Description

Ann Gets Credit Morphological:

The dorsal surfaces are covered in smooth, unfolded skin, with low levels of warts, while the ventral surfaces are smooth and wartless. There is a presence of an anal sheath opening at the mid-thigh level. On the limbs, no ulnar folds or tubercles are present, and the frogs possess a 2 – 2 – 3 – 3 pattern of subarticular tubercles on Fingers II - V (Anganoy-Criollo et al 2022). There are no lateral fringes on the fingers. When the hind limbs are held at right angles from the body, the heels touch. No tubercles are present on the knees, heels, or tarsus. The toes bear lateral fringes and have basal webbing with a formula of I 1 - 1^- II ⅓ - 1 ⅓ III 1 - 2 ¼ IV 2 ¼ - 1⁺ V. The digits have poorly defined scutes, and digit tips do not expand to form pads. Breeding males lack nuptial pads (Lynch 1982).

Diagnosis:

A distinctive synapomorphy only present in H. edwardsi and its closest relatives, is the presence of an elongated cloacal sheath. Hyloxalus edwardsi can be distinguished from other closely related frogs, which also possess anal sheaths and lack vocal slits, such as H. jhoncito and H. ruizi, by H. edwardsi lacking finger fringes (present in H. jhoncito) and by the presence of teeth. Additionally, H. edwardsi has a brown underside with white spots in contrast to the solid colored venter of H. ruizi (Lynch 1982, Grant et al. 2006, Anganoy-Criollo et al. 2022).

Coloration:

Live specimens of H. edwardsi are a medium brown, with heavy dark brown spotting on the dorsum that may be so dense that it appears reticulated. The center of the spots may appear light because of warts. There may be faint yellow dorsolateral stripes that extend from the eye to the arm. The lips can be spotted white or pale yellow. The flanks are darker brown with lighter brown spots. The hidden surfaces of the limbs are dark olive to pale brown with more brown spots. The limbs are barred and have distinct spots. The ventrum is olive to brown and speckled with yellow spots that are more pale on the throat. In larger individuals, the ventral surface of the body is cream with brown reticulations; in smaller individuals these surfaces are cream with brown spots. The throat and ventral surfaces of the limbs are overall pale brown with cream spots, but also have a slight orange tint. Spots are absent from the ventral surface of the lower leg, which is a darker brown. The lateral margin of the forearm and posteroventral margin of the thighs are also darker brown without spots. The ventral surface of the hands and feet are dark brown. The iris of the frog is bright copper with black horizontal streaks and reticulations (Lynch 1982).

Variation:

At the time of the species description there were not enough individuals to determine sexual variation. However, larger individuals appear to have faint yellow dorsolateral stripes that extend from the eye to the arm (Lynch 1982).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Colombia

View distribution map in BerkeleyMapper.

Hyloxalus edwardsi can be found in caves, forests, and wetlands on both slopes of the the Cordillera Oriental of Columbia, specifically in La Cueva de las Moyas (Lynch 1982) and the Páramo de Cruz Verde (Anganoy-Criollo et al. 2022). It occupies streams within caves and crevices in paramos ecosystems at elevations of 3030 - 3300 meters. These two locations are isolated, as in between them is a stretch of grazing land for cattle that is not suitable for the species (IUCN 2017).

Life History, Abundance, Activity, and Special Behaviors
Hyloxalus edwardsi is a rare, semi-aquatic species that can be found in caves, near the mouth, and forest lands. They can be found in the edges of soil fissures and in streams 1.0 - 0.5 m deep, the latter of which they escape to when disturbed from soil fissures. Juveniles are found under rocks in shallow (2 - 3 cm deep) streams (Lynch 1984, Anganoy-Criollo 2013).

A unique distinction of this species, is that the vocal sacs are absent (Lynch 1982), which indicate that calling is absent in this species.

Anuran species that can be found on the surface, outside of the cave, in the area of H. edwardsi range include Dendropsophus labialis, Hyloxalus subpunctatus, Pristimantis bogotensis, Pristimantis elegans, and Hyloscirtus bogotensis, the latter of which can also be found in the caves (Lynch 1982).

