For decades, local adaptation has been studied at the phenotypic level through reciprocal transplant experiments, where the differential survival of individuals is measured in various habitats. However, what is far from being substantiated is the genetic basis of this differential survival.  In order to investigate the genomic basis of local adaptation, we crossed Arabidopsis thaliana lines from genetically and geographically differentiated populations, planted seeds of parents and their hybrid offspring reciprocally in the field, and tracked temporal changes in allele frequencies at multiple genetic markers.  In July 2006, nearly 600,000 total seeds from parents and F2 offspring of 6 crosses were sown in a block design at three sites each in northern and southern Sweden.  Plots of each parental and hybrid type were subsampled for leaf tissue three times throughout a single generation of these annual plants, and seed set was estimated to assess lifetime fitness.  Genotyping is currently underway using a panel of 149 SNP markers from across the genome.  

Results/Conclusions

Preliminary genotype data from southern sites suggest that seedling survival of parental lines in southern Sweden is consistently biased towards southern parents. Further, instead of the expected ratio of 50:50 (the proportion at which parental lines were sown), the trend across lines is a significant deviation in the direction of southern parental lines.  These preliminary results support the hypothesis that native populations in Sweden may be locally adapted, and suggest that natural selection is an important force in maintaining the genetic differentiation between them.