Crinia georgiana is a short or squat froglet that appears flattened and has a large head and short limbs. Characteristic of its family, this frog has long and unwebbed fingers and toes. The dorsal skin can be smooth, but it is usually bumpy or tubercular, while the underside is finely granular. The genus is polymorphic, however, meaning there is great variation in colour and texture of the skin within each species. In addition, some individuals may have a backside with skin folds, while others do not. Its colouring ranges from orange to brown to almost black on its back and may include brown marbling or brown stripes on either side of its back, which aid in camouflage. The belly of males is dirty-grey, while females have a bright white abdomen; both have a white spot at the base of each limb. The groin and anterior and posterior surfaces of the thigh are bright red and the upper eyelids are either red or golden. Its hands are pale in colour. These traits are characteristic of the quacking frog and make it easily distinguishable from other species.
Tadpoles are golden in colour and their tail is transparent.
Females are usually 30–36 mm, while males most often range from 24 to 32 mm, although the smallest calling males can be as small as 20 mm. Although the difference in size between males and females is not significant enough to constitute dimorphism, there is an unusually large variation in size of males in this species, which may be attributed to pressures of sexual selection.
This froglet is endemic to Australia, and is found only in south west Western Australia from Gingin in the north, inland to Dumbleyung and east to Cape Le Grand. Most are distributed along the coast, with very few inland due to the necessity of water for survival, especially during breeding, which occurs in water.
It is estimated that there are more than 50,000 adults currently present in the species with the population size remaining stable or increasing slightly. Crinia georgiana is classified as a popular species.
The quacking frog is listed as “Least Concern” in terms of its conservation status based on its distribution and presumably large population. Its status is not currently determined to be threatened, though habitat loss due to human settlement and development along the coast of Western Australia may later pose a threat. Fortunately, much of its range is coincidentally located in protected areas, which may alleviate the effects of this threat. However, a certain fungus has been found in some specimens, so parasites may endanger their status in the future.
Because water is essential to this species, it is confined to areas of the coastal plains and forests where water is abundant particularly in winter, when breeding occurs. It is often found in shallow water near sandstone settlements or in marshy bogs. In addition, the quaking frog is known to live amongst vegetation or in anthropogenic habitats (i.e., those that result from the activity of humans) such as agricultural lands and rural gardens where water is likely to be plentiful.
Diet and feeding habits
In general, the diet of a frog is largely made up of insects, although mites, snails, earthworms, spiders, and other small animals are also consumed. Smaller frogs risk being eaten by larger frogs, as cannibalism is not uncommon. While larger frogs will sometimes feed on fish, it does not appear that this is prevalent among Crinia georgiana. Occasionally, grass, seeds, petals, and other vegetation will be found in the stomachs of frogs, but this is assumed to be accidental. In other words, the frog eats the plants only because other prey was resting on it.
Most frogs catch their prey via a flick of their tongue. The tongue is coated in a sticky secretion, which allows for the adhesion of the prey to the tongue. The catch is then taken into the mouth and swallowed right away, as frogs do not chew their food and many do not even have teeth. Members of Crinia do have vomerine teeth, which are pairs of teeth-like plates on the roof of the mouth that slant inward, but they appear to be rather unimportant. Once the food is in the stomach, the stomach compresses and abdominal muscles aid in digestion and expulsion of waste.
The call of the quacking frog, just as its name suggests, is described as closely resembling the quack of a duck. There are usually 1–4 quacks in a sequence, but there can be up to 12 and males will respond to the calls of other males with the same amount of notes. The calls are used to attract females who are ready to mate. The call is distinct and loud, and these frogs will respond to imitations of their call.
Reproduction and development
Crinia georgiana breeds mainly in the winter months, from July to October, usually near granite outcrops, in shallow murky pools. Breeding has also been known to occur in puddles and wheel ruts.
Amount of rainfall affects the timing of breeding, as this species usually breeds in temporary ponds that are only full after rain. Temperature can affect the rate of egg lying, which slows when ambient temperatures are very low. However, since water temperature is usually warmer than air temperature, it is unlikely that the water temperature will drop below 2 °C, the temperature necessary to significantly decrease breeding activity. Lunar phasing also affects mating, with higher rates occurring around the full moon. Although it is unclear why this is so, it can be inferred that the sexual activity of both males and females is synchronised by this variable.
Fertilisation occurs via amplexus, which lasts about 23 minutes. Amplexus is a form of copulation in which the male grasps the female with his front legs while she lays her eggs and he simultaneously releases fluid containing sperm.
Matings in this species are relatively unique in that quacking frogs are polyandrous; about half of all matings involve more than one male, and possibly up to nine, resulting in a brood of offspring with multiple paternities. Polyandrous mating is more likely among smaller males, as large males can monopolize and dominate the female during amplexus. This does not appear to be beneficial, as the efficiency of the sperm does not differ significantly in terms of sperm number, size, motility, and longevity between large and small males. Furthermore, when a single male mates with a female, there is a 90–95% chance that fertilization will be successful, while there is only a 64% chance of success when three to five males mate with one female. Often this drop is due to fights that arise when other males join in an existing act of copulation, reducing the likelihood of successful sperm transfer. Therefore, there is no benefit to polyandry in terms of offspring survival to offset the high cost of reduced fertilization success and occasional female mortality. It is thus unclear why polyandry is prevalent in this species, although it could possibly be due to males wanting to increase their chances of procreation with a limited number of females.
When there is a high density of males in an area, they will fight over access to the females, with the larger males usually succeeding and gaining access to the female. Calling also decreases when densities are high, with larger males calling much more frequently than smaller males. Smaller males may refrain from calling in order to conserve energy. Energy is limited due to their size and would only be wasted by trying to compete with larger males. Females are more likely to mate with a calling male, so in order to increase the likelihood of mating success, smaller, non calling males will often engage in “satellite” behaviour, especially at low densities. This involves associating themselves with a calling male, and when the female approaches and she and the larger male begin to mate, the smaller male will join and thus force group spawning. Group spawning also occurs at high densities when a male that has secured a calling site mates with a female and others then join in after. The larger, calling male will secure the preferred dorsal amplexus position, while inferior males are forces to take on ventral or dorsolateral positions.
The mating, and thus the laying of eggs, occurs in seeps that are shallow and temporary and often dry up before tadpoles metamorphose (roughly 4–7 weeks). This results in unique adaptations, such as the development of Crinia Georgiana tadpoles in eggs that are very large relative to those of other species. This allows them to mature earlier and cope with unpredictable climates. Within the species, tadpoles with larger eggs are more likely to survive to the stage of metamorphosis. Females that lay smaller eggs also lay more of them; it is logical that since smaller eggs have a decreased chance of survival, a female would produce more to increase the chances of regenerating the species. Egg size and number of eggs laid varies unpredictably from female to female, so it is unclear why some lay large eggs while others lay small ones, but more of them.
It has been determined that although tadpoles with limited foodstuff (i.e., a smaller egg) have a higher rate of mortality, those that do survive can still complete metamorphosis at the same rate as those that have plentiful food. In addition, if water levels drop, tadpoles can speed up development so as not to remain in such a fragile state while water, a critical resource, is limited. This indicates that the quacking frog has developed adaptations that allow for its survival in the dry climate of Western Australia.
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