Chordata-Amphibia

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**Introduction to Amphibians **

The word amphibian means two lives. This is because amphibians are given the reputation of being able to live on both land and water, but this is not true for all species considered amphibians. Some salamanders, and caecilians spend their entire lives in aquatic or terrestrial environments and may not ever lose their larval features, a process called paedomorphosis. the most famous amphibian, the frog, the first part of their life occurs as a tadpole in the water. The tad pole is the larval stage of a frog. It has gills, a lateral line system, and a long finned tail; it is also an herbivore. It has no legs and swims by undulating like its fish-like ancestors. The second life begins when the tad pole develops into a frog. It grows legs, loses its gills and lateral line system; then it grows lungs, external eardrums, and a digestive system adapted for a carnivorous diet. It then moves onto shore and restarts life as a hunter.

Although amphibians are characterized as living on land and water, most generally must spend their time in or near water. Amphibians can be most easily found in humid, damp environments like swamps and rain forests: they rely heavily on their moist skin for gas exchange, and some, that lack lungs, depend solely on gas exchange on their skin and in their oral cavity.



**Three orders of Amphibians **

Modern day amphibians have three main groups: order Urodela, order Anura, and order Apoda. There are approximately 4,800 species of amphibians: 500 species of order Urodela, 4200 species of order Anura, and 150 species of Apodans.

Urodela means “tailed ones,” and they are more commonly known as salamanders. There are approximately 500 species of salamanders, and they can be entirely aquatic, entirely terrestrial, or part both.



Anurans are more specialized than urodeles for moving on land. Anuran means “tail-less one.” Anurans are more commonly known as frogs. Most frogs undergo metamorposis, a process that is the namesake of all amphibians. They are the most dispersed of amphibians. (KS) 9

Apodans are legless and nearly blind and look similar to earthworms externally. Apoda means “legless ones.” Interestingly, they have actually evolved to having no legs since they evolved from a legged ancestor. They are usually referred to as caecilians and they inhibit tropical areas where they generally burrow into the moist soil of the forest; others live in freshwater ponds and streams.



**Evolutionary History **

Amphibians are considered the first tetrapods, vertebrates with four limbs, to spend a substantial portion of their time on land; their ancestors evolved from very specialized fish, the lung fish, that was adapted to living in shallow aquatic habitats (shallow lakes, the littoral zone [in deeper lakes] and the netric zone [in seas]). Tetrapods are defined as having legs as the key derived homology, a trait that basically causes a separation in classification between two species. For this reason, the ancestors of amphibians are included as tetrapods and considered as the first tetrapods; however, amphibians are the first __terrestrial__ tetrapods.

The organisms that lived at the boundary between land and water still used a respiratory system that utilized gills, but additionally, these organisms had developed a buccal pumping system (defined in respiration section) that utilized lungs so gas exchange could occur in shallow waters and on dry land. Leg-like appendages were an additional advantage in this terrain because as plant life continued to expand (supplying a large quantity of organic matter especially in pond regions) the terrain became increasingly dense. This made swimming difficult, so paddling and walking became a large advantage in the shallow water habitats.

In addition to evolutionary advantageous traits, Amphibians had an abundance of food sources as well as little competition, so they easily became a dominant species during the carboniferous period; the carboniferous period was “the age of amphibians.”

Amphibians evolved about 400 million years ago; the environment of the Earth had dried up, and the fish needed to adapt to the change in the environment. The variety of amphibians evolved around 360 to 230 million years ago, a period of time characterized by alternating wet and dry periods. (RG) [4]



**Defining Characteristics (list) **

1. Three chambered heart 2. Have larval stage and adult stage <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 0pt 0.5in; text-indent: -0.25in;">3. Carnivorous (feed on insects) <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 0pt 0.5in; text-indent: -0.25in;">4. Close ties between water and land <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 0pt 0.5in; text-indent: -0.25in;">5. Reproduce in moist environments (mostly in aquatic habitats) <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt 0.5in; text-indent: -0.25in;">6. Generally most have lungs as adults and gills as larva (there are exceptions especially in order Urodela) <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt 0.5in; text-indent: -0.25in;">7. They are vertebrates <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt 0.5in; text-indent: -0.25in;">8. Seem to all have mucus covered skin

