AY Honors/Life cycle of a frog

Template:Otheruses Template:Taxobox begin Template:Taxobox image Template:Taxobox begin placement Template:Taxobox regnum entry Template:Taxobox phylum entry Template:Taxobox classis entry Template:Taxobox ordo entry Template:Taxobox end placement Template:Taxobox section subdivision Archaeobatrachia
Mesobatrachia
Neobatrachia
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Full list of families Template:Taxobox end

Frog is the common name for amphibians in the order, Anura. There is often a distinction made between frogs and toads, based on appearance, however there is no scientific distinction. The only family exclusively given the common name "toad" is Bufonidae, but many species from various other families are also called "toads". "True frogs" are of the family Ranidae.

Characteristics

Template:Main Frogs range in size from less than 50mm to 300mm (the Goliath frog, Conraua goliath, from Cameroon). Frogs can have horizontal pupils, like tree frogs and true frogs, vertical pupils, like the painted frogs, or cross shaped eyes, like Peron's tree frog (Litoria peronii).

The skin unkeratinized and hangs loosely on the body because of the lack of loose connective tissue, and can be smooth or warty.

Generally, frogs have long legs with webbed toes, and tree frogs have discs on their toes to aid in climbing. The true frogs have a tongue with two lobes on its free end; which is attached in front. Frogs have three eyelid membranes: one transparent to protect the eyes underwater, and two which are translucent to opaque like human eyelids. They have a tympanum on each side of their head, which is involved in hearing.

Croaking

Many species of frog have deep calls, or croaks. Frog noise tends to be spelt (for English speakers) as "crrrrk" in Britain and "ribbit" in the USA. This difference is due to the different species within each region(e.g. Rana temporaria in Britain and Rana pipiens (leopard frog) etc in the USA.) The croak of the American bullfrog Rana catesbiana is sometimes spelt "jug o' rum". The Ancient Greeks (for example Aristophanes) spelt the croak of the usual Greek species of frog as "korax" or "brekekekex co-ax co-ax": that species is probably Rana ridibunda. Small tropical frogs tend to have higher-pitched calls. Rigveda book 7 hymn 103 describes frogs with different calls (gomāyu = "having a voice like a cow's" and ajamāyu = "having a voice like a goat's") calling when the rains bring the breeding season.

Poison

Some species of frog secrete toxins from their skin. These toxins deter predatory animals from eating them, and some are extremely poisonous to humans. Generally the frog obtains the poison from the insects or animals they eat. The Australian corroboree frogs pseudophryne corroboree and pseudophryne pengilleyi have been discovered to be able to manufacture a unique alkaloid which is not derived from their diet (Daly). Some natives of the Amazon area extract poison from the poison dart frog and put it on their arrowheads when hunting. Poisonous frogs tend to advertise their toxicity with bright colours.

Distribution and status

Frogs are found nearly worldwide, but they do not occur in Antarctica and are not present on many oceanic islands.

In many parts of the world, the frog populations have declined drastically since the 1950s. Many environmental scientists feel that amphibians, and frogs in particular, may be excellent biological indicators of ecosystem function because of their location on the food web, their permeable skins, their typically bi-phasic life (in both water and on land). Although habitat loss is certainly one of the most important features of most declines; pollutants, climate change, parasitic infestation, introduction of non-indigenous predators/competitors, and infectious diseases (see Chitrid fungus) have also been implicated.

Life cycle

The life cycle of frogs contains many stages. Typically, the male frogs of a species will assemble at a still water source. They will then call, collectively becoming a chorus of frogs. The call is unique to the species, and will attract females of that species.

The male and female frog, will then undergo amplexus. This involves the male mounting the female. The female then releases her egss, which the male frog covers with a sperm solution before the eggs make contact with the water. Once the eggs come in contact with the water, they will swell, and form a protective coating. The eggs are typically brown or black, with a clear, gelatine like, covering.

