The Australian green tree frog (Ranoidea caerulea/Litoria caerulea), also known as simply green tree frog in Australia, White's tree frog, or dumpy tree frog, is a species of tree frog native to Australia and New Guinea, with introduced populations in the United States and New Zealand, though the latter is believed to have died out. It is morphologically similar to some other members of its genus, particularly the magnificent tree frog (R.splendida) and the white-lipped tree frog (R.infrafrenata).
Larger than most Australian frogs, the Australian green tree frog reaches 10cm (4in) or more in length. Its average lifespan in captivity, about 16 years, is long compared with most frogs. Docile and well suited to living near human dwellings, Australian green tree frogs are often found on window sills or inside houses, eating insects drawn by the light. The green tree frog screams when it is in danger to scare off its foe, and squeaks when it is touched.
Original print of the Australian green tree frog, published in John White's Journal of a Voyage to New South Wales. Artist: S. Stone
The Australian green tree frog is a member of the family Hylidae and is placed in the subfamily Pelodryadinae, which is endemic to Australia and New Guinea and includes over 100 species in the genera Ranoidea and Nyctimystes.[2] The common name of the species, "White's tree frog", is in honour of John White's first description in 1790.[3][4] The green tree frog was the first Australian frog to be scientifically described; the original specimen found its way into the collection of Sir Joseph Banks, but was destroyed when the Hunterian Museum at the Royal College of Surgeons in London was bombed in World War II.[5]
Young male specimen sitting on leaf
The species was originally called the "blue frog" (Rana caerulea) despite its green colour. The specimens White sent to England were damaged by the preservative and appeared blue.[3] The colour of the frog is caused by blue and green pigments covered in a yellow layer; the preservative destroyed the yellow layer and left the frog with a blue appearance. The specific epithet, caerulea, which is Latin for blue, has remained.[6] This frog is sometimes referred to as Pelodryas caerulea in the scientific literature.[6] In Australia, the frog is also known more simply as the "green tree frog", but that name is often given to the most common green arboreal species in a region, such as the American green tree frog (Hyla cinerea).
A 2020 study showed that Litoria caerulea is actually a species complex that includes recently identified species such as Litoria mira, which is endemic to New Guinea.[7]
Description
The green tree frog is a plump, rather large tree frog, and can grow up to 11.5cm (4.5in) in length, with fully grown females being slightly larger than males. A distinctive fatty ridge is seen over the eye, and the parotoid gland is moderately large. The iris is golden and has a horizontally slit pupil, and the tympanum (a skin membrane similar to an eardrum) is visible just behind the eye. The limbs are short and robust, and large adhesive discs are at the end of the digits which provide grip while climbing. The fingers are about one-third webbed, and the toes nearly three-quarters webbed. The dorsal colour depends on the temperature and nature of the environment, ranging from brownish- or greyish-green to bright emerald green. The frog occasionally has small, irregularly shaped white spots on its back. Males have a greyish, wrinkled vocal sac under the throat, while the throat of females is white. The ventral surface in both sexes is creamy-white and rough in texture.[3][8]
This frog is similar in appearance to the magnificent tree frog (R.splendida), which inhabits only north-western Australia. Older members of that species have very large parotoid glands, which cover the entire top of their heads and droop over their tympana. The parotoid gland of the green tree frog is much smaller, and it also lacks the yellow speckling on the back and the yellow markings on the hand, groin, and thigh.[9] It can be distinguished from the white-lipped tree frog (giant tree frog N.infrafrenatus) by the distinct white stripe that species has along the edge of the lower jaw and extending to the shoulder, which is not present in the green tree frog.[10]
Some arboreal hylid frogs, e.g. the Australian green tree frog (Litoria caerulea), benefit from two hygroscopically-enabled hydration processes; transcutaneous uptake of condensation on their skin and reduced evaporative water loss. Their wiping behaviour spreads hygroscopic secretions from the parotoid gland across their skin, facilitating both methods.[11]L. caerulea's skin structure, the hygroscopic coating and an advantageous temperature gradient combine to boost condensation and moisture uptake.
