Amphibians

by Kids Discover

Amphibians (frogs and salamanders are the main types) are a super-cool, freaky group of animals. Although amphibians need to live in or near water to survive, individual species have evolved incredible adaptations that allow them to survive in wild places all over the world.

When lots of different species live in one place, it’s called a biodiversity hotspot. The Imbabura tree frog hangs out in the forests of Ecuador, which is a mega-hotspot for amphibians, with over 400 known species. (Dr. Morley Read/ Shutterstock)

The hottest spot in the entire world for salamanders is the mountain streams of Appalachia in the southeastern United States. This red salamander is one of at least 75 different species living there. (Jason Patrick Ross/ Shutterstock)

The word “amphibian” is from the Greek word amphibios, which means “double life.” In a sense, amphibians are two kinds of animal in one. When they’re young, they live in water and have gills like fish. When they become adults, they are more like reptiles, living on land and breathing air.

You may already know the typical lifecycle of an amphibian. The mother deposits a mass of jelly-like eggs in a freshwater pond or stream. Then the eggs hatch into larvae (tadpoles in the case of frogs), which swim around like fish. After a few weeks, the larvae begin to go through metamorphosis, growing arms and legs and radically changing form. Finally, the adults hop or crawl onto land.

But not all amphibians follow the rules. In fact, some species have very unusual lifecycles.

The axolotl is a rule-busting salamander that completely skips metamorphosis. That means it keeps its juvenile form for its entire life, remaining aquatic and keeping its feathery gills. Astonishingly, it can also regenerate its own body parts, growing new ones if it loses a leg or even an eye. (Pan Xunbin/ Shutterstock)

The strawberry poison-dart frog doesn’t play by the rules either, and it raises its young its own way. Here’s how: The mother lays her eggs on land, and the father brings drops of water to the eggs to keep them moist. When the eggs hatch, the mother carries the tadpoles on her back to vase-shaped plants in the treetops that hold tiny pools of water. She leaves each tadpole in its own private pond and comes back every few days to deposit unfertilized eggs for the tadpole to eat. Thanks, Mom! (Dirk Ercken/ Shutterstock)

The banded horned tree frog takes parental care one step further. The mom frog carries her eggs on her back. This species skips the tadpole phase and the babies are born on her back as tiny froglets. Both mom and babies are super-camouflaged, looking like dried leaves found on the forest floor. (Brian Gratwicke/ Flickr)

Newts are closely related to salamanders but undergo an extra stage of development. Newt tadpoles develop into land-dwelling juveniles called “efts.” The efts live on land for several years and then change into adults that go back to living in the water. This red eft will ultimately turn dark olive in color and grow a broad, flat tail that is good for swimming. (Marc Parsons/ Shutterstock)

Glass frogs don’t skip any typical steps of amphibian development, but they do lay their eggs on land—usually on moist leaves overhanging stream banks. When the eggs hatch, the tadpoles just slide into the water below. And here’s an amazing amphibian fact: A glass frog’s skin is nearly see-through. Sometimes you can actually see the organs inside its body. (Dr. Morley Read/ Shutterstock)

Amphibians have been around for a very long time. Early fossils show that the first amphibians evolved from fish over 300 million years ago. That’s way before the first dinosaurs stomped into existence.

Since amphibians first showed their slimy skins millions of years ago, they have evolved into a fascinatingly varied group, including over 7,000 species worldwide. Amazingly, scientists still find new amphibian species all the time. In 2012, nearly 200 new ones were discovered.

Amphibians have evolved strategies to live in all sorts of places—from ponds in the middle of big-city parks to treetops high in the canopies of remote rain forests. This “flying” tree frog from southern China has webbing between its toes. When it leaps from branch to branch, it spreads its toes and gains extra glide time. (Reptiles4all/ Shutterstock)

One of the most incredible and special things about amphibians is their skin. Although many adult amphibians have lungs, almost all adult amphibians “breathe” primarily through their skin. Their skin is so moist and their blood vessels are so close to the surface that they can draw oxygen directly into their bloodstreams. However, their skin has to remain wet to make it possible for them to get oxygen this way, which is why amphibians like to live in wetland habitats. Land-dwelling amphibians also have the ability to ooze mucus from special glands to keep their skin moist. Sometimes, as in the case of poison-dart frogs, the mucus contains toxins to ward off predators.

