Southern gastric-brooding frog
Rheobatrachus silus Liem, 1973
Queensland Legislative Status: Endangered
Endemicity: Queensland Endemic
Description: A moderately large, aquatic frog, males 30-44mm, females 41-54mm (Ingram 1983, Tyler & Davies 1983a). Dorsal surface is brown, or olive brown to almost black, usually with obscure darker blotches on the back. A dark streak runs from the eye to base of the forelimb. There are darker cross-bars on the limbs, and pale and dark blotches and variegations on the digits and webbing. Ventral surface is white or cream with yellow markings on limbs. Skin is shagrened or finely granular above, and smooth below. Snout is blunt and rounded, with the eyes and nostrils directed upwards. Eyes are large and prominent, located close together and close to front of head. Tongue is largely adherent to the floor of mouth. Typanum is hidden. Fingers lack webbing, while toes are fully webbed. Digits have small discs. (Cogger 2000, Liem 1973, Tyler & Davies 1983a).
Call: Call is a loud staccato, consisting of 30-34 pulses repeated in a long series, lasting 260-290 min/s. Dominant frequency is 1000 Hz, with less emphasises frequency bands at 500,700,1200 and 1400 Hz (Tyler 1983b).
Tadpole: Unknown
Reproduction: Breeding activity occurs between October and December and appears dependent on summer rains (Ingram 1983). This species features a unique reproductive mode in which eggs or early larvae are swallowed by the female and complete their development in the stomach (Tyler & Carter 1982). Hormones produced by the young inhibit the digestive secretions of the stomach and inactivate the upper intestine, a process of special interest to the medical community (Tyler 1984). Larvae rely on yolk reserves throughout development (Tyler & Davies 1983b). Up to 25 young are brooded in this fashion, emerging from the mother's mouth as fully formed metamorphs about 6-7 weeks (Tyler & Davies 1983b). the digestive tract returns to its normal state and the female recommences feeding within four days (Tyler 1983a). Maximum longevity is at least 3 years (Ingram 1983).
Habitat: Rheobatrchus silus is an aquatic species and has never been located more than 4m from water. This species is restricted to rocky perennial streams, soaks and pools in rainforest and tall open forest with a closed understorey. It prefers rock pools and backwaters with leaf litter and rocks in which to shelter (Ingram 1983).
Rheobatrachus silus is most active during the warmer months, between September and April, abundance decreasing as conditions become drier in winter (Ingram 1983). It is not known where these individuals go during this period, but it is believed they hibernate in deep crevices in the rocks (Ingram 1983, Liem 1973, McDonald pers obs). Individuals may be active night or day, particularly after rain. They establish home ranges in and around suitable pools, spending extended periods partly submerged and immobile. When heavy rain falls the males move away from the water, sometimes up to four metres, and call from sheltered hollows or crevices above the pools (Ingram 1983).
Distribution: Rheobatrachus silus is restricted to elevations of 400-800m in the Blackall and Conondale Ranges, south-eastern Queensland. Rheobatrachus silus has not been sighted in the wild since 1981 and may be extinct. Continued efforts to relocate the species have failed (Hines et al.1999).
Latitude: Between 26&186; 34' and 27&186; 47';
Longitude: Between 152&186; 32' and 152&186; 53'.
Status: R. silus is one of five species of upland rainforest stream-dwelling frogs which has declined in south-eastern Queensland during the last 18 yrs (Ingram & McDonald 1993). The species underwent an unanticipated decline in winter 1979 (Tyler & Davies 1985, Czechura & Ingram 1990) and the last sighting occurred September 1981 (Richards et.al. 1993). Searches have continued unsuccessfully, most recently in November 1999 (Ingram & McDonald 1993, H. Hines pers comm). Last known specimen died in captivity November 1983 (Tyler & Davies 1985).
Threatening Processes: The causes of the population decline remain unknown. Tyler & Davies (1985) found no obvious evidence that over collecting, pollution from logging or gold panning, or drought were responsible for the population decline. Current research is examining the possibility that a fungus may have caused the decline of this species (Berger et al 1998, Berger et al 1999). Information on disease investigations and management can be located at http://www.jcu.edu.au/school/phtm/PHTM/frogs/ampdis.htm.
Management Recommendations: Recovery Plan for Rheobatrachus silus and Taudactylus diurnus by Wayne E. Martin, Keith R. McDonald and Harry B. Hines 1997 recommends the following actions:
1. Ongoing survey of historical sites and sites with suitable habitat.
2. Provision of public information and education to raise awareness regarding this species.
References:
Cogger, H.G. 2000. Reptiles & Amphibians of Aust. Reed New Holland:Sydney.
Czechura, G.V. & Ingram, G.V. 1990. Taudactylus diurnus and the case of the disappearing frogs. Memoirs of the Qld Museum. 29(2):361-365.
Hines, H., Mahony, M and McDonald K.R. 1999. An Assessment of Frog Declines in Wet Subtropical Australia. In Campbell, A (ed), 'Declines and Disappearances of Australian frogs'.(Environment Australia, Department of the Environment and Heritage: Canberra). 234 pp.
Ingram, G.J. 1983. Natural History. Pp. 16-35 In Tyler, M.J. (ed). The Gastric Brooding Frog. Croome Helm, London.
Liem, D.S. 1973. A new genus of frog of the family Leptodactylidae from S-E. Qld, Australia. Memoirs of the Qld Museum. 16(3):459-470.
Richards, S.J., McDonald, K.R., Alford, R.A. 1993. Declines in populations of Australia's endemic tropical rainforest frogs. Pacific Conservation Biology 1:66-77.
Tyler, M.J. 1985. Gastric brooding: A phenomenon unique to Australian frogs. Search. 16(5-6): 157-159.
Tyler, M.J. and Carter, D.B. 1982. Oral birth of the young of the gastric-brooding frog Rheobatrachus silus. Animal behaviour 29 : 280-282.
Tyler, M.J. & Davies, M. 1983a. Superficial features Pp. 5-15 In Tyler, M.J. (ed). The Gastric Brooding Frog'. Croome Helm, London.
Tyler, M.J. & Davies, M. 1983b. Larval development. Pp. 44-57 in Tyler, M.J. (ed). The Gastric Brooding Frog. Croome Helm, London.
Tyler, M.J. & Davies, M. 1985. The Gastric Brooding Frog. Pp. 469-470 In Grigg, G., Shine, R. & Ehmann, H (eds). Biology of Australasian Frogs & Reptiles. Royal Zoological Society of NSW, Sydney.
Last updated: 30 August 2005