Local Differentiation Among Populations of Arabis stelleri var. japonica in a Sand Dune Habitat

Abstract

Local variation in ecological and genetic traits was analysed in the perennial herb Arabis stelleri var. japonica in a sand dune area in western Japan. Plants of this species are established in three contiguous habitats (subpopulations): sand dune, forest and an ecotonal zone between both habitats. Morphological, ecological and genetic traits of A. stelleri var. japonica plants were analysed to discover the extent of microdifferentiation among these subpopulations. All plants in nine quadrats were marked and followed during 2 years. The ecotonal zone presented the highest number of mature individuals per quadrat. Plants may produce the same number of shoots per plant but rosette size was larger in plants from sand dune and forest subpopulations than the ecotone. Plants in the sand dune showed the highest number of large capsules per plant. Mortality of seedlings and mature plants was slightly higher in the ecotone than in the other two subpopulations. Sand dune plants had the highest variation among quadrats in almost all traits measured. In the electrophoretic analyses, 21 loci were detected on twelve enzyme systems. Fifteen loci were monomorphic and six loci had 1·2 alleles per loci. Genetic distances and genetic identity Nei's values were very similar among subpopulations (means I = 0·994, D = 0·006). The total genetic diversity (HT) was 0·340 and the within-population component (Hs) was 0·333 indicating low genetic differentiation among subpopulations. Gene flow varied between genes but most of the values were high (mean Nm = 188·3). Subpopulations of A. stelleri showed differentiation in morphological and ecological traits and low genetic differentiation in the loci studied. This may be related with the plastic response of plants to different microenvironments and a significant gene flow between habitats.