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.