Most people only think of frogs when they think of amphibians. Although frogs make up most of the amphibian group, there are two other amphibians, including salamanders and a worm-like amphibian called caecilians. Amphibians can be found on all continents in the world except for Antarctica and the Arctic.
Characteristics of amphibians:
- Ectothermic (cold-blooded)
- Brumate
- Live on land and water
- Vertebrates
- Can smell, see, and hear
- Vocalize
- 4 legs except for some salamanders and caecilians
- Have teeth but swallow their prey whole
- Have lungs and a permeable skin
- Carnivorous
- Toxic skin
- Complex life cycle
Amphibians come in a range of sizes. The smallest is a frog known as paedophryne amanuensis from New Guinea, which is the size of a housefly. The largest is the Chinese Giant Salamander which can grow to six feet in length and weigh 140 pounds. What are the characteristics that link such diverse animals?
Cold-Blooded / Ectothermic Animals
Amphibians are ectothermic creatures. This means that they cannot regulate their body temperature using metabolic means. They are reliant on the environment for warmth because their bodies cannot heat their blood to maintain a constant body temperature. Thus, they are described as being cold-blooded animals. Amphibians have adapted their behavior to keep up their body temperature by making the most of the environmental heat.
How Do Amphibians Stay Warm?
Amphibians spend a lot of their time basking in the sun. They are often seen sunbathing on rocks. They do this because rocks retain heat and are warmer than the soil or grass. A problem with this behavior is that tarmac roads also retain heat like rocks. Amphibians are seduced into basking on the roads, and many are killed by vehicles. Amphibians also burrow under leaf piles and logs or dig themselves deep into the earth below the frost line to stay warm during winter.
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How Do Amphibians Stay Cool?
Amphibians do not like excessive heat, and they combat this by being active mostly at night. They prefer to live by water sources and enter the water or burrow down into the cool, moist leaf litter when temperatures increase.
Do Amphibians Hibernate?
Amphibians brumate. Brumation is a hibernation-like state where their metabolism slows right down, and energy is conserved. Amphibians have periods when they wake up during the brumation and drink to sustain the body’s fluid levels.
Can Frogs Survive Being Frozen?
Two frog species are not as good at digging burrows, and they have developed a unique adaptation for winter. The Hyla crucifer (spring peepers) and Rana sylvatica (wood frogs) become frozen, and their hearts stop beating during frigid winter temperatures.
Their internal organs store high concentrations of glucose. Glucose lowers the freezing point of water and so the internal organs can remain unfrozen. In addition, glucose provides energy for the internal organs to sustain cell life. When the temperature warms, these frogs warm-up and “come back to life.”
Amphibians Live On Land And Water
The word amphibian is based on the Greek word amphibios’ which means “living a double life.” Their name, therefore, refers to an amphibian’s ability to live on land and in the water at different stages in the life cycle. Most amphibians spend the larval stage in water. The larval stage is when the eggs hatch, and in frogs and toads, they form tadpoles. In salamanders and caecilians, the larva is similar to the adults.
The larvae of amphibians spend all their time in the water while they develop and grow. Once the larvae have undergone a metamorphosis and are juveniles, they leave the water and live on land or split their time between the two.
Amphibians Are Vertebrates
Vertebrates are animals that have a spine or backbone. All amphibians have spines and so are classed as vertebrates. Vertebrates have a nervous system partly enclosed in the spine and a muscular system consisting of bilateral or paired muscles. Vertebrates have a clearly defined head surrounding a brain, and there are three paired sense organs, namely eyes, nostrils, and ears. There is usually an internal skeletal system.
Amphibians Can Smell
Amphibians have small openings in the roof of their mouths. These are known as external nares. They lead directly into the mouth. Scents are taken into the mouth, and the nares are also used for breathing. Some species of amphibians use chemicals with specific scents to communicate.
