Evaporative water loss in insular populations of Anolis cristatellus (Reptilia: Sauria) in the British Virgin Islands. III. Response to the end of drought and a common garden experiment

Evaporative water loss in Anolis cristatellus from the British Virgin Islands was negatively correlated with the aridity of their habitats. Phenotypic plasticity and/or differential mortality of less well-adapted individuals allowed rapid changes within populations. Here we report the results of two studies intended to differentiate between the two processes. We took advantage of the end of a major drought to study the rapidity with which populations recovered from unusually dry conditions. Population values changed rapidly from those measured in the past. There was no correlation between long-term habitat aridity and measured water-loss rate, but the multiyear correlation between aridity and skin resistance to water loss persisted. We also conducted a common garden experiment in which animals from the wettest and driest habitats were housed under intermediate conditions for one month. We detected no change in skin resistance to water loss in any of the three populations we studied; however, the mass of lizards from Sage Mountain increased significantly during the experiment, and their water loss per unit mass decreased significantly. These results support the existence of both phenotypic plasticity and genetic differences resulting from rapid selection within populations. The magnitude and relative importance of the two, however, remain to be determined.