Description
Charadrahyla esperancensis is a moderately sized, slender-bodied frog described from four males with a snout vent length range of 44.3 - 48.9 mm. The flat head is as wide as it is long. One of the species’ diagnostic characteristics is a distinct rostral keel on the protruding snout. In the dorsal view, the snout is pointed or slightly pointed while in the lateral view, it is rounded with a sharp decline to the nostrils. The nostrils are oval, slightly protruding, and directed posterolaterally. The distinct canthus rostralis has sharp angles. The internarial region is slightly concave and the loreal region is concave. The interorbital region is slightly larger than a third of the head width. The eyes take up slightly more a quarter of the head width. The distinct tympanum is round, a little more than half the size of the eye, and located slightly more than one tympanum diameter away from the eye. The mostly distinct tympanic annulus is obscured by the supratypmanic fold on the dorsal edge. The supratympanic fold is distinct, thick, and extends posteroventrally from orbit to forearm (Canseco-Marquez et al. 2017).

The skin on the dorsal surface is smooth, while the ventral surface is granular. The skin on flanks between the forelimbs and hind limbs is conspicuously thick and smooth. The belly and ventral surface of the thighs has a granular texture. There are no axillary membranes or thoracic folds. The cloaca opening is directed posteroventrally and located at the midlevel of the thighs (Canseco-Marquez et al. 2017).

A dermal fold is present on the wrist. The hand has a webbing formula of I2 – 2½II2 – 2½III2½ – 2IV or I2 – 2½II1½ – 2½III2 - 2IV. The long, slender fingers have slight lateral fringes and a relative length of I < II < IV < III. The fingers end in large, rounded terminal discs of which fingers II, III and IV are approximately the same width as the tympanum while the disc of finger I is about half the width. Large, round subarticular tubercles that are about 2/3rds the size of the discs, are present. Smaller, distinct, round supernumerary tubercles that are about half the width of the discs are also present (Canseco-Marquez et al. 2017).

When the hindlimbs are adpressed at right angles to the body, the heels overlap. When adpressed along the body, the tibotarsal articulation reaches beyond the snout. The tibia is longer than the foot. There is no tarsal fold. A distinct, large, oval inner metatarsal tubercle is present but there is no outer metatarsal tubercle. The long, slender toes have a webbing formula of I1 – 1½II1 – 2III1 – 2IV2 – 1V or I1 - 1II1 - 1½III1 - 2IV2 - 1V and end in terminal discs that are slightly smaller than the fingers. The toes have distinct subarticular tubercles that are large, round, elevated, and about half the width of the discs and inner metatarsal tubercle. The toes also have small, round supernumerary tubercles that are arranged in rows along the proximal axis of the phalanges (Canseco-Marquez et al. 2017).

Charadrahyla esperancensis can be distinguished from other members of the genus by its protruding snout with a distinct rostral keel that slopes downward from the lip to the nostril, the lack of vocal slits, and round yellow spots on the flanks and thighs. More specifically, it differs from C. nephila due to the focal species' smaller size, smaller dark brown spots on the dorsum, and lack of dark transverse bars on fingers. Charadrahyla esperancensis can be distinguished from C. taeniopus by locality and by having a rostral keel, a pointed snout, lacks of vocal slits, and hypertrophied webbing (Canseco-Marquez et al. 2017).

In life, the dorsal side of the body and head are pale brown, although some live adult males were also found to have an olive-green dorsum and copper brown head. On the lateral surfaces of the head, there is a dark brown mask beginning at the nostrils and continuing to the tympanum. The dorsum has irregular, distinct, small dark brown spots. The flanks are dark brown and have various numbers of large, irregular yellow spots. The dorsal surface of the limbs is pale brown with dark brown transverse bars. The anterior and posterior surfaces of limbs have irregular, rounded, small yellow spots. The disks on the fingers are darker than the finger itself. The ventrum, including the ventral surface of the thighs is pale cream. There may be some brown mottling on the throat. The palpebral membrane is clear (Canseco-Marquez et al. 2017).

In preservative, dorsum of the body, head and lateral surfaces of the head can be brownish-green or gray, mottled with irregular dark spots. The limbs also turn dull gray with dark transverse bars. Small cream spots can be seen on the anterior and posterior surfaces of the thigh. The flanks are pale to dark brown and the yellow spots fade to cream. The throat becomes pale brown and, if mottling is present, it becomes cream. The chest retains the cream coloring while the belly and undersurface of thighs range from pale brown to gray. The palpebral membrane becomes grey (Canseco-Marquez et al. 2017).

