Cyto-nuclear linkage disequilibrium resulting from admixture

Previous studies of North American populations of the invasive plant Silene latifolia showed significant cyto-nuclear linkage disequilibrium (CNLD) between SNP variants of a mitochondrial gene (atp1) and the most common allele at nuclear microsatellite loci. Fields et al. (2014) hypothesized that this CNLD arose partially as a consequence of admixture that occurred during the colonization of North American (NA) populations of S latifolia via seed dispersal from genetically differentiated European populations that represent a portion of the native range of this species. In order to evaluate the plausibility of the admixture hypothesis, as opposed to metapopulation processes alone, we estimated CNLD for these same loci using data collected from eastern (EEU) and western (WEU) European populations of S. latifolia known to be genetically differentiated and likely sources of the spread of the study species to North America. We show that the CNLD found previously in NA populations of S. latifolia can be attributed to admixture of the previously isolated European demes coupled with decay since that time. Our applied framework allows the separation of the forces generating and dissolving statistical associations between alleles in cytoplasmic organelles and the nuclear genome and may thus be of utility in the study of plant or animal microbiomes.