A single gene with pleiotropic effects accounts for the Scottish endemic taxon Athyrium distentifolium var. flexile

Experiments were conducted to determine the genetic relationship between th e alpine fern Athyrium distentifolium and the Scottish endemic taxon A. dis tentifolium var. flexile. Segregation of the taxa was studied after growing sporophytes from spore fa milies, and after selfing and crossing gametophytes. The growth of both gam etophytes and sporophytes was measured under a range of nutrient regimes. The distinction between the two taxa is due to variation at a single gene w ith pleiotropic effects expressed at both the sporophyte and gametophyte st ages. A. distentifolium sporophytes (genotypes A(D)/A(D) or A(D)/A(F)) are taller, have fewer fronds, and produce fewer spores than A. distentifolium var. flexile sporophytes (genotype A(F)/A(F)). Gametophytes containing the A(F) allele have a 50% higher growth rate than those with the A(D) allele o n a range of media. The polymorphism may be maintained by a balance between selection for and a gainst the A(F) allele at the gametophyte and sporophyte stages of the life cycle, respectively. Implications for the conservation of the A. distentif olium var. flexile taxon are discussed.