Genetic diversity and population structure of the serpentine endemic Calystegia collina (Convolvulaceae) in northern California

We used enzyme electrophoresis to evaluate genetic diversity in 32 populati ons of Calystegia collina, a clonal plant species endemic to serpentine out crops in northern California (USA). Of 34 loci examined 56% were polymorphi c, but on average only 17% were polymorphic within local populations. Neith er the total number of alleles nor the number of multilocus genotypes diffe red significantly between populations in small vs. large serpentine outcrop s. Genetic and geographic distances between populations were positively cor related, but this relationship was not significantly affected by the isolat ion of serpentine outcrops. Populations were highly differentiated (F-st = 0.417) and little genetic variation was explained by geographic region or s erpentine outcrop. Observed heterozygosity within populations almost always exceeded Hardy-Wei nberg expectations. In many populations, all 30 sample ramets were uniforml y heterozygous at one or more loci yet were genetically variable at other l oci. These results imply that many C. collina populations originate from on e or a few genetic founders, with little recruitment from seeds. Genetic va riation within uniformly heterozygous populations must be the product of mu ltiple, closely related founders or somatic mutations within the population . We conclude that vegetative reproduction, perhaps coupled with somatic mu tation, helps maintain genetic diversity in these isolated but long-lived p opulations.