Natural selection causing microsatellite divergence in wild emmer wheat atthe ecologically variable microsite at Ammiad, Israel

Genetic diversity at 28 microsatellite loci was studied in a natural popula tion of Triticum dicoccoides at the Ammiad microsite, north of the Sea of G alilee, Israel. This microsite was subdivided into four major habitats, Nor th, Valley, Ridge and Karst, and further subdivided into nine subhabitats. The units thus defined showed strong and highly significant differentiation in ecological factors; in particular with respect to cover, proximity and height of rocks, and surface soil moisture after early rains. The results s howed that allele distributions at microsatellite loci were nonrandom and a ssociated with habitats. Significant genetic differentiation and variation in repeat number were found among subpopulations in the four major habitats and nine subhabitats. Habitat-specific and -unique alleles and linkage dis equilibria were observed in the Karst subpopulation. The subpopulations dwe lling in drier habitats and subhabitats showed higher genetic diversities a t microsatellite loci. These results suggest that natural selection, presum ably through aridity stress, acts upon microsatellite divergence predominan tly on noncoding sequences, thereby contributing to differences in fitness.