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Green and golden bell frog

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Green and Golden Bell Frog
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Amphibia
Order:
Anura
Family:
Hylidae
Genus:
Litoria
Species:
L. aurea
Binomial name
Litoria aurea

The Green and Golden Bell Frog (Litoria aurea) is a ground-dwelling tree frog native to eastern Australia. It is also known as the Green Bell Frog, Green and Golden Swamp Frog and Green Frog. Measuring 11 centimetres (4.3 in) in length, the Green and Golden Bell Frog is one of the largest Australian frogs.

Many populations, particularly in the Sydney region, are in areas of frequent disturbance, including golf courses, disused industrial land, brick pits and landfill areas. Once one of the most common frogs in south-east Australia, the Green and Golden Bell Frog has undergone major population declines, leading to its current classification as globally vulnerable. Population numbers have continued to decline and major threats include habitat loss and degradation, pollution, introduced species, and parasites and pathogens, such as the amphibian chytrid fungus.[1]

Taxonomy

The common name, "Green and Golden Bell Frog", was first adopted by Harold Cogger in his 1975 book Reptiles & Amphibians of Australia. Before Cogger's book, its common names were "Golden Frog" and "Golden Treefrog". The Green and Golden Bell Frog has many physical and behavioural characteristics representative of ranids, and was therefore originally classified as Rana. It has a pointy snout, long legs, and almost complete toe webbing; the tympanum is large and distinct and the overall body shape is similar to many Rana species. Many frogs in the Rana genus are mostly aquatic, and only travel over land during periods of rainfall, as does the Green and Golden Bell Frog. It was removed from the genus because of several anatomical differences with the family Ranidae. The bone and cartilage structural formations of the Green and Golden Bell Frog are closest to those of species in the family Hylidae, hence the move from Ranidae to Hylidae.

Litoria aurea (left) was first classed as a species of the genus Rana (right). There are many physical similarities including a pointy snout, long legs, and almost complete toe webbing. The overall body shape is similar to many Rana species.

The Green and Golden Bell Frog was first described as Rana aurea by Lesson in 1827. It has since undergone 20 classification changes, and was first named Litoria aurea 37 years later by Günther, only to be changed another nine times before being described again as Litoria aurea.[2] The species is now classified within the Litoria aurea complex, a closely related group of frogs in the Litoria genus. This complex is scattered throughout Australia, with three species occurring in south-east Australia, one in northern Australia and two in south-west Western Australia. The complex consists of the Green and Golden Bell Frog (Litoria aurea), Growling Grass Frog (Litoria raniformis), Tablelands Bell Frog (Litoria castanea), Dahl's Aquatic Frog (Litoria dahlii), Spotted-thighed Frog (Litoria cyclorhynchus) and the Motorbike Frog (Litoria moorei). The ranges of both L. raniformis and L. castanea overlap with the Green and Golden Bell Frog; this as well as physical similarities may make it difficult to distinguish between the species. The Tablelands Bell Frog has not been seen since 1980 and may now be extinct, although the large yellow spots present on its thighs help distinguish it from the Green and Golden Bell Frog. The Growling Grass Frog, which is very similar to the Green and Golden Bell Frog, can only be readily distinguished by raised bumps on the dorsal surface.

Distribution

File:Aurea Distribution.PNG
The historic (grey) and the current (black) distribution of the Green and Golden Bell Frog
File:Laurea range in New Zealand.PNG
The distribution of Litoria aurea in New Zealand

The Green and Golden Bell Frog is native to south-eastern Australia. Prior to its population decline, the distribution ranged from Brunswick Heads, in northern New South Wales, to East Gippsland, in Victoria[3] and west to Bathurst, Tumut and the Australian Capital Territory.[4]

The current distribution now ranges from Byron Bay in northern New South Wales to East Gippsland in Victoria, with populations mostly occurring along the coast. In New South Wales, it has undergone severe declines in both range and abundance since the 1960s. However, no similar declines have been reported in Victoria. In New South Wales it has disappeared from all highland areas above 250m (820 ft) except for a population at Captains Flat. A study of populations along coastal New South Wales indicated that many of them are very small, usually consisting of fewer than 20 adults. However, there are six known populations that support more than 300 individuals. Two are located in the Sydney metropolitan area, two in the Shoalhaven and another two on the New South Wales mid-north coast.[5] It is estimated that the Green and Golden Bell Frog has disappeared from at least 90% of its former range.

The Green and Golden Bell Frog survives in some areas of Sydney, one of which is the Brickpit at Homebush Bay (the proposed site for the tennis courts for the 2000 Sydney Olympics). When the Green and Golden Bell Frog was found in the Brickpit, the tennis courts were built at another location, and the population has been monitored since its discovery. The Green and Golden Bell Frog has become an unofficial mascot for the Homebush Bay area.

The Green and Golden Bell Frog occurs on two islands off the east coast of Australia: Broughton Island off Port Stephens and Bowen Island at Jervis Bay. It has been introduced to New Zealand, where it has become common, and to the Pacific Islands of New Caledonia and New Hebrides.

Physical description

A Green and Golden Bell Frog with a mostly bronze colouration.