Larva
Throughout the larval stage, the body lengths of two tadpoles at Gosner stage 25 measured 19.8 and 22.5 mm, and the total length measured 47.4 and 51.3 mm. The body depth is three-fourths of the greatest body width and is the broadest on the posterior end. In a dorsal view, the body is shaped like an elongated ellipse. The larvae have a rounded snout in both the dorsal view and profile. The anterolaterally-directed nostrils are placed midway between the eyes and the tip of the snout. Their eyes are small, positioned dorsolateral, and widely-spaced. The larvae have small, anteroventral-directed mouths. The median two-fifths of the upper lip lacks papillae, but the rest of the mouth features two rows of small labial papillae. Their beaks are relatively robust; the upper beak has long and thin lateral processes while the lower beak is broad and V-shaped, with two upper rows of denticles and three lower rows of denticles. They have a sinistral spiracle and a dextral-opening cloacal tube. The dorsal and ventral fins of the tadpoles are of equal depth, except on the anterior quarter of the tail, in which the dorsal fin is only about half the depth of the caudal musculature at the midlength of the tail. The tail fins themselves do not taper (Lynch 1982).

Hyloxalus edwardsi can be differentiated from H. subpunctatus by the former having a notched upper jaw sheath with higher and more evident serrations and having the spiracle located in the first anterior third of the body (Anganoy-Criollo 2013).

In life, the larvae are brown on the top, while the ventrum and throat are transparent. The tail musculature is pale olive or cream with dense brown spots that also extend onto the fins (Lynch 1982).

Tadpoles can be found in larger streams that are 0.3. - 0.5 m deep (Lynch 1982).

Trends and Threats
Hyloxalus edwardsi is listed as “Critically Endangered” on the IUCN Red List and the species has not been documented in the wild since 1996. They are threatened the most by habitat loss due to conversion to timber forests and water pollution from urban runoff. Other threats include agricultural and aquaculture disruption and wood and pulp plantations. The species is not known in any protected areas (IUCN 2017).

Relation to Humans
There are no records of H. edwardsi being collected or used by humans (IUCN 2017).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Urbanization
Subtle changes to necessary specialized habitat
Habitat fragmentation
Local pesticides, fertilizers, and pollutants
Long-distance pesticides, toxins, and pollutants
Climate change, increased UVB or increased sensitivity to it, etc.

Comments

Phylogenetic Relationships:

Synonyms:

Hyloxalus edwardsi was named Colosthethus edwardsi when first described (Lynch 1982).

Common names of this species are Edwards’ Rocket Frog or Edwards’ Poison Frog.

References
Anganoy-Criollo, M. (2013). Tadpoles of the High-Andean Hyloxalus subpunctatus (Anura: Dendrobatidae) with description of larval variation and species distinction by larval morphology. Papéis Avulsos de Zoologia, 53(15), 221-224. [link]

Anganoy-Criollo, M., Viuche-Lozano, A., Enciso-Calle, M. P., Bernal, M. H., & Grant, T. (2022). The enigmatic Hyloxalus edwardsi species group (Anura: Dendrobatidae): phylogenetic position, a new species, and new putative morphological synapomorphies. Herpetologica, 78(4), 253-267. [link]

Grant, T., Frost, D. R., Caldwell, J. P., Gagliardo, R. O. N., Haddad, C. F., Kok, P. J., ... & Wheeler, W. C. (2006). Phylogenetic systematics of dart-poison frogs and their relatives (Amphibia: Athesphatanura: Dendrobatidae). Bulletin of the American Museum of Natural History, 2006(299), 1-262. [link]

IUCN SSC Amphibian Specialist Group. 2017. Hyloxalus edwardsi. The IUCN Red List of Threatened Species 2017: e.T55074A85893381. https://dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T55074A85893381.en. Accessed on 26 February 2023.

Lynch, J. (1982). Two new species of poison-dart frogs (Colostethus) from Colombia. Herpetologica, 38(3), 366–374. [link]

Species Account Citation: AmphibiaWeb 2024 Hyloxalus edwardsi: Edwards’ rocket frog <https://amphibiaweb.org/species/1557> University of California, Berkeley, CA, USA. Accessed Dec 26, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Dec 2024.

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