Australian toadlets and water frogs

(Myobatrachidae)

Class Amphibia

Order Anura

Family Myobatrachidae

Thumbnail description
Small to large frogs in which the first two presacral vertebrae are not fused, and in which are seen widely varying reproductive modes, ranging from fully aquatic to direct development and including some bizarre forms of parental care

Size
0.6–3.1 in (16–79 mm)

Number of genera, species
21 genera; 121 species

Habitat
Streams, alpine meadows, seasonally arid open forest and grasslands, woodlands, temperate rainforest

Conservation status
Extinct: 3 species; Critically Endangered: 5 species; Endangered: 1 species; Vulnerable: 5 species; Data Deficient: 17 species

Distribution
Australia (including Tasmania) and southern New Guinea

Evolution and systematics

The fossil record is poor and based on studies of the ilium, believed to be the most diagnostic of disarticulated bones. The extant species Crinia signifera and C. georgiana have been recorded from Pleistocene deposits, whereas C. remota, also an extant species, has been recorded from a deposit of unknown age, probably Holocene or late Pleistocene. An extinct species, C. presignifera, has been identified from the Oligo-Miocene of Queensland. No subfamilies are recognized.

The relationships of the Australopapuan ground frogs have been the subject of much argument. Originally believed to be part of the widely distributed family Leptodactylidae, they were placed in a single family, Myobatrachidae, in 1973 on the sole basis of distribution. An argument was raised at this stage that knowledge of the subfamilies Myobatrachinae and Limnodynastinae was insufficient to decide whether they were different enough from each other to merit familial status. Composition of the subfamilies has been subject to dispute, with two enigmatic genera, Mixophyes and Rheobatrachus, being of uncertain affinities. Mixophyes has been placed within the Limnodynastinae uncritically, but Rheobatrachus has been placed variously in either the Limnodynastinae or Myobatrachinae or even in its own subfamily or family.

Monophyly of the two major subfamilies (leaving aside the two questionable genera) has never been in dispute, but monophyly of Myobatrachidae has yet to be established. Attempts to answer this question have relied on early studies that were shown to be based on spurious data (probably owing to misidentification of the material under examination). Family or subfamily status of these two lineages is likely a semantic argument in the absence of new data, but within the Myobatrachidae as recognized here, relationships of all genera recognized in 2001, except Rheobatrachus, have been established using mitochondrial genes. The monotypic genus Bryobatrachus has been shown to be the sister taxon to C. tasmaniensis (both taxa are endemic to Tasmania) and, pending morphologic investigation of the generic status of this lineage, has been placed in Crinia.

The monotypic genus Spicospina is the sister taxon to Uperoleia, which resolves the enigmatic biogeographical observation of an absence in southwestern Australia of this speciose and widely distributed genus. Classification issues relate to the status of C. tasmaniensis and C. nimbus and to the familial position of Rheobatrachus.

Physical characteristics

Apart from the larger aquatic species (Rheobatrachus) with fully webbed toes, myobatrachids are small frogs, varying from slender, long-legged froglets to squat, short-legged toadlets. Some are highly modified as frontward burrowers with thickened snouts, broad hands, and reduced digits; some dig backward with two raised, compressed metatarsal tubercles; and many others have an unmodified terrestrial or semiaquatic body form.

Most frogs vary from dull slate gray to brown, often with bright flash markings in the groin or armpits or both, but others are brilliantly colored with yellow and black, as in the Corroboree frog, Pseudophryne corroborree, or with blue, orange, and red, as in Spicospina flammocaerulea.

Features of the skeleton and muscles indicative of this family include the lack of fusion of the first two presacral vertebrae, the shape of the alary processes of the hyoid (broad and winglike except in Rheobatrachus), and the relationship of the

superficial muscles of the throat and of the leg muscles, (except in Rheobatrachus). The finger and toe discs are small or absent in members of this family.

Distribution

Species are found throughout Australia and Uperoleia mimula and Crinia remota have been recorded in southern New Guinea. Myobatrachids occur in sand dunes close to the oceans through intermediate elevations to the alpine meadows of the Australian Alps in the Great Dividing Range.

Habitat

Adults live in habitats ranging from seasonally arid grasslands to sand dunes in which no surface free water is available to temperate rainforest to open woodland to alpine meadows and to rainforest streams. Larvae develop in permanent streams, temporary ponds, nests in damp mossy habitats, underground egg membranes, and the stomachs of female parents as well as the hip pockets of males.

