Heritable transgenerational fitness variation correlates with copper resistance in the clonal duckweed Spirodela polyrhiza

ABSTRACT Transgenerational effects can vary among genotypes of a given species; however, we cannot yet predict the direction and magnitude of the transgenerational effects. Here, we explored whether a genotype´s transgenerational fitness effects correlate with plant resistance and the production of specialized metabolites. Thereto, we exposed monoclonal, single-descendant lineages from 56 globally distributed genotypes of the clonal duckweed Spirodela polyrhiza to five generations of control conditions or copper excess, followed by five generations without stress, and then measured plant fitness and phenotypes in both environments. Previous copper excess reduced fitness variation within genotypes, while generating heritable and repeatable differences in transgenerational fitness effects among genotypes: genotypes in which previous stress increased fitness under recurring conditions in comparison to controls tended to show reduced fitness when the stress was absent, and vice versa. The transgenerational fitness effects correlated with copper resistance: the more susceptible a genotype, the more its offspring suffered from ancestral stress in the absence of recurrent stress; however, these offspring tended to be more resistant to copper excess, likely by protecting the photosystem II. Together, these findings show that transgenerational fitness effects are heritable, variable and can be anticipated from stress resistance.