Genetic variation,breeding system evolution,and conservation of the narrow sand dune endemic Stellaria arenicola and the widespread S. longipes (Caryophyllaceae)

Genetic variation was examined by electrophoresis in 14 populations of Stellaria arenicola, an endemic of the Athabasca sand dunes in northern Saskatchewan, Canada, and seven populations of S. longipes, its progenitor. Three of the 5. longipes populations were sympatric with the endemic. Populations of the endemic were found to have fewer alleles per polymorphic locus (2.21 vs. 2.37), fewer polymorphic loci (29.9 vs. 33.8), and lower genetic diversity (0.087 vs. 0.107) than populations of the progenitor. Genetic identities for all pairs of populations were high (0.932 to 1.000). The endemic had one novel allele and shared ten alleles with progenitor populations from the sand dunes that were not found in other populations of S. longipes. Populations of both species were found to partition most of their genetic variation within populations. An investigation of the multilocus outcrossing rates revealed that S. arenicola had higher rates of selling and biparental inbreeding than S. longipes. This study suggests that partial genetic isolation through a shift in the breeding system, in addition to previously reported strong directional selection, has been important in the sympatric evolution of the endemic S. arenicola. The close genetic relationship between populations of S. arenicola and S. longipes found on the Athabasca sand dunes supports the suggestion that the endemic evolved while sympatric to the gene pool of the progenitor species that is found presently in the region.