The fire salamander keeps its skin moist by producing slimy mucus and hiding in damp places under rocks and fallen wood. The bright colors are meant as a warning. When bothered, the fire salamander squirts toxin from poison skin glands near its neck. (Daniel Prudek/ Shutterstock)

When frightened, the Amazon milk frog secretes a milky white mucus that is poisonous to predators. (Aslustsky/ Shutterstock)

Every species of amphibian is unique, colorful, and fascinating. Unfortunately, these creatures are in serious trouble all over the world. Many amphibians have already gone extinct and hundreds of species, maybe thousands, are endangered. One of the biggest threats to amphibians is the chytrid fungus, which causes an infectious disease called chytridiomycosis. The infection attacks the amphibians’ skin, which is very vulnerable, and can quickly lead to death. As many as 200 species have already been wiped out.

One of the most threatened species, the Panamanian golden frog, is the national animal of Panama. It’s like the bald eagle is to the United States. One unique thing about this frog is that it doesn’t have eardrums. To communicate, it waves an arm in the air to let other frogs know it’s there. Unfortunately, about 10 years ago, the chytrid fungus ripped through the frogs’ river valley habitat, and they are now gone from the wild. Scientists and conservationists (people who want to save animals and their habitats) rescued some healthy golden frogs from the wild before the disease could get to them. Now, the frogs are being raised in captivity, and scientists hope one day to return the frogs to their Panama river homes.

This Panamanian golden frog is being sheltered at an amphibian rescue center. In addition to raising many critically endangered species in captivity, scientists are studying the chytrid fungus and searching for a cure. (Brian Gratwicke/ Flickr)

In Panama, the golden frog is so popular that its image is everywhere. (Brian Gratwicke/ Flickr)

Sometimes the chytrid fungus is the final blow to a species that’s already threatened by habitat destruction, climate change, or pollution. But amphibian lovers are trying to fight back. Here’s what’s happening with the Kihansi spray toad. This yellowish little toad lives beside a powerful waterfall in Tanzania, Africa. There, the spray from the waterfall had created a wonderful, wet micro-habitat. These toads are unusual in that they don’t lay eggs and there is no tadpole phase. The tiny baby toads are born fully formed and ride around on their mothers’ backs. In the past, the call of the Kihansi toad could be heard all around the falls. But about ten years ago, the construction of a new dam drastically reduced the spray from the falls and changed the toad’s habitat. That, combined with the chytrid fungus and the introduction of pesticides into the river above the falls, caused the Kihansi spray toad to vanish from the wild. Rescued toads were raised in zoos—and in 2012, 2,000 were released back into the wild in Tanzania. Now there’s an artificial sprinkler system that recreates the spray from the falls. Everyone involved in the reintroduction project is crossing their fingers that the captive-raised toads will re-populate their old home.

The Kihansi spray toad’s natural habitat is wet and misty. (David W. Leindecker/ Shutterstock)

Biologists recently discovered that the skin of the Australian green tree frog may be as good as a medicine cabinet. It produces a chemical called “caerin” that has been shown to destroy the deadly human immunodeficiency virus (HIV). (Andrew Lam/ Shutterstock)

Biologists recently discovered that the skin of the Australian green tree frog may be as good as a medicine cabinet. It produces a chemical called “caerin” that has been shown to destroy the deadly human immunodeficiency virus (HIV). (Andrew Lam/ Shutterstock)

Amphibians are an important part of ecosystems around the world. They eat insects and other small invertebrates that can sometimes be pests, and they help keep our environment in balance. As scientists study amphibians, they are discovering that many have features that could be helpful to people. The special skin of amphibians produce all kinds of unusual chemicals, and some of those chemicals can fight diseases that hurt humans. For example, the phantasmal poison frog makes a chemical that can be used as a powerful painkiller. And the fire-bellied toad produces a substance that can reduce high blood pressure.

Written by Margaret Mittelbach
 
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