GENE FLOW AMONG SMALL POPULATIONS OF A SELF-INCOMPATIBLE PLANT - AN INTERACTION BETWEEN DEMOGRAPHY AND GENETICS

We assessed the effects of population size and genetic relatedness on rates of pollen gene Bow into experimental populations of the insect-p ollinated, self-incompatible plant Raphanus sativus. We created synthe tic populations of sizes 2, 5, 10, and 20 with three genetic structure s (full siblings, half siblings, and unrelated plants). Following poll ination in a natural setting, we conducted a simple paternity exclusio n analysis using the allozyme genotypes of progeny to measure apparent gene flow and Monte Carlo simulations to estimate total gene flow. Es timates of apparent pollen gene flow rates ranged from 0 to 100% and w ere similar in rank to estimates of total gene Bow. There were signifi cant effects of population size and relatedness on the rate of apparen t gene flow, and there were significant population size by relatedness interactions. Populations of size 2 had higher gene flow rates than l arger populations, gene flow being negatively associated with the leve l of cross-compatibility (as measured by hand pollinations). Gene Row into populations of size 2 was also negatively associated with the dis tance to the nearest population of size 10 or 20. These results sugges t that interactions among demography (population size), genetics (cros s-compatibility), and ecology (pollinator behavior) are important infl uences on pollen gene flow rates into small plant populations.