We tend to think of frogs and toads as fairly common creatures, varying only in color and size. Dr. William Duellman has done extensive studies of the amphibian order Anura which includes more than 3800 separate species of frogs. His studies show enormous frog reproduction variations.
Some frogs lay eggs in clutches near, but not in, the water. They glue the eggs to vegetation or rocks where the tadpoles drop into the water when the eggs hatch. Other frogs lay eggs in a protective foam that protects the eggs and provides food and water that can last for up to ten days. One-fifth of all frog species hatch into froglets instead of tadpoles. Each four-legged froglet has an attached yolk to supply nutrition until it can catch its own food. The males of one frog species glue themselves to the back of the larger females. The female digs a burrow in the ground to lay the eggs. She then wets the eggs with water from her bladder, and the male fertilizes the eggs.
The males of the African hairy frog develop rigid hairlike extensions of their skin during breeding, so when the male sits on the eggs, he protects them from predation. In the poison dart frog of Costa Rica, both sexes guard the eggs. When they hatch, the female brings unfertilized eggs to the tadpoles to eat until they can find food on their own. The females of the Jamaican tree frog lays water-filled capsules along with the eggs to provide adequate water for the tadpoles. In some species, the tadpoles crawl onto the back of either parent. Some frogs have pouches on their backs that hold eggs that have gill-like structures that enable the embryos to breathe.
Other unconventional frog reproduction variations include Darwin’s frog in Chile. The male scoops up the newly hatched tadpoles into his mouth and broods them there for several weeks until they mature. Even more bizarre is an Australian frog in which the female swallows the eggs after fertilization and incubates them in her stomach. This process, called gastric-brooding, usually takes six weeks in which the female does not eat. The tadpoles secrete a substance called prostaglandin E-2, which neutralizes the hydrochloric acid and pepsin normally used for digestion.
All of these reproductive strategies are designed to cope with different environments. Frogs can exist in a desert or a tropical rain forest or even a polar area. Survival is only possible because their reproductive systems are designed to fit the environment in which they live. The intricacy of frog reproduction variations is an excellent example of the intelligence and design God has built into the simplest of living things.
— John N. Clayton © 2020
To read more, you can find it in Scientific American, July 1992, pages 80-87. Available digitally HERE.