Common mist frog

Common mist frog
Conservation status
Endangered (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Anura
Family:	Hylidae
Genus:	Ranoidea
Species:	R. rheocola
Binomial name
Ranoidea rheocola (Liem, 1974)
Synonyms
Mosleyia rheocola (Wells & Wellington, 1985) Litoria rheocola Liem, 1974

Litoria rheocola, more commonly known as the Common Mist frog, is a species of tree frog native to north-eastern Queensland, Australia. Litoria rheocola is a medium-sized frog and is an Australian Torrent Treefrog (Litoria nannotis group). The common mist frog is found in remote, mountainous areas, and near rocky, fast-flowing rainforest streams such as those in northeastern Queensland, Australia. They are rather sedentary frogs, which keeps them mostly restricted to the stream environments that they are born into, preferring sections of the stream with riffles, many rocks, and overhanging vegetation.

Characteristics

Male vs. Female

Fully grown Litoria rheacola can measure anywhere from 27 to 41 millimeters in length and often weigh between 1.2 and 4.5 grams. Female Litoria rheocola are larger than males. Whereas males measure at around 31 millimeters in length, the female mist frog is on average 36 millimeters long. Similarly, the average adult male mist frog weighs an average of 2.0 grams while the adult female mist frog averages around 3.1 grams.

Physical Appearance

The common mist frog is a dull grey or brown color in appearance, with tubercles (small rounded protrusions) and dark, irregular markings on its dorsal surface. The frog’s underside is characterized by granular white skin. The common mist frog will also often have a distinct line between its eyes. Like many other frogs, the mist frog’s fingers are partly webbed, with webbing reaching the second-subarticular tubercle at the end of the first phalanx, and its toes are completely webbed. Both their fingers and toes have large discs. The mist frog’s tympanum (outer ear) is covered by a layer of skin, but is still visible. Litoria rheocola have a relatively slender build and possess a protruding, triangular snout.

The common mist frog has obscure dark bands that run along the side of its snout from the eye and ear to the shoulder. The male nuptial pads are small and unlike other male Torrent Treefrogs, they do not have enlarged arms. Additionally, the tips of their snouts are pointed.

Litoria rheocola tadpoles have large mouthparts that they use to cling to nearby rocks. They also possess muscular tails that aid in swimming against a current. mist frog tadpoles have been described as torrent-dwelling, and having flat bodies, with large suctorial mouthparts.

Ecology and Behavior

A common mist frog in the posture for water conservation

The Common mist frog inhabits the riparian zone of fast-flowing streams in rainforests and wet sclerophyll forests of eastern tropical North Queensland. Males call from the edge of the streams, between rocks, or in overhanging vegetation to attract mates. The call is a long "wreek" sound. Breeding occurs throughout the year, with peak calling occurring between November and March. About 46-63 eggs are laid beneath rocks, to prevent them from being washed away with the stream. The tadpoles are stream-dwellers, and have suctorial mouthparts to allow them to survive in fast-flowing water.

Male common mist frogs have a repetitive rising ‘wreek’ call, which can be heard throughout the entire year. This call is most easily heard during the warmer seasons as the males are typically quieter in colder temperatures. Litoria rheocola display sex-specific variations in foraging behavior. This results in male and female common mist frogs having very different diets and eating patterns. Male mist frogs tend to have more restricted foraging activity than females and also display greater fidelity to a specific breeding site.

Habitat and Distribution

Map of the Wet Tropics of Queensland

The common mist frog can be found throughout the Wet Tropics of Queensland, Australia from north of Ingham to the Big Tableland south of Cooktown, as well as from the Broadwater Creek National Park to Amos Bay, northern Queensland, Australia. Litoria rheocola are primarily found along rainforest streams, near riffles, cascades, and waterfalls, as well as in wet sclerophyll forests. They have been observed perching on vegetation, rocks, logs, and roots along streams. During the day, they can also be found in piles of leaves beside flowing streams. They also have been found inhabiting similar streamside microhabitats outside of rainforests. The common mist frog used to inhabit areas from sea level to mountainous areas reaching an elevation of 1200 meters. However, the mist frog can no longer be found in habitats that are above 600 meters, having disappeared from sites above this altitude in the early 1990s. In fact, it is now even rare to find the mist frog in habitats that are above 400 meters. Due to such environmental constraints, the common mist frog’s area of occupancy has been restricted to approximately 6000 square kilometers in total.

Endangerment

A key factor that is largely responsible for the common mist frog’s (and other Australian Torrent Treefrogs’) endangered status is Chytridiomycosis. Chytridiomycosis is a disease that is caused by the chytrid fungus Batrachochytrium dendrobatidis. This parasitic fungus attacks the skin cells of amphibians and disrupts their osmoregulatory and transport functions, altering electrolyte concentrations in the blood. This disease can ultimately cause cardiac arrest once the fungal population on the host organism reaches a high enough density. B. dendrobatidis is strongly influenced by temperature, with the optimal temperature for growth being between 15 and 20 degrees Celsius. Due to the pathogen's vulnerability to temperature, the prevalence of this disease among amphibians is strongly connected to the seasons. The common mist frog and other frogs in similar habitats are more vulnerable to infection by B. dendrobatidis during the colder months, especially in areas of higher elevation. By the mid-1990s, chytridiomycosis had eliminated the majority of Litoria rheocola at elevations greater than 400 meters above sea level. Habitat modification has also greatly impacted the species, with about 20% of tropical rainforests in northeastern Queensland being cleared in 1983. The common mist frog has disappeared from most upland sites south of the Daintree River.

