Evidence of genetic variation in traits and fitness
In addition to the large and consistent plastic effects of the environment on phenotype and fitness, there were also genetic differences among the populations from the eight different water bodies. Although we cannot be sure that samples taken from different sites represent different genotypes, studies on natural populations ofL. minor have shown considerable among-site genotype diversity at similar geographical scales to ours (Vasseur et al. 1993, Cole and Voskuil 1996, Xue et al. 2012), and it’s reasonable to assume that samples taken from different sites represent different genotypes (Ho 2018). By removing environmental variation through common garden growth assays, we can estimate the variation in fitness due to genetic differences. With the microbiome absent, we found small but significant differences in fitness and phenotype among genotypes, indicating some genetic control of these traits. This is consistent with previous work that find large differences in fitness among clones, for example, Ziegler et al. (2015), who, in a common garden assay of 13 species ofLemnaceae detected a greater amount of variation in growth rate among genotypes of the same species than variation among species or even genera. Finally, we also detected small genotype by environment (GxE) interactions for both fitness and phenotype in the absence of the microbiome. Although plants from all sites responded in a similar direction to light and nutrients, the magnitude of these responses differed among genotypes indicating the presence of variation in the genetic control of phenotypic plasticity.