**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Acquiring and Digesting Food **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Frogs can catch their prey using their vision sense and reflexes as they can easily nab moving insects (Ms. Murphy from Psych. said this). They can easily nab insects with their sticky tongues, and the tongue is located on the front of the frog’s mouth. Because amphibians are carnivores, they have a digestive system adapted to a carnivorous diet. Common preys of amphibians are insects like flies or termites.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Amphibians, being carnivores, would rather eat living animals than dead ones, although their feeding is opportunistic. Frogs can only target prey that is moving, but aquatic amphibians can target their food by scent will consume non-moving food. Most amphibians have very large mouth to consume prey- larger amphibians will eat almost anything, and can consume other animals such as mice, small snakes and reptiles, birds, and other amphibians. Typically, however, adult amphibians eat insects, snails, slugs, and spiders. Amphibian larvae (for frogs, better known as tadpoles) are aquatic, and feed upon aquatic invertebrates, plants, and detritus. Tadpoles are also well known for sometimes exhibiting cannibalistic behavior. (TM)(13)(14 )



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(Video illustrates how frog jumps at insect then catches it with it's tongue)

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(Video shows a frog catching a fly in real time)

**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Sensing the Environment **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Caecilians are nearly blind so they must rely on other senses in order to sense their environment. Frogs, however, seem to rely on their vision and use motion vision to catch prey. The senses of sight and hearing are well-developed in most amphibians, so the most important sense organs are the eyes and ears. (DB) (1)

Most amphibians hunt in low light conditions and are nocturnal so they have adapted exceptional night vision; these amphibians can be identified by their vertical, slit-shaped pupils. The amphibians with rounder pupils tend to see better in brighter light. The significance of eye sight varies for each amphibian though, usually dependent upon their habitat. The caecilians for example live in almost complete darkness and have little to no vision. (CW) (12) Amphibians such as frogs and salamanders hear sounds just as humans do, but they also have the ability to hear vibrations in the ground. The vibrations travel up their front legs to their shoulder blades, then to a muscle that connects to the ear. This hearing can be very sensitive to the amphibians; they can hear approaching predators as well as insects digging within the soil. (CW)(12)

"Remarkably, frogs actually use their eyes to help them swallow food. When the frog blinks, its eyeballs are pushed downwards creating a bulge in the roof of its mouth. This bulge squeezes the food inside the frog’s mouth down the back of its throat." [MS] [|3]



**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Locomotion **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">All three of the major orders of Amphibians are specialized to live in certain environments under certain conditions: this means that they will all have their own fashion of locomotion that is adapted to their lifestyle. Salamanders can both walk and swim since they live in both terrestrial and aquatic habitats. They have a peculiar way of walking; they walk in a side to side manner---kind of swaying as they move: salamanders move in a similar fashion to early tetra pods.

Video: media type="youtube" key="-MNwPVeRaBQ" width="425" height="350" align="center"

(observe how the salamander moves in a swaying fashion)

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Frogs have an even more unique way of moving. They have very powerful leg muscles which allow them to hop quickly across land. Tadpoles, however, must swim, as they have no legs. They swim in an undulating manner similar to fish and early tetrapods.

Video: media type="youtube" key="GGOQikRytB4" width="425" height="350" align="center"

(shows the strength of the frog's leg muscles)

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Lastly, caecilians, which live in burrows and streams, depend on crawling and burrowing as their two main means of transport as they have no legs to do any more complicated movement.

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(Just watch a few seconds. It shows how caecilians<span style="font-family: arial,helvetica,sans-serif; font-size: 13px; line-height: 19px; white-space: normal;"> slither/crawl.)

**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Respiration **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Amphibians can use either a lung system or a gill system. The gill system is generally for larva and some amphibians which spend their entire lives in aquatic habitats, but the amphibian lung system is quite unique. The actual lung is not very special, but the method of gas exchange is very different. Some amphibians can have gas exchange occur directly with the environment; this occurs at their skin. Others utilize a buccal pumping system to help the draw air into their lungs. In the Buccal pumping system, the animal drops the floor of its mouth, sucks in air, and raises floor of the mouth. This process forces air down into the lungs. What is unique about amphibians is that some start out with gills, and as the develop, they develop and utilize a lung system (tadpole uses gills but frog uses lungs). Even more unique is that early amphibians utilized both lungs and gills so that they could survive in both terrestrial and aquatic habitats. All gas exchange occurs across the skin in amphibians when they are completely submerged. Because of this, blood that comes into the right atrium has a higher oxygen concentration than the blood coming from the lungs. When this happens, the blood vessels leading to the lungs constrict, which reduces blood flow; this conserves energy. (18)(SM)

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">[Buccal Pumping Analogy: The process is similar to drinking water: one drinks water (sucks air into mouth), by opening mouth (lowering floor of mouth), swallows water (air), by gulping to force water into the stomach (closing then raising floor of mouth forcing air into lungs).]



