Experimental detection of rapid evolutionary response in natural lizard populations

Abstract

MANY studies of geographical variation within species^1–7, including those using numerical hypothesis tests^3–10, have demonstrated a relationship between patterns of phenotypic and environmental variation. But relatively few rigorously tested direct demonstrations of current selection in natural populations exist^11–14. Here we present evidence of a rapid response to selection from a field manipulation of the Dominican lizard, Anolis oculatus. There is considerable altitudinal and longitudinal variation in climate and vegetation on the island of Dominica¹⁵. We have recorded complex patterns of geographic variation in morphology (body size and shape, colour pattern and scalation), which we have shown to correlate (both univariately and multivariately) with these patterns of ecological variation¹⁶ by numerical hypothesis testing^10,17,18. Populations of several ecotypes of the species were translocated into large-scale experimental enclosures, and monitored over a period of two months. The magnitude of the difference in multi-variate morphology between survivors and non-survivors within each enclosure was found to correlate with the magnitude of the difference between the ecological conditions of the enclosure site and the original habitats. Similar relationships were found for three indices of fitness of survivors.