How Amphibians Use Color


With over 8,000 species of amphibians, it should be no surprise that they come in a varied kaleidoscope of colors.

Amphibians use color to camouflage themselves, blending into their surroundings to stay safe from predators or make finding their prey easier. Some frogs, such as poison-dart frogs containing toxins, are brightly colored to warn predators that they will not be tasty.

The colors are produced by pigment granules in the upper layer of their skin by pigment-containing cells (chromatophores) in the lower layer.

These special cells contain a sac full of pigment connected to muscle fibers. As the muscles contract, the sac stretches, and the pigment covers a larger area. They can enlarge sacs at will, changing the colors on different parts of their bodies or all of them simultaneously.

Many tropical frogs are green from a deposit of a bile pigment called biliverdin in their tissue and bones. The colors are from a combination of absorption and reflection of light and diffraction and physical color.

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Blue frog

Changing Colour

Many of the 8,000 species of amphibians can change their color by dispersing or concentrating pigment in the pigment-containing cells called chromatophores. The change typically takes a few minutes as the changes are under hormonal control.

Changing their color allows amphibians to regulate their body temperature. Dark-colored bodies absorb energy more rapidly than light colors. A frog seen under the hot sun is usually pale, while it will generally be darker at night. If their body is partly shaded, they can have two colors on different body parts.

Another reason for changing their color is to filter out ultraviolet light. UV light can damage body tissue and cause sunburn.

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Camouflage

The patterns and colors of amphibians are often used for camouflage (crypsis.) This allows them to feed on their prey without being detected. However, and more importantly, it also stops them from becoming prey. Amphibians have many predators depending on where they live, and their color is essential to their defence.

Many amphibians are toxic as they contain toxins in their skin. These can range from fatal to their prey or can make them nauseous. However, their first line of defense is camouflaging so that they don’t get bitten in the first place.

Amphibians either employ a pattern that allows them to match their usual habitat or with colors that break up the outline of their body.

Many toad species resemble dead leaves, with many having fleshy horns and a stripe down the middle. These can be extremely hard to see, even when looking for them.

Studies have shown that the color of some amphibians matches their habitat precisely. Snakes such as pit vipers feed on frogs and use infrared receptors to find their prey. However, some species of frogs fit their background, not in the visible spectrum but also when looked at in infrared.

Amphibians may not seem to have much in common with killer whales. However, along with other marine mammals, killer whales have light-coloured undersides and a dark top. Some amphibians also have these color patterns as well. This makes them less visible when viewed from below against the daytime sky.

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Brightly Coloured

Some amphibians don’t camouflage themselves from predators or prey but are brightly colored. As their name suggests, the poison-dart frogs are highly toxic and colorful. Their color is believed to have evolved to warn off potential predators. There are over 100 species of poison dart frogs, and they come in many different colors. It is believed that their toxicity comes from their prey as captive poison-dart frogs, which are fed other food, are not found to be as toxic.

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Patterns

While some amphibians, such as the poison-dart frogs, only use bright colors to warn off predators, some combine camouflage with colors. Some amphibians, such as fire-bellied toads, have a camouflage pattern on top but display a bright orange color when viewed from below.

Some frogs have bright colors only on some parts of their bodies. These areas are hidden when the frog rests, but the colored flanks and thighs show color when they move. This serves to confuse any predators that might attempt to feed on them.

When viewed from behind, the South American false-eyed frog looks like it has two large eyes. These confuse any predators trying to sneak up on them from behind. White’s tree frogs have a spot on their nose, which may help when confronted by a snake, although we also know that frogs can see in infrared, so that it may serve as a communication device.

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Colourful newt

Sexual dimorphism

It is well known that reptiles such as chameleons can change their color, but other animals, including fish, will also change color. This can be done to stay safe in their environment or to enable them to breed. However, some amphibians can also change their color.

Markings and colors are also signs of sexual dimorphism, with females often sporting different colors or markings than males. This is more prevalent in daytime species such as the poison-dart frogs found in Trinidad, which turn black and fight other black males, turning brown only if they lose.

Some frog species gather in groups of hundreds or thousands to mate. Because it would be difficult to track who is male or female, males often change color to yellow, possibly to warn other males away rather than to attract females. The color change can take an hour rather than the rapid transformation of reptiles such as chameleons.

Different amphibians often inhabit the same range, and the patterns can help tell them whether they are looking at one of their own or another species.

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