Leading-edge populations do not show low genetic diversity or high differentiation in a wind-pollinated tree
Climate changes can shift species’ ranges. Knowledge on genetic variation of the leading-edge populations provides critical information to understand responses and adaptation of plants to projected climate warming. To date, the research into genetic variation of leading-edge populations has been limited, particularly in the role of wind-mediated pollen flow in maintaining high genetic variation. Castanopsis sclerophylla (Fagaceae) is a wind-pollinated and gravity-dispersed tree. In the present study, we used seven polymorphic microsatellites to genotype 482 samples from five leading-edge and 12 non-edge populations. Significant effects of recent population bottleneck events were found in three of the five leading-edge populations, indicating that the leading-edge populations might have been recolonized after the Last Glacial Maximum. Genetic diversity was higher, though not significantly, in leading-edge than in non-edge populations. Relationship between genetic diversity and latitude indicated an increasing trend of genetic diversity towards leading-edge populations. No significant difference in genetic differentiation was found between leading-edge and non-edge populations. The inconsistence with the general predictions by leading-edge colonization model could be explained by high gene flow via pollen grains. Pollen-mediated gene flow could maintain high genetic diversity within and low differentiation among leading-edge populations. In response to climate warming, high genetic variation may provide leading-edge populations raw materials for evolutionary adaptation to future environmental conditions.