Most species start out as aquatic tadpoles and metamorphose into land-living animals. As tadpoles in an aquatic system, they are very sensitive to pollutants. So a number of my colleagues use tadpoles as monitors of water pollution. In the frog world, males are the vocal sex, calling to attract females, says Dr. Linda Maxson. What's more, the male frog is a single-minded swain, Maxson says.
Most species have an external fertilization mode known as amplexus.
The male grabs the female from behind, waits until she extrudes her eggs, and then fertilizes them. He'll stay on hours, maybe days, until something happens that makes him realize his mistake.