Another possible cause of the common mist frog’s observed population decline is the activity of feral pigs (Sus scrofa) in areas that were previously inhabited by L. rheocola. Feral pigs are responsible for much of the damage to riparian habitats.

Recovery Plan

While the common mist frog is an endangered species, there are different factors that inspire hope in the potential to prevent the continued decline in the species’ population and potentially increase their numbers. One key factor is that much of the areas inhabited by the common mist frog are protected within World Heritage-listed national parks. In others their environment is largely protected from buildings and modern development. Additionally, a set of protocols designed to minimize the spread of diseases that threaten the mist frog’s survival has also been established. The movement of mist frog tadpoles has also been greatly restricted, ensuring that mist frog progeny are not separated from their parents, improving their chances of survival and later reproductive success.

There are also plans to reintroduce the common mist frog to habitats in which the mist frog once inhabited, but no-longer do for a variety of reasons. Such efforts will likely involve transplanting common mist frog populations to those previously populated areas in which the common mist frog will likely have the greatest fitness.

Scientific research can also play a big role in increasing the mist frog population. Much research can be done on the spread and potential prevention of the deadly Chytridiomycosis disease that has eliminated so much of the common mist frog population. Developing a treatment for Chytridiomycosis could save the lives of countless mist frogs.

Population Structure, Speciation, and Phylogeny

The common mist frog is one of four of the Australian Torrent Treefrog species (Litoria nannotis group). The four species of Litoria are the common mist frog (rheocola), the Mountain mist frog (nyakalensis), the Australian Waterfall frog (nannotis), and the Armoured mist frog (lorica). Unfortunately, all four of the Australian torrent treefrog species have declined since 1990 and are all classified as endangered species by the International Union for Conservation of Nature (IUCN), with the Litoria rheacola gaining this endangered status in 2001.

Home Range and Territoriality

Male common mist frogs have been observed foot-flagging, which is thought to be a way to communicate to other male frogs that they have encroached on the flagger's territory. Foot-flagging is when a male frog fully extends his back leg and foot into the air, then drags it back down against the ground. This is a behavior that is not unique to the common mist frog, as it has been observed in more than ten other frog species.

Diet

The diet of Litoria rheocola consists of a range of terrestrial and aquatic prey including dipterans, coleopterans, hemipterans, formidisae, aranaea, dipteran larvae, trichopteran larvae and ephemeropteran larvae. They are quite indiscriminate in their selection of prey, consuming what is most available in their habitats. Litoria rheocola display a seasonal shift in prey selectivity, feeding more indiscriminately during the dry season. This pattern is likely due to the fact that during drier seasons there is simply less food available to the mist frog.

Reproduction, Mating, and Life Cycle

Litoria rheocola call and breed year-round, with their reproductive behavior decreasing with colder temperatures. Breeding seems to peak in the Australian summer, between November and March. Male common mist frogs have been observed to call from rocks and vegetation around streams and creeks . Litoria rheocola has a low frequency call, with an average dominant frequency of around 2.5 kHz.

To increase probability of successful mating, male L. rheocola display inter-male spacing. This behavior is demonstrated by male common mist frogs spreading out; males are rarely observed closer than one meter from another male conspecific. The common mist frog’s inter-male spacing is likely a territorial response to a low population of female mist frogs. Such spreading prevents male common mist frogs from interfering with one another’s mating. Like other Torrent Treefrogs, the male common mist frog possesses spinose nuptial pads, which are believed to help male frogs grasp females during amplexus, or the mating position of frogs or toads. After mating, female common mist frogs deposit their eggs in gelatinous masses underneath rocks in fast-flowing water. Litoria rheocola eggs are large and uncolored. The tadpoles hatch among the rocks in a riffle. After hatching, tadpoles feed on algae, while adults feed on a variety of invertebrates. The male mating call is a regular, repeated, long-drawn single note, sounding like a rather nasal "wreek wreek wreek".

References

• Barker, J.; Grigg, G.C.; Tyler, M.J. (1995). A Field Guide to Australian Frogs. Surrey Beatty & Sons. ISBN 0-949324-61-2.
• "Amphibian Species of the World - Litoria rheocola Liem, 1974". Retrieved 2006-12-04.
• "DEH Species Profiles - Litoria rheocola - Common Mistfrog". Archived from the original on 2012-11-28. Retrieved 2006-12-04.
• "AmphibiaWeb". Retrieved 2006-12-04.