Genetic differentiation over a spatial environmental gradient in wild Rubus ideaus populations

The distribution is examined of molecular (random amplified polymorphic DNA) markers within and between 12 wild raspberry (Rubus ideaus) populations ranging over 600 m altitude and 40 km distance from a lowland area of extensive raspberry cultivation to remote upland sites. Most individuals are distinct, suggesting that seedling recruitment is the main means of propagation, but mean genetic similarities within sites (> 80%) are much greater than between sites (> 50%), suggesting a hindrance to gene movement between sites. Sites of genetically distinct populations can be grouped in lowland, valley and upland clusters; genetic similarity between sites decreased at slightly > 4% per 100 m difference in altitude from c . 80% between adjacent sites to 50% at 600 m altitude difference. Together with physiological data collected previously, the molecular evidence confirms that wild populations are more diverse than cultivars and suggests little gene flow from cultivated to wild, a result perhaps of reproductive asynchrony and little opportunity for seedling recruitment in established populations. The cause of the genetic differentiation between sites is not known and requires further study.