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Conservation of Frogs All animals are affected by parasites, and amphibians are certainly no exception. In fact, because they live in moist, humid conditions conducive to life in general, they may catch more than their share. Certainly, many parasites such as the platyhelminth flatworms, leeches and insects prefer or may only to be able live and/or breed in such conditions. More recently, polluted waters have meant amphibians have been more likely to get bacterial infections form water.
An example of an obvious parasite on local
frogs is provided by the endemic Australian genus of Batrachomyia flies. It
seems quite common in the Green Eyed Tree Frog Litoria genimaculata of Wet
Tropics streams. The adult lays an egg under the skin. This then hatch into a
larva that is relatively large compared to the frog host, thus resulting in a
hideous looking lump on the back or shoulder. The larvae poke a breathing hole
through the amphibian's skin. It eventually emerges, often killing the frog host
in the process. From there, it pupates in the ground.
Population crashes and extinctions in frogs A fungus has also been implicated in some of the declining and disappearing frog populations around the world. The fungus has been identified as Batrachochytrium dendrobatidis and has dermal and systemic effects on the infected frogs. The fungus may have actually already been naturally present in the frog populations, with a particular stress may have bringing it up to such threatening levels. A cooperative study between James Cook University and NASA suggested there was a correlation between the time just before the population crashes, and certain climate extremes. There were also suggestions that the disease may have spread from captive specimens. The stress in the populations of these frogs may have been previous to the crashes and indicated by disabilities or abnormalities in individual frogs. By incredible scientific fortune, surveys of amphibians were actually being undertaken before, during, and after the `crash'. The surveys measured limbs of the caught frogs and found evidence of asymmetry. This is a technique often utilized in the analysis of insect ecology to detect population stress.
Of the amphibians, only the frogs are found in
Australia. Frogs can be simply defined as tailless amphibians. They have two
shorter front limbs and two very long hind limbs. This body plan facilitates
jumping very effectively and this design has obviously been successful as it has
changed little over million of years. Like other amphibians, frogs skins are
relatively permeable; that is many liquids and gases can pass through into their
body. Frogs thus require a moist environment for this reason and for
reproduction, and are also thus sensitive to environmental conditions.
"Tree Frogs" Family Hylidae This family is found in many different environments all over the world. There are more than 790 species in 40 genera (Cogger and Zweifel 1998). The highest diversity of species is found in the wetter forests of Australia, New Guinea and most especially tropical South and Central America, where about two thirds of the species of this family occur. This is most likely where then tree frogs originated, with a fossil record going back to more than 50 million years (Cogger and Zweifel 1998). They are generally absent from the polar regions and much of Africa (EOTAW 1977, Cogger and Zweifel 1996). However, in Africa there is another closely related family that replaces them. Hylids are very attractive and photogenic frogs. They are quite often the types of frogs that are featured in books, magazines and T-shirts. They generally have long limbs, rounded toe discs and large mouths. The eyes tend to be laterally placed on the head and directed forward (Cogger and Zweifel 1998); presumably to be effective in judging distances when leaping and catching their prey. However, as this is a highly diverse family, these physical features tend to vary quite a bit. Like other Tree Frogs in other families, there is often a flattened area of round skin called a disc on the end of the digits. The discs secrete a sticky substance from mucus glands in the skin (EOTAW 1977). If the toe pads are examined under a microscope one can see interlocking irregularly shaped cells with narrow gaps (Martin 199-) It is these gaps that catch onto tiny irregulations on the climbing surface, even glass. They have extra discshaped piece of cartilage in each digit of the fingers and toes which allows the disc to be pressed up against a surface even when the finger or toe is at an angle (EOTAW 1977, Cogger and Zweifel 1998). The detailed pattern of irregulations can also occur on the skin of the underside of the stomach (Martin 199-), which explains why many frogs squeeze their stomach against a window to increase the surface area.
Like most frogs, they need to return to water
to breed, with nearly all of them laying eggs in water. Subsequently they have a
free swimming aquatic tadpole stage. Some may lay their eggs on vegetation
overhanging water, so when tadpoles hatch they plop into the water below (Cogger
and Zweifel 1998). Others may breed in holes or vegetation that holds water,
such as the bromeliads of the Neotropics (Cogger and Zweifel 1998). The tadpoles
tend to have laterally placed eyes, to see below and above the waterline (Cogger
Beonos and Zweifel 1998) and feed by filtering microscopic food particles (Cogger
and Zweifel1998).
"Lacelids"
Nyctimystes spp. Most of the 20 or so species of Lacelids are found only in New Guinea; another one or two (depending on classification), are found in the Cape York region of Australia. They are normally found in vegetation and on rocks around fast flowing streams in tropical rainforest.
As most Lacelids live near rainforest streams,
they breed in fast flowing water (Nightingale 1992). The eggs are large and have
the tendency to clump together (Nightingale 1992) and thus not get washed away.
Tadpoles have a strong sucker mouth to cling to rocks and vegetation and avoid
being swept away downstream (Nightingale 1992). They are also thus strong
swimmers, with a flattened body, low tail fns and dorsally placed eyes (Cogger
and Zweifel 1998) and a muscular tail (Freeman 1998). |
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