[MUSIC PLAYING] BRIAN WORTHINGTON: Hi, I'm Brian.
AUDREY BOWE: And I'm Audrey.
BRIAN WORTHINGTON: We're both students at Cornell University studying herpetology. Herpetology is the study of reptiles and amphibians.
AUDREY BOWE: But today, we're going to be talking only about amphibians.
BRIAN WORTHINGTON: So what are amphibians?
AUDREY BOWE: Amphibians are a diverse group of organisms, including the salamanders, the frogs, and the caecilians.
BRIAN WORTHINGTON: Amphibians do not produce their own body heat. They're what we call ectothermic, meaning they require an outside source of heat. Amphibians depend on their environment to warm themselves and may bask out in the sun just like some reptiles do to absorb heat. But if an amphibian becomes too warm, they must retreat to a shady, cool location.
AUDREY BOWE: Amphibians are found worldwide, but have greatest diversity in the tropical rain forests of South America, Africa, Asia, and Australia. No matter where you are, amphibians are most common in areas that are moist or wet.
BRIAN WORTHINGTON: There are two big reasons for this. For one, almost all amphibians breathe through their skin. But to breathe through their skin, they need to keep their skin moist. A thin layer of water helps the exchange of oxygen through their skin.
An amphibian that is out in dry air for too long may become unable to breathe through its skin.
AUDREY BOWE: The second reason is that once an amphibian lays her eggs, these eggs have to be kept moist in order to keep them from drying out. Unlike reptile or bird eggs, these eggs lack a protective covering or shell to keep from drying out. Instead, many amphibians lay hundreds of eggs together within a jelly-like coating. This is called an egg mass, and the coating protects the eggs from drying out.
BRIAN WORTHINGTON: If you look around a pond during the early months of spring, you may be able to find an amphibious egg mass.
AUDREY BOWE: Ancient amphibians were among the first vertebrate animals, or animals with backbones, to live on land. But just like many of their living relatives, they had to be in or nearby water in order to breathe. Not only that, but they always had to return to the water in order to reproduce or lay their eggs.
BRIAN WORTHINGTON: As we mentioned earlier, there are three main groups of amphibians-- the frogs, the salamanders, and the caecilians. Although similar, each group has its own unique characteristics, including body size, structure, where they live, and how they behave.
AUDREY BOWE: Frogs and toads are the largest group of amphibians with the greatest number of species, over 6,300. They're found worldwide, but are especially abundant in the tropics.
Many frogs live in or near water, but can also be found living high up in trees or even underground.
BRIAN WORTHINGTON: Frogs and toads come in a huge variety of color. Some can easily blend in with their surrounding habitat because they're green, brown, or gray in color. This coloration makes them hard to spot. And this is called camouflage.
Green frogs, a common inhabitant of backyard ponds, are a great example of this camouflaged coloration.
AUDREY BOWE: Toads, which are a specific kind of frog, have rough, pebbly skin that doesn't dry out very easily. This makes them much better adapted for life away from water. And they can live in areas that are arid or dry, like the desert.
In addition to having drier, generally tougher skin, toads also have two parotoid glands located right behind their eyes. These glands produce toxins which ward off predators.
BRIAN WORTHINGTON: Similarly, some frogs secrete a toxin from the surface of their skin. Many of these toxic frogs are brightly colored, warning a would-be predator that they're foul-tasting and shouldn't be eaten. This type of defense is called warning coloration, and it's performed by many types of frogs and salamanders.
AUDREY BOWE: Although the back of this fire-bellied toad is camouflaged, her belly is brightly colored to show predators not to eat her.
BRIAN WORTHINGTON: One of the most well-known traits of frogs and toads is that they have huge hind legs meant for hopping and leaping. Being able to move in this sudden and explosive way helps these animals to avoid potential predators.
AUDREY BOWE: Salamanders are as diverse in appearance as snakes and lizards. Most salamanders as adults have four legs which they use for walking or swimming.
BRIAN WORTHINGTON: Other salamanders never develop legs large enough to walk or swim with. Instead, they move very similar to an eel or a snake.
Some salamanders live their entire lives in the water, while others only live in the water for certain stages of their life cycle.
AUDREY BOWE: The hellbender, a salamander native to New York State, lives its entire life under water. Found in rivers, often under large rocks, can grow to be up to 2 and 1/2 feet long.
BRIAN WORTHINGTON: The largest salamander in the world, and the largest amphibian for that matter, is the Chinese giant salamander, a close relative of the hellbender. This salamander lives in Asia, and can grow to almost six feet in length.
AUDREY BOWE: Caecilians look like the amphibian version of a worm or a snake. They're elongate, limbless, and have poor vision. Caecilians are found in tropical regions of South America, Africa, and Asia, but are rarely seen because they live almost exclusively underground or under water.
Among the amphibians, there are many species of frogs and salamanders, but not many caecilians.
BRIAN WORTHINGTON: So now that you know the basic amphibian groups, let's talk about the life cycle of these animals.
AUDREY BOWE: Have you ever seen a tadpole?
BRIAN WORTHINGTON: Tadpoles are the larval stage of frogs and toads. After hatching from an egg, a tadpole has no limbs, only a tail. As they grow, tadpoles will develop their back legs first, followed by their front legs. As soon as the tadpole begins to grow its front legs, its tail begins to shrink and it starts looking just like a small frog.
