Spatiotemporal allozyme divergence caused by aridity stress in a natural population of wild wheat, Triticum dicoccoides, at the ammiad microsite, Israel

Spatiotemporal diversity at 35 allozyme loci was assayed over 6 years in 1,207 individuals of wild emmer wheat (Triticum dicoccoides) from a microgeographic microsite, Ammiad, north Israel. This analysis used new methods and two additional sample sets (1988 and 1993) and previous allozymic data (1984-1987). This microsite includes four major habitats (North-facing slope, Valley, Ridge, and Karst) that show topographic and ecological heterogeneity. Significant temporal and spatial variations in allele frequencies and levels of genetic diversity were detected in the four subpopulations. Significant associations were observed among allele frequencies and gene diversities at different loci, indicating that many allele frequencies change over time in the same or opposite directions. Multiple regression analysis showed that variation in soil-water content and rainfall distribution in the growing season significantly affected 10 allele frequencies, numbers of alleles at 8 loci, and gene diversity at 4 loci. Random genetic drift and hitch-hiking models may not explain such locus-specific spatiotemporal divergence and strong allelic correlation or locus correlation as well as the functional importance of allozymes. Natural ecological selection, presumably through water stress, might be an important force adaptively directing spatiotemporal allozyme diversity and divergence in wild emmer wheat at the Ammiad microsite.