2.a. Variation within populations
Genetic variation is abundant within all populations, but Northern and Southern populations have noticeable differences when individual populations are analyzed. Northern populations have slightly less inbreeding and slightly higher allelic richness on average than individual Southern populations, potentially indicating that Northern populations are interbreeding across larger distances, creating more genetically cohesive units across the northern U.S. The higher levels of allelic richness are also believed to be a good indicator of a population’s ability to adapt to future environmental changes (Caballero & Garcia-Dorado, 2013), further supporting the hypothesis that Northern populations are leading the geographic expansion of I. scapularisin North America. Meanwhile, populations at the dividing boundaries of our quadrants (e.g., North Carolina and Ohio) have the highest levels of allelic richness, likely resulting from the Northern and Southern genetic groups interbreeding in these areas. In contrast, Southern populations have higher degrees of inbreeding, indicating there is less gene flow occurring among collection localities sampled in the south, creating more distinctive genetic groups.