Introduction

(Main, 1992; Tyler, 1982; Tyler, 1994; Tyler & Davies, 1986)

The scientific species name of the green tree frog (caerulea) was taken from the Latin word for blue. In Europe, where specimens were first received, the preservative had turned them blue which was probably an unknown effect at the time. Originally named Rana caerulea, Litoria caerulea, was the first frog collected from Australia. The type specimen was collected by Joseph Banks, and was in the Hunterian Museum at the Royal College of Surgeons in London until destroyed in the blitz during WW2. It is protected in all states except South Australia. The earliest positive find of a 'caerulea type' fossil was from remains in the Lake Palankur area in South Australia which date from the Oliocene.

Young Adult

Taxonomy:

(Barker et al.,1995; Hutchison & Maxon, 1987; Tyler and Davies 1978.)

The 'caerulea' species group consists of Litoria caerulea, L. splendida, L. infrafrenata, L.cavernicola and L. gilleni. the closest related species group is the 'aruensis' group. Both L. caerulea and L. splendida have large head glands. In L. splendida these cover the entire head area whilst in L. caerulea they are located at the rear. The closest related species to L.caerulea is L. gilleni which is a smaller species. L. cavernicola differs as its vomerine teeth are situated behind the choanae and it entirely lacks the head glands.

Description

(Barker et al., 1995; Cameron and Cogger 1992; Clyne, 1969 ; Cogger, 1988 ; McDonald, 2000; Swan, 2001; Tyler & Davies, 1986; Tyler et al.,1994.)

Litoria caerulea is a large size, robust arboreal frog with both fingers and toes having enlarged prominent discs. It is variable and changeable in colour through light green, dark green, olive, brown or grey to even almost black. The skin of these frogs is highly pored. Its smooth dorsal surface can, in some regions, have white spots. The back of their thigh can appear dull pinkish or reddish brown. They have a white stripe along the hind edge of the lower leg and the outer edge of the fifth toe. The granular ventral area and throat are white although throats of breeding males may be green-tinged.The posterior of the thigh is pink to red-brown.They have a prominent glandular ridge above their eardrum, which
is easily seen. The irises of the eyes are heavily gold flecked. The tympanum is distinctive and large. Vomerine teeth are obvious and are found to the rear and between the choanae.Legs are moderately long and fingers one third webbed and their toes are three quarters
Both fingers and toes are webbed and webbing is well developed. Large inner and outer metatarsal tubercles are present.

Size (snout-vent). Recorded maximum for this species is 100mm. Maximum size for males is between 66mm and 77mm with females larger, ranging between 60 and 110mm.

Call

(Barker et al., 1995; Cameron and Cogger, 1992; Cogger,1985; Clyne, 1969; Frith, 1987; McDonald, 2000; Swan, 2001; Tyler, 1982; Tyler, 1995; Williams et al., 2000.)

Litoria caerulea's call is very loud and will often 'drown out' the calls of smaller and softer frogs within a chorus. Wark, wark wark:Cwark,cwark, cwark:' a deep cawk repeated continuously", a loud bark and various combinations of these are all attempts to describe the call in words. As with all frog calls identification is simpler by listening. (CLICK HERE) This frog can often be heard calling out of breeding season, from high in a tree, if the humidity is high or if it rains.These out of season calls aren't usually protracted. Breeding males will often stop their continuous calling if another male is close by and its call is out of sync and subsequently restart in synchronization. Litoria caerulea is also known to vocalize with a high pitched 'scream' when under attack by a predator.

Biology/Physiology etc.

( Davies and Withers, 1992; Chia et al,. 2000; Donnellan et al., 2000; Federale et al, 2006; Pukala et al 2006; Robbins and Rogers, 2006; Shine et al., 1989; Tracey and Christian, 2005; Swan, 2001; Tyler and Davies, 1978; Warburg et al, 2000; Williams et al, 2000; Williams et al, 2006; Young and Tracey, 2005)

One of the three largest Australian Anura, Litoria caerulea has a skull broader than it is long and cartilaginous intercalary structures. It possesses pedunculate alary processes on the hyoid plate.

