Frequent long-distance gene flow in a rare temperate forest tree (Sorbus domestica) at the landscape scale.

Precise empirical data on current gene flow by pollen, both with respect to distance and abundance, is crucial to understand whether habitat fragments are functionally connected. Based on a large-scale inventory ( approximately 100 km(2)) in which all individuals of a naturally scattered forest tree (Sorbus domestica) were mapped, we inferred current gene flow by pollen using genetic paternity analysis. We detected an extensive network of effective pollen transfer. Although short pollen flow distances were most abundant, 10% of the assigned pollen donors were more than 2 km away from their female mating partners, and 1.8% were even at a distance of 12-16 km. This latter pollen flow shows that current long-distance gene flow over a fragmented landscape clearly occurs. Pollen dispersal was well described by a fat-tailed inverse curve. Using parentage analysis of established trees, maternally inherited chloroplast markers and diameter at breast height measurements as an indicator of individual tree age, we were able to infer regular seed dispersal distances over several hundred metres up to more than 10 km. We conclude that in temperate, insect-pollinated and animal-dispersed tree species such as S. domestica, fragmented subpopulations are functionally connected by gene flow through both pollen and seed.