Pollination and gene flow in white clover, growing in a patchy habitat

In insect-pollinated plants, the effects of habitat fragmentation on gene flow are mediated through the foraging behaviour of pollinators, which will be modified by the relative attractiveness and density of resource patches and the relative constancy of pollinators to a target species and/or patch. Bee-mediated gene flow between groups of self-incompatible plants was quantified using five selection lines of white clover (Trifolium repens L.) with isoenzyme markers. The objectives were to investigate whether pollen flow and consequent gene flow reflected bee patch constancy and how pollen flow varied with distance and vegetation between donor and recipient plants. Groups of five clover plants were positioned on grass/herb patches, sown within a field of barley. Each group of plants contained one clover line. Seed paternity in three cohorts of inflorescences was determined using starch gel electrophoresis. Most (92%) of the sampled seed was sired by plants from the same group as the recipient plant. There was a significant negative relationship between pollen flow and distance between plant groups, and pollen flow declined significantly over time. There was some evidence that a strip of barley between the grass/herb patches acted as a barrier to pollen flow. In conclusion, pollen and gene flow reflected the bee patch constancy observed in a previous experiment, and short distances of separation (26 m) between plant groups led to restricted bee-mediated pollen flow.