CONTINGENCY AND DETERMINISM IN REPLICATED ADAPTIVE RADIATIONS OF ISLAND LIZARDS

The vagaries of history lead to the prediction that repeated instances of evolutionary diversification will lead to disparate outcomes even if starting conditions are similar. We tested this proposition by exam ining the evolutionary radiation of Anolis lizards on the four islands of the Greater Antilles. Morphometric analyses indicate that the same set of habitat specialists, termed ecomorphs, occurs on all four isla nds. Although these similar assemblages could result from a single evo lutionary origin of each ecomorph, followed by dispersal or vicariance , phylogenetic analysis indicates that the ecomorphs originated indepe ndently on each island. Thus, adaptive radiation in similar environmen ts can overcome historical contingencies to produce strikingly similar evolutionary outcomes.