Scientific research is isolating many different chemicals from the skin secretions and glandular secretions of the green tree frog, among others. Peptides from the skin in Litoria caerulea are known to contain antibiotic and anti-hypertension properties. Neuropeptides and anti-microbal peptides are secreted from the dorsal glands. These include caerins (named for this species). The composition of peptides seems to vary from area to area, perhaps from diet and/or genetic differences between discreet populations which may reflect phylogenic relationships and seasonality. Noxious bio active chemicals are also secreted from the hypertrophied parotoid glands, which may aid in defense. 33 peptides have been listed for Litoria caerulea. Within population studies of the peptide profiles have shown no great difference, whilst between population studies have shown they may vary considerably.These peptide profiles, in populations that have been tested, have shown that the greatest difference in the peptide load is between the Northern Territory and the Western Australian group (northern group) and the eastern group (roughly coastal Queensland). A further group in PNG has also been reviewed. Future investigations into these differences may reveal sub-species. Other tests done show that some combination of chemicals in the skin or other glands effectively repel mosquitoes. Both sexes have all types of glands. Hybrid offspring between between L. caerulea and L. splendida have been successfully raised in captivity and have yielded skin peptides from both parents as well as peptides different from either parent. Caerulean, previously extracted from this species, is now manufactured artificially and is used in humans to regulate blood pressure.

Able to tolerate high temperatures, Litoria caerulea has been shown to have a body temperature close to ambient, diurnally, when exhibiting its water holding posture. It has shown a moderate to relatively high cutaneous resistance to water loss, year round - when compared to other species. The Litoria caerulea skin secretions also contain 30% lipids which are partially credited with this species' remarkable ability to withstand dry conditions with little shelter in arid zones whilst losing comparatively little water. Lipids are also present in the parotoid glands as well as cutaneous glands. Litoria caerulea has been found to be capable of very fast water uptake through the skin, even when highly dehydrated, as soon as it is available.

The green tree frog possesses a primitive kind of tongue system called "mechanical-pulling tongue mechanism". The tongue is relatively short (for frogs) and so the entire body is used to 'pounce' at prey with the tongue protruding only 60% of the length of the jaw. Some findings suggest that L.caerulea may be 'right-handed", when it comes to climbing, inferring cerebral lateralization

L. caerulea has large pads and the remarkable ability to cling to the smoothest surfaces ie: window glass. Tests conducted on this capability show that this achieved by a combination of mucous secretions, the regular hexagonal shape of the pad cells and boundary friction between the cells and the surface adhered to. A suggestion has been made that tyre designers could learn a lot from this.

This species has a diploid chromosome number of 26

Typical breeding habitat for this species on Magnetic Island

Ecology and Behaviour

(Barker et al., 1995; Cameron and Cogger,1994; Cogger, 1988; Clyne, 1969; Friend and Cellier, 1990, Frith, 1987,1995 , Shine et al., 1989, Smith et al., 2003, Smith et al., 2004; Swan, 2001; Tyler, 1994; Tyler,1982; Tyler and Davies, 1992; Tyler et al 1994; Williams et al., 2000)

Good jumpers and climbers, Litoria caerulea is able to live up to 23 years in captivity. Although in no danger of extinction, loss of habitat has possibly caused the disappearance of Litoria caerulea from many populated urban and city areas, including Sydney, where they once thrived. They can diurnally occupy rock crevices, trees, hollow logs, bushes, ground vegetation, swamps, stream sides and human structures such as toilets etc. One study in the Northern Territory showed that although Litoria caerulea can be found in a wide variety of habitats in the wet season, in the dry times they were mostly found in taller trees outside the monsoon forest areas such as melaleuca spp. They appear to have a 'homing' ability, in such, that if they are removed from their territory they will quickly return. Tolerant of handling by humans L. caerulea tend to disregard their presence.

Active nocturnal predators, the diet of adults is thought to be mostly seasonally available insects but large specimens have been known to consume small birds, bats, mice and even reptiles as well as other frogs. On Magnetic Island Litoria caerulea has been observed hunting on the ground as well as arborally ,on rocky outcrops and high on human structures. Specimens studied in the Northern Territory revealed a preference for hunting place rather than a preference between food species (insects). Individuals 'pounce and grab with mouth and tongue and use their arms and hands to 'push' food into their mouths. Their eyes are without bony sockets and are thought to assist swallowing.

