Population genetic(k)s of lyme disease vector, Ixodes scapularis

The tick species Ixodes scapularis (Acari: Ixodidae) is the main vector in the U.S. for Borrelia burgdorferi, the causative agent of Lyme disease. This tick’s range is expanding from historic locations in the eastern, mid-Atlantic, and north-central US which increases the geographic risk for Lyme disease. In the northeast, I. scapularis nymphs have been found to host-seek higher in the leaf litter than southern nymphs, increasing the probability of human encounters. The northern behavior is associated with higher levels of B. burgdorferi in the environment and this behavioral difference is consistent in reciprocal common gardens indicating a genetic link to behavior. Understanding the genetic variation present in I. scapularis will be beneficial to predicting future Lyme disease risk, especially by identifying where northern I. scapularis genotypes are expanding. To investigate the genetic variation present across the geographic range of I. scapularis, flat adults from 25 populations were analyzed. We used triple-enzyme restriction-site-associated DNA sequences (3RAD) analyzed with STACKS v2.3 to identify about 1,106,256 alleles among the populations, and after stringent filtering 4,014 high quality loci. Overall, our data shows that I. scapularis populations in the northeast have the least genetic variation and there are northeast genotypes present in most proposed hybridization zones. This information can be used in future behavioral and crossbreeding experiments to understand how I. scapularis phenotypes associated with Borrelia transmission are inherited and what effect this has on the behavioral differences between the populations.