Epigenetics of drought-induced trans-generational plasticity: consequences for range limit development

Offspring phenotypes may be altered by environments that their parents lived in. These environmentally-induced trans-generational effects may be mediated by epigenetic mechanisms such as DNA methylation. Little is known about the role of such epigenetic effects in evolution; however, it is expected to facilitate evolution. To expand geographic range, it is thought that most species would have to adapt via evolution by natural selection to stressful environments beyond range boundaries. Contrary to expectations, we show that DNA methylation in an upland mustard species may underlie a drought-induced trans-generational tradeoff that may constrain the process of adaptation to stressful environments at lower elevations. Genetic variation gives plants the potential to adapt to stressful environments that often exist beyond their geographic range limits. However, various genetic, physiological or developmental constraints might prevent the process of adaptation. Alternatively, environmentally induced epigenetic changes might sustain populations for several generations in stressful areas across range boundaries, but previous work on Boechera stricta, an upland mustard closely related to Arabidopsis, documented a drought-induced trans-generational plastic trade-off that could contribute to range limit development. Offspring of parents who were drought treated had higher drought tolerance, but lower levels of glucosinolate toxins. Both drought tolerance and defence are thought to be needed to expand the range to lower elevations. Here, we used methylation-sensitive amplified fragment length polymorphisms to determine whether environmentally induced DNA methylation and thus epigenetics could be a mechanism involved in the observed trans-generational plastic trade-off. We compared 110 offspring from the same self-fertilizing lineages whose parents were exposed to experimental drought stress treatments in the laboratory. Using three primer combinations, 643 polymorphic epi-loci were detected. Discriminant function analysis (DFA) on the amount of methylation detected resulted in significant combinations of epi-loci that distinguished the parent drought treatments in the offspring. Principal component (PC) and univariate association analyses also detected the significant differences, even after controlling for lineage, planting flat, developmental differences and multiple testing. Univariate tests also indicated significant associations between the amount of methylation