**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Metabolic Waste Removal **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Adult amphibians remove wastes through the process of converting ammonia into urea. Ammonia is very toxic and must be diluted by water. For fishes and amphibians that live solely in aquatic environments, ammonia can be easily excreted since it is diluted by the large body of water surrounding the organism. Urea is the next most energetically efficient option for removing nitrogenous wastes. Urea is produced in the liver by a metabolic cycle which combines ammonia with carbon dioxide. Urea is then carried by the circulatory system into the kidneys, the major excretory organs.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">This is very advantageous because ammonia is much more toxic than urea, and urea can be easily stored and transported at high concentrations. This prevents water loss. The trade off is that energy must be spent to produce urea from ammonia. For this reason, it is more efficient to excrete ammonia directly when in an aquatic environment and excrete urea in terrestrial environments.

**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Circulation **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Amphibians have a three chambered heart with 2 atria (receives blood) and 1 ventricle (pumps blood). The ventricle pumps blood into a forked artery that splits into the pulmocutaneous and systemic circulations. The pulmocutaneous circulation takes the blood to the gas exchange organs, chiefly the lungs and skin, where blood becomes oxygenated and releases carbon dioxide to the environment. The blood then returns to the left atria. This re-oxygenated blood goes back into the ventricle where it is pumped through the body through the systemic circulation. The deoxygenated blood returns to the heart at the right atria. This is called double circulation; it is more efficient than the gill system that fish (and larval forms of amphibians like tadpoles) use because it basically pumps blood twice in one circulation.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">The three chambered heart system results in a faster more efficient way to quickly get oxygen to the muscles, brain, and organs. There is a flaw with the three chambered heart system as oxygen rich and oxygen poor blood mix in the ventricle. This is countered, however, by a ridge that diverts oxygen rich blood into the systemic circuit and oxygen poor blood into the pulmocutaneous circuit.



**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Self Protection **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Frogs are often camouflaged and have skin glands which secrete distasteful and often poisonous mucous. They utilize cryptic coloration, aposematic coloration, Batesian mimicry, and Mullerian mimicry as defense mechanisms. Amphibians use cryptic coloration to blend in with their environments, which makes them more difficult to be spotted by predators.



<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">They also use aposematic coloration to warn off predators from trying to eat them. Aposematic coloration serves as a warning that says “I’m poisonous.” This coloration is used throughout nature and predators learn to associate certain, specifically bright, colors with poisonous organisms.



<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Some amphibians use Batesian mimicry as a way to elude predators. Batesian mimicry is when a harmless organism looks like a dangerous one; this causes predators to avoid that prey as they get it confused with the dangerous organism. <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;"> <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">The top three frogs are all poisonous frog species; the bottom three are not poisonous, but they mimic the species of frog above them to protect themselves. This is an example of Batesian mimicry, described above. (RG) [|(17)]

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Other amphibians use Mullerian mimicry, two harmful species look similar, so that their predators learn more quickly that a certain look is dangerous, and the predator quickly learns to avoid organisms with that dangerous look.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Aposematic coloration, Mullerian mimicry, and to an extent even Batesian mimicry heavily rely on operant conditioning, trial and error learning, in order to be successful. They rely on predators learning what not to eat, and the predator remembering what not to eat.

**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Temperature Balance **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Amphibians are ectothermic, cold blooded; they have low metabolic rates which do not significantly influence their body temperature. When amphibians are exposed to air, they cool rapidly due to the evaporation of water on their moist body surfaces. This makes keeping themselves warm difficult. Amphibians have made behavioral adaptations to solve this issue; they move to areas where solar heat is available. If it is too hot, they seek shade and other cooler areas to cool down. Some species can even vary the amount of mucus they secrete as response to regulate cooling.


