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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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.

frogs are evil

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 and 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, introduction of non-indigenous predators/competitors, and infectious diseases (see Chytrid fungus) have also been implicated.

File:Dscn1922-frog.jpg

Frog skeleton

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. Some species have satellite males who do not call but intercept females approaching one of the calling males.

The male and female frog, will then undergo amplexus. This involves the male mounting the female. The female then releases her eggs, 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 metamorphosis, in which they will develop legs, and lungs, to become a froglet, resembling an adult but retaining a vestigial tail. The final stage of development from froglet to adult frog involves apoptosis (programmed cell death) of the tail. 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

Diversity of reproductive behaviours

Many species of frog deviate from the life cycle outlined above in one or several ways. Some species lay eggs on leaves above ponds, with a coating designed to retain moisture. The tadpoles drop into the water upon hatching. Other species exhibit brood care and will carry the eggs and tadpoles on their legs (e.g. the midwife toad, Alytes spp.), in special folds on their backs, or in their stomachs (e.g. the gastric brooding frogs, Rheobatrachus spp.).

In yet other species, the tadpoles overwinter and hence metamorphose at a much larger size.

Diet and Predators

All adult frogs are carnivores, and usually eat invertebrates such as: insects, worms and spiders. However, a few of the larger species may eat larger prey, such as small mammals, fish and smaller frogs. Some frogs use their sticky tongues effectively in catching fast-moving prey, while others capture their prey, and force it into their mouth with their hands.

Most tadpoles are herbivores, eating moss, or filtering small plant particles through their gills. During the process of metamorphosis, their intestine will shorten to accommodate a carnivorous diet. Some species of frogs are carnivorous at the tadpole stage, and will usually eat small larvae and small fish.

Many animals eat frogs. These include birds, large fish, snakes, otters, foxes, badgers, coatis etc. Tadpoles and eggs are predated by fish, newts, predatory diving beetles, and birds such as kingfishers. Cannibalism has also been observed among tadpoles.

Taxonomy

Distinction of frogs and toads

A problem commonly associated with Anurans, is the distinction between frogs and toads. This distinction has no scientific basis, and only refers to the common name of a species. Most frogs in the Ranidae family (true frogs) and Hylidae family (tree frogs) are considered frogs, whereas all those within the Bufonidae family (true toads) are considered toads. However, many families, and even genera, have a mixture of frogs and toads, so there is no taxonomic basis.

The distinction between frogs and toads usually given to the Anurans is; frogs are smooth and moist skinned, while toads have dry, warty skin. An exception can be made for the Fire-bellied toad (Bombina bombina). While its skin is slightly warty, it prefers a watery habitat.

Hybridisation

Many Anurans readily hybridise. For instance, the Edible Frog (Rana esculenta) is a hybrid of the Pool Frog (R. lessonae) and the Marsh Frog (R. ridibunda). Bombina bombina and Bombina variegata similarly form hybrids, although these are less fertile, giving rise to a hybrid zone.

Frogs in culture

• Frog legs are a delicacy in China, France, and in many parts of the American South, especially Louisiana. The French custom of eating frog legs is the source of the English use of the derogatory nickname "frogs" for French people.
• In the Bible (Exodus 8) a plague of frogs are sent upon Egypt
• 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."

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.

• File:Froggunso.JPG

  Sgt. Frog (Keroro Gunso)
  Sgt. Frog (aka Sergeant Keroro [ケロロ軍曹 "Keroro Gunsō"], portrayed by Kumiko Watanabe) is a humorous frog-like alien invader who winds up on Earth in the manga and anime series of the same name created by Mine Yoshizaki in 2004. Keroro licensed product merchandise is immensely popular on both sides of the Pacific.
• The Crazy Frog is a cartoon creature resembling a frog, the 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.

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
• FrogsShort video clips of calling frogs and interviews with scientists about frog issues, including declining and malformed frog causes