Collaborative Research: Does genetic load drive mating system evolution? Tests in an explicit historical context

Evolution is an ongoing process, but it depends strongly on the past. While nearly everyone acknowledges this fact, it has been difficult to quantify the relative importance of historical and more recent selection pressures as explanations of trait variability in nature. This project examines factors that shape the amount of self-pollination in natural populations. While the selfing rate is often viewed as an adaptation to the current selective environment, a significant fraction of this variation, however, may reflect historical evolution in response to colonization during range expansion. In populations of Campanula americana, we have examined paired-end RAD-seq polymorphism, greenhouse studies of fixed and segregating genetic load, field studies of pollen limitation and reproductive assurance, and population-genetic inferences of selfing rates in 24 populations across its geographic range. This work has shown that the ability to self (i.e. autonomy) has little impact on reproductive assurance and that this variation is unrelated to the pollination environment. However, there is a clear association of autonomy with a population’s genetic load, suggesting a historical process of repeated founder events associated with this evolutionary transition.