The Green and Golden Bell Frog is a large, stout frog, with adults ranging from 4.5 cm (1.8 in) to 11 cm (4.3 in) in length. However, typical specimens measure 6–8 cm (2.4–3.2 in).[6] This makes the Green and Golden Bell Frog one of the largest Australian frogs. Mature male Green and Golden Bell Frogs are generally smaller than mature females, and the colour of the dorsal surface varies greatly in both sexes. It may be almost completely green, of shades from dark pea-green to bright emerald; green with metallic, brassy, dull copper-brown, or gold markings; or almost completely bronze. During the cooler months (May-August), however, when the frogs are inactive, colouration may darken to almost black.

A creamy-white or pale yellow stripe, bordered above with gold and below with black, extends from behind the eye, across the tympanum to the groin. This stripe rises to form a dorso-lateral fold towards the groin. Another stripe of the same colour begins below the eye and continues to the shoulder. The abdomen is cream or white, and has a coarsely granular texture. The legs are green, bronze, or a combination of both, and the inside thigh and groin are blue-green. Males develop a yellowish colouration to the vocal sac on the throat when mature. The pupil is restricted to a horizontal slit and the iris is golden-brown with a black streak that runs from the corners of the pupil to the horizontal limits of the eye. The tympanum is distinct and ovular in shape. The Green and Golden Bell Frog has enlarged toe discs to aid in climbing. The fingers are free from webbing and the toes are almost completely webbed, as this species is often found in water. When in breeding condition, males develop nuptial pads on their thumbs, which are used to grip females during mating.

Ecology and behaviour

A member of the tree frog family, the Green and Golden Bell Frog spends much time basking in the sun on rocks and reeds. It is unusual as frog in that it is often active during the day. When handled, this species secretes a slimy acrid mucus.[7] This substance consists of 17 aurein peptides, with 13 showing broad-spectrum antibiotic and anti-cancer activity; these assist in fighting off harmful microorganisms.[8]

The Green and Golden Bell Frog is generally associated with coastal swamps, woodland, and forest. However, populations have also been found at former industrial sites (e.g., the Brickpit). Its habitat requirements have been difficult to determine, as it has been found in a wide range of water bodies except fast-flowing streams.[9] It is most typically found in short-lived freshwater ponds that are still, shallow, unshaded and unpolluted, and it tends to avoid waters that contain predatory fish, whether native or introduced. The frog prefers water bodies that support emergent vegetation such as reeds and bullrushes for basking, and winter habitats consist of available shelters around the breeding site. Grassy habitats are usually close at hand to provide suitable terrestrial feeding grounds.

The Green and Golden Bell Frog reproduction depends on water temperature and salinity. Salinity affects tadpole development and metamorphosis, while breeding generally only occurs in ponds that measure 20°C or above. The Green and Golden Bell Frog tadpoles are able to tolerate salinity levels of six parts per thousand (ppt) without any apparent effects, while salinity of 8 ppt or higher decreases growth rates and increases mortality rates. On the other hand, salinity levels of at least 1-2 ppt can be beneficial to the Green and Golden Bell Frog because this kills pathogens such as the chytrid fungus.[10]

The voracious adults have a very broad diet, including insects and other frogs, even of the same species. The tadpoles feed on detritus, algae and bacteria. Natural predators include wading birds and snakes, and the tadpoles are taken by tortoises, eels and other fish as well as a range of invertebrate predators.

Reproduction

The Green and Golden Bell Frog breeds in the warmer months from October to March. During the breeding season, males call whilst floating in the water. The call is a deep growl which has been described as a four-part "craw-awk, crawk, crok crok" that has been likened to the sound of a motorbike changing gears. An average of 5000 eggs are deposited amongst aquatic vegetation in a gelatinous mass, but a clump of 11682 has been recorded.[11] Initially the mass floats, but sinks up to 12 hours after laying, or when disturbed. Two to three days later, the tadpoles hatch out and will complete metamorphosis between 2 and 11 months, depending on the temperature of the water and available food.[12] Breeding occurs in a significantly higher proportion of sites where no predatory fish are present and water bodies are ephemeral rather than permanent. Populations in Victoria, however, have been recorded as breeding in permanent ponds as readily as they do in ephemeral ponds.[13]

The tadpoles of the Green and Golden Bell Frog are large, reaching 80 mm (3.15 in) in length, but size varies greatly, with smaller tadpoles being more common. The body is usually as wide across as it is deep. The fin has a yellow tinge and is considerably arched. The musculature is moderate and tapers to a fine point as does the fin. The body wall is translucent yellow with darker areas over the abdomen. Just before its limbs form, the tadpole begins to develop the greenish colouration of the adults. Metamorphs resemble the adults and average about 2.6 cm (1 in) in length.

Conservation status

The numbers of Green and Golden Bell Frogs are estimated to have declined by over 30% in the past ten years.[14] It is listed as globally and nationally vulnerable, and as endangered under the New South Wales Threatened Species Conservation Act, 1995. There are many factors thought to be responsible for the dramatic decline of this species. Habitat fragmentation, the introduction of predatory fish and alteration of drainage regimes all seem to be involved. Population declines are closely related to the introduction of the Eastern Mosquitofish (Gambusia holbrooki), a species native to North America that has been introduced in an attempt to control mosquito larvae. Laboratory studies have demonstrated that the tadpoles of the Green and Golden Bell Frog are extremely susceptible to predation by this fish. Other factors thought to affect this species include predation by introduced mammals such as cats and foxes, changes to water quality at breeding sites, herbicide use, and loss of habitat through the destruction of wetlands. Although, because of this species ability to survive in degraded, polluted environments; habitat destruction and pollution are unlikely to be the main causes of population declines. The amphibian chytrid fungus appears to have led to at least some, and perhaps most, of the major declines observed through the 1970s and 1980s.

The Green and Golden Bell Frog has been the subject of much research and monitoring. This is important to the improvement of conservation measures. This research focuses on the development of management measures to keep the introduced mosquitofish under control. Other strategies being devised will allow for the development and improvement of suitable habitat, to increase the reproductive success of the species. Parallel to these measures, community awareness programmes have also been proposed.

In 1998 a captive breeding program was set up by the herpetofauna staff at Taronga Zoo in Sydney, sponsored by the ASX Frog Focus. The purpose of the program was to help preserve declining populations of Green and Golden Bell Frogs in the Sydney region. It involved the captive breeding of wild frogs and releasing large numbers of tadpoles back into the wild, habitat restoration and post-release monitoring. The program was intially titled Frog Focus Botany as Botany was the orginal focus site. Thousands of tadpoles were released into a site in Sir Joseph Banks Reserve and post-release monitoring was done by the local community. It was also the first time that school students had been involved with endangered species monitoring.[15] The program has since branched off into several other areas. Between 1998 and 2004, tadpoles were released into specially designed ponds and dams on Long Reef Golf Course at Collaroy in northern Sydney. Green and Golden Bell Frogs had previously been located in the area, however the population had since been lost. Although a large number of tadpoles were released during the program it had almost no success. Adult Bell Frogs are occasionally found on the golf course, however a permanent breeding population is yet to be established.

Notes

  1. ^ "IUCN Redlist - Information on classification and treats of Litoria aurea". Retrieved 2006-07-27.
  2. ^ "American Muesum of Natural History, Amphibian Species of the World - Synonymys of Litoria aurea". Retrieved 2006-07-27.
  3. ^ Gillespie G.R. 1996. "Distribution, habitat and conservation status of the Green and Golden Bell Frog Litoria aurea (Lesson, 1829) (Anura: Hylidae) in Victoria." Australian Zoologist 30: 199-207.
  4. ^ Osborne W.S., Littlejohn M.J. and Thomson S.A. 1996. "Former distribution and apparent disappearance of the Litoria aurea complex from the Southern Tablelands of New South Wales and the Australian Capital Territory." Australian Zoologist 30: 190-198.
  5. ^ White A.W. and Pyke G.H. 1996. "Distribution and conservation status of the Green and Golden Bell Frog Litoria aurea in New South Wales." Australian Zoologist 30 (2): 177-189.
  6. ^ White A.W. and Pyke G.H. 1996. "Distribution and conservation status of the Green and Golden Bell Frog Litoria aurea in New South Wales." Australian Zoologist 30 (2): 177-189.
  7. ^ Barker, J.; Grigg, G.C.; Tyler, M.J. (1995) Surrey Beatty & Sons.. A Field Guide to Australian Frogs - The Litoria aurea complex, page 99.
  8. ^ "The antibiotic and anticancer active aurein peptides from the Australian Bell Frogs Litoria aurea and Litoria raniformis the solution structure of aurein 1.2. - Tomas Rozek, Kate L. Wegener, John H. Bowie, Ian N. Olver, John A. Carver, John C. Wallace and Michael J. Tyler - The FEBS Journal". Retrieved 2006-08-06. {{cite web}}: Check |url= value (help)
  9. ^ "Habitat requirements for the green and golden bell frog Litoria aurea (Anura: Hylidae) - Pyke, GH; White, AW - Australian Zoologist. May 1996". Retrieved 2006-08-01.
  10. ^ "Green and Golden Bell Frog Management Plan Part 11" (PDF). 2005. Retrieved 2006-07-29. (PDF)
  11. ^ van de Mortel, T.F. and Goldingay, R. 1996. "Population assessment of the endangered Green and Golden Bell Frog Litoria aurea at Port Kembla, New South Wales." Australian Zoologist. 30(4):398-404.
  12. ^ Daly, G. 1995. "Observations on the Green and Golden Bell-Frog Litoria aurea (Anura: Hylidae)." Herpetofauna. 25(1):2-9.
  13. ^ Gillespie, G.R., 1996. "Distribution, habitat and conservation status of the Green and Golden Bell Frog Litoria aurea (Lesson 1829) (Anura: Hylidae) in Victoria." Australian Zoologist 30, 199–207.
  14. ^ "IUCN RedList - Litoria aurea (under "Justification")". Retrieved 2006-07-31.
  15. ^ "Taronga and Western Plains Zoo - Frog Focus Botany". Retrieved 2006-08-06.

References

External links

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