Embryo and Embryonic Development

Embryonic development ordinarily is considered to begin with the formation of the fertilized egg called the zygote. In the case of North American leopard frogs, zygote formation occurs in breeding ponds or wetlands in the early spring. During winter, the frogs reside in the cold water of northern lakes. When the ice melts and the days grow longer, the frogs leave the cold lakes and seek shallow ephemeral bodies of water. Water has a high specific heat, which means that lakes resist a change in temperature. The shallow water of breeding ponds warms readily, which is essential for both ovulation (the release of eggs) and embryo development. Male frogs clasp mature female frogs and this may encourage egg release. The clasping male releases sperm as the eggs are extruded. A female may release as many as 3,000 eggs which, when fertilized, results in a potential of 3,000 embryos.