Population structure and genetic diversity of invasive Phyla canescens: Implications for the evolutionary potential

Population bottlenecks during founder events tend to constrict the genetic diversity in introduced populations, thereby limiting their evolutionary potential and subsequent ability to adapt to their new environment. Paradoxically, rapid evolutionary changes have been recently found to be widespread in invasive species and have been proposed as a precursor to successful invasions. Information about population structure, introduction history and genetic diversity is essential for addressing this paradox and testing evolutionary hypotheses for any specific invasive species. In this study, we used microsatellite markers to investigate the genetic properties that may underpin the evolutionary potential of the invasive herb Phyla canescens, for which rapid, selection-driven evolution has already been demonstrated. Population structure and genetic diversity were compared between the native (South America) and two introduced ranges (eastern Australia and southern France). South American populations included all the 64 alleles found in the study and most individuals belonged to two distinct genetic clusters originating from northwest Argentina and central Argentina respectively. Invasive populations in eastern Australia and southern France were most closely linked to the central Argentine cluster. Microsatellite results also showed both a reduced genetic diversity at the population level, and the occurrence of a significant genetic bottleneck in many introduced populations. Our results suggest that P. canescens can undergo rapid, selection-driven evolution despite significant population bottlenecks and reductions in diversity. The question about the ‘genetic paradox’ for P. canescens therefore is how much genetic diversity is enough to underpin rapid evolution, or whether it is the type of diversity rather than the amount that is important.