ATTERNS AND LEVELS OF POLLEN-MEDIATED GENE FLOW IN LATHYRUS LATIFOLIUS.

While gene flow can be an important force in evolution, few direct measures are available in the plant literature. Descriptions of gene movement within populations are more common, but have primarily involved crop species and artificially constructed populations. In this study, fractional paternity procedures were used to examine patterns of pollen movement over two years within two sites of Lathyrus latifolius, a bumblebee-pollinated, self-compatible perennial legume. Study sites consisted of 15 to 23 semi-discrete flowering patches that contained 1 to 29 distinct genotypes. Distributions of gene movement distances within the study sites differed significantly from that expected under random mating. Mean gene movement was 14 m. On average, 17.6% (range = 0-52%) of matings occurred within a flowering patch. Outcrossing rates, estimated from paternity analysis, ranged from 0.87 to 0.90 across sites and years. Significant heterogeneity occurred among maternal individuals with respect to outcrossing and immigration rates, indicating that mating patterns were idiosyncratic to each plant. Apparent rates of pollen flow into the sites ranged from 5 to 15%, while estimates of total pollen flow into sites ranged from 16 to 46%. Significant increases in immigration rates between years were associated with decreases in the density of flowering plants. © 1993 The Society for the Study of Evolution.