Embryonic Temperature Adaptations in Highland Rana pipiens

Abstract

Embryos of leopard frogs from an altitude of 3,700 feet in Moravia, Costa Rica, have a slow rate of development and narrow limits of temperature tolerance. The slow embryonic development may be causally associated with a long growing season. Ordinarily the length of the growing season becomes progressively shorter as the altitude or latitude increases, and most cold-adapted ranid embryos possess a rapid developmental rate. However, the climate in the central highlands (3,000-5,000 feet) of Costa Rica is not typical of elevated regions. The year-round temperate condition at Moravia apparently precludes selection for a rapid developmental rate in the leopard frogs of this region. The narrow range of embryonic temperature tolerance may be correlated with the small variations in environmental temperatures. The outcome of hybridization experiments between leopard frogs from Moravia, Costa Rica and northern localities in the United States are discussed in light of the above results.