Behavior

Most species are nocturnal or crepuscular, but the day frogs of the genus Taudactylus are active during daylight hours. Species found in the wet/dry tropics are strictly seasonal, as are most temperate species. A few species are active and call after rain throughout the year. Members of the genus Uperoleia burrow to escape the dry season in seasonally arid areas and remain underground until the rains come, whereas the two frontward-burrowing genera Myobatrachus and Arenophryne spend daylight hours underground irrespective of the season.

Male Uperoleia lithomoda wrestle with intruding males if challenged at their calling sites. Vocalizations are part of the ensuing struggle. Females of Crinia georgiana can be clasped simultaneously by as many as five males, resulting in multiple paternity of the eggs but with reduced fertilization success compared with single matings. This has been attributed to intense conflict between males attempting to mate with a single female, and usually the conflict is resolved when extra males clasp the female in suboptimal positions, such as ventrally.

Feeding ecology and diet

Some species (e.g., Arenophryne) feed mostly on ants, and Myobatrachus feeds almost exclusively on termites. All species are arthropod feeders. Type of prey is restricted by the gape of the mouth and seasonal availability. No species is known to eat other frogs. Myobatrachus live in termite mounds; hence, prey items are readily available. Most other frogs feed opportunistically.

Reproductive biology

Most myobatrachids are strictly seasonal breeders, but some frogs breed in all seasons. Those in the wet/dry tropics respond to monsoon rains, though many species of Uperoleia call throughout much of the wet season. Some males (e.g., Assa) call away from nesting sites, whereas others call beside water and, after females have selected them, move to the water in amplexus. Arenophryne and Myobatrachus call from underground. Crinia nimbus and Taudactylus call during the day, but all other species call in the evening and at night. Female Uperoleia inundata approach a calling male from behind and wriggle underneath him when he is in full voice. He rapidly deflates his vocal sac and clasps her in the inguinal region, and they move to water to deposit eggs. Female Assa follow the male to the nesting site, and female Crinia georgiana often are subjected synchronously to attempted matings by multiple males.

Myobatrachids have a wide range of reproductive modes, but they do not include foam nesting. Uperoleia, many species of Crinia, Paracrinia haswelli, and Taudactylus all lay aquatic eggs and have free-swimming tadpoles. Others, such as some species of Geocrinia and all Pseudophryne except P. douglasi lay terrestrial eggs that develop out of water for differing periods of time and then hatch at times of rains and are flushed or wriggle into the water.

The eggs of Arenophryne and Myobatrachus are laid underground, undergo the entire larval period within jelly membranes, and hatch as froglets. One of the most unusual reproductive modes is exhibited by Assa, in which the newly hatched larvae wriggle up the flanks of the male, lodge in a pair of inguinal pouches, and undergo their entire development at these sites. Rheobatrachus has an equally unusual form of reproduction, in which the larvae develop in the stomach of the female.

Conservation status

Rheobatrachus silus, R. vitellinus, and Taudactylus diurnus are listed as Extinct. In addition, five species are Critically Endangered; one is Endangered; five are Vulnerable; and 17 are Data Deficient. Taudactylus acutirostris, which the IUCN lists as Critically Endangered, is categorized as extinct by the 2002 Environment Australia Threatened Species List.

Many species have restricted distributions, with endemic centers in southwestern Australia, Tasmania, Kimberley, Pilbara, and Cape York, which increases their vulnerability. The presumed extinct species may have been decimated by chytrid fungus; no known anthropogenic influence can be cited. Other factors that may influence frog survival are herbicides, pesticides, urbanization, salinization, and fire.

Significance to humans

Secretions of pharmacological activity have been isolated from the skins of Uperoleia, Taudactylus, and Pseudophryne. None has been developed further. Skin secretions are potentially toxic, though studies of toxicity have not been undertaken.

