Map of study region depicting Appledore Island within the Isles of Shoals and in relation to the northeastern US coastline.

<p>Dashed gray lines represent state boundaries. Circles represent generalized population sampling locations on the mainland, with larger circles indicative of 4+ samples, and smaller circles of one. Appledore Island is highlighted in green (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111856#pone.0111856.s001" target="_blank">Figure S1</a> for fine-scale Appledore Island sampling).