The Herpetological Journal

pp. 47-53
Authors: Hoffman, Joy

Abstract: Many species of terrestrial amphibians can absorb water by pressing a highly vascularised region of the ventral abdominal skin against a moist surface. The degree of dehydration needed in order to evoke this response varies from species to species, suggesting that they make different use of the opportunity to use surface water for hydration. Most of the species that have been studied are each confined to a fairly narrow ecological niche, and the differences in their responses make sense in the light of their natural history. Consequently, it was of interest to compare populations of a single species living in different regions to see whether differences in the response to the presence of moisture are characteristics of the species or are related to local conditions. The steep north-south gradient of increasing aridity in Israel and the presence of populations of the toad Bufo viridis throughout the country provided an opportunity to make such a comparison. The frequency of this water seeking response (WR) in fully hydrated toads and the sensitivity of WR to raised plasma osmolality were determined in laboratory-acclimated samples collected from three sites in Israel, one from north-west Italy and one from Kyrgyzstan. These sites differed in altitude and climatic characteristics (mean annual temperature and total annual rainfall). A negative correlation was found between the frequency of WR and the annual rainfall at the sites where samples were collected, suggesting that WR is not a fixed characteristic of this species. The observed differences between populations are discussed with reference to evolved adaptations to aridity and the past evolutionary radiations of the species.

Keywords: ADAPTATION TO ARIDITY, OPPORTUNISTIC HYDRATION, GREEN TOADS, AMPHIBIAN