Surviving the Squeeze: Genomic Analysis of a Successful Invasion by European Common Wall Lizards ( Podarcis muralis ) in North America (Ohio, USA )

Invasive species that undergo a founder event may experience a decline in genetic diversity yet still establish successful populations. A possible example is a population of the common wall lizard (Podarcis muralis) in Cincinnati, Ohio, USA, which was founded following an introduction in the 1950s of a small number of individuals from Europe. We used whole genome sequences of individuals from source and introduced populations to assess the origin, demographic history, population structure, and possible signatures of adaptation in this successful lizard introduction. We first confirmed that the introduced lizards in Ohio are Podarcis muralis using phylogenetic analysis. Patterns of genetic diversity indicate introduced lizards in Cincinnati went through a short-term bottleneck with increased inbreeding but then rapidly increased in population size, thus minimising losses in genetic diversity. Comparisons of genomic variation between source and introduced populations demonstrate that populations in Cincinnati represent a subset of source genetic variation and show minimal losses of overall genetic diversity. Comparisons of mutation load between source and introduced populations reveal only small increases in load in introduced populations. Finally, tests for selection on the basis of outlier analyses detect targets for potential positive selection in multiple regions of the genome of introduced individuals, suggesting possible adaptation to a novel environment. Overall, we suggest that rapid population growth and possible adaptation have allowed the founding population of introduced lizards to evade the potential negative genetic impacts of small population size and successfully colonise a novel environment.