Species accounts

List of Species

Sandhill frog

Arenophryne rotunda

taxonomy

Arenophryne rotunda Tyler, 1976, False Entrance Well Tank, Edel Land, Shark Bay, Western Australia.

other common names

English: Round frog.

physical characteristics

This is a small species; males are 1–1.3 in (26–33 mm), and females are 1.1–1.3 in (28–33 mm). These frogs have short limbs and broad hands with reduced phalanges on the first digit. The dorsal skin is mottled with small warts and ridges and often a pale mid-dorsal stripe.

distribution

The narrow range extends from Kalbarri north to Shark Bay and Dirk Hartog Island, Western Australia.

habitat

This frog lives in seasonally arid sand dunes close to the coast with no surface free water.

behavior

The frog burrows head first into the sand and takes shelter during the day at the interface of damp and dry sand at the top of the water table at depths that are seasonally variable. At night they walk around on the dunes leaving characteristic tracks.

feeding ecology and diet

Probably catholic and opportunistic in their feeding, their diet consists mainly of ants as well as beetles, arachnids, spiders, and true bugs. Individuals have been observed at night with their heads down openings of ant nests, where they presumably are feeding.

reproductive biology

Males call from underground from about April until July, and pairs form, also underground, by November, sometimes in aggregations at the same site. About five months later, directly developing eggs are deposited about 31.5 in (80 cm) underground over a period of three months.

conservation status

Not threatened. Although this species has a restricted distribution, it is locally abundant.

significance to humans

None known.

Hip pocket frog

Assa darlingtoni

taxonomy

Crinia darlingtoni Loveridge, 1933, Queensland National Park, McPherson Range, Queensland, Australia.

other common names

English: Pouched frog, marsupial frog; French: Rainettes-àbourse; German: Beutelfrösche.

physical characteristics

In this small species, males are 0.6–0.7 in (15–19 mm), and females are 0.7–0.8 in (18–21 mm). The pointed snout expands into a broad body, which is gray, pale brown, or pinkish brown to red dorsally; a dark stripe commencing anteriorly to the nostrils extends posterolaterally, passing through the eye and terminating midway along the flank. The toes lack fringes and webbing but have slightly expanded tips. Vomerine teeth are absent.

distribution

This small frog inhabits the mountain ranges on the New South Wales/Queensland border and the McPherson Ranges in northeastern Australia.

habitat

Found in deeply-shaded leaf litter in montane rainforest, the frogs take shelter under rocks, vegetated soil banks, or overhangs.

behavior

Little known. Reproductive behavior more well known.

feeding ecology and diet

The feeding ecology of this species is unknown, but it feeds on arthropods.

reproductive biology

Males call from leaf litter or under logs; when approached by females, they increase the intensity of their calls and lead the female to a nesting site, where inguinal amplexus occurs. Eggs are laid in two layers on moist, decomposing leaves deep in the leaf litter or on soil under leaf litter. The female attends the nest during this time. After several days (11 in captivity), the male covers the egg mass with the anterior part of his body as the jelly capsules rupture; using tail movements, the hatchling tadpoles move up his flanks and enter one of the bilateral inguinal pouches (up to six in each pouch). Tadpoles lack a spiracle and are supplied with yolk. Fully formed froglets emerge either frontward or backward 48–69 days later.

conservation status

Not threatened.

significance to humans

None known.

Moss frog

Crinia nimbus

taxonomy

Bryobatrachus nimbus Rounsevell Zeigeler, Brown, Davies, and Littlejohn, 1994, 984 ft (300 m) north of Lake Esperance, Herz Mountains National Park, Tasmania.

other common names

None known.

physical characteristics

This species is small; males are 0.7–1.1 in (19–27 mm), and females are 1–1.2 in (25–30 mm). The frogs have maxillary teeth and no reduction in the bones of the ear. The last two presacral vertebrae fuse with the sacrum; the dorsum has consistent

markings of a chevron-shaped patch between the eyes and dark parallel lines extending posteriorly from the shoulder, with a second pair of dark patches laterally on the posterior part of the body. The fingers and toes lack fringes and webbing.

distribution

This frog occurs in mountains in southern Tasmania ranging from sea level to 3,600 ft (1,100 m).

habitat

The species is confined to subalpine moorland or implicate rainforest.

behavior

This cryptozoic species hides under low vegetation or in breeding chambers, often in cushions of sphagnum moss, lichens, or similar vegetation. The frogs do not appear to aggregate or to use open surface water.

feeding ecology and diet

Nothing is known about the feeding ecology or diet of this species, but it probably feeds on arthropods.

reproductive biology

The call is a series of "toks"; frogs call diurnally in spring and early summer from the ground in dense vegetation or from breeding chambers. Egg capsules are extremely large, with an ovum diameter of about 0.2 in (4 mm) and a capsule diameter of about 0.6 in (15 mm); clutches of four to 16 eggs are laid in moss or lichens. The jelly capsules break down, and the entire period of larval development takes place in the liquefied jelly. Tadpoles do not feed, and the oral disk lacks keratinous jaws or labial teeth. Tadpoles spend the winter under snow and metamorphose after about 395 days.

conservation status

Not threatened.

significance to humans

None known.

