Embryonic Temperature Adaptations and Relationships in Toads

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Abstract
A comparison of the limits of temp. tolerance and rates of development of the eggs of members of the toad spp. complex, Bufo americanus, B. terrestris, B. fowleri, and B. woodhousi, reveals differences which can be correlated with geographical distr. and breeding habits. Embryos of B. americanus have the lowest min. and max. limiting temp. for normal development, which correlates with the fact that this sp. has the most extensive n. distr. and is the characteristic form at higher altitudes. Eastern B. fowleri embryos from similar latitudes, which breed later and at higher environmental temps., are less resistant to low exptl. temps. in the embryonic stages, but are more tolerant of high temps. Embryos of B. fowleri from Louisiana, B. woodhousi from Texas and Oklahoma, and B. terrestris from South Carolina and Louisiana were found to tolerate the highest temps. but are clearly most susceptible to the low temps. A comparison of the rates of development of these 4 spp. reveals a relationship which is interpreted to indicate that B. americanus is closely allied to B. terrestris and that B. fowleri is closely related to B. woodhousi.