Testing a bottleneck hypothesis for soybean aphid (Aphis glycines) during colonization on soybean

The soybean aphid (Aphis glycines) is an invasive pest that has rapidly spread across North America. Such large-scale dispersal suggests a high rate of adaptability and success in new environments. A. glycines is a heteroecious, holocyclic species, that alternates among sexual reproduction on the primary host, buckthorn tree (Rhamnus spp.) and asexual reproduction on its secondary host, soybean. Previous studies reported low genetic differentiation in soybean late-season populations, but suggested high levels of differentiation in earlier-collections. Given the short range of hosts and the annual dispersal pattern, we hypothesized that soybean aphid populations undergo a bottleneck during the transition and dispersal to the second host, soybean. Using the microsatellite markers, we compared the genetic diversity and differentiation of eleven North American early-collected populations. Our results indicated significant gene diversity (heterozygosity) in most populations, but overall low allelic polymorphism. No population exceeding four alleles per locus, however, when compared to the late-collections of previous studies, the majority of early samples had at least one more allele per locus. Data from this study supports the hypothesis of bottlenecks effecting soybean aphid populations at the moment of host transition, which is further intensified by clonal asexual reproduction.