Invasion genomics of the soybean aphid (Aphis glycines) in the United States

Initial populations of invasive species are commonly characterized by limited population and gene pool size, rendering them susceptible to genetic drift and inbreeding depression. Despite their limited genetic variation, many invasive populations exhibit rapid adaptive evolution, expressing advantageous phenotypes in response to novel ecological pressures in their invasive range.  The soybean aphid (Aphis glycines) is an invasive pest of soybean in the United States that is native to East Asia. The species experienced a significant bottleneck upon invasion and suffered a significant loss of allelic diversity. Despite this genetic reduction, the invasive soybean aphid population has demonstrated rapid adaptation overcoming ecological challenges including host plant resistant soybean and novel overwintering hosts. To investigate this rapid adaptive ability we utilized genotyping-by-sequencing (GBS) to perform a single nucleotide polymorphism (SNP) based genome scan  of native (China and South Korea) and invasive (United States) soybean aphid populations. Using FST-based outlier analyses of population allele frequencies we identified genomic regions exhibiting signatures of selection, allowing the identification of loci putatively involved in the aphid’s invasive success. Further, selective signatures were utilized to identify genomic mechanisms that allowed soybean aphids to retain adaptive genetic material during the invasion bottleneck. In addition, these analyses allowed for the identification of possible populations of origin for the invasive North American population.