Amphibians Can See Color
Frogs and salamanders have retinas that contain green rods, which enables them to see different colors. Many amphibians are bright, colored and they need to see these colors for communication purposes. Caecilians have eyes, but they are covered by skin and do not function, making the caecilian blind. As the caecilian spends its life underground, the lack of vision does not hamper it in any way.
Amphibians have No External Ears
Amphibians have no external ears, as is seen in mammals. The ear is situated just behind the eye. Sound waves are directed onto a tympanic membrane that transmits the sound waves down a channel to the inner ear. The inner ear has two structures known as the papilla amphibious and the papilla basilaris. Amphibians can hear equally well in water, air, or below ground.
Amphibians Vocalize To Communicate
Some amphibians, especially frogs, use vocalizations to communicate with each other. The loudest frogs in the world are the Puerto Rican Coqui that creates sounds at 70 – 80 decibels – that is the same noise level as a petrol-driven lawnmower.
Amphibians have Four Legs
Amphibians have four legs, except for caecilians that do not have any limbs. Some aquatic species of salamanders have lost their legs, or their legs have become much reduced in size. Caecilians lost their legs as an evolutionary adaptation as they burrow underground, and legs are not needed. They have hard skulls, which they use to push soil out the way as they move underground.
Amphibians Swallow Their Prey Whole
Many amphibians have teeth. They are found only at the front of the mouth on the upper jaw. They are known as vomerine teeth and are used for holding or catching prey. They are not used for chewing or tearing. Amphibians swallow their prey whole whether they have teeth or not.
Amphibian’s Digestive System
Amphibians have a digestive system that consists of two parts. An esophagus joins the mouth and the stomach, and a lower portion connects the stomach and the anus.
Amphibians have a Permeable Skin
Amphibians have smooth, slimy skin that is relatively thin. It is permeable and allows liquids and gases to pass through the skin. The permeability enables the amphibian to take in oxygen and expel carbon dioxide through the skin. This process is known as cutaneous respiration.
The moist skin facilitates the exchange of gases, but it also means that amphibians lose water through their skins. Amphibians must have access to water or damp environments where they can replace lost fluids. Mucous glands maintain the moisture of the skin in the skin.
Amphibians Have Lungs
Amphibians truly are animals who like to have the best of both worlds. Not only do they get oxygen through their skins, but they also have lungs for breathing in most cases. Some salamanders do not have lungs and rely solely on cutaneous respiration. Tadpoles and some amphibians that only live in the water have gills instead of lungs. Amphibian lungs are more primitive than mammalian lungs and usually have a limited capacity.
Amphibians Are Carnivorous
Amphibians are carnivorous, meaning their diet consist of meat. Frogs will eat anything they can find that is a suitable size. Insects, slugs, spiders, snails, other frogs, and even mice, small birds, fish, and bats, depending on the frog’s size. Tadpoles eat vegetation in the water but will also eat tiny organisms and insect larva. One frog, the Brazilian Tree Frog, is a vegetarian and eats only plants and berries.
Salamanders eat slugs, snails, mice, fish, crustaceans, frogs, other salamanders, and insects. The large salamanders also eat snakes and very commonly other salamanders. Although caecilians look like worms, they do have a mouth full of sharp teeth. They use this to eat earthworms and other invertebrates.
Amphibians Have Toxins On Their Skin
Many frogs and salamanders have toxins on their skin which they use to protect themselves from predators. Some of these toxins, such as the toxin of the poison dart frog, are deadly. The most poisonous amphibian is the golden dart frog. These frogs obtain toxins from their diet by harvesting poison from the insects and centipedes they eat. The toxins are stored in glands on the skin and released when needed. Not all amphibians have the deadly toxin. Some just taste bad and cause the predator to foam at the mouth.
Amphibian Produce Eggs Without A Shell.
Amphibians lay eggs that do not have a calcified shell. The eggs are surrounded by jelly and are commonly laid in standing freshwater. Sometimes eggs are laid on a leaf above the water level, and as the larva hatch, they drop off into the water.
