FROGS ARE A YARDSTICK OF BIODIVERSITY

by Whit Gibbons

February 27, 2005


Frogs are some of the most amazing animals on earth. Most people think of a frog as an animal that hops, and that’s true. Frogs do hop. But more than 4,000 different species of frogs, toads, and treefrogs live in the world today. And each one offers an intriguing look into the wonders of biodiversity.

Consider the diverse range of frogs’ mating calls. Most have a song of sorts, such as the bullfrog’s booming call in summer and the spring peeper’s high-pitched notes in early spring. The ducklike sound of squirrel treefrogs around houses during summer rains and the beautiful trill of brown garden toads during warm spring rains add to the audio repertoire of frog diversity. In the Southeast alone, with only a few dozen species, a wide range of mating calls can be heard by those who venture into river swamps at night. The snoring sound of river frogs, gruntlike call of pig frogs, and eerie, wavering whistle of the bird-voiced treefrog are all natural noises of southeastern wetlands.

Most North American frogs have fairly simple life cycles, mating in wetlands, with the male clasping the female until she lays eggs, which he then fertilizes. The eggs hatch into tadpoles after a few days, and the tadpoles stay in the wetland until they metamorphose into little toads or frogs. The adults, meanwhile, are long gone, back into the surrounding woods. But frogs characteristic of the tropics have a variety of reproductive behaviors.

For whatever reasons, tropical frogs have evolved some of the most intricate and remarkable reproductive strategies known for any land animals. For example, Darwin’s frog of South America is a strange-looking creature with a pointed nose; it breeds on land instead of in the water. After the eggs are laid and fertilized, the female leaves, and the male stays around for about three weeks. Once the larvae begin to move within the eggs, the male sucks them up into his mouth and proceeds to brood them in his vocal sacs. Approximately 50 days later the young emerge from the male’s mouth, fully formed.

Many frogs exhibit parental care by moving their eggs or tadpoles from one location to another, actually carrying them on their backs. But females of one of the tropical American poison dart frogs take parental care to another level with a behavior known in no other amphibian-feeding their young. After laying eggs, the female takes each tadpole, one at a time, and deposits it into the water-filled angle between the stem and leaf of a bromeliad plant. She visits each tadpole once a week, and as she approaches the leaf where the tadpole resides, she peers into the water. If the tadpole thrashes, she deposits an unfertilized egg that serves as food for the tadpole. If the tadpole does not move, she assumes it is dead or gone, and she does not deposit an egg.

One of the most amazing and unusual forms of parental care ever recorded in any animal was that involving the gastric brooding frog of Australia. In this species, the female swallowed eggs shortly after fertilization. The larvae resided in her stomach for several months, getting no nutrition from the mother. Nor did the mother herself feed during this time. But finally it was all over, and the young crawled out of their mother’s mouth after hatching. The sad part of the story, however, is that since its discovery in the 1970s, the species has apparently gone extinct in the wild, and the few in captivity have died. Not only does the gastric brooding frog represent the loss of a biological novelty, medical science has lost an unusual opportunity to understand the stomach by studying features and behaviors found in no other organism.

Most American frogs and toads do not have bizarre reproductive behaviors, but they are nonetheless fascinating. Check out the following Web site to see, hear, and read about some of those living in your area: wwknapp.home.mindspring.com/GAFrog.Toad.html. Frogs, toads, and treefrogs are intriguing creatures, and the more familiar people are with them, the more likely they are to support the idea of protecting these creatures and their habitats.



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