 * Osmotic Balance**

Amphibians will only have to adapt to water loss when they are living on land. The issues they face are very similar to the issues they face to keep cool in an environment that is too hot (see section labeled Temperature Balance) or keeping warm when it is to cool. Their inability to stay warm is due to evaporation of water on their moist body surfaces. This causes them to cool rapidly. In addition to this, they also have to have behavioral and physiological adaptations to overcome dehydration and drying out when they are on land. The major behavioral adaptation is to, obviously, seek shade and cooler areas when it becomes too hot. Some frogs have a physiological adaptation which allows them to regulate their temperature through regulating their water loss: they can vary their mucus secretions on their skin. This allows them to increase or decrease rate of evaporation maintaining both temperature and osmotic balance.

**<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%;">Reproduction **

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">(MC)

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Because amphibian eggs lack shells and are susceptible to dehydration, they must be laid in a moist environment. Fertilization occurs externally with males grasping females and spilling sperm over the egg as females shed eggs. Some species show type 1 survivorship curves and behave as k strategists while others show type 3 survivorship curves and behave as r strategists. Some species can house eggs on their backs, in their mouths, or in their stomachs. Others can even retain eggs in the female's reproductive tract. A few tropical tree frogs stir their eggs into moist foamy nests that reduce dehydration and drying affects. Salamander/Newt reproduction is internal fertilization without actual sexual intercourse. (MLK)[|3]

<span style="font-family: 'Times New Roman',serif; font-size: 16px; line-height: 18px;">**Characteristics of Amphibians (Summary of Info in Wiki)**

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Amphibians have a three chambered heart. This allows them to be able to quickly get oxygen to their muscles, organs, and their brain. Amphibians are generally carnivores as adults, but as larva they can be either carnivores or herbivores (tadpoles are herbivores but frogs are carnivores). They have evolved from fish-like early tetrapods and are adapted to living on land. This means that they have developed systems to combat dehydration and water loss. They excrete urea when living in a largely terrestrial habitat, and when they live in aquatic habitats they secrete ammonia directly into their environment, which is more energetically efficient.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Amphibians have several behavioral ways and physiological ways to cope with water loss and temperature regulation, since they are ectoderms, meaning they are cold blooded, and cannot maintain a body temperature different than the temperature of the environment. Some can control the mucous concentration on their skin to help prevent or accelerate evaporation of water. In general, all amphibians use similar behavioral mechanisms to tolerate temperatures. They live in warmer regions where sun light is abundant. They will move to shady regions and other cooler regions like burrows or under moist leaves to help release heat when it becomes too hot.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt; text-indent: 0.5in;">Amphibians use a plethora of defensive mechanisms to protect themselves from predators. They utilize aposematic coloration, Batesian mimicry, Mullerian mimicry, and cryptic coloration (all terms defined in section labeled Self Protection).

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">They have also developed specialized respiratory systems to allow them to thrive in a terrain where they will be alternating between aquatic and terrestrial environments. Some use lungs while others use gills. Those that use lungs breathe through a method called buccal pumping. Buccal pumping is similar to swallowing air (further explained in respiration section), and it allows the organisms to breathe more efficiently in shallow water terrains. Some directly exchange gas with the environment through their skin.

<span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Bibliography for Pictures (in order that pictures and videos appear): <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">1. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">2. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">3. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">4. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">5. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">6. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">7. (video) [|www.youtube.com] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">8. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">9. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">10. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">11. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">12. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">13. [] 14. [] 15. [] 16. [] 17. [] 18. @http://www.snow.edu/allans/biology1320/amphibia.html <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Bibliography for sources: <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">Campbell, N.C., Reece, J.R. (2002). //Biology.// (Sixth Edition). San Francisco: Benjamin Cummings. <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">1. [] <span style="font-family: 'Times New Roman',serif; font-size: 12pt; line-height: 115%; margin: 0in 0in 10pt;">2. [] 3. [] 4. []

Review Questions:

1. Why can’t amphibians maintain their body temperatures very easily? What behavioral adaptions have they made to help maintain this homeostasis? (CC)
2. In the process of circulation, what makes amphibian unique? How does this make amphibians efficient, and at what? (MP) 3. What are the three major kinds of amphibians? What separates them from each other? (JS) 4. How do the reproductive systems of amphibians influence their habitat? (LJ) 5. How do amphibians keep from drying out when they are on land? discuss both mechanical and behavioral adaptations for this. (GR) 6. Explain the ways frogs protect themselves through mimicry. (SI)