Some female frogs and toads carry the eggs on their backs. Fertilization in frogs, toads, and salamander usually takes place outside the body. The male frog positions himself on the female’s back, and he ejects sperm as she lays the eggs. Salamanders commonly deposit a sperm pocket in freshwater.
The female salamander takes the sperm pocket into her body through her cloaca, and internal fertilization occurs. The salamander eggs may be laid in water, or some species retain the eggs in the body. Hatching and even metamorphosis in some cases occur within the female salamander’s body.
Caecilians use internal fertilization. The male caecilian has a cloacal extrusion similar to a penis known as a phallodeum. The phallodeum is inserted into the female’s cloaca, and they remain in this position for two to three hours. Some caecilians lay the eggs in the water. Some retain the eggs in the body, where they develop to different stages depending on the species.
Gestation Period Of Amphibians
Frogs and toads usually take approximately ten days to hatch after the fertilized eggs are laid in the water. The timing is dependent on the water temperature. Warm water will allow for quicker hatching, sometimes in as little as three days. Colder water delays hatching, which ensures the tadpoles’ survival as colder water will have fewer organisms in it for food. Salamanders can take anywhere from three weeks to two years for the development of larva.
Amphibians have A Complex Life Cycle
Amphibians have complex life cycles that go through different stages. The various amphibians have differences in how they develop, but they all still go through several stages. Metamorphosis is involved in the life stages.
Frog Life Cycle
The life cycle of frogs has four stages. The first stage is when the female frog lays eggs. They lay thousands of eggs in one batch. Many eggs are lost due to predation, and some eggs may dry out and become non-viable.
The eggs take an average of ten days before the second stage when the tadpoles hatch. Tadpoles have no legs and use a fish-like tail for swimming. They do not have lungs and use gills for breathing. During this stage, the tadpole goes through a metamorphosis, and the back legs begin to develop.
The third stage is when the frog becomes a froglet, and the tail shortens, and the lungs begin to grow. The front legs start to form.
The fourth stage is the final one and is an adult frog. The frog can live on both land and water, and they eat insects, crustaceans, snails, and slugs. Frogs can live from three to twenty years, depending on the species and the environmental conditions.
Life Cycle Of A Salamander.
Salamander larvae can either hatch outside the female’s body or inside her body. The eggs hatch into larvae, which look quite similar to the adult salamanders. They breathe with external gills and have teeth which they use for feeding. They have four fully developed legs, and they are carnivorous.
The larval stage can last anything from a few days to two years. Salamanders go through a metamorphosis from the larval stage, losing their gills and developing lungs. The skin thickens, eyelids and a tongue develop, and the fins reduce in size until they eventually disappear. There is not a dramatic difference between larvae and adult salamanders.
Life Cycle Of A Caecilian
The caecilian hatch from eggs that have been laid in mud or on land. Only 25% of eggs hatch larvae outside of the female caecilian that undergo metamorphosis to become adult caecilians. During the larval stage, they live in water, and once they become adults, they move to live on land. The other 75% of eggs hatch inside the female’s body. There is not a lot known about caecilians, and further study is needed.
Amphibians Live All Over The World
Amphibians are found all over the world except in the Arctic and Antarctica. The most biodiversity amongst the amphibians is found in areas where the climate is warm and moist. In these climates, amphibians can thrive. It is much harder for amphibians to live in cold temperatures as they are ectothermic. Some of them have adapted and manage to live in colder regions of the world.
Conclusion
Amphibians have three main orders: they are frogs, salamanders, and caecilians. They evolved from fish, and this is seen in the aquatic larval stage. Gills are used for breathing, but lungs develop as the larva grows, allowing the amphibian to live on land as an adult. Some amphibians remain semiaquatic their whole lives. Their most permeable skin allows for cutaneous respiration. Amphibians are found almost all over the world and have adapted to different climates.
