amphibian-pic.jpg
(http://www.domestic-animals.com/popups/amphibian-pic.jpg)
Amphibian means "Two Lives"
-Sam Blatchford
Edited by: Omer Zaidi
Hilary Stepansky
Sarah Schwarzschild
Grace Rehnquist
Yasheka Sharma
NK
Rachel Kornetsky

Jesse Carmen
Josh Czik
Kevin Nayer
SS
AR
Vonai Moyo
Brittany Marcus-Blank
Meru Nangia
Hanna Zhu
Sarah Vlach
Daisy Joo
DP
Becca Levenson
Ethan Richman

The diagnostic characteristics that define the group


Amphibians came from lung fishes, early ancestors of what we call today amphibians. They evolved into tetrapods. Tetrapods were the first of their kind to have a sturdy skeleton with 4 sturdy legs. An amphibian is defined by the fact that it spends the first half of its life living in water and breathing with gills and the second half of its life living on land and using lungs for respiration. In many ways young amphibians resemble fish more than their parents because they have no legs and swim by wriggling their tails. (11) (BMB) Amphibians are vertebrates and are divided into three distince orders: Urodeles (newts and salamanders), Anurans (frogs and toads) and gymnophiones (caecilians).(4, NK) As the Greek name “amphibios,” meaning “both lives” implies, amphibians spend their lives, either in different stages or simultaneously, in water and on land. Typically, adult amphibians are better adapted to life on land than in water, while their larval phases are entirely aquatic. For much of their lives, which may last a couple of months or several years depending on the species, the larval amphibians bear little resemblance to their adult forms, but in a matter of weeks or even days, the once fish-like larvae metamorphose, or transform, into their terrestrial air-breathing adult froms. (8) (SS) See picture below for a visual description of the different staged life of amphibians (14 DJ).

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The metamorphosis of a Bufo bufo. (14 DJ)


Acquiring and digesting food


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This green tree frog munches on a bat it has captured, a rare example of an amphibian eating a vertebrate (OZ) (http://www.batcon.org/newsletter/enews-1203/frog_eating_bat.jpg)

Amphibians have a digestive system adapted to one of a carnivorous animal. It starts with the mouth of the amphibian. The mouth contains teeth that are feeble and practically useless. The tongue, however, of amphibians, especially frogs is highly developed and specialized. The amphibians were the first animal to develop a tongue. The tongue is normally folded back into the throat of the frog and can easily be whipped out to catch prey, such as insects. Many frogs have developed a specialized tongue that is sticky to aid in the catching of prey. The mouth then leads to the esophagus, which carries the food down to the stomach. The stomach leads to the small intestine, where the large part of digestion occurs. Digestive glands, such as the pancreas and liver, are attached to the small intestine via ducts such as the gall bladder. Liquid waste travels from the kidneys to the ureters and them to the urinary bladder. Solid waste travels through the large intestine. Both liquid and solid waste material leaves the body by way of the cloaca and the cloaca vent, which is where sperm and eggs are also excreted from. (11 Nangia)(HS 1)
Amphibians eat many types of small insects, worms, and other invertebrates, organisms lacking a backbone or spinal cord. There are several methods used to aquire food. Frogs and toads tend to lunge at their prey, but the prey must be in motion for it to be recognized as food. Some species hunt mainly by eyesight and will engage in a chase after the prey is sighted. Other species use their sense of smell to locate food. (12) (BMB)


Sensing the environment


One of the first terrestrial organisms they had an abundance of food which enabled them to thrive in their environment. Amphibians are ectotherms therefore they sense their environment in order to control their body core temperature. Moving into the heat when they get cold and moving into the shade when it gets too hot.
Amphibians lack external ears, but many have well developed inner ears. Frogs have the best hearing of all amphibians, due to the fact that they have a middle ear. Smelling and tasting is accomplished with the help of the Jacobson's organ, which is located in the roof of the mouth. Caecilians use a pair of tentacles to detect chemical changes in the environment. (4) [KN]

