10.10: Amphibian Evolution and Ecology

Would you eat this?

This is a plate of frog legs! Many people would view this dish as a tasty treat. As you can see, one way amphibians are important to people is that they can be used as a food source.

Role of Amphibians

Humans have used amphibians for a number of purposes for thousands of years, if not longer. Amphibians play significant roles in many food webs and are thus an important part of many ecosystems. For example, frogs keep insect populations stable. Extinction of frogs, or just significant decreases in the frog population, would probably have serious consequences for agricultural crops.

Humans have also consumed amphibians, especially frogs, probably since they first ate meat. More recently, amphibians have been tremendously useful in research.

Amphibians as Foods

Amphibians play important roles in many ecosystems, especially as middle players in many food chains and food webs. In addition to consuming many worms and insects and other arthropods, and even some small reptiles and mammals and fish, they are prey for turtles and snakes, as well as some fish and birds. Tadpoles keep waterways clean by feeding on algae.

Frogs are raised as a food source for humans. Frog legs are a delicacy in China, France, the Philippines, northern Greece, and the American south, especially the Frensh-speaking parts of Louisiana. Only the upper joint of the hind leg is served, which has a single bone similar to the upper joint of a chicken or turkey wing. They are commonly prepared by grilling or deep frying, sometimes breaded, though they can also be served with garlic, or turned into a soup or stew. Some estimates have well over a billion frogs harvested a year as food. That's about one frog harvested for every seven people on the planet.

Amphibians in Research

Amphibians have long been used in scientific research, especially developmental and physiological processes, largely due to their unique ability to undergo metamorphosis, and in some species, to regenerate limbs.

Amphibians are also used in cloning research. Cloning involves making identical copies of a parent organism, and the large amphibian egg helps in this process. They are also used to study embryos because their eggs lack shells, so it is easy to watch their development.

The African clawed frog, Xenopus laevis, is a species that is studied to understand aspects of developmental biology. It is a good model organism because it is easy to raise in a lab and has a large embryo, which is easy to study (Figure below). Many Xenopus genes have been identified and cloned, especially those involved in development. Developing Xenopus embryos can be easily observed and studied with a basic microscope, though the eggs are large enough to see without a microscope. Because of their size, the exact developmental stage after fertilization can be easily determined. This allows proteins that are used at a specific developmental time to be collected and analyzed. Identification of Xenopus genes and proteins has allowed the identification of corresponding genes and proteins from humans.

Many environmental scientists believe that amphibians, including frogs, indicate when an environment is damaged. When species of frogs begin to decline, it often indicates that there is a bigger problem within the ecosystem. This could have dramatic effects on food webs and ecosystems.

Figure \(\PageIndex{1}\): Frog embryos are often studied to better understand how development works.

Amphibians in Popular Culture

Amphibians can be found in folklore, fairy tales, and popular culture. Numerous legends have developed over the centuries around the mystical properties of the salamander. Its name originates from the Persian words for “fire” and “within," so many of these legends are related to fire. This connection likely originates from the tendency of many salamanders to live inside rotting logs. When placed into the fire, salamanders would escape from the logs, lending to the belief that the salamander was created from flames.

Unforgettable amphibians Kermit the Frog (Figure below) and his popular saying “It’s not easy being green.” Frogger, from the video game of the same name, has been teaching children about the dangers of the road and alligator-filled moats for years. And all it takes is a kiss from a princess to turn a frog into a prince, as told in The Frog Prince story.

Figure \(\PageIndex{2}\): Kermit the Frog balloon is flown at the Annual Macy's Thanksgiving Day Parade.

Summary

• Frogs are raised as a food source in many parts of the world.
• Amphibian embryos are ideal to study development since they lack a shell.

Review

1. Describe the role of amphibians in the food chain.
2. How are amphibians important in environmental science?
3. Describe one way amphibians are used in research?