ARE A YARDSTICK OF BIODIVERSITY
by Whit Gibbons
February 27, 2005
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
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
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.
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.
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.
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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