There is variation in digit webbing, patterning, coloration. More specifically, the amount of webbing between fingers II and III toes I, II, and III varies slightly (see above). With regards to patterning, the number of transverse limb bars ranges on the forearm from 3 – 4, the thigh from 4 – 5, and the tibia from 6 – 7. Mottling on the throat and spotting on the flanks is also variable. Dorsal coloration vary from brown to olive-green. No females were described in the species description, leaving the potential for sexual dimorphism open (Canseco-Marquez et al. 2017).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico

View distribution map in BerkeleyMapper.

Charadrahyla esperancensis is found at a single location in the village of La Esperanza located in the Sierra de Juárez in northern Oaxaca, Mexico at an elevation of 1640 m. The species was discovered near a mountain stream in a cloud forest diverted by the Oaxaca-Tuxtepec highway. The vegetation in the forest includes treeferns and oaks. The forest has an average rainfall annually of 2 m and a mean temperature of 18 degrees Celsius. The stream is less than 5 m wide, has a substrate composed of pebbles and rocks, and has several falls (Canseco-Marquez et al. 2017).

Life History, Abundance, Activity, and Special Behaviors
The species appears to be nocturnal as they moved a considerable distance at night (Canseco-Marquez et al. 2017).

Other anuran species that C. esperancensis is sympatric with include Charadrahyla nephila, Craugastor polymniae, C. spatulatus, Duellmanohyla ignicolor, and Incilius spiculatus, all of which have elevated threat statuses due to habitat destruction (Canseco-Marquez et al. 2017).

Trends and Threats
The forests in this region used to be exploited by a paper factory. However, this deforestation has ceased, and this area is now one of the best remnants of this specific vegetation thanks to community conservation efforts. The forest is crossed by a two-lane highway, which is a threat to the species, as the frogs typically try to cross the highway at night and during rainfall (Canseco-Marquez et al. 2017). The species may also be affected by climate change and disease caused by Batrachochytrium dendrobatidis (Lips et al. 2004).

Relation to Humans
Locals of La Esperanza have voluntarily conserved over 4000 hectares of montane cloud forests to preserve species such as C. esperancensis (Canseco-Marquez et al. 2017).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Urbanization
Disturbance or death from vehicular traffic
Habitat fragmentation
Disease
Loss of genetic diversity from small population phenomena
Climate change, increased UVB or increased sensitivity to it, etc.

Comments
The species authority is: Canseco-Márquez, L., Ramírez-González, C.G., González-Bernal, E. (2017). ''Discovery of another new species of Charadrahyla.'' Zootaxa, 4329(1), 64-72

At the time of the genus description, Charadrahyla, was composed of five species: C. altipotens, C. chaneque, C. nephila, C. taeniopus, and C. trux; this was determined by 56 transformation in the ribosomal genes as well as the nuclear and mitochondrial proteins. The genus Megastomatohyla is closely related to Charadrahyla (Faivovich 2005). By 2019, three more species were described, C. tecuani by Campbell et al. (2009), C. esperancensis by Canseco-Márquez et al. (2017), and C. sakbah by Jiménez-Arcos et al. (2019). Genetic analysis is needed to reveal the relationships within the genus.

The genus, Charadrahyla, was named in 2005 by Faivovich et al. The name is derived from the Greek word for “ravine”, “charadra”, in reference to where the frogs in this genus are found.

The species epithet is from the Spanish word “Esperanza” in reference to the town where the species is found and is in recognition of the community’s efforts to preserve biodiversity of the local cloud forest (Canseco-Marquez et al. 2017).

References

Campbell, J. A., Blancas-Hernández, J. C., Smith, E. N. (2009). ''A new species of stream-breeding treefrog of the genus Charadrahyla (Hylidae) from the Sierra Madre del Sur of Guerrero, Mexico.'' Copeia, 2009(2), 287-295. [link]

Canseco-Márquez, L., Ramírez-González, C.G., González-Bernal, E. (2017). ''Discovery of another new species of Charadrahyla Anura, Hylidae) from the cloud forest of northern Oaxaca, México.'' Zootaxa, 4329(1), 64-72. [link]

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]

Jiménez-Arcos, V.H., Calzada-Arciniega, R.A., Alfaro-Juantorena, L.A., Vázquez-Reyes, L.D., Blair, C., Parra-Olea, G. (2019). ''A new species of Charadrahyla (Anura: Hylidae) from the cloud forest of western Oaxaca, Mexico.'' Zootaxa, 4554(2), 372-385. [link]

Lips, K. R., Mendelson, J. R. III, Munoz-Alonso, A., Canseco-Marquez, L. and Mulcahy, D.G. (2004). ''Amphibian population declines in montane southern Mexico: resurveys of historical localities.'' Biological Conservation, 119, 555-564.

Species Account Citation: AmphibiaWeb 2019 Charadrahyla esperancensis: Espernza Treefrog <https://amphibiaweb.org/species/8703> University of California, Berkeley, CA, USA. Accessed Dec 24, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 24 Dec 2024.

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