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Rheobatrachus silus

By Erica Semeyn

Geographic Range

This species of frog is only found in the Blackall and Conondale Ranges in Southeastern Queensland, Australia (Barker, 1995).

Habitat

This frog is mostly aquatic and is found in rocky creek beds, adjacent pools, and rock pools in the Australian rainforest. It also lives along the rocky streams of the moist eucalyptus forest.

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

The length of the oval-shaped R. silus ranges in females from 45 to 54 mm, and 33 to 41 mm in males. Extremely large eyes dorsally protrude from its small, flattened head (Tyler, 1983). The skin color on its back ranges from dull gray to slate, with obscure dark and light patches. When the background is pale, a broad brown and posteriorly curved, superocular bar is detectable (Barker, 1995). Its belly is marked with large creamy patches on a white surface. The feet of this frog are extensively webbed to suit its aquatic lifestyle.

  • Sexual Dimorphism
  • female larger
  • Range length
    33 to 54 mm
    1.30 to 2.13 in

Development

Gastric brooding frog tadpoles develop in their mother's stomach for 6 to 7 weeks. The tadpoles do not feed during this time, as they lack tooth rows. The young develop at different rates and are birthed when they are ready; expelling all of the juvenile frogs may take several days.

Reproduction

The reproductive habits of the gastric brooding frog set it apart from other species. The breeding age for this frog is about two years. The process of egg deposition and amplexus has never been observed; it is only known that the eggs are ingested through the mouth (Barker, 1995). The female swallows between 18 and 25 fertilized cream-colored eggs, which develop in her stomach. During this 6 to 7 week period, the colorless tadpoles lack tooth rows and do not feed. The female also stops feeding entirely because of the egg jelly and chemicals secreted by the tadpoles which switch off the production of hydrochloric acid in the stomach wall (A.N.C.A., 1996). The entire digestive system shuts down, which prevents the digestion of the young. Birth is accomplished by the female widely opening her mouth and dilating her esophagus. The offspring are propelled from the stomach to the mouth, and then hop away.

The breeding season occurs during the spring and summer months. Though the warm temperatures of these months aren't essential for reproduction, rain and moisture are necessary (Tyler, 1983).

  • Range age at sexual or reproductive maturity (female)
    2 (low) years
  • Range age at sexual or reproductive maturity (male)
    2 (low) years

Each female gastric brooding frog contributes yolk to her eggs, and then after they are fertilized, she swallows them and carries them in her stomach for 6 to 7 weeks. During this time, her digestive system shuts down and she cannot eat. Once the young are fully developed and expelled from her mouth, she has no further contact with them. Male gastric brooding frogs contribute nothing to the next generation except their sperm.

  • Parental Investment
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • protecting
      • female

Lifespan/Longevity

In captivity, individual R. silus have lived up to 3 years.

  • Range lifespan
    Status: captivity
    3 (high) years

Behavior

These frogs are not very active and they often remain in the same position for several hours at a time. They are neither strictly nocturnal nor diurnal (Tyler, 1983). They are fast and powerful swimmers, but often just drift or float ventral side up in the water. Though aquatically adapted, they travel a great deal on land. They are only capable of leaping 25 cm, which makes them potentially easy prey.

Communication and Perception

The advertisement call of the southern gastric brooding frog is a pulse with a slight upward inflection lasting for 0.5 seconds, repeated every 6 seconds.

Food Habits

The diet of R. silus consists mainly of small live insects. Once the prey is captured, the frog manipulates it further into the mouth with its forelimbs. Soft-bodied insects are eaten at the water surface, while stronger prey are taken underwater for consumption. Rheobatrachus silus has been observed catching insects on land as well as in water (Tyler, 1983).

  • Animal Foods
  • insects

Predation

The two major predators of R. silus, white-faced herons and eels, inhabit the same streams as the frogs. The leaves from eucalyptus trees and stones along the stream banks aid in hiding this species from predators. When grasped, as an escape mechanism, they excrete a coat of mucus that enables them to slip away.

Economic Importance for Humans: Positive

The ability to shut down the secretion of powerful digestive acids could have an important bearing in the medical treatment of humans who suffer from gastric ulcers.

Conservation Status

The gastric brooding frog has limited distributions, which has been detrimental to its existence. It is listed as endangered in the Appendix of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. In 1973, when this species was discovered, they were extremely abundant, and believed common. Astonishingly, less than a decade after their discovery, they seemingly disappeared without a trace. There are several speculated causes for the population crash: drought, over-collection by herpetologists, habitat pollution by the logging industry and by the damming of the creeks for the gold-panning industry (Tyler, 1985). This species' permeable skin makes them especially susceptible to the pollution in their aquatic environment.

This species is currently listed as Extinct by the International Union for the Conservation of Nature. No individuals have been observed in the wild since 1981, despite extensive searches.

Other Comments

Gastric brooding frogs cannot be tamed and always struggle when handled.

Contributors

Erica Semeyn (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

marsh

marshes are wetland areas often dominated by grasses and reeds.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Australian Nature Conservation Association. 1996. http://www.anca.gov.au/plants/manageme/frogprod.htm.

Barker, J., G.C. Grigg & M.J. Tyler. 1995. A Field Guide to Australian Frogs. Surrey Beatty & Sons. Chipping Norton, Australia

Duellman, W.E., Linda Trueb. 1986. Biology of Amphibians. Mcgraw-Hill Book Co. New York, New York.

Sanders, Ingrid. 1996. Platypus Frog. http://www-mugc.cc.monash.edu.au/~ctemp3/platypus.htm (link no longer valid)

Tyler, M.J. 1983. The Gastric Brooding Frog. Biddles Ltd. Great Britain.

Tyler, M.J., M. Davies. 1985. The Gastric Brooding Frog. The Biology of Australian Frogs and Reptiles (pg 469-470).

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