of the body, making the tail deeper than the body. The tail has a rounded tip that is directed downward (Köhler et al. 2015, 2016).
Megastomatohyla pellita adults can be distinguished from many other local hylids by a combination of the transverse bars on their limbs, 3/4th webbing, and lack of tympanum. More specifically, the focal species is smaller than Megastomatohyla mixomaculata and has a yellowish tan dorsum rather than M. mixomaculata’s reddish brown. From the physically similar, Charadrahyla pinorum, the focal species can be differentiated by a proportionally smaller head, transverse bands, tubercles below the anal opening, and osteological characters of the naris, sphenethmoid, and quadratojugal (Duellman 2010).
Megastomatohyla pellita tadpoles can be distinguished from other stream breeding tadpoles in Oaxaca by having a tooth row formula of 7/10 rows of keratodont teeth. Specifically, this feature distinguishes them from Charadrahyla altipotens, C. juanitae, C. pinorum, Exerodonta melanomma, E. sumichrasti, Hyalinobatrachium fleischmanni, Incilius occidentalis, I. marmoreus, Plectrohyla cembra, P. hazelae, P. pentheter, P. thorectes, Ptychohyla leonhardschultzei, Rana forreri, and R. sierramadrensis (Köhler et al. 2016).
In life, the dorsal coloration of adult M. pellita is a pale yellowish tan with slightly darker tan or olive-brown markings on the dorsal side. However, the frog displays the ability to change color. At night, when the frogs are most active, they appear yellowish tan with reddish brown spots. During the day they are mostly pale brown with transverse lines on the limbs, scattered specks on the dorsum, and a soft olive-green line between the eyes. The irises are a pale bronze. The hands, feet, and thighs are all a dull yellow. There is a creamy, white stripe present on the outer edges of the forearms and ankles. There is also a distinct, short strip above the anal opening. The belly is white. In preservation, the dorsal surface of the frog becomes a pale tan with dark brown marks in the occipital region and body. The anterior and posterior surfaces of the thighs lose their pigment. The rest of the arms, shanks, and feet are tan with brown transverse bars. The ventrum becomes cream colored (Duellman 2001).
In life, tadpoles have olive colored dorsal and lateral surfaces with light to dark brown blotches or mottling and light to dark yellow stipples. On the dorsolateral region of the snout, there is a greenish-white blotch. The iris is pale yellow with dark brown suffusions around the edges. From the lateral view, the oral discs is a pale greenish-brown but is otherwise pale yellow on the anterior portion and fades to cream at the posterior. The keratodonts and jaw sheaths are black. The posterior region of ventrolateral margin of the body is pale yellow. The spiracle has a light yellow opening. The ventroposterior portion of the body is blue-black with pale yellow blotches and stipples. The tail musculature is greenish-white with dark brown suffusions and a smoke white blotch located on the central, lateral region. The tail fins have pale brown stipples and greenish-gray capillary-like reticulum patterning (Köhler et al. 2015).
The number of crosswise bars on the lower leg of the frog can vary based on individual and ranges from one to four. The small black flecks on the dorsal side of the frogs may sometimes be absent or not easily visible. In adults, males have a total of 7 - 12 teeth, while females have 8 - 12 teeth (Duellman 2001)
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Mexico
Life History, Abundance, Activity, and Special Behaviors
Megastomatohyla pellita lacks vocal slits and a vocal sac, and therefore are not thought to have a mating call (Duellman 2001). Breeding occurs in permanent streams (Santos-Barrera and Canseco-Marquez 2004).
Trends and Threats
Possible reasons for amphibian decline
General habitat alteration and loss
Megastomatohyla pellita was originally categorized as a member of the genus Hyla, but was moved to the new genus, Megastomatohyla, in 2005 based on a large scale phylogenetic analysis of approximately 5100 base pairs of 12S, tRNA valine, 16S, and cytochrome b mitochondrial DNA and five nuclear genes. At the time of the genus naming, four species from the Hyla mixomaculata group were proposed for the genus, M. mixe, M. mixomaculata, M. nubicola, and M. pellita, however, only one species of the new genus was used in the analyses (Faivovich et al. 2005). A follow up analysis using both M. mixe and M. pellita found that they were more closely related to each other than to the next sister group, which contained Charadrahyla juanitae, C. nephila, and C. taeniopus (Faivovich et al. 2018). However, an analysis of the genus is still needed to illuminate the species relationships within the genus.
The genus name, “Megastomatohyla” is derived from the Greek words, “mega” and “stomatos” meaning “large” and “mouth”, respectively, and refers to the large oral discs of the larvae in the genus (Faivovich et al. 2005).
The specific epithet, “pellita” is Latin for “covered in skin” referring to the fact that the external tympanum is concealed by skin (Duellman 2001).
Duellman, W. E. (2001). The Hylid Frogs of Middle America. Society for the Study of Amphibians and Reptiles, Ithaca, New York.
Faivovich, J., Haddad, C. F. B., Garcia, P. C. A., Frost, D. R., Campbell, J. A., Wheeler, W. C. (2005). ''Systematic review of the frog family Hylidae, with special reference to Hylinae: phylogenetic analysis and taxonomic revision.'' Bulletin of the American Museum of Natural History, (294), 1-240. [link]
Faivovich, J., Pereyra, M.O., Luna, M.C., Hertz, A., Blotto, B.L., Vásquez-Almazán, C.R., McCranie, J.R., Sánchez, D.A., Baêta, D., Araujo-Vieira, K., Köhler, G., Kubicki, B., Campbell, J.A., Frost, D.R., Wheeler, W.C., Haddad, C.F.B. (2018). ''On the monophyly and relationships of several genera of Hylini (Anura: Hylidae: Hylinae), with comments on recent taxonomic changes in Hylids.'' South American Journal of Herpetology, 13(1), 1-32. [link]
Köhler, G., Trejo Pérez, R. G., Canseco-Márquez, L., Méndez de la Cruz, F., Schulze, A. (2015). ''The tadpole of Megastomatohyla pellita (Duellman, 1968) (Amphibia: Anura: Hylidae).'' Mesoamerican Herpetology, 2, 146–152. [link]
Köhler, G., Trejo-Pérez, R. G., Reuber, V., Wehrenberg, G., Méndez-de la Cruz, F. (2016). ''A survey of tadpoles and adult anurans in the Sierra Madre del Sur of Oaxaca, Mexico (Amphibia: Anura).'' Mesoamerican Herpetology, 3, 640–660. [link]
Santos-Barrera, G. Canseco-Márquez, L. (2004). “Megastomatohyla pellita.” The IUCN Red List of Threatened Species 2004: T55592A11325496. Downloaded on 02 June 2019.
Originally submitted by: Devon Feaster (first posted 2019-10-18)
Edited by: Ann T. Chang (2019-10-21)
Species Account Citation: AmphibiaWeb 2019 Megastomatohyla pellita: Oaxacan Yellow Treefrog <https://amphibiaweb.org/species/901> University of California, Berkeley, CA, USA. Accessed Jun 7, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 7 Jun 2023.
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