Vocal sac-brooding frogs

(Rhinodermatidae)

Class Amphibia

Order Anura

Family Rhinodermatidae

Thumbnail description
Small frogs; green, tan, or brown (or a combination of these colors) with a distinctive fleshy proboscis at the tip of the snout

Size
Snout-vent length to 1.3 in (33.0 mm)

Number of genera, species
1 genus; 2 species

Habitat
Forest and open areas; often near streams

Conservation status
Data Deficient: 2 species

Distribution
Chile, Argentina

Evolution and systematics

No fossils have been described for the family.

Frogs belonging to the family Rhinodermatidae have been included in the families Brachycephalidae, Dendrobatidae, and Leptodactylidae at various times. Since 1971 they have been recognized in their own family.

Rhinoderma rufum was originally named Heminectes rufus. These frogs were later considered to be a local variant of Rhinoderma darwinii, rather than a valid species. Subsequent work suggested that Heminectes is a synonym of Rhinoderma. The new combination of Rhinoderma rufum was proposed based on differences in the mating call, karyotype, larval development, and male parental care between the two species. No subfamilies are recognized.

Physical characteristics

Rhinodermatids are small frogs; males range from 0.9–1.2 in (22–31 mm), females from 1–1.3 in (25–33 mm). The tympana (external eardrums) are indistinct. The most distinctive external characteristic is a fleshy proboscis, found in both sexes and all age classes. The forelimbs and hind limbs are rather long and slender. These frogs are extremely variable in color. Dorsally, they may be uniformly tan, brown, or reddish brown; uniformly pale green or dark green; or a combination of brown and green, in variable patterns. The underside has blotches of black and white. Brooding males are easily distinguished by their enlarged vocal sacs.

Distribution

Vocal sac-brooding frogs are found in central to southern Chile, and in Argentina near the Chilean border. Many populations have declined or disappeared from their historical sites during the past 15 years.

Habitat

These terrestrial frogs are found in wet temperate southern beech forest (Nothofagus), often near slowly running streams or in swampy areas, and in open areas around human habitation.

Behavior

Both species exhibit seasonal patterns of activity. They take refuge during the colder months, presumably under moss or logs on the ground, and breed during the warmer months. Both species are primarily diurnal. Territoriality has not been reported.

Feeding ecology and diet

The feeding ecology and diet of these frogs have not been studied. Anecdotal field observations suggest they opportunistically

eat insects and other small invertebrates. In captivity they eat fruit flies, aphids, and juvenile crickets. Both species are sit-and-wait predators, that is, they sit in one place and snap up prey that come within striking distance.

Reproductive biology

Breeding is seasonal. Males call from land to attract females. Eggs are fertilized on moist ground, and males attend the eggs. Just before the eggs hatch, the males take the eggs into their mouths, where they slide into the vocal sacs. In Rhinoderma darwinii, the tadpoles develop within the vocal sac until they metamorphose 50–70 days later. In Rhinoderma rufum, the male releases the tadpoles into water, where they continue to develop for an unknown period of time.

Conservation status

Both species are listed as Data Deficient by the IUCN. However, Rhinoderma rufum is listed as Endangered and R. darwinii as Vulnerable by CITES. Possible reasons for population declines and disappearances include habitat destruction and modification, climate change, and detrimental effects from increased levels of ultraviolet radiation. No specific efforts are known to be underway to protect these species.

Significance to humans

None known.

Species accounts

List of Species

Darwin's frog

Rhinoderma darwinii

taxonomy

Rhinoderma darwinii Duméril and Bibron, 1841, Valdivia, Chile. No subspecies are recognized.

other common names

French: Le rhinoderme de Darwin; German: Darwin-Nasenfroschs; Spanish: Ranita de Darwin, sapito de Darwin, sapito vaquero.

physical characteristics

These are small frogs; males are up to 0.9–1.1 in (22–28 mm), females are 1–1.2 in (25–31 mm), with moderately developed membranes between the first and second toes and between the second and third toes. The membrane between the third and fourth toes is smaller, and there is no membrane between the fourth and fifth toes. The metatarsal tubercle is evident, but less prominent than in R. rufum.

distribution

This species occurs in central and southern Chile, from the province of Maule south to the province of Aisén, from 0–4,921 ft (0–1,500 m) elevation. In Argentina, the frogs occur near the border with Chile, in the provinces of Neuquén and Río Negro.

habitat

The frogs are found both in primary and in disturbed forest. They are also commonly found in open areas around human habitation, and in open wooded or grassy areas. Most individuals are found in or near swampy areas or slowly running water.

behavior

This species is primarily diurnal, but males also call at night. Some individuals display an unusual behavior when disturbed. They flip over onto their backs, revealing their contrasting black and white undersides. If a frog near a stream is frightened, it may jump into the water and float downstream on its back.

feeding ecology and diet

Darwin's frogs are sit-and-wait predators. By day, they sit in one place and snap up moving insects and other small invertebrates that come within striking distance.

reproductive biology

The male mating call is a rapidly repeated "piiiip, piiiiip, piiiiip, piiiiip." Calling is most prevalent beginning in the spring

and continuing through the breeding season (November through March).

