The Vertebrates: Amphibians (Revised, 1985)

[Music] animal life on the earth appears in a dazzling variety of different [Music] forms but one thing that all animals have in common is is the need for oxygen some animals are adapted to take in oxygen from the air others are adapted to use oxygen dissolved in water and a few animals do both at different stages in their lives these tadpoles belong to a class of animals called amphibians which means both kinds of life during the first few months after hatching they use water as their source source of oxygen but most amphibians go through a dramatic change called metamorphosis that transforms them into air breathing animals as this tadpole grows it will gradually change into a frog there are several species of frogs and they are closely related to the various species of toads frogs and toads are amphibians that have no taals in the adult stage there are are also several species of salamanders a group of amphibians that still have tals after metamorphosis salamanders are found in many parts of the world but they are most common in the moist climates of Northern Europe and North America toads and frogs have an even wider range they can be found on every continent except Antarctica and so almost all over the world one of the sounds that announce the return of spring is the mating call of a frog or toad each species has its own unique call this Cricut frog like most male frogs and toads has a large vocal sack under its chin the Frog draws air into its lungs then closes its mouth and sends the air into the vocal sack that produces the loud croaking sound that will attract a female of the same species Springtime is also the mating season for many species of salamanders the male salamander performs an elaborate courtship dance to attract a female salamanders of most species are not able to produce loud sounds so they have no mating call when the two salamanders are ready to mate the male releases a small packet of sperm held together by a kind of jelly then the female draws the sperm packet up into her body to fertilize her eggs frogs have a different procedure the male frog HS onto the female in a tight grip and the eggs are fertilized as they are laid [Music] frog eggs are covered with a jelly that holds them in a large clump the thick jelly soaks up water and prevents the eggs from drying out the eggs laid by a female toad are formed into long strings rather than a [Music] clump the young animals that emerge from these these eggs and from the eggs of other amphibians are called larve and the larv of frogs and toads are tadpoles the larv are water breathing animals the first stage of amphibian life instead of lungs they have feathery gills that work much like the gills of fish you can see the gills on both sides of this tadpole's head [Music] only a few days after hatching the tadpole begins to change these outer gills are covered by a fold of skin the tadpole breathes by taking in water through its mouth the water passes over the gills which have a network of many small blood vessels oxygen dissolved in the water is absorbed by the blood and then the water is pumped out through a small hole called a spiracle a tadpole has two spiracles one on each side of its body for food tadpoles depend mainly on small water plants but other animals are also looking for food adult salamanders are among the many predators that use tadpoles as a food supply of the thousands of tadpoles that hatch in this Pond each spring only a few survive to complete the dramatic process of [Music] metamorphosis at first the changes take place rather slowly after about 3 months the tadpole's hind legs have developed and now the changes happen more quickly front legs grow out from under the Gill covers and the gills themselves are gradually absorbed as the lungs become fully developed now the growing tadpole must come to the surface for air for a while the tadpole does not eat its tail is being reabsorbed and used for nourishment before long the tail is almost gone and the process of metamorphosis is nearly complete and meanwhile other young amphibians have also been changing this salamander larvae with its feathery gills is transformed into an adult salamander with lungs used for breathing air but there are some amphibians that never enter this second stage of Life the mud puppy is a species of salamander that keeps its gills and remains a water breathing larvae all its life but most amphibians do undergo metamorphosis as adults they have lungs but these lungs are simple sacks that can't provide all of the oxygen the animal needs air is also absorbed through the surface of the mouth and throat and through the skin this is possible because the skin is quite thin and well supplied with blood vessels so oxygen can be absorbed by the blood and carbon dioxide can be released the thin skin also allows water to be absorbed by the body amphibians don't drink water and so to prevent the body from drying out the skin must be kept moist special glands in the skin secrete a mucus that makes the skin slippery and helps to prevent drying but even with this protection an amphibian must always have a supply of fresh water to keep its skin moist in order to survive that's why amphibians are most common where there is plenty of water a freshwater Pond a river or a marsh or swamp and yet there are few species that can survive even in a dry climate they burrow underground to find water so they are not often seen in these places other amphibians can be found in a forest living in the trees or on the ground some species live all their lives on land or in the trees but others return to a pond or stream during the breeding season there's one species of of salamander that has two distinct stages in its adult life the red spotted no lives on land usually in a forest for 2 or 3 years then there is a change in its skin color and the noot will leave the forest and spend the rest of its life in the water of a pond although it will come to the surface to breathe air so depending on the species amphibians can be found in many different environments and each species must be adapted to its environment in order to survive frogs that spend much of their time in water have webbed hind feet that help them in swimming but toads and some land frogs have little or no webbing tree frogs have small suction cups on their toes these tiny discs help them to hold on to the side of a tree or shrub there are other adaptations that help amphibians to evade Predators frogs and toads have eyes that can see almost a full circle around them if danger is cited the frog or toad can escape by using its powerful hind legs for jumping or [Music] swimming toads and a few other amphibian species have glands in the skin that secrete a poison that can ward off a predator another defense is camouflage the color and pattern of an amphibian May blend with its surroundings allowing it to hide from an [Music] enemy some tree frogs and other amphibians can camouflage themselves by actually changing their appearance on a green leaf this tree frog is green but when it moves to the bark of a tree its color gradually changes and it Blends more closely with its new surroundings [Music] but survival also depends on finding food amphibians sometimes eat worms snails or small fish but the major part of their diet is insects most frogs and toads have long sticky tongues that can be flipped forward with amazing speed to capture an insect frogs and other amphibians make up one class of animals within a larger group called vertebrates animals with backbones there are two major types of vertebrates one type includes mammals and birds which are called warm-blooded animals they maintain a constant high body temperature using energy from the food they eat other vertebrates are called coldblooded reptiles fish and amphibians have a body temperature that varies with the temperature of their surroundings in Colder Weather the cold blooded animals become less active as their body temperature Falls freezing temperatures can threaten life itself amphibians of some species Survive by spending the winter at the bottom of a lake or Pond sometimes partly buried in mud or gravel they remain here without moving and their life processes slow down to a minimum the small amount of o oxygen needed is taken in through the skin rather than the lungs this inactive state is usually called hibernation even though it is different from the true hibernation of warm-blooded animals other amphibians find protected places on land where they can spend the winter in the same inactive State then as spring begins the warmer temperatures provide the energy to raise the body temperature of the resting amphibians and the cycle of life has been renewed for frogs toads and salamanders it is a life of two kinds the life of a water breathing larvae Changed by the process of metamorphosis into an air breathing adult amphibian [Music]