Metamorphosis

Frogs & Friends

Metamorphosis is a vital part of evolutionary history of amphibians in which their fishlike, gill-breathing larvae turn into lung-breathing terrestrial amphibians. Metamorphosis also means to get the optimum out of both worlds, water and land, which definitely leaves amphibians with an evolutionary advantage.

All amphibians are vertebrates with water-permeable, glandular skin with no scales, feathers or fur. They lay eggs without a protective calcareous shell, the spawn. Larvae hatch from these eggs, which breathe through gills and often look completely different to their parents. Only after metamorphosis do they take on the appearance of the adults and become lung-breathing animals. Therefore, they are easily distinguishable from reptiles, even though newts and lizards look very similar at first glance. But reptiles have dry, scaly skin and no larval state.

Most frogs need to be around a water source to reproduce. During springtime, the water will be teeming with spawn clutches, each containing hundreds of frog eggs. Once an egg hatches, a small, legless, fish-like creature emerges. This frog offspring is called a tadpole.

Tadpoles grow in a matter of days within the soft gelatinous eggs before leaving their protective shell. Tadpoles don’t have any limbs or fins but swim propelled by their wide tail, only. They still breathe through their gills. Tadpoles feed on algae and aquatic plants.

After about ten weeks, the hind legs of tadpoles start to develop. They’re still tiny when they first begin to grow.

After about three months, the front legs begin to develop as well and the tail slowly starts to recede into the body. Also the lungs develop in preparation for the great transition onto land. How fast the tadpole transforms depends on environmental factors.

The final sprint: Tadpoles shortly before transitioning to land.

Just landed! As soon as the shift from gill-breathing to lung-breathing is completed, the young frog crawls out of the water onto land. Its diet also switches to ‘adult food’.

However, the transition has not been completed yet. The tale still needs to shrink and eventually disappear. This is when a tadpole has developed into a froglet and is to begin a life as frog.

All that remains of this young white-lined leaf frog's life as a tadpole is a small tale stump.

No rule without exemption! It is quite certain that the most original strategy among anurans for successful reproduction is the one with eggs deposited in water and tadpoles living in the water until transitioning to land. However, since there is all kinds of threat lurking in water a lot of alternative reproduction strategies have evolved.

Marsupial frogs, for example, incubate their eggs in a skin pouch, similar to a kangaroo, only that this pouch is located on the back.

A very unique reproductive strategy is the one of the Surinam toad. Being a bizarre creature by its look to begin with, the Surinam toad performs skillful underwater somersaults to ensure that the clutch of eggs end up on the back of the female.

There, it will be rapidly overgrown by skin until eventually the mini creatures break free from their mothers back - an alien like burst out.

Another form of reproduction is the one employed by tropical frogs, like for example the Wallace's Flying Frogs. Here, foam nests, either floating on water or hanging on plants, serve as shelter for deposited eggs. The tadpoles, once ready, will somehow make their way out of the foam or just simply fall into the below water.

The South American Darwin's frogs have a highly unusual method of brooding and rearing their young. After the female frog has left up to forty eggs in the leaves, the male frog would swallow the clutches and store the eggs in a gular pouch where they develop into tadpoles. 3-4 weeks later, when metamorphosis is complete, they hop out as fully formed young froglets.

The spectacular reproduction of Darwin's Frog: The Darwin's frog is one of around 2000 threatened amphibian species of the world. For the whole story of the Darwin's frog project, including pictures of the unique 'birth' of a froglet, feel welcome to visit the Frogs & Friends website.

Scientists have recorded 39 different strategies so far for frogs and toads to take care of their offspring. However, they all have one thing in common: In the end, there will be a fully formed, small froglet representing the start of a new amphibian generation.

Frogs & Friends
Credits: Story

Exhibition by Frogs & Friends
Exhibition curators: Björn Encke & Annette Kinitz

Text to illustrations: Interactive trip by Frogs & Friends
Art Director: Sebastian Baurmann
Illustration and Animation: Jonas Lieberknecht
Text: Lena Thiele, Heiko Werning

“Wallace’s flying frog” Video Material: Günther Rath
Illustration Darwin’s frog reproduction: Klaus Busse

Photographs:
European tree frog: Emanuele Biggi/Minden Pictures
White-lined leaf frog: Pete Oxford/Minden Pictures
Marsupial frog: Michael&Patricia Fogden/Minden Pictures
Wallace's Flying Frog: Stephen Dalton/Minden Pictures
Surinam toad: David Massinem
Woodfrog on land: Steve Byland
Algae eating tadpoles and tadpole hind legs: Morley Read
Frog on spawn: Matteo photos

With the support of the Interactive Media Foundation gGmbh (IMF)

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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