Genetic structure, allozyme habitat associations and reproductive fitness in Gypsophila fastigiata (Caryophyllaceae)

Relationships between allozyme differentiation, habitat variation and individual reproductive success were examined in local populations of a perennial herb, Gypsophila fastigiata, on the Baltic island of Oland (Sweden). Relatively little (c. 2%) of the total allozyme diversity in this largely outcrossing species is explained by differentiation between sites tens of kilometres apart. The low level of geographic differentiation suggests that gene flow between sites is, or has recently been, extensive. Yet the component of allozyme diversity due to differentiation between plots (only tens of meters apart) within sites is 3 times larger than the between-site component of diversity. Allozyme variation, especially at the Pgi-2 locus, is significantly associated with habitat variation within sites. Different allele x habitat combinations for the Pgi-2 locus are associated with differences in individual reproductive fitness. Differential selection in different local habitats may thus contribute to the fine-scale structuring of genetic diversity within sites.