Thermal Relations of Some Tropical Frogs Along an Altitudinal Gradient

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Abstract
Temperate-zone amphibians generally show an acclimation response of tolerance to high temperatures (CTMax), and several wide-ranging species have been found to have a negative correlation between elevation and CTMax. Fewer tropical species have been examined, but Heatwole et al. (1965) reported that the Puerto Rican frog Eleutherodactylus portoricensis failed to show an acclimation response, but did show a negative correlation between elevation and CTMax. Subsequently, E. portoricensis, as originally understood, was found to consist of a widespread species (Eleutherodactylus coqui) and a species restricted to high elevations (E. portoricensis) (Thomas 1965). CTMax was determined for these two species, and we found that differences previously believed to be attributable to elevation are, in fact, interspecific differences. There were no differences in CTMax of E. coqui from different elevations, but E. portoricensis had significantly lower CTMax. E. coqui failed to show an acclimation response. The few species of tropical amphibians that have been investigated suggest that, unlike most temperate-zone species, some tropical species fail to slow an acclimation response, and some fail to show a negative correlation between CTMax and elevation.