Population genetics of the Gulf Coast tick

The Gulf Coast tick (GCT), Amblyomma maculatum Koch, has undergone a massive range expansion over the last 30 years and is now found well outside of its historic range of the Gulf Coast region. Tick dispersal is intrinsically linked to the movement of their hosts. The prevailing hypothesis for Gulf Coast tick range expansion has been tick drop offs from migratory birds as they fly north to their breeding grounds, though other mechanisms may contribute. Gulf Coast ticks have been found on over 70 animal species, representing substantial variance among their dispersal capacities. We assessed the genetic structure of GCT populations across much of the United States. Using a broad network of collaborators (ESA constraints prevented inclusion from author list), we amassed over 400 individual ticks from 18 states within the current range of Gulf Coast tick, representing over 50 unique sites. We hypothesized that the leading edge of the expansion would exhibit similar or higher levels of genetic variability than populations in the historical range. This would be consistent with recurring gene flow into the populations at the leading edge and suggest that a mixture of both long distance and short distance dispersal may occur. Our work will help understand the varying mechanisms of tick movement at a broad spatial scale, which can in turn inform potential avenues of intervention to limit tick spread.