Tadpole
The tadpoles' appearance changes throughout their development. When newly hatched, they are 8mm (0.3in) long and when fully developed, 44mm (1.7in). They are initially mottled with brown, and increase in pigmentation (to either green or brown) during development. Their undersides are initially dark, but later become lighter in hue. The eggs are brown and are wrapped in a clear jelly; they are 1.1 to 1.4mm (0.043 to 0.055in) in diameter.[6]
The call is a low, slow brawk-brawk-brawk, repeated many times. For most of the year, the frogs call from high positions, such as trees and gutters, but during the breeding season, they descend to near the ponds and pools, where they breed. Like many frogs, green tree frogs call not only to attract a mate, but also to advertise their location outside the mating season. They are particularly vocal after rain, but the reasons for this are unclear. They emit a stress call when they are in danger, such as when being attacked by a predator or when a person steps on the log in which one is concealed.[8]
Distribution and habitat
Specimen climbing a tree
The green tree frog is native to northern and eastern regions of Australia and to the lowlands of New Guinea. Distribution is limited mostly to areas with warm, wet tropical climates. Its range spans from Irian Jaya to Port Moresby, and is most abundant on Daru Island. The IUCN suggests "scattered locations" in both New Guinea and Indonesia.[1] In Australia, its range extends from the Kimberley region of Western Australia through the Northern Territory and Queensland to north and central New South Wales and the extreme northeasterly part of South Australia. Its total extent of land occupancy is around 4,078,600 square kilometres (1,574,800sqmi).[12]
The species has been introduced to both the United States and New Zealand. In the United States, it is restricted to two regions within Florida, where it was possibly introduced through the pet trade. Only small populations have been found there, and whether they have caused any ecological damage as an invasive species is unknown.[13] In New Zealand, several individuals were liberated in various locations in 1897 and 1899, and a further accidental introduction was made in the 1940s. No sightings have been reported of this species since the 1950s.[14]
Depending on their location, green tree frogs occupy various habitats. They prefer moist forests but are not strictly limited to tropical rainforests.[8] They are often found in the canopy of trees near water bodies, but also occupy terrestrial habitats well away from water. They favour old stands of Eucalyptus, where the trees have hollows in which water collects. They are common along inland waterways and can survive in swamps (among the reeds) or in grasslands in cooler climates.[15]
Green tree frogs are little troubled by the presence of humans and often live in close association with them. They sometimes stray inside houses and are found in such places as sinks and toilets. They can also be found on outside windowsills at night, eating insects attracted to the light, and they may gather under outdoor lighting for the same reason.[3][15] They sometimes occupy tanks (cisterns), downpipes (downspouts), and gutters, as these have high humidity and are usually cooler than the external environment. They may be drawn to the downpipes and tanks during the mating season because the fixtures amplify their calls.[8] Green tree frogs seem to have homing abilities, being able to return to locations from which they were caught from a considerable distance after being displaced.[5]
Ecology and behaviour
An Australian green tree frog in a spider's web after eating the spider
Australian green tree frogs are very docile and unafraid of humans.[8] They are nocturnal[3] and come out in early evenings to call (in spring and summer) and hunt for food. During the day, they find cool, dark, and moist areas, such as tree holes or rock crevices, in which to sleep. They are not a rainforest species, but make use of the rain that falls almost daily and collects on leaves and in crevices, to keep themselves moist. Their skin exudes a waxy coating that helps prevent evaporation. In dry periods, they avoid desiccation by concealing themselves in a cool spot, perhaps by burrowing, and enveloping themselves in a cocoon made of shed skin and mucus.[8]
The diet of the green tree frog consists mainly of insects such as moths, cockroaches, and locusts. They also eat spiders and can include smaller frogs and even small mammals (including bats[16]) among their prey.[6][8]Frog teeth are not suited to cutting up prey, so the food item must be small enough to fit inside its mouth.
Green tree frogs often show up after rain
Many frogs flick out their sticky tongues at prey and the victim sticks to the tip and is drawn back into the mouth and consumed. A green tree frog uses this technique for smaller prey; for larger items, however, it pounces, then pushes the prey into its mouth with its hands.[5]
The frog has a few native predators, among them snakes and birds. Since the European settlement of Australia, non-native predators have been introduced, primarily dogs and cats.[17] The species has an average life expectancy in captivity of 16 years, but some have been known to live over 20 years.[8]
Reproduction
Breeding occurs between November and February.[12] During the mating season, the males call from slightly elevated positions close to the still-water sources in which they choose to breed.[8] Clumps of between 200 and 2000 eggs are laid which initially float, but sink within 24 hours. The development of the tadpoles takes about six weeks, after which they undergo metamorphosis and leave the water as juvenile frogs.
