Maternal Environment Influences Propagule Pressure of an Invasive Plant, Raphanus raphanistrum (Brassicaceae)

Abstract

Premise of research. Weedy species that invade new areas may experience shifts in environmental conditions across generations. Since maternal environments can significantly influence embryo development, shifts in maternal environments could alter the ability of offspring to colonize.Methodology. Here, we report the results of a set of field experiments that study adaptive transgenerational plasticity across three generations using the agricultural, annual weed, Raphanus raphanistrum. We grew replicate lineages across a gradient of experimentally manipulated soil moisture conditions (control rain [×2], no rain, double normal precipitation) for two generations (maternal and offspring) and transplanted individuals of each population to manipulated or unmanipulated soil moisture conditions. We then measured the consequences of the maternal and offspring soil moisture manipulations on traits critical for weediness in the second generation of plants and third (grandchild) generation of seeds.Pivotal results. Maternal moisture environments significantly influenced offspring development. Offspring of parents from relatively dry environments were significantly smaller (reduced seed biomass, floral displays, and size at reproduction) and less fecund, while offspring of parents from relatively wet environments were significantly larger and more fecund compared with related offspring whose parents had been grown under control moisture conditions. The relative differences among lines grown under various maternal environments were intensified when they were grown in a common environment.Conclusions. Weediness is a product of the population genetics of colonists and environmental characteristics of the invaded environment. Plastic responses to abiotic variation experienced by the maternal parent or offspring may also influence the outcome of dispersal, potentially increasing the relative rate of movement or