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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 tree frog native to eastern Australia. Also known as the Green Bell Frog, Green and Golden Swamp Frog and Green Frog, the Green and Golden Bell Frog is large compared to other Australian frogs, at a length of up to 11 centimetres (4.3 in), 3 centimetres (1.2 in) shorter than the Giant Tree Frog (Litoria infrafrenata), Australia's largest frog. 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, parasites and pathogens, such as the amphibian chytrid fungus.[1]

Taxonomy

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

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 not kept in the genus Rana because of several anatomical differences between the Green and Golden Bell Frog and the family Ranidae. The bone and cartilage structural formations of the Green and Golden Bell Frog are closest to that of species in the family Hylidae, hence the move from Ranidae to Hylidae.

The Green and Golden Bell Frog was first described as Rana aurea by Lesson in 1827. It has since undergone 20 scientific classification changes, and was first named Litoria aurea 37 years later by Günther, only to be changed another 9 time before being redescribed as Litoria aurea.[2] The species is now classified within the Litoria aurea complex. 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 constists of the Green and Golden Bell Frog (Litoria aurea), Growling Grass Frog (Litoria raniformis), Yellow Spotted Tree Frog (Litoria castanea), Dahl's Tree Frog (Litoria dahlii), Spotted Thighed Frog (Litoria cyclorhynchus) and the Western Green and Golden Bell Frog (Litoria moorei). Only the ranges of L. raniformis and L. castanea overlap with the Green and Golden Bell Frog, and the general body shape and colouration are similar. The Yellow Spotted Tree Frog has large yellow spots present in the thighs and not being seen for a number of years and may now be extinct, 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
Current distribution of Litoria aurea in black against the historical distribution in grey.
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 northen 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 are very small, usually consisting of less than 20 adults. However, there are six know 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]

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 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 centimetres (1.8 in) to 11 centimetres (4.3 in) in length. However, typical specimens measure 6–8 centimetres (2.4–3.2 in).[6] 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. However, during the cooler months (May - August) 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 restricts 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 clearly 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 have swollen thumbs, as they develop nuptial pads used to grip females during mating.

Ecology and behaviour

The Green and Golden Bell Frog is a member of the tree frog family, spending a large amount of time basking in the sun on rocks and reeds. They are unusual, in that they are often active during the day. When handled this species secretes a slimy acrid mucus.[7] This substance consists of seventeen aurein peptides, with thirteen showing wide-spectrum antibiotic and anticancer activity, this assists in fighting off harmful micro-organisms.[8]

The Green and Golden Bell Frog is associated with coastal swamps, woodland, forest and populations have been found in dis-used industrial sites (eg; 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. Water bodies that support emergent vegetation such as reeds and bullrushes for basking are preferred, 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 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. Eggs are laid amongst aquatic vegetation. An average of 5000 eggs are deposited in gelatinous mass, but a clump of 11682 has been recorded.[10] 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.[11] Breeding occurs in a significantly higher proportion of sites where no predatory fish are present and water bodies are ephemeral rather than permanent. However populations in Victoria have been recorded as breeding in permanent ponds as readily as they do in ephemeral ponds.[12]

The tadpoles of the Green and Golden Bell Frog are large, reaching 80mm 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 their limbs form, the tadpoles begin to develop the greenish colouration of the adults. Metamorphs resemble the adults and average around 2.6 centimetres (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.[13] It is listed as globally and nationally vulnerable, and under the New South Wales Threatened Species Conservation Act, 1995, endangered. 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. Losses of this frog are closely related to the introduction of the Eastern Mosquitofish (Gambusia holbrooki), native to North America and introduced as 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. Given this species ability to live in disturbed habitat, pollution and habitat loss are unlikely to be the main cause of the population decline, although they may contribute. 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. Such research is focusing on the development of management measures to keep the introduced mosquito fish under control. Other strategies being devised will allow the development and improvement of suitable habitat in order to increase the reproductive success of the species. In parallel to these measures, community awareness programmes have also been proposed.

Green and Golden Bell Frog reproduction depends on temperature and salinity of the water. Salinity affects tadpole development and metamorphosis, while breeding generally only occurs in ponds that are 20°C or above. Green and Golden Bell Frog tadpoles are able to tolerate salinity levels of 6 parts per thousand (ppt) without any apparent affects, while salinity of 8 ppt and above 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.[14] Both these factors need to be taken into account when planning for the development of Green and Golden Bell Frog habitat.

Cited references

  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." Aust. Zool. 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. ^ 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.
  11. ^ Daly, G. 1995. "Observations on the Green and Golden Bell-Frog Litoria aurea (Anura: Hylidae). Herpetofauna." 25(1):2-9.
  12. ^ 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.
  13. ^ "IUCN RedList - Litoria aurea (under "Justification")". Retrieved 2006-07-31.
  14. ^ "Green and Golden Bell Frog Management Plan Part 11" (PDF). Retrieved 2006-07-29.

References

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