Ruthven's frogs

(Allophrynidae)

Class Amphibia

Order Anura

Family Allophrynidae

Thumbnail description
Small frog that dwells in trees around streams and rivers in lowland tropical forest; body is elongate and covered dorsally with small spicules

Size
Females: 0.85–1.20 in (22–31 mm); males: 0.80–0.95 in (20.6–24.6 mm)

Number of genera, species
1 genus; 1 species

Habitat
Lowland tropical rainforest, particularly around streams and rivers

Conservation status
Not threatened

Distribution
South America

Evolution and systematics

Allophryne ruthveni was described by Helen Gaige in 1926. The type locality is at Tukeit Hill below Kaiteur Falls in British Guiana. Since its description, the relationship of this frog to other frogs has been an enigma. In the original description, Gaige placed it in the toad family, primarily because it lacks teeth. The name Allophryne comes from the Greek allos, meaning "other," and phrynos, meaning "toad," presumably because the author considered the species to be another kind of toad. Other authors considered this frog to be a treefrog or a glass frog, because of the nature of the bones supporting the toe discs. Later researchers examined the internal structure of the toe discs and determined that this character in Allophryne is different from that in treefrogs or glass frogs. Those researchers supported placing Allophryne in a separate group. No subfamilies are recognized.

Physical characteristics

The dorsal color of this small frog varies from bronze or grayish brown to gold with darker mottling; gold or yellowish brown narrow dorsolateral stripes are present. A variable amount of spotting occurs on the throat of both males and females, although the vocal sac in males is always dark without spots. The vocal sac expands greatly when an individual is calling; it can exceed the size of the head. Sharp spicules, larger and denser in males, are embedded in the skin. The tips of the toes are expanded into discs. The body is elongate, and the head slopes in lateral profile.

Distribution

The frog inhabits the Amazon and Guianan forests from Venezuela through Guyana, Suriname, and French Guiana to Amapá, Brazil, south of the Amazon River in Pará, and west to Rondônia.

Habitat

Individuals generally are found near streams or rivers in lowland forests. Breeding congregations occur around flooded pools, which may form in depressions in the forest or as a result of rising rivers or heavy rains.

Behavior

During the rainy season, when they are not breeding, individual frogs sit out at night on leaves several feet above the ground, in the general vicinity of streams or rivers. An individual found in Amapá, Brazil, was taken from a terrestrial bromeliad. A gravid female was taken from the stomach of the snake Leimadophis reginae; the snake had been collected on the bank of a river in Surinam.

Feeding ecology and diet

No information is available on feeding or diet of this species.

Reproductive biology

Breeding in this species has been observed in the months of March, May, and July and generally is associated with the rainy season. Males call from the edges of small temporary ponds in the forest or from the flooded edges of rising rivers. In northern Brazil a few individuals have called from positions on the leaves of small trees several meters from the edge of a small pond after heavy rainfall. In southern Venezuela, individuals have called from small trees and bushes near a flooded depression in the forest. Perhaps the most dramatic observation was the explosive breeding event witnessed in March in Pará, Brazil, when several hundred individuals appeared on one evening after only a few individuals had been found in the area during the preceding two months. This congregation was found in a flooded area created by the rising of the Rio Xingu, a large tributary of the Amazon River. The chorus occurred near the end of the rainy season and seemed to be triggered when the river reached a critical stage of flooding.

The call of this species has been described as a series of short notes or of low, raspy trills. A recording of the call from an individual in Roraima, Brazil, disclosed that the calls are given at a rate of 18 notes per minute. During a breeding event observed in the La Escalera region of Venezuela, a pair of frogs in axillary amplexus was found on a branch about 5 ft (1.5 m) above water. This pair was placed in a plastic bag, where the female subsequently deposited approximately 300 pigmented eggs. The eggs did not survive to hatching.

Conservation status

Although not threatened according to the IUCN, the conservation status of this frog is largely unknown, primarily because the frog is rarely encountered. Large areas in the Amazon region and in other places where the frogs occur are being deforested continually; thus, populations of this secretive frog are likely being destroyed before they are discovered.

Significance to humans

This frog has been an enigma since its discovery in 1926, because it cannot be placed within any other known frog clade. Until 1984 it was thought to occur only in the Guianan forests well north of the Amazon River. In 1984, 1985, and 1987 specimens were found considerable distances south of the Amazon River in Amazon rainforest. The discovery of this frog in the Amazon region as recently as the 1980s indicates how much remains to be learned not only about this frog but also about the vast, largely biologically unexplored Amazon region. By 2002 the tadpoles of this species, which could hold clues to the relationship of this species to other frogs, still had not been described.

Resources

Books

Caldwell, Janalee P. "Diversity of Amazonian Anurans: The Role of Systematics and Phylogeny in Identifying Macroecological and Evolutionary Patterns." In Neotropical Biodiversity and Conservation, edited by A. C. Gibson. Los Angeles: Mildred E. Mathias Botanical Garden Miscellaneous Publications, 1996: 73–88.

Periodicals

Caldwell, Janalee P., and M. S. Hoogmoed. "Allophrynidae." Catalogue of American Amphibians and Reptiles (1998):666.1–666.3.

Gaige, H. T. "A New Frog from British Guiana." University of Michigan, Occasional Papers of the Museum of Zoology 176 (1926): 1–3.

Hoogmoed, M. S. "Notes on the Herpetofauna of Surinam. II. On the Occurrence of Allophryne ruthveni Gaige (Amphibia, Salientia, Hylidae) in Surinam." Zoologische Mededelingen Leiden 44, no. 5 (1969): 751–781.

Lynch, J. D., and H. L. Freeman. "Systematic Status of a South American Frog, Allophryne ruthveni Gaige." Miscellaneous Publications, Museum of Natural History of the University of Kansas 17, no. 10 (1966): 493–502.

Janalee P. Caldwell, PhD