As mentioned previously Litoria caerulea is a very effective water conserver and has the ability to lose up to 45% of body water before dying. Tests conducted in 1969 showed that water loss in individuals can be halved when they engage in 'congregation' behaviour. As the title suggests numbers of Litoria caerulea group together,diurnally in a shelter, such as a hollow limb with their lateral surfaces pressed together in addition to utilising their normal 'water holding' positions .In conditions where water is readily available , this species is known to 'sun bask'

Head butting movements with the hind end raised and the body partially inflated are thought to be a defensive posture associated with noxious secretions from the large paratoidal glands.The secretion of these chemicals is preceded with an odour that has been described as "nutty". The odour producing chemical has been identified as a cyclic amide 2-pyrrolidone. In a confined space with prolonged exposure this chemical may even effect people. It is thought that the smell is produced as a warning of the release of more noxious chemicals such as histamines and seratonin which are believed to irritate the sensitive tissues inside the mouth of a potential predator. Predators include birds ie: kookaburras, currawongs etc.,snakes and varanids as well as carnivorous mammals.

Reproduction

(Anstis, 2003; Barker et al, 1995; Dziminski and Alford, 2005; Lee and Jamieson, 1993; Tyler and Davies, 1978; Tyler and Davies, 1986; Tyler, 1994; Tyler et al., 1994)

This species is widely distributed so the breeding season will vary geographically and climatically
Generally calling begins with the first heavy summer rains in November/December. Season finishes Feb-Mch depending on local conditions.Tree heights provide calling positions for males, nocturnally, leading into the breeding season. Then they will descend to the ground, head for water and use rocks and lower vegetation to provide adjacent calling perches just above ground level. On Magnetic Island this species has been heard calling throughout the entire season (pers obs). Males capture and hold females in amplexis driving them into water. Amplexicant couples prefer still waters but where these are unavailable they will use running water.

During amplexis, females lay between 200 and 3000 eggs (Clutch size measured in the Townsville area varied between 1570 and 4406 (Dzimiinski, 2000 in Anstis)). In this species there is a positive correlation between the the mass of the female and the number of eggs per clutch. The intense pressure under which the females release their eggs can propel them through the sperm mass (fertilizing them as they go) to a distance of up to 500cm further. Ovum colour is off-white at the vegetable pole and dark brown at the animal pole. The spermatozoon of the males of this species and the other genus members have a similar morphology and size. In Litoria caerulea it is approximately 18µm long with a tail length of 35µm.

Large clumps of spawn are formed in a roughly circular patch on the water surface, sinking within 24 hrs to the substrate. Fertilised eggs have a diameter of apx. 1.1 - 1.4mm. Hatching usually occurs 3-4 days after fertilisation.

Tadpoles are moderately large, mottled brown in colour and have a roughly oval body shape when viewed from above. The tooth formula is 2,2/3. They are roughly cylindrical to roundish in shape and their abdomen sections are wider across than deep. They have a roundish shaped snout with eyes at the sides that have a goldish coloured iris. A sheen of copperish gold covers the underside. Their tails are arched to a high degree and tail musculature may be striped.They have been known to reach a sizes of 45-130mm. Tadpoles predominantly consume vegetable matter and have a wide range - between surface and substrate.

Tadpoles have usually metamorphosised in 4-5 weeks (38 days at a temperature of 30°C has been recorded).The time to metamorphosis point will always vary in length depending on the local environmental conditions ie temperature, evaporation.Tadpoles of this species have been known to over-winter. Metamorphs resemble adults but have a dark brown stripe along the side of the head which has disappeared by the juvenile stage (older than a few weeks). Metamorphs on Magnetic Island have been observed, in numbers, sun basking on grass beside running waters (Pers obs.). Small metamorphs may be daytime active to avoid being consumed by their elders.

Metamorph

L. Corbett /C. Lane

Amplexis                            

      metamorph                                    

All photos taken by C. Lane unless otherwise credited

Audio: C. Lane