The Amphibian Ear (KN) (13)
The Amphibian Ear (KN) (13)




Locomotion


At first tetrapods adapted with appendages for the purpose of moving around in the shallow water and weeds with ease. These appendages were not used on land for tens a millions of years. Frogs use their hind legs to hop around on land. In their tadpole stages, amphibians use a tail to swim around in water. They use body muscle contractions to propel themselves through the water(10 VM). Once they have matured, the tail and gills are reabsorbed and the legs begin to grow (OZ). Frogs and toads have hind legs that are longer and stronger than their forelegs, which aids in jumping. Frogs make use of their long hind-limbs in jumping, hopping, swimming, burrowing, and climbing(10 VM). Zoologists believe that adult frogs and toads do not have tails because it would make them unable to jump.Caecilians have no limbs at all; they burrow in the soil by using their strong skulls and swim by moving their muscular bodies back and forth (AR) [9].



Respiration


Amphibians can have both gills and lungs through out their life time. Starting out as a baby most amphibians live in the water where they have gills. As they mature lungs develop and they start living on land. Amphibians breathe through their skin or through lungs. Amphibians that breathe through lungs use buccal pumping. Buccal pumping is when the animal drops the floor of the mouth which sucks air in then closes the mouth and raises the floor forcing air into the lungs. Amphibians have lungs that are not as efficient as humans' lungs, so a dry environment is not favorable to an amphibian. This is why many amphibians tend to live in wet, moist environments. Since the lungs of amphibians are not that efficient, gas exchange (the movement and exchange of materials) through their skin is replaced for this, allowing for a very adequate respiratory system. (Jesse Carmen) (6). Amphibians can also obtain oxygen through their permeable skin (7 SES). Tiny blood vessels within the skin take up this oxygen (7 SES). These blood vessels are called capillaries (7 SES). While most amphibians use lungs or gills as the main part of their respiratory system, some amphibians, like salamanders for example, only use their skin to take in oxygen (7 SES).



Metabolic waste removal


Metabolic waste removal is essential to life. Without the ability to excrete waste nothing would be able to survive. Amphibians mainly excrete urea in their early years. Urea is created in a vertebrates (amphibians) liver and then is transported to its kidneys. Urea has a great advantage over ammonia because it is so much less toxic about 100,000 times less. Since urea takes so much water to excrete safely it is ideal for aquatic animals. Once amphibians make the transition from their aquatic biome to a terrestrial one they switch over to excreting ammonia. This saves the amphibians a lot of energy and makes them more efficient on land. It takes more energy to form urea, which is made by combining ammonia with carbon dioxide, than it does to form ammonia [HZ]. Therefore, as tadpoles, it is more favorable to form ammonia, since the water would dilute (decrease the amount of ammonia in a certain volume of water) the ammonia and make it more less toxic (1) [HZ].



Circulation


Amphibians have a 3 chambered heart (one ventricle and two aorta). The ventricle (the pump of the heart) pumps blood to two circuits of blood flow. The two circuits of blood flow are pulmocutaneous and systemic. The Pulmocutaneous circuit deals with the defusion of oxygen through lung and skin capillaries then returning to be pumped through the systemic circuit. This circuit carries oxygen rich blood throughout the body at a high pressure. It is much better for oxygen rich blood to be pumped at a higher pressure because the oxygen can get to the vital organs and the brain faster. Double circulation is very helpful because it delivers more pressure in pumping oxygen rich blood throughout the body.
Gas exchange happens over a semipermeable membrane also known as the amphibians skin. A semipermeable membrane means somethings can get through and others cannot.

external image image.tiff
http://www.daviddarling.info/images/circulatory_system.jpg
This is a diagram of an amphibians circulatory system, diagraming its three chambered heart. It shows how blood enters and leaves the heart and how blood is passed through the amphibians body. The diagram also shows how amphibians take have CO2 in their body, which they change into oxygen when it is passed through their lungs, this oxygen is then passed to the heart to make the high pressure oxygen rich blood that is passed through the body.