As pets
The green tree frog is one of the most popular pet frogs throughout the world. Its docile nature and long life expectancy make it an attractive choice for exotic pet owners. It is also one of the easier frogs to maintain; its diet is broad and it has a strong resistance to disease. One problem commonly associated with keeping this species as a pet is overfeeding; green tree frogs tend to become obese if overfed. In the wild, exertion of energy is required for a frog to capture its prey. However, in captivity, they are usually given live feed in a confined space. This lessens the activity needed for feeding, resulting in weight gain. An overweight member of the species deposits fat layers over the top of the head and body, giving it a "dumpy" appearance, thus the name "dumpy tree frog".[8][18]
The rover fireflies of the genus Photinus (including the common eastern firefly of North America) are poisonous to these frogs, and an incident has been reported in which a firefly was fed to a green tree frog, which subsequently died.[19]
In suburban areas, this frog is threatened by pollution and by predation by domestic animals. Also, some of the frogs have been found to be infected with the chytrid fungus which causes the fatal amphibian disease chytridiomycosis. The frog's status in New Guinea is poorly studied, but in 2002, some 75,000 individuals were exported from Indonesia as part of the pet trade, and this may impact populations in some locations. The frog is present in a number of protected areas in New Guinea, and it has been successfully bred in some Australian zoos. Overall, the main threat to this species is the potential for a widespread disease epidemic.[1]
Use in research
Although frogs have lungs, they absorb oxygen through their skin; for this to occur efficiently, the skin must be moist. A disadvantage of moist skin is that pathogens such as molds and bacteria can thrive on it, increasing the chance of infection. To counteract this, frogs secrete peptides that destroy these pathogens. The secretion from the paratoid gland of the green tree frog contains 25 caerins, a group of peptides with antibacterial and antiviral properties. The caerins produced by frogs of this species from different geographical localities have subtle but reproducible differences.[21] The secretions also contain caeruleins, which have the same physiological effects as CCK-8, a digestive hormone and hunger suppressant.[22] These caeruleins now have a number of clinical applications.[5] Several peptides from the skin secretions of the green tree frog have been found to destroy HIV without harming healthy T cells.[23][24][25]
The fungus Batrachochytrium dendrobatidis, the causal agent of chytridiomycosis, is causing declines in many species of amphibians, but the secretions produced by the green tree frog and certain other Australian species of frog (Litoria chloris and Litoria genimaculata) are protective against this fungus. The peptides inhibit the growth of the fungus in vitro and these frog species are believed not to be in decline.[26]
Green tree frogs are sometimes used as model animals in research.[27] The structure of their toe pads was used to investigate the microstructure and properties of the epithelium that allows the animals to adhere to wet surfaces.[28]
Related Research Articles
The cane toad, also known as the giant neotropical toad or marine toad, is a large, terrestrial true toad native to South and mainland Central America, but which has been introduced to various islands throughout Oceania and the Caribbean, as well as Northern Australia. It is a member of the genus Rhinella, which includes many true toad species found throughout Central and South America, but it was formerly assigned to the genus Bufo.
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura. The oldest fossil "proto-frog" Triadobatrachus is known from the Early Triassic of Madagascar, but molecular clock dating suggests their split from other amphibians may extend further back to the Permian, 265 million years ago. Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforest. Frogs account for around 88% of extant amphibian species. They are also one of the five most diverse vertebrate orders. Warty frog species tend to be called toads, but the distinction between frogs and toads is informal, not from taxonomy or evolutionary history.
The green and golden bell frog, also named the green bell frog, green and golden swamp frog and green frog, is a species of ground-dwelling tree frog native to eastern Australia. Despite its classification and climbing abilities, it does not live in trees and spends almost all of its time close to ground level. It can reach up to 11 cm (4.5 in) in length, making it one of Australia's largest frogs.
Ranoidea chloris, commonly known as the red-eyed tree frog or orange-eyed tree frog, is a species of tree frog native to eastern Australia; ranging from south of Sydney to Proserpine in mid-northern Queensland.
The white-lipped tree frog is a species of frog in the subfamily Pelodryadinae. It is the world's largest tree frog and is found in Australia. Other common names include the New Guinea treefrog, giant tree frog, and Australian giant treefrog.
The magnificent tree frog, also known as the splendid tree frog, is a species of tree frog first described in 1977. It has a limited range, only occurring on the north-western coast of Australia in the Northern Territory and Western Australia. It has a similar appearance to, and can be confused with, the closely related White's tree frog.
Tyler's tree frog or the southern laughing tree frog is an arboreal species of tree frog. It is native to eastern Australia where it occurs from south-eastern Queensland to the southern coast of New South Wales. It is generally a coastal species and is not found inland.
