Genetic Variation, Translocation Heterozygosity, and Seed Dormancy in Clarkia williamsonii

Laboratory studies of four populations of Clarkia williamsonii indicate that substantial genetic variation exists at a large number of loci in populations with high frequencies of translocations, these populations are hypothesized to be inbred periodically because of drought-induced reductions in population size. Less genetic variation is present in populations with a low frequency of translocations. Field studies of 10 populations of C. williamsonii indicated a substantial seed bank that may be quiescent during periods of drought. Consequently, our data support the hypothesis that translocation heterozygosity serves to buffer against the effects of inbreeding, which may occur in natural populations of this generally outcrossing annual plant. During the drought years, translocations are "pumped" into the seed bank; the seed bank serves to maintain further genetic variation over time. We also hypothesize that translocation heterozygosity may be associated with larger plant size, which may confer a selective advantage under highly competitive conditions in the rangeland habitat of cismontane California.