AUDREY BOWE: This transition from the larval or tadpole stage to adulthood is called metamorphosis, and occurs not only in frogs and toads but also in salamanders.
BRIAN WORTHINGTON: However, salamanders in their larval stages have big feathery gills on the outside of their head used for breathing underwater. Some salamanders that live under water for their entire lives keep those external gills into adulthood. Unlike tadpoles, salamander larva develop their front legs first, followed by their back legs. And they keep their tail throughout development.
AUDREY BOWE: As adults, many amphibians move to land and will only return to water to lay eggs. Other amphibians will spend their entire lives in the water. Still, others move to land as juveniles, but then back to the water as adults.
BRIAN WORTHINGTON: Can you hear that? Can you guess what kind of animal that is? That is the call of spring peeper, a frog so small that it could sit comfortably on top of a quarter. But what are they doing making all that noise?
AUDREY BOWE: Well, when you're that small, it can be difficult to contact other members of your species who you may want to talk to. Unless that is, you found a way to communicate with one another.
BRIAN WORTHINGTON: When animals communicate, they're sending information from one to another. Right now, I'm communicating with you, telling you how awesome amphibians are. Just like humans, some amphibians make noises to communicate.
AUDREY BOWE: So in order to attract mates, male frogs and toads will use vocal calls to communicate and attract females. They make this sound by pushing air over their vocal cords between their lungs and their resonating throat sac, also called a dewlap.
BRIAN WORTHINGTON: Communication doesn't always need to be vocal. In fact, communication can involve body language and even movement. You may not think of dancing as a form of communication. But in the spotted salamander, males dance for females as a part of courtship.
Courtship behavior is a lot like flirting. For instance, if a male salamander is "dancing" for a female salamander, he's trying to win her favor.
AUDREY BOWE: But there's a catch. A female salamander may not want to mate with the first male who dances with her. Instead, she may like to choose from a number of males. This selective choosing of mates based on attractiveness is called mate choice.
BRIAN WORTHINGTON: You might see three or more males dancing for a single female. Each is attempting to catch her attention, and the female will choose the best one to reproduce with.
In order for the system to work however, multiple males and females must be able to find each other. But how do so many frogs toads, and salamanders know how, when, and where to meet?
AUDREY BOWE: In temperate regions during the spring and early summer, often with the first warm rains of the season, hundreds of amphibians will emerge from their winter burrows and make their way to the ponds and streams where they hatched as eggs and lived as larva. We call this mass emergence.
BRIAN WORTHINGTON: Amphibians of many different species gather in huge numbers, and every single individual is able to identify other members of his or her species and identify potential mates. This is all done through communication.
After reproducing, a female will then lay her eggs in a jelly-like egg mass.
AUDREY BOWE: Mass emergence benefits amphibians by providing a time and place for males and females to meet and reproduce. It may also serve to overwhelm would-be predators, increasing the chance that any one amphibian survives.
Watching this emergence out in the wild is an amazing experience. Everywhere you turn, you might see a toad, a frog, or a salamander.
Looking into a pond or stream where these animals gather, you might see hundreds or thousands of eggs in their masses, and females busy laying them.
BRIAN WORTHINGTON: If you come back in a few weeks, you may see hundreds of frog, toad, and salamander larva swimming in the pond.
AUDREY BOWE: So now we followed the amphibian life cycle from egg, to larva, to adult, and back to the egg again. But this cycle can be easily interrupted. Our actions as humans can result in a break in this life cycle.
BRIAN WORTHINGTON: Amphibians are hugely affected by the health of their environment. And for this reason, they're called an indicator species. This is because their health is a good indicator of the health of their habitat, of their surroundings.
Events such as pollution, habitat loss, and climate change can have devastating impacts on amphibian populations.
AUDREY BOWE: Additionally, while migrating many amphibians must cross roads or other obstacles to get to their breeding grounds from their overwintering grounds. Because they may be hit by cars or otherwise injured, this poses a huge threat to the health of the populations of amphibians living in the area.
Additionally, while migrating many amphibians must cross roads or other obstacles to get from their overwintering grounds to their breeding grounds. Because they can get run over by cars or otherwise injured, this poses a huge threat to amphibian populations.
BRIAN WORTHINGTON: A good way to get involved is to join a group that monitors areas where amphibians cross the road during mass emergence. By alerting drivers that frogs, toads, and salamanders are crossing the road in front of them, you can help save hundreds of lives. This will help to ensure the survival of the population for years to come.
AUDREY BOWE: Once you help these animals make it safely to their breeding grounds, listen as hundreds of frogs call, and watch as thousands of salamanders dance, each one trying to find a mate.
BRIAN WORTHINGTON: You can observe these awesome animals and their behaviors in your own backyard or nearby park.
AUDREY BOWE: So get outside and explore the awesome world of amphibians.
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How are amphibians adapted to water and land? How do they communicate to each other? Cornell University Naturalist Outreach students highlight the remarkable diversity of amphibian adaptations. This video is a co-production of Dr. Linda Rayor, the Ithaca College Park Media Lab, and NYS 4H.