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Abstract:
The model plant, Arabidopsis thaliana, has a native range throughout Eurasia and North Africa and introduced
populations have been found on several additional continents. Through the RegMap and 1001 Genomes projects,
high resolution genetic data has been obtained for thousands of A. thaliana populations that are mostly distributed
throughout the Northern Hemisphere. To gain insight into the genetic variation and demographic history of
introduced populations of A. thaliana in the Southern Hemisphere, we collected plants from four ecologically
diverse sites at the southernmost end of the species distribution in Patagonia, Argentina. Two of the sites were
spaced 5 km apart on the south side of Lake Buenos Aires and two neighboring sites were selected 70 km away
on the north side of the lake. Individuals collected exhibited a wide range of phenotypic characteristics. We
analyzed the genetic diversity by low-resolution SNP genotyping and whole-genome sequencing. We also
performed whole-genome sequencing of the DNA from an herbarium specimen collected from this region in 1967.
We found that individuals from all four present-day populations were essentially genetically uniform across 149
SNP markers. Whole-genome sequencing revealed that only a small fraction of the genome was segregating
among these strains. Genetic comparisons with the RegMap panel and 1001 Genomes data suggested a likely
European origin for these populations. Sequencing data from the herbarium specimen revealed that the presentday
populations are essentially the same as they were nearly half a century ago. We conclude that populations of
A. thaliana in Patagonia were likely founded by an extremely small number of individuals and that phenotypic
plasticity may have contributed to their persistence in the region despite their limited genetic diversity.
