GENETIC DIFFERENTIATION IN SILENE DIOICA METAPOPULATIONS - ESTIMATIONOF SPATIOTEMPORAL EFFECTS IN A SUCCESSIONAL PLANT-SPECIES

Silene dioica is a diploid, dioecious, perennial, insect-pollinated he rb and part of the deciduous phase of primary succession in Skeppsvik Archipelago, Gulf of Bothnia, Sweden. These islands are composed of ma terial deposited and left underwater by melting ice at the end of the last ice age. A rapid and relatively constant rate of land uplift of 0 .9 cm per year continually creates new islands available for colonizat ion by plants. Because the higher deposits appear first, islands diffe r in age. Because it is possible to estimate the ages of islands and p opulations of plant species belonging to early stages of succession, t he genetic dynamics occurring within an age-structured metapopulation can be investigated in this archipelago. Fifty-two island populations of S. dioica of known ages, sizes, and distances from each other were studied through electrophoretic data. A number of factors increase the degree of genetic differentiation among these island populations rela tive to an island model at equilibrium. Newly founded populations were more differentiated than those of intermediate age, which suggests th at colonization dynamics increase genetic variance among populations. The very old populations, which decrease in size as they approach exti nction, were more differentiated than intermediate-aged populations. I solation by distance occurs in this system. Colonizers are likely to c ome from more than one source, and the migrant pool model best explain s colonization events in the archipelago. Degree of environmental expo sure also affects population differentiation.