Single nucleotide polymorphisms for landscape genetic analysis of the soybean aphid, Aphis glycines

Since its introduction in 2000 to North America, soybean aphid (Aphis glycines) has spread across much of the U.S. and Canadian soybean growing regions, and has become one of the most damaging insect pests of soybean. Because of its ability to colonize and overcome ecological boundaries, it is important to understand the migration and genetic events that drive the adaptation of A. glycines. Given the lack of genetic information from soybean aphid at a multiple population scale, we conducted population genetic analyses using eight North American locations. Soybean aphids were collected twice at each location (early and late during the soybean season) to evaluate genetic differences in both time and space. To analyze genetic structure, we used six microsatellite markers and developed twenty-six SNP markers to calculate within-population frequency parameters and genetic distance among populations. A pairwise comparison showed significant variability in the genetic distance of early vs. late populations (P=0.002), and a Principal Component Analysis showed strong differentiation among early populations while closer genetic relationship among late populations. Furthermore, early populations showed a significant deviation (P<0.05) from Hardy-Weinberg equilibrium for a large portion of the loci tested. From these results we can conclude that early in the season soybean aphid populations undergo limited migration; however, as the summer progresses, asexual reproduction and population increase lead to migration and genetic homogenization of the populations.