Stochastic Processes during Invasion: The Influence of Population Size on Style-Morph Frequency Variation in Lythrum salicaria (Purple Loosestrife)

Premise of research. During biological invasion, the genetic diversity of populations may be reduced by founder events and genetic drift. The floral polymorphism tristyly provides an exceptional opportunity to investigate the influence of stochastic forces on the maintenance of genetic polymorphism, because small population size leads to a characteristic signature of morph loss from populations. Here, we investigate the relations between population size and morph-frequency variation in invasive populations of tristylous Lythrum salicaria in Ontario, Canada. We also compare our results to a similar survey conducted 25 years ago in the same region.Methodology. We surveyed the size and morph ratios of 114 L. salicaria populations in 2013. We calculated the relations between population size and style morph absence, population size and style morph evenness, and the number of populations lacking particular style morphs. For comparison of the patterns of morph-frequency variation between surveys, we used a sampl...