Local signatures of founding populations confound examination of adaptive divergence in invasive populations

Abstract A detailed understanding of population genetics in non-native populations helps us to identify drivers of successful introductions. However, separating adaptive change from local signatures of founding populations represents a conceptual and technical difficulty when dealing with invasive populations. The history of introductions, as well as the process of range expansion, can confound interpretation of putative adaption in response to a novel environment. Here, we investigate putative signals of selection in Australian populations of introduced common starlings, Sturnus vulgaris, by examining population wide Single Nucleotide Polymorphisms (SNPs) and identifying SNP outliers associated with environmental variables. We determine that geographic distance plays a strong role in the genetic structure of populations, and that this is most likely strongly influenced by genetic differences in the founding populations, as well as modern day population connectivity. Examining candidate SNPs under putative selection indicated that local adaption has likely occurred, however, strong patterns in genetic variation, likely from founding populations, were visible in SNPs that were strongly associated with environmental variables. When examining putative adaption in invasive populations, we encourage critical interpretation of signatures of selection. Even strongly associated loci and environmental variables, when examined closely, may contain distinct footprints of invasion history or invasion expansion gradients, confounding analysis of the history of selection in these populations.