Genetic Diversity and Differentiation
Genetic variation among I. scapularis populations differed
depending on geographic location of the populations being compared. Our
overall FST value was 0.176, with paired population
FST values ranging from 0 – 0.417. Northern-to-Northern
comparisons had a mean FST of 0.049 (min = 0, max =
0.302, median = 0.029), and the Southern-to-Southern comparisons had a
mean FST of 0.189 (min = 0.002, max= 0.367, median =
0.175) (See Supplemental Table 3 for all pairwise FSTvalues). These comparisons showed that Northern populations are more
closely related to other Northern populations than Southern populations
are to each other.
To further investigate population differentiation, focal populations
from each quadrant were chosen based on their dispersed geographic
locations and how well they represented their quadrant (Southeastern
Atlantic quadrant represented by Aiken County, SC and Osceola County,
FL; Southern Gulf quadrant by Rapides County, LA; Upper Midwest quadrant
by Monroe County, WI; and Northeastern quadrant by Washington County,
RI), and site-specific statistics were then calculated. Comparing
populations across the Northern and Southern boundary produces a higher
level of genetic differentiation across more loci, and Southern
populations have more differentiation at more loci with other Southern
populations, than when you compare Northern to Northern (Supplemental
Figures 1A-C).
Basic diversity statistics (Table 1) confirm genetic variation within
all populations. In general, Northern populations have a slightly higher
level of allelic richness than those in the South, and populations close
to the dividing boundaries of our quadrants have higher levels than
populations farther to the north or south. The Southern populations also
have a slightly higher degree of inbreeding (average=0.27) compared to
northern populations (average=0.22). Additional results, including AMOVA
and Hardy-Weinberg equilibrium analyses, are given in the supplemental
text.