Self protection


Most amphibians are ether extremely well camouflaged or very brightly colored. The use of camouflage would be to avoid predators and being brightly colored would be to warn predators that they are very poisons. Also, Amphibians hide or stay still in the presence of danger. Frogs have warning calls that alert other members of the population. Some salamanders and frogs, when disturbed, arch their backs, stiffen, and rock on their bellies. Other salamanders and frogs have flash colors that warn predators away. Some amphibians have toxic skins which predators learn to avoid. Some species mimic the coloration of toxic species so that they are safe as well. (3. Sharma) Some species of salamanders have tails that break off when they are attacked, allowing the salamander to quietly escape as the predator pursues the twitching tail(10 VM).
external image poison-dart-frog.jpgThis is an image of a poison dart frog. This species of frog is found in the rainforest and is known for the powerful toxins it secretes through its skin. These poisons are made up of toxic alkaloids, which they get by eating certain ants and other insects. (JAC) http://www.tropical-rainforest-animals.com/Poison-Dart-Frogs.html



Osmotic balance


During the earlier stages of an amphibians life osmotic balance for the most part is controlled by excreting large amounts of diluted urine and managing their salt intake by eating a lot and using their surroundings. Once amphibians become mature enough to live on land they grow thicker skin and mange water intake by eating lots of moist foods and living in swampy environments. These processes are called osmoregulation. Osmoregulation is when a vertebrate regulates the bodies water content and salute compassion with a closed circulatory system. The purpose of this is to maintain the cytoplasm of the bodies' cells. This is to insure that the body functions properly. A closed circulatory system is more efficient then an open one.



Temperature balance


Amphbians are Ectotherms, also known as cold blooded. This means that amphibian's bodies do not regulate their body temperature outside factors do. This being said Amphibians relay on behavioral techniques to regulate their body temperature. Behavioral techniques include when an amphibian gets to hot it will move into a cooler area also known as a micro climate. This is the only way Amphibians are able to regulate their own body temperature.Amphibians can sometimes change their own skin color, which can be considered a means of protection when it helps camouflage the amphibian (7 SES). However, changing their own skin color can help to regulate their temperature (7 SES). Lighter skin colors help reflect heat more than dark colors, so depending on the amphibian's temperature it will change to lighter or darker colors (7 SES).

Evolution of Amphibia from Fish

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http://aigbusted.com/resources/fish_evolution.jpg

It is pretty well accepted that the first amphibians were fish with under-developed legs that came to live on land around 400 million years ago. They are thought to have arisen from lobe-finned crossopterygian fishes(10 VM). As to whether amphibians actually arose from several lineages is questionable. The characteristics of vertebrae, teeth, and skull bones form the basis for these hypotheses of the lineage of amphibians, however, additional developmental and variational data are necessary to support these ideas(10 VM). Because getting oxygen that is dissolved in water takes more energy the air, it also makes sense that some fish might evolve lungs . The selection pressure for evolving legs is thought to be the need to migrate when smaller pools of water dried up, to find more food, and/or to be safe from predators as amphibians are thought to be the first animals on land. Scientist are unsure about which type of fish that amphibians evolved from, but they believe it was one of three types of lobe-finned fish. Possible candidates are the lungfish (which have gills and lungs), the coelacanths (which have four arm-link fins), or the extinct rhipidistians. (5) (RK)

Review Questions:
  • Describe three ways that amphibians can protect themselves. (SV)
  • How are Amphibians able to obtain enough oxygen and circulate the oxygen through their bodies? (DP)
  • How do many species of amphibians protect themselves from danger? (BL)
  • What adaptations do amphibians have that allow them to live in diverse environments? (RJS)
  • What is the difference between an amphibian and a fish? (ER)

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