2014 | VOLUME 30 | ISSUES 1-4
Physiological response of Bufo viridis (Laurenti, 1768) populations across an aridity gradient
Bufo viridis (also known as Pseudepidalea viridis), a semi-terrestrial anuran found in climates ranging from temperate to semi-desert, has both behavioural and physiological defences against the threat of dehydration; it is also able to tolerate a wide range of salinities. We examined the prediction that those populations inhabiting drier environments will have a compensatory physiological response to dehydration. To that end we compared laboratory-acclimated samples of toads collected from three sites in Israel, one in north-west Italy, and one in Kyrgyzstan differing in the level of annual rainfall in their natural habitats. When kept on damp soil without access to free water, measurements of changes in body mass, plasma osmolality, and the concentrations of urea and major electrolytes in the plasma revealed no significant differences in the physiological responses of toads from the different sites. This contrasts with the negative correlation that had previously been found between the frequency of a behavioural, water-seeking response and annual rainfall at these same sites. The results are discussed in the light of what is known about the evolutionary history of the species. It is suggested that, because drought resistance and euryhalinity are both features of general osmotic stress tolerance, these properties may have evolved initially in the species’ area of origin as a response to fluctuations in the salinity of inland water bodies; later, when the species migrated into arid regions, it was an exaptation enabling the toads to tolerate water shortage.
Published: 31 January 2014