Altitudinal and Interspecific Differences in the Rehydration Abilities of Puerto Rican Frogs (Eleutherodactylus)

Abstract

Eleutherodactylus antillensis is a climbing frog that is widely distributed in grassy lowland habitats that often become dry between rainstorms. The closely related species E. coqui has an altitudinal range that extends from the same lowland sites occupied by E. antillensis to mountaintops that are almost continually wet. The frogs lose a substantial quantity of water by evaporation during activity on dry nights and can regain that water by absorption from the substrate of their daytime retreats. Lowland frogs of both species rehydrate more rapidly from aqueous solutions than highland E. coqui. When water uptake is expressed per cm² of surface area, E. antillensis rehydrates more rapidly than E. coqui. This relationship probably represents differences in hormonal responses to dehydration. These responses are complex because the rate of water uptake is not related to solution water potential by a simple physical relationship. The small body sizes of E. antillensis and lowland E. coqui probably facilitate rehydration in natural habitats in which suitably moist substrates are limited in occurrence and area.