Seminar Two
Evolution of sexuality
Internal versus external fertilization

The pair of tiny glass frogs (so named because their abdominal skin is semi-transparent) is in amplexus, meaning the male rests atop the female, awaiting her release of eggs onto the leaf. He will try to be the first and only male to fertilize her eggs.

A tiny tadpole will develop inside each gelatinous egg, ready to fall off the leaf into the water of a stream below. If a predator such as a snake starts to eat the eggs, the tadpoles will drop off sooner than they would have otherwise, provided that they are close to being ready anyway.

This reproductive strategy involves external fertilization, that is, fertilization outside of the female body. Unlike internal fertilization it provides a male with certainty of paternity. Don't forget this little detail. It is of profound importance in animal behavior, and we will look at it again in the context of human behavior.