ADAPTIVE DIFFERENTIATION FOLLOWING EXPERIMENTAL ISLAND COLONIZATION IN ANOLIS LIZARDS

If colonizing populations are displaced into an environment that is of ten very different from that of their source(1), they are particularly likely to diverge evolutionarily, the more so because they are usuall y small and thus likely to change by genetic restructuring or drift(2, 3). Despite its fundamental importance, the consequence of colonizatio n for traits of founding populations have primarily been surmised from static present-day distributions(1,2,4,5), laboratory experiments(6) and the out-comes of haphazard human introductions(7-9), rather than f rom replicated field experiments. Here we report long-term results of just such an experimental study. Populations of the lizard Anolis sagr ei introduced onto small islands from a nearby source, differentiated from each other rapidly over a 10-14-year period. The more different t he recipient island's vegetation from that of the source the greater t he magnitude of differentiation. Further, the direction of differentia tion followed an expectation based on the evolutionary diversification of insular Anolis over its entire geographic range, In addition to pr oviding a glimpse of adaptive dynamics in one of the most extensive ge neric radiations on earth, the results lend support to the general arg ument that environment determines the evolution of morphology.