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Eggs

            Frogs start out as fertilized eggs. The haploid egg, (Haploid is one set of DNA coding, for the entire frog. Adult frogs are diploid, meaning they get half their DNA from one parent and the other half of their DNA from the other parent.), of the female is fertilized by the haploid sperm of the male. The egg will continually divide and grow until it becomes a tadpole. In some species this process takes a few days in others it takes months.

Tadpole

            Anyways, we now have a tadpole, which is a frog in its larval form. And, right now it is nothing like an adult frog. Tadpoles are herbivores, for the most part. Sure some species have tadpoles that can be carnivorous, eating other tadpoles or frog eggs, but for the most part they eat the microscopic plant life of ponds or streams where they live. Eventually a change occurs called metamorphosis. This can happen either days or years into the tadpole’s life, again depending on the species.

Metamorphosis

            Once metamorphosis starts the tadpole will fast and be almost immobile for awhile. It is a hard life, because now there is an increased risk of predation along with a big change in the tadpole’s life. When metamorphosis is complete the tadpole will have become an adult froglet. In some species, however, the frog skips the tadpole stage developing right into a tiny froglet in its egg.

Adult

            Now the frog is an adult. It will live out its life feeding and trying not be eaten for the rest of the rainy season or spring or summer season depending on where it lives. Eventually the frog will hibernate or estivate depending on its habitat.

Hibernation/Estivation/Inactive Period

            In colder areas a frog will survive the winter/cold weather season by a process called hibernation. This starts out slowly, gradually so the frog can prepare itself. As the temperature drops over a series of weeks the frog’s temperature will drop. Remember, frogs are ectothermic. The frog will use all that glycogen it’s been storing in its liver and convert it into glucose. A frog can produce up to a hundred times its normal levels of glucose during this period. Then it places that glucose into its cells of the vital organs, because the glucose is a frog’s antifreeze. It lowers the freezing temperature of the water in those cells. But what about the rest of the cells? Well, the water around them will end up freezing. And during this cold weather the frog will remain inactive, its breathing and heart rate will become really slow.

            Other species don’t live in cold climates. Just the opposite. They live in hot, dry climates such as deserts. These species carry out what is called estivation. Basically they burrow underground to escape the heat and avoid water loss. Unlike hibernation, which can last for up to the entire winter season, estivation may only happen every day while the sun is out and the frog comes out at night. Or it may last years for some species who only come out of the ground every few years when the cool, rainy weather returns. During this time it is underground the frog is pretty much inactive.

Active Period

            Then comes the active season. This season occurs after hibernation or extended periods of estivation. From hibernation the weather begins to warm again as the spring season returns. First the vital organs thaw out. This allows metabolic activity to pick up again so the rest of the body can defreeze and the frog is no longer a “frogsicle”. Usually when hibernation ends it’s the spring season, almost time for breeding.

Breeding Season

            Next, comes breeding season. This season is marked by either an increase in rainy weather, or an increase in daylight, or an increase in temperature. Pretty much this is during the spring or summer season for many species. But for other species, such as those in tropical climates, it is known as the rainy season. Either way when one or more of these changes occur, the frogs know. They then migrate to their breeding grounds. Once there, they mate and produce more fertilized eggs. Beginning the cycle again. For many species, after the eggs are fertilized they leave the breeding grounds and continue on eating and trying not to be eaten themselves for the rest of their active season. They will continue the cycle over the years by returning to their breeding grounds when it is time to breed. But, for other species they don’t just leave the fertilized eggs right away. They show some form of parental care, by protecting the eggs until they become tadpoles or tiny froglets. And the cycle continues to circle.

Works Cited:

Behler, J. L., & Behler, D. A. (2005). Frogs: A chorus of colors. New York, NY: Sterling Publishing Co., Inc.

Beltz, E. (2005). Frogs: inside their remarkable world. Buffalo, NY: Firefly Books Ltd.

Gamlin, L., & Rohan, A. (1998). Mysteries of the rain forest. New York: The Reader’s Digest Association Limited.

Photo taken by Caty Jones

Wood frog next to wood frog eggs

Spring 2008

Mongabay.com

Rhett A. Butler - San Francisco, CA.

1999-2008.

Mongabay.com

Rhett A. Butler - San Francisco, CA.

1999-2008.

Mongabay.com

Rhett A. Butler - San Francisco, CA.

1999-2008.