Southern Gastric Brooding Frog
(Rheobatrachus silus)
EX
Overview
This frog employed one of the most original life-history strategies in the animal kingdom – gastric brooding. Females would swallow their fertilised eggs and allow the young frogs to develop into tadpoles, and subsequently froglets, in her stomach. During the brooding period the female’s digestive process would shut down and her stomach would become so bloated that her lungs would collapse under the pressure, forcing her to rely solely on gas exchange through her skin for respiration.
Urgent Conservation Actions
It is thought that the cause of the species disappearance is probably due to the infection of a virulent pathogen, most probably the chytrid fungus.
Distribution
Southeast Queensland, Australia.
Media from ARKive
ARKive video - Habitat of southern gastric-brooding frog
ARKive image - Southern gastric-brooding frog
ARKive video - Destruction of forest causing silt build up in stream habitat of southern gastric-brooding frog
ARKive video - Southern gastric-brooding frog in tank and still of young in adult's mouth
Evolutionary Distinctiveness
Order: Anura
Family: Myobatrachidae
The Myobatrachidae family arose during the early Cretaceous period around 100 million years ago; in evolutionary terms, members of the Myobatrachidae are as different from their closest relatives, the Limnodynastidae (the Australian ground frogs), as mice are to elephants. Frogs in the family Myobatrachidae show unusual forms of parental care, including the brooding of young in the stomach in the gastric brooding frogs, unique in the animal kingdom, and the Australian marsupial frog which has ‘pockets’ of skin on either side of their body where the tadpoles are carried until they metamorphose.

The genus Rheobatrachus contains two species of ground dwelling frog which were endemic to eastern Australia, the northern gastric brooding frog (Rheobatrachus vitellinus) and the southern gastric brooding frog (Rheobatrachus silus), but are now extinct. In both of these species development of the young occurred in the stomach, as their name suggests.

Until recently the genus was placed in its own family, Rheobatrachidae, however a recent genetic study indicated that the two species of gastric brooding frog are closely related to the barred frogs (Mixophyes spp.), another ground dwelling frog genus found in eastern Australia and New Guinea. This study uses classification which places the gastric brooding frogs in the sub-family Rheobatrachinae within the family Myobatrachidae (the parental-care frogs).
Description, ecology and habitat
The southern gastric brooding frog was first discovered in 1972 in pristine rainforest in the Blackhall and Conodale Ranges in south east Queensland. Here it occupied a small range of less than 1,400km2 and was restricted to elevations between 350 – 800m.

This species inhabited clear, cool, fast flowing streams in the catchments of the Mary, Stanley and Mooloolah Rivers, which flow through pristine rainforests. These streams are generally boulder-strewn, and individuals hid between or beneath boulders in the main stream or backwaters.

This frog was small and oval in shape with females ranging in length from 45-54 mm and males in the range of 33-41 mm. Individuals possessed large eyes that protruded upwards from their small, flattened head. The skin colour on their backs ranged from dull grey to slate, while the belly was white with creamy patches. As an adaptation for their strict freshwater lifestyle, this species had extensively webbed feet.

The southern gastric brooding frog employed one of the most original life-history strategies in the animal kingdom –brooding of the young within the stomach of the mother. Females would swallow their fertilised eggs and allow the young frogs to develop into tadpoles, and subsequently froglets. During the brooding period the female’s digestive process would shut down and her stomach would become so bloated that her lungs would collapse under the pressure, forcing her to rely solely on gas exchange through her skin for respiration. It was observed that during pregnancy females remained completely active even though their buoyancy and centre of gravity were affected to the point that when resting they floated vertically, rather than horizontally, in the stream.
Factors leading to extinction
Following its discovery in 1972 the southern gastric brooding frog was thought to be relatively abundant across its range until 1979. A study in 1976 revealed that there were 78 individuals in a population of the species located in the headwaters of Booloumba Creek in the Conondale range. The species declined rapidly and disappeared in a relatively short period of time, and the last individual was seen in the wild in 1979. Since then concerted efforts and surveys have tried to locate the species without any success.

The exact cause of the species’ decline is still not known. Because of the rapid nature of its extinction it is difficult for researchers to pin-point an exact cause. Although there was a small amount of commercial logging operations within the species’ range, the effects of which were never investigated, individuals were present in the logging catchments from 1972 through to 1979. It is now thought that the cause of the species disappearance is probably due to infection within the population of a virulent pathogen, most probably the chytrid fungus Batrachochytrium dendrobatidis which has been implicated in the declines of many amphibian species worldwide.

It is now known that the southern gastric brooding frog was one of the first of a series of amphibian extinctions that occurred from the late 1970s until the early 1990s within Queensland and the Northern territories. This series of extinctions began in southeast Queensland with the declines of this species and the southern day frog, Taudactylus diurnus. It continued into the mid 1980s with the disappearance of the northern gastric brooding frog, and the severe decline in numbers of the northern day frog, Taudactylus eungellensis. Finally several species on the Big Tableland of northern Queensland became extinct in the early 1990s. This wave of population decline and species extinction occurred at a rate of about 100 km per annum and is typical of epidemics spreading within a population without immunity.
Links
References
AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: amphibiaweb. Accessed: 23 April 2007.

Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.

Ingram, G.J. 1983. Natural History. The Gastric Brooding Frog. Tyler, M.J.,editor. 16-35. Croom Helm. London.

IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. Global Amphibian Assessment. Accessed on 23 April 2007.

Laurance, W.F., McDonald, K.R., Speare, R. (1996) Epidemic Disease and the Catastrophic Decline of Australian Rain Forest Frogs. Conservation Biology, Vol. 10, No. 2. pp. 406-413.

Meyer, E, Newell, Hines, H, May, S, Hero, J-M, Clarke, J & Lemckert (2004) Rheobatrachus silus In: IUCN 2006 IUCN Red List of Threatened Species. IUCN Red List of Threatened Species Accessed 30th April 2007.

Roelants, K, Gower, D.J., Wilkinson, M, Loader, S.P., Biju, S.D., Guillaume, K, Moriau, L, Bossuyt, F. (2007) Global Patterns of Diversification in the history of Modern Amphibians. PNAS. Vol 104. No. 3 pg 887 – 892.

Tyler, M.J. (1994) Australian Frogs: A Natural History. Cornell University Press.

Tyler, M.J. and Davies, M. 1983. Superficial features. The Gastric Brooding Frog. Tyler, M.J.,editor. 5-15. Croom Helm. London.

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