Conclusions
Frond area and root length varied widely in the field and were correlated with natural levels of resource availability, with plants investing more biomass into the tissue responsible for the uptake of the resource that is in short supply. This was most striking for root length, for which variation among sites was more than sixfold, and strongly correlated with levels of dissolved phosphorus. This large phenotypic variation in the field was overwhelmingly a result of phenotype plasticity, and not local adaptation. Despite the predominance of environmental variation in both traits, there was also a genetic basis to these traits that persisted when environmental variation was removed. We recorded surprisingly high levels of genetic variation in phenotype and fitness within sites, which itself indicates the presence of strong purifying selection of about 1% per generation and the potential to counter environmental change. Future work should focus on uncovering mechanisms responsible for maintaining such high levels of genetic variation in L. minor. The continued development ofLemnaceae as a model system in experimental population genetics (Acosta et al. 2021), community ecology (Laird and Barks 2018) and eco-evolutionary dynamics (Hart et al. 2019) promises illumination in understanding the larger mechanisms responsible for maintaining diversity more generally.
Acknowledgments: We thank Rachel Takasaki, who helped with data collection. This experiment was supported by a Discovery Grant from the Natural Science and Engineering Research Council of Canada to GB and an Alexander Graham Bell Canada Graduate Scholarship from the Natural Science and Engineering Research Council of Canada to MDJ.
Authors’ contributions: MDJ lead the field survey and performed the common garden experiment. Analysis was done jointly by MDJ and GB. The manuscript was written by MDJ. GB contributed substantially to revisions. The study was conceived by GB with input from MDJ.
Competing interests: The authors declare no competing interests.
Data availability: Raw data from which all figures were generated will be stored in the Dryad repository before publication of the article.