ARE POPULATIONS ISLANDS - ANALYSIS OF CHLOROPLAST DNA VARIATION IN AQUILEGIA

The degree to which conspecific populations are interconnected via ong oing gene flow remains an important focus of evolutionary biology. One major difficulty in distinguishing ongoing gene flow from historical subdivision is that either process can generate similar estimates of a pparent gene flow. Thus, gene flow estimates themselves are insufficie nt to distinguish between these alternatives. However, genetic data co upled with additional information about demography and distribution do allow a distinction to be made. Here we address the specific question , does gene flow link populations of Aquilegia? In a survey of a 525 B .P. chloroplast DNA fragment sampled from 251 individual plants from 1 8 populations of three taxa, five haplotypes were identified. No signi ficant relationship between geographic distance and apparent gene flow between population pairs existed. Further, the estimated level of gen e flow was entirely compatible with a historical subdivision of Aquile gia populations during the late Pleistocene or early Holocene. Therefo re, these patterns of variation are due not to ongoing gene flow, but rather to historical association among populations. Thus Aquilegia pop ulations may be considered as distinct evolutionary entities with rega rd to seed-mediated processes. As a result, comparative analysis of ec ological traits undergoing potentially rapid evolution (e.g., life his tories, mating systems, inbreeding depression) should be possible in t hese taxa.