Description
Atelopus oxyrhynchus is a slender-bodied Atelopus (Boulenger 1903) with a male snout-vent length range of 39 – 49 mm and a female snout-vent length range of 46 – 58 mm (Dole and Durant 1974). The head is longer than wide, with a flat top, vertical sides, and a pointed snout. The nostrils are located midway between the snout and the eyes. The eyelid length is shorter than the distance between the eyes. The trunk is roughly two to two and a half times the length of the head and has large smooth warts on the sides, posterior portion of the body, and on the limbs (Boulenger 1903). A ridge of glandular bumps on the back is typical of the species (La Marca 1983). The forelimbs are long and slender and the moderate fingers are depressed and swollen at the tips. The first finger is well-developed, but short and broad. The tubercles in the carpal and subarticular regions are indistinct. The hind limbs are relatively short; when extended, the tibio-tarsal articulation reaches between the scapular region and posterior edge of the eye. The toes are short, depressed, and partially webbed. The skin of the belly is granular or areolate. Males have a internal subgular vocal sac (Boulenger 1903).

Atelopus oxyrhynchus can be differentiated from Atelopus sorianoi by coloration and the tendency of the former to have more tubercles in both males and females than A. sorianoi, whose density of tubercles varies by sex. Also the focal species’ has a curved canthus rostralis, unelevated squamosals, and often have bands on the canthal rostralis and supratympanic regions (La Marca 1983).

In preservative, the background dorsal coloration of A. oxyrhynchus ranges from lemon-yellow, yellow, olive brown, or orange red. Lemon-yellow morphs may or may not have a vermilion-red blotch on the belly. Yellow morphs have an orange-red ventrum. Olive brown morphs have a variable number of dark brown dorsal spots, a dark lateral stripe that extends from the snout, and a lemon-yellow belly (Boulenger 1903).

The coloration of the species is variable. The frog also displays sexual dimorphism with the female being larger than the males and females having more slender forelimbs. Males of the species have an internal subgular vocal sac (Boulenger 1903). Males of the species also often tend to be spinier than the females (La Marca 1983). Males and females can also be differentiated based on the shape of the thumb, with females having long, slender, and pointed thumbs while males have short, broad, and blunted thumbs with horny pads at the base (Dole and Durant 1974).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Venezuela

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (1 records).

Atelopus oxyrhynchus is endemic to a small portion of the Venezuelan Andes in closed canopy montane cloud forests near the city of Mérida, State of Mérida, in the Cordillera de Mérida at elevational ranges between 2,100 – 3,500 m asl (La Marca et al. 2010). The species tends to live away from nearby streams in home ranges during the non-breeding season, but moves towards the streams during the breeding season (Dole and Durant 1974).

Life History, Abundance, Activity, and Special Behaviors
Atelopus oxyrhynchus is a photophilic, diurnal species (La Marca et al. 2010). The species is known for being slow and clumsy. Researchers have observed that the activity level of this species is influenced by seasonal precipitation. During the wet season, they can be found active on the forest floor. They have two peak activity periods, between March to mid-May and again in August or September, coinciding with migration to and from streams during the breeding season to lay eggs. Fewer animals were found during the dry season when individuals are thought to shelter in tree root crevices and under leaf litter to reduce moisture loss and avoid predation. However, there was no correlation between the number of frogs found and temperature or humidity (Dole and Durant 1974).

Home range fidelity has been reported in A. oxyrhunchus, however, there is no evidence of intraspecific territoriality and home ranges are known to overlap. The size of their home range has been recorded as 56.2 ±79.9 m² for males and 32.6 ±29.9 m² for females (Dole and Durant 1974).

Males and females locate each other within their overlapping forest home ranges. However unmated males will seek females at the stream later in the breeding season, often unsuccessfully. Unpaired male A. oxyrhynchus have been observed perching on logs near freshwater streams where they were found calling to females. Some females do start migrating to streams before being paired, but are likely clasped by a male before arriving at the stream (Dole and Durant 1974).

Breeding pairs undergo amplexus for an extremely extended period of time, with one pair remaining in amplexus for 125 days. In a 1974 study, the shortest period of amplexus observed was 18 days (Dole and Durant). In the same study, pairings of males and females started as early as December, and the number of paired frogs increased in subsequent months until mid-March. Pairs rarely switch partners. The mated pairs engage in amplexus in their home ranges away from streams before making short migrations to nearby streams to spawn between May through July, all the while still in amplexus. During amplexus the female can still capture prey but the male is limited to whatever prey comes close enough to catch or to subsisting off of built up fat reserves. However, females also bare the energetic cost of carrying males. Due to the drawn out nature of the species’ amplexus, individuals are at greater risk of starvation or injury (Dole and Durant 1974).

Once at streams, between May and early-July and peaking in June, egg deposition occurs quickly and both sexes returned to their home ranges (Dole and Durant 1974). The eggs are laid in a chain formation (La Marca et al. 2010).

The young, upon hatching, exhibit indirect development, starting life off as tadpoles. There is very little published information on the tadpoles of A. oxyrhynchus, but other tadpoles in the Atelopus genus have sucker like mouths that are used to attach to rocks in turbid streams (McDiarmid 1971).

Atelopus oxyrhynchus are brightly colored, likely as a form of aposematism, which is a defense mechanism that warns predators of the fact that they are chemically defended (McDiarmid 1971). The chemical defense which A. oxyrhunchus presents is the very potent tetrodotoxin (Mebs and Schmidt 1989).

Adults consume a wide variety of insects including beetles, mites, ants, and flies (Durant and Dole 1974). The species is not very fast and are small in size, which limits their ability to hunt faster species of prey. Therefore ants and mites make up the majority of their diet, as opposed to the faster flying insects or large species such as beetles and butterflies (Dole and Durant 1974, McDiarmid 1971).

Trends and Threats
Populations of A. oxyrhynchus have drastically declined, and this formerly common and conspicuous species has not been found in the wild since 1994. The IUCN Red List, which lists the species as “Critically Endangered”, has stated several potential reasons for the frogs decline. It is likely that the largest factor in the rapid decline of A. oxyrhynchus is exposure to the fungus chytridiomycosis, which causes a fatal infection and is highly contagious (La Marca et al. 2010).

Habitat loss from agriculture, past forestry operations, and mining has likely also affected the species survival. The species is thought to potentially persist in two different protected areas, Parque Nacional Sierra Nevada and Parque Nacional Sierra de la Culata (La Marca et al. 2010).

Lastly, droughts between 1975 and 1990 may have also contributed to the species decline (La Marca et al. 2010).

Even though a large portion of the historic range of A. oxyrhynchus falls within protected land, the IUCN still recommends that any discovered remnant population be taken into captivity and used to start an ex-situ conservation initiative (La Marca et al. 2010).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Prolonged drought
Habitat fragmentation
Disease
Climate change, increased UVB or increased sensitivity to it, etc.

Comments
The species authority is: Boulenger, G. A. (1903). “LIX.—Descriptions of new batrachians in the British Museum." Annals and Magazine of Natural History. 12:71, 552-557.

Atelopus oxyrhynchus is thought to be closely related to A. carbonerensis and A. sorianoi (La Marca 1983).

The species epithet, “oxyrhynchus” is derived from two Ancient Greek words, together meaning pointed or sharp snout.

A distinguishing feature of Atelopus oxyrhynchus is the frogs’ skin, which contains tetradotoxin, obtained from its food (Durant and Dole 1974).

References

Boulanger, G.A. (1903). ''LIV.—Descriptions of new batrachians in the British Museum.'' Annals and Magazine of Natural History, 12(71), 552-557.

Dole, J. W., Durant, P. (1974). ''Movements and seasonal activity of Atelopus oxyrhynchus (Anura: Atelopodidae) in a Venezuelan cloud forest.'' Copeia, 1974(1), 230-235.

Durant, P., Dole, J. W. (1974). ''Food of Atelopus oxyrhynchus (Anura: Atelopodidae) in a Venezuelan cloud forest.'' Herpetologica, 30(2), 183-187.

La Marca, E. (1983). ''A new frog of the genus Atelopus (Anura: Bufonidae) from a Venezuelan cloud forest.'' Milwaukee Public Museum Contributions to Biology and Geology, 54, 1-12.

La Marca, E., García, I., Albornoz, R., García-Pérez, J.E. 2010. Atelopus oxyrhynchus. The IUCN Red List of Threatened Species 2010: e.T54535A11163352. http://dx.doi.org/10.2305/IUCN.UK.2010-2.RLTS.T54535A11163352.en. Downloaded on 21 February 2017

McDiarmid, R. (1971). ''Comparative morphology and evolution on frogs of the neotropical genera Atelopus, Dendrophryniscus, Melanophryniscus and Oreophrynella.'' Bulletin of the Los Angeles County Museum of Natural History, 12, 1-66.

Mebs, D., Schmidt, K. (1989). ''Occurrence of tetrodotoxin in the frog Atelopus oxyrhynchus.'' Toxicon, 27(7), 819-822.

Species Account Citation: AmphibiaWeb 2018 Atelopus oxyrhynchus: Rednose Stubfoot Toad <https://amphibiaweb.org/species/68> University of California, Berkeley, CA, USA. Accessed Dec 23, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 23 Dec 2024.

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