The eggs will hatch after a short time, releasing tadpoles. The tadpoles are entirely aquatic, and undergo the most develpoment in the life cycle. They will undergo metamorphisis, in which they will develop legs, and lungs, to become a froglet, resembling an adult but retaining a vestigial tail. Finally the froglet develops into an adult frog. Typically, tadpoles are herbivores, feeding mostly on algae, whereas juvenile and adult frogs are rather voracious carnivores.

Most temperate species of frog reproduce in the period between late autumn to early spring. In the UK most common frog populations produce frogspawn in February although there is wide variation in timing. Water temperatures at this time of year are relatively low and typically between four and 10 degrees celsius. Reproducing in these conditions helps the developing tadpoles because dissolved oxygen concentrations in the water are highest at cold temperatures. More importantly, reproducing early in the season ensures that appropriate food is available to the developing frogs at the right time.

• Frogspawn closeup.JPG

  Frogspawn

• Tadpoles 10 days.JPG

  10 days: Tadpoles

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  8–12 weeks: Froglet

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  12–16 weeks: Adult frog

Diet and Predators

Most frogs eat insects such as mosquitoes, earthworms, small fish and spiders. However, a few of the bigger species may eat larger prey, such as small mammals and smaller frogs. Some frogs use their sticky tongues effectively in catching fast-moving prey, while others capture their prey in their mouth with speed and agility.

Many animals eat frogs. These include birds, large fish, snakes otters, foxes, badgers, coatis etc. Tadpoles and eggs are predated by fish, and birds such as king fishers.

Frogs in popular culture

Frogs feature prominently in folklore and fairy tales in many cultures, such as the story of The Frog Prince. Similarly, numerous fantasy settings (such as the Final Fantasy videogames) include magic spells that turn people into frogs, such as the frog character in the videogame Chrono Trigger.

• In the 1992 animated movie Freddie as FRO7, Frederick, an enchanted frog prince with magical powers, becomes a modern-day secret agent.
• The crazy frog is a cartoon frog and character of the most downloaded ringtone in the UK.
• Probably the most famous frog in the entertainment world is the Muppet character Kermit the Frog.
• Until recently, the American TV network The WB (Warner Brothers) used Michigan J. Frog, a frog in a tuxedo as their logo. Michigan J. Frog was the singing, dancing star of the 1955 Warner cartoon, "One Froggy Evening".
• Frogger is an early electronic arcade game which features a frog that must cross a busy road and river.
• Frogs fall from the sky in various urban myths and notably in the movie Magnolia. This may derive from incidents when frogs are picked up by a tornado, or when a sudden migration of frogs happens overnight.
• The behavior of frogs illustrating nonaction is a myth. ("Take a pot of hot water and a frog. Throw the frog into the pot. What do you think will happen? The obvious, of course: the frog will jump out. Who likes hanging around in a pot of hot water? Now ... [t]ake a pot of cold water, put the frog in it, and place the pot on the stove. Turn on the heat. This time something different will occur. The frog, because of the incremental change in temperature, will not notice that it is slowly being boiled." from "Life and Death in the Executive Fast Lane" by Manfred Kets de Vries) Professor Doug Melton, Harvard University Biology Department, says, "If you put a frog in boiling water, it won't jump out. It will die. If you put it in cold water, it will jump before it gets hot -- they don't sit still for you." [1] A frog put anywhere that doesn't kill it will jump, "they don't sit still for you."
• Paul McCartney's " Rupert and the Frog Song" was released in 1984 and reached no.3 in the British Charts.

External links

• The Whole Frog Project - Virtual frog dissection and anatomy
• Disappearance of toads, frogs has some scientists worried - San Francisco Chronicle, April 20, 1992
• The Lily Pad - Frog information, care, and culture
• Racing Frogs Game - Create, Train, Motivate and Feed your own little froggy friend
• The Froggy Page - Frog fun
• Dart Den - Dart frog resource and forums
• Xenbase - A Xenopus laevis and tropicalis Web Resource
• Time-lapse video showing the egg's development until hatching
• Frogs (1977) - when frogs go bad