Temperature Adaptations of Amphibian Embryos

A simple equation is used to describe the rate of development of amphibian embryos between any two developmental stages at various temperatures. This equation yields values for two constants describing the adaptive temperature and the relative time for development at this temperature for every species. The constants can be used to measure adaptability of the embryos to temperature and to study the process of temperature adaptation during speciation. Genetic adaptation to temperature is a very slow process in the amphibia. Many species develop in nature at temperatures near the limit of their adaptive range rather than at optimal temperatures. Different geographical races within one species may show significant differences in their adaptive temperatures. These are, however, considerably smaller than the differences between the actual environmental temperatures encountered by the embryos. In some species no differences between the adaptive temperatures of different geographical races can be found. Variable selection of the time and place for egg deposition by the adults partially overcomes the relatively strict requirements of their early embryos. The urodela as a group show a considerably more limited range of adaptive temperatures than the anura, suggesting that their limited geographical distribution is due to a lack of adaptability of their embryos to high environmental temperatures.