The genomic impacts of rapid range expansions

Human-mediated change has resulted in the expansion of many species into novel habitats. Range expansions have been described demographically as either pulled or pushed, depending on the number of individuals on the leading front, and can leave distinct genomic signatures within the genome. The recent expansions of Agrilus planipennis, Lycorma delicatula, and Dendroctonus ponderosae represent different types of range expansion which can be analyzed by coupling rigorous monitoring of recent expansions with whole-genome assemblies to provide a strong comparative framework with which to study the genomic signatures of expansion type. Here, we synthesize range expansion theory in the context of these recent expansions and generate hypotheses on the expected patterns of genomic change. We then outline statistical and genome-structural methods that can be used to identify putatively adaptive loci, leveraging the increased genomic resolution provided by whole-genome assemblies. Finally, we complement the overarching expansion hypotheses with a discussion of using a top-down approach to identify loci under selection, using cold tolerance traits as an example. With these methods we can better understand the risk of further spread and persistence of these expanding insect populations, as well as establish a framework for quantifying the adaptive potential of other expanding species.