The Blue Mountains tree frog also called the variegated river tree frog is a species of tree frog in the subfamily Pelodryadinae. It is endemic to southeastern Australia and is found in eastern Victoria and in southeastern New South Wales. The Jenolan Caves tree frog, a population formerly separated as Litoria jenolanensis, is nowadays included in this species.
The dainty green tree frog, also known as the graceful tree frog, is a species of tree frog in the subfamily Pelodryadinae. It is native to eastern Queensland, and north-eastern New South Wales, Australia and ranges from northern Cape York in Queensland to Gosford in New South Wales, with a small and most likely introduced population in Hornsby Heights in Sydney. It is one of two faunal emblems of the City of Brisbane.
Amphibians of Australia are limited to members of the order Anura, commonly known as frogs. All Australian frogs are in the suborder Neobatrachia, also known as the modern frogs, which make up the largest proportion of extant frog species. About 230 of the 5,280 species of frog are native to Australia with 93% of them endemic. Compared with other continents, species diversity is low, and may be related to the climate of most of the Australian continent. There are two known invasive amphibians, the cane toad and the smooth newt.
Roth's tree frog, or the northern laughing tree frog, is a species of tree frog native to northern Australia and southern Papua New Guinea. Roth's tree frog is a common frog, closely related to Peron's tree frog and Tyler's tree frog.
The desert tree frog, or little red tree frog, is a species of tree frog native to Australia, southern New Guinea, and Timor. It is one of Australia's most widely distributed frogs, inhabiting northern Australia, including desert regions and much of temperate eastern Australia. It is one of the few Australian tree frogs to inhabit arid, tropical, and temperate climates.
Phyllomedusa bicolor, the giant leaf frog, bicolor tree-frog, giant monkey frog, or waxy-monkey treefrog, is a species of leaf frog. It can be found in the Amazon basin of Brazil, Colombia (Amazonas), Bolivia, and Peru, and can also be found in the Guianan Region of Venezuela and the Guianas, and in Cerrado of the state of Maranhão in Brazil.
The green-eyed treefrog is a species of Australasian treefrog in the subfamily Pelodryadinae that occurs in the Wet Tropics of Australia.
The Wendessi tree frog is a species of frog in the subfamily Pelodryadinae.
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This family of antibacterial peptides are secreted from the granular dorsal glands of Litoria aurea, Litoria raniformis, Litoria citropa and frogs from genus Uperoleia. Amongst the more active of these are aurein 1.2, aurein 2.2 and aurein 3.1; caerin 1.1, maculatin 1.1, uperin 3.6; citropin 1.1, citropin 1.2, citropin 1.3 and a minor peptide are wide-spectrum antibacterial peptides.
Michael J. Tyler dubbed "The Frog Man", was an Australian herpetologist and academic, noted for his research on frogs and toads, chiefly with the University of Adelaide.
Ranoidea mira, also known as the chocolate frog, is a species of tree frog in the subfamily Pelodryadinae, and is part of the Ranoidea caerulea species complex. It was discovered in New Guinea by a research team led by Griffith University.
Litoria viranula is a species of frog in the family Hylidae, endemic to New Guinea. It is in the same species group with Litoria bicolor.
↑ Oliver, Paul M.; Rittmeyer, Eric N.; Torkkola, Janne; Donnellan, Stephen C.; Dahl, Chris; Richards, Stephen J. (2020). "Multiple trans-Torres Strait colonisations by tree frogs in the Litoria caerulea group, with the description of a new species from New Guinea". Australian Journal of Zoology. 68 (1): 25. doi:10.1071/ZO20071. hdl:10072/404938. ISSN0004-959X.
↑ Waugh, Russell J.; Stone, David J.M.; Bowie, John H.; Wallace, John C.; Tyler, Michael J. (1993). "Peptides from Australian frogs. Structures of the caeridins from Litoria caerulea". Journal of the Chemical Society, Perkin Transactions 1. 5 (5): 573–576. doi:10.1039/P19930000573.
↑ Woodhams, Douglas C.; Rollins-Smith, Louise A.; Carey, Cynthia; Reinert, Laura; Tyler, Michael J.; Alford, Ross A. (2006). "Population trends associated with skin peptide defenses against chytridiomycosis in Australian frogs". Oecologia. 146 (4): 531–540. Bibcode:2006Oecol.146..531W. doi:10.1007/s00442-005-0228-8. PMID16205955. S2CID1325449.
↑ Von Esse, F. V.; Wright, K. M. (1974). "Effect of intracoelomic propofol in White's tree frogs, Pelodryas caerulea". Bulletin of the Association of Reptilian and Amphibian Veterinarians. 9 (7–8).
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