Observations made in captivity reveal that a male leads a female to a sheltered place that serves as the site for egg deposition. After considerable courtship movements by both frogs, the female crawls underneath the male. He holds onto her very loosely, in contrast to the typical strong amplectant hold of most frogs.

Darwin's frogs deposit and fertilize large eggs (about 0.16 in/4 mm in diameter) on land. In a population studied from the far south of the range, clutch size was estimated to be three to seven eggs. The male stays near the eggs for about 20 days, until the eggs are nearly ready to hatch. At that point, the male takes the eggs into his mouth where they enter his vocal sac and soon hatch. The tadpoles develop within the vocal sac for the next 50–70 days. After the young metamorphose, they crawl back into the father's mouth. The father opens his mouth and the froglets hop out onto land.

The tadpoles lack the typical morphology of free-swimming tadpoles. They do not have external gills, spiracle, beak, or keratinized teeth, and their caudal fins are poorly developed.

Studies of the lining of the vocal sacs of brooding males suggest that the epithelial cells secrete a substance that is taken up by the tadpoles through their skin. Tracers experimentally introduced into the lymphatic sacs moved into tissues of the tadpoles, further supporting the idea that tadpoles receive nutrients from the lining of the vocal sac.

conservation status

Listed as Data Deficient by IUCN but Vulnerable by CITES. Although the frogs are locally common in some areas (particularly at low elevations), populations are declining or disappearing in other areas (especially at high elevations). The causes of these declines and disappearances are unknown, but habitat destruction is a major threat. Some areas that previously supported dense populations of Darwin's frogs are now planted in non-native pine or eucalyptus, or have been converted to pastures or human residential areas. Climatic change may also be affecting the species, as the climate throughout much of the range is warmer and drier than it was 15–20 years ago. The frogs may also be affected by increased levels of ultraviolet radiation, as the frogs are diurnal and often bask in sunlight.

significance to humans

None known.

Chile Darwin's frog

Rhinoderma rufum

taxonomy

Heminectes rufus Philippi, 1902, Vichuquén, Chile. No sub-species are recognized.

other common names

Spanish: Ranita de Darwin de Chile, sapito de Darwin de Chile.

physical characteristics

Small frogs (males to 1.2 in [31 mm], females to 1.3 in [33 mm]), with membranes between each of the toes; the membranes between the first and second and the second and third toes are especially well developed.

The metatarsal tubercle is more prominent than in R. darwinii.

distribution

Central Chile, from the province of Bío-Bío north to the province of Maule, between 164 and 1,640 ft (50 and 500 m) elevation.

habitat

These frogs are found on the ground, in southern beech (Nothofagus) forest, usually near slowly running water.

behavior

No study of behavior under natural field conditions has been published.

feeding ecology and diet

Presumably these frogs are sit-and-wait predators that feed on small insects and other small invertebrates.

reproductive biology

The male mating call is a rapid "pip, pip, pip, pip," with long pauses between repetitions. These frogs deposit and fertilize their eggs on moist ground. The eggs are smaller than those of R. darwinii, about 0.10 in (2.4 mm) in diameter on average. Clutch size is estimated to be 12–24 eggs. After about eight days, the male takes the eggs into his vocal sac. The eggs hatch there, and the tadpoles remain in the vocal sac until they have developed horny jaws and the digestive tract has elongated and spiraled. At that point, the male releases the tadpoles into water. The tadpoles undergo free-swimming aquatic development for an unknown number of days until metamorphosis.

conservation status

Listed as Data Deficient by IUCN and listed on CITES. Investigators have been unable to find any individuals within the past decade. Historically, they occurred in a very restricted area. Much of their known habitat is currently planted in non-native pine or eucalyptus, or has been converted to pasture or human residential areas.

significance to humans

None known.

Resources

Periodicals

Busse, Klaus. "Bemerkungen zum Fortpflanzungsverhalten und zur Zucht von Rhinoderma darwinii." Herpetofauna 13 (1991): 11–21.

Crump, Martha L. "Natural History of Darwin's Frog, Rhinoderma darwinii." Herpetological Natural History 9, no. 1 (2002): 21–30.

Formas, Ramón, Emilio Pugin, and Boris Jorquera. "La identidad del batracio Chileno Heminectes rufus Philippi, 1902." Physis Sección C. Buenos Aires 34 (1975): 147–157.

Goicoechea, Oscar, Orlando Garrido, and Boris Jorquera. "Evidence for a Trophic Paternal-Larval Relationship in the Frog Rhinoderma darwinii." Journal of Herpetology 20 (1986): 168–178.

Jorquera, Boris. "Biologia de la reproducción del genero Rhinoderma." Anales del Museo de Historia Natural Valparaíso 17 (1986): 53–62.

Jorquera, Boris, Emilio Pugin, and Oscar Goicoechea. "Tabla de desarrollo normal de Rhinoderma darwini." Archivos de Medicina Veterinaria 4 (1972): 1–15.

Jorquera, Boris, Emilio Pugin, Orlando Garrido, Oscar Goicoechea, and Ramón Formas. "Procedimiento de desarrollo en dos especies del genero Rhinoderma." Medio Ambiente 5 (1981): 58–71.

Martha Lynn Crump, PhD