Defining Populations
For this study, collected ticks were grouped into shared geographical regions (i.e., putative populations) and collection time periods (Table 1, Figure 1). A population was defined as at least seven ticks collected within the same year and the same collection area (Davey & Blaxter, 2010). Collection areas in this study were defined at the county level and will be referred to by county name; however, for animal and passive collections we assumed that ticks in a given population may have originated in surrounding counties due to the travel of hosts and hunters. One population included in this dataset, from Owen County, Kentucky which shares a border with the sample population from Franklin County, Kentucky, has only four individuals. Our original plan was for collection sites sharing a county border to be combined as a single population for analysis, but during preliminary analysis (see below) we determined that ticks from these two counties had different genetic signatures, so we retained them as separate populations.
For reference purposes and data visualization only (i.e., not analysis), populations were further defined into quadrants of the eastern U.S. These divisions were designed to divide the collection area of I. scapularis in this project into four areas of similar size, while considering the two proposed convergence zones in the Ohio River Valley and at the boarder of southern Virginia. We separated north from south at latitude 36.5407 following the northern borders of North Carolina, Tennessee, and Arkansas, and then separated east from west at longitude -84.7856 following the border of Ohio and Indiana. This created our quadrants referred to as Northeast (>36.5407 and >-84.7856), Upper Midwest (>36.5407 and <-84.7856), Southeastern Atlantic (<36.5407 and >-84.7856), and Southern Gulf (<36.5407 and <-84.7856) (Figure 1).