Eungella torrent frog

Taudactylus eungellensis

taxonomy

Taudactylus eungellensis Liem and Hosmer, 1973, Eungella National Park, 33.6 mi (54 km) west of Mackay, Queensland, Australia.

other common names

English: Eungella day frog.

physical characteristics

This is a small to medium-size frog; males are 1–1.1 in (25–28 mm), and females are 1.1–1.4 in (28–36 mm). The frogs have relatively powerful hind limbs; the finger and toe discs are clearly expanded, and the terminal phalangeal bones are T-shaped. The dorsal surface is smooth or granular and gray or brown with irregular darker brown patches. Ventrally, the skin is smooth and white with yellow suffusions on the lower abdomen and thighs.

distribution

The frog occurs only in the Clarke Range, mostly in Eungella National Park, in central and eastern Queensland, Australia.

habitat

Frogs are found on rocks, boulders, and waterfalls in fast-flowing streams at elevations of 490–3,280 ft (150–1,000 m) in disturbed and undisturbed rainforest.

behavior

This species is both diurnal and nocturnal and communicates visually by head bobbing and by waving the hind legs.

feeding ecology and diet

Nothing is known, but it probably feeds on arthropods.

reproductive biology

The call resembles a gentle rattling sound. Tadpoles have weakly keratinized jaws but lack labial tooth rows. The oral disc is small, almost ventrally positioned, and surrounded by a complete row of papillae—all adaptations to fast-flowing streams.

conservation status

This species is listed as Endangered by the IUCN. It was one of the stream frogs that partially vanished in the 1980s, but small relict populations appear to be maintaining themselves. The three largest populations are in the same catchment, and no populations are now known from the southern and northern areas of the former distribution.

significance to humans

None known.

Southern gastric brooding frog

Rheobatrachus silus

taxonomy

Rheobatrachus silus Liem, 1973, Kondalilla National Park, Queensland, Australia.

other common names

English: Southern platypus frog.

physical characteristics

This was a medium-size species; males were 1.3–1.6 in (33–41 mm), and females were 1.8–2.1 in (45–54 mm). The species had a small head with large, dorsally protruding eyes and powerful hind limbs with fully webbed toes. The dorsum was dull gray to slate with obscure darker and paler patches.

distribution

Apparently the range was restricted to the Conondale and Blackall Ranges in southeast Queensland.

habitat

This aquatic species usually was found in perennial streams in closed forest.

behavior

This frog was a strong swimmer but would drift in the water. The species was observed sitting on exposed rocks and was capable of traveling across land through moist habitat.

feeding ecology and diet

Insects were taken either from the stream surface or from surrounding rocks by grabbing with the mouth and using the hands to push in the prey.

reproductive biology

Males called with a soft pulsed note of about 33 pulses and a low dominant frequency. Females swallowed either the large, unpigmented eggs or the newly hatched tadpoles (not known which), and the entire development through metamorphosis took place inside the stomach; 18–25 young were brooded in this manner for six to seven weeks. Tadpoles were supplied with yolk, and neither they nor the mother fed throughout this period. The stomach wall became thin and vascular, and gastric acid secretion was switched off in response to prostaglandin E₂, which was secreted by the egg capsules and developing tadpoles. When fully formed, the young were released through the mother's mouth over a period of about six days. The female arched her back and dilated her esophagus, and the young were ejected onto her tongue and climbed out. About four days after birth of the last young, the female resumed feeding, and the stomach converted to its pregestation condition.

conservation status

This species is listed as Extinct by the IUCN and Environment Australia and has not been seen in the wild since 1981. The reasons for its disappearance remain unknown. The habitat was logged during their persistence in large numbers, and few frogs were collected for scientific purposes, but dead and dying frogs were seen in 1977.

significance to humans

The mechanisms for switching off acid secretion by these frogs are the same used in medicine today for gastric ulcers.

Resources

Books

Anstis, M. Tadpoles of South-eastern Australia: A Guide with Keys. Sydney: Reed New Holland, 2002.

Barker, John, Gordon C. Grigg, and Michael J. Tyler. A Field Guide to Australian Frogs. Chipping Norton, Australia: Surrey Beatty, 1995.

Campbell, A., ed. Declines and Disappearances of Australian Frogs. Canberra, Australia: Environment Australia, 1999.

Cogger, H. G. Reptiles and Amphibians of Australia. 6th edition. Sydney: Reed New Holland, 2001.

Cogger, H. G., E. E. Cameron, and H. M. Cogger. Zoological Catalogue of Australia. Vol. 1, Amphibia and Reptilia. Canberra, Australia: Australian Government Publishing Service, 1983.

Ehmann, H., and G. Swan. "Reproduction and Development in the Marsupial Frog Assa darlingtoni (Leptodactylidae: Anura)." In Biology of Australasian Frogs and Reptiles, edited by G. Grigg, R. Shine, and H. Ehmann. Chipping Norton, Australia: Surrey Beatty and Sons, 1985.

Littlejohn, M. J., M. Davies, J. D. Roberts, and G. F. Watson. "Family Myobatrachidae." In Fauna of Australia. Vol. 2A, Amphibia and Reptilia, edited by C. J. Glasby, G. J. B. Ross, and P. Beesley. Canberra, Australia: AGPS, 1993.

Roberts, J. D. "The Biology of Arenophryne rotunda (Anura: Myobatrachidae): A Burrowing Frog from Shark Bay, Western Australia." In Research in Shark Bay, Report of the France-Australe Bicentennary Expedition Committee, edited by P. F. Berry, S. D. Bradshaw, and B. R. Wilson. Perth, Australia: West Australian Museum, 1990.

Tyler, M. J., ed. The Gastric Brooding Frog. London and Canberra: Croom Helm, 1983.

Periodicals

Byrne, P. G., and J. D. Roberts. "Simultaneous Mating with Multiple Males Reduces Fertilization Success in the Myobatrachid Frog Crinia georgiana." Proceedings of the Royal Society Biological Sciences Series B 266, no. 1420 (1999): 717–721.

Liem, D. S., and W. Hosmer. "Frogs of the Genus Taudactylus with Descriptions of Two New Species (Anura: Leptodactylidae)." Memoirs of the Queensland Museum 16, no. 3 (1973): 435–457.

McDonald, K. R. Rheobatrachus Liem and Taudactylus Straughan and Lee (Anura: Leptodactylidae) in Eungella National Park, Queensland: Distribution and Decline. Transactions of the Royal Society of South Australia 114, no. 4 (1990): 187–194.

Mitchell, N., and R. Swain. "Terrestrial Development in the Tasmanian Frog Bryobatrachus nimbus (Anura: Myobatrachinae): Larval Development and a Field Staging Table." Papers and Proceedings of the Royal Society of Tasmania 130, no. 1 (1996): 75–80.

Mitchell, N., R. Swain, and R. S. Seymour. "Effects of Temperature on Energy Cost and Timing of Embryonic and Larval Development of the Terrestrially Breeding Frog Bryobatrachus nimbus." Physiological and Biochemical Zoology 73, no. 6 (2000): 829–840.

Read, K., J. S. Keogh, I. A. W. Scott, J. D. Roberts, and P. Doughty. "Molecular Phylogeny of the Australian Frog Genera Crinia, Geocrinia and Allied Taxa (Anura: Myobatrachidae)." Molecular Phylogenetics and Evolution 21, no. 2 (2001): 294–308.

Retallick, R. W. R., and J.-M. Hero. "The Tadpoles of Taudactylus eungellensis Liem and Hosmer and T. liemi Ingram (Anura: Myobatrachidae) and a Key to the Stream-Dwelling Tadpoles of the Eungella Rainforest in East-central Queensland, Australia." Journal of Herpetology 32, no. 2 (1998): 304–309.

Rounsevell, D. E., D. Ziegeler, P. B. Brown, M. Davies, and M. J. Littlejohn. "A New Genus and Species of Frog (Anura: Leptodactylidae: Myobatrachinae) from Southern Tasmania." Transactions of the Royal Society of South Australia 118, no. 3 (1994): 171–185.

Tyler, M. J. "Crinia tchudi (Anura: Leptodactylidae) from the Cainozoic of Queensland, with the Description of a New Species." Transactions of the Royal Society of South Australia 115, no. 2 (1991): 99–101.

Organizations

Environment Australia. GPO Box 787, Canberra, ACT 2601 Australia. Phone: 61 (2) 6274-1111. Web site: <http://www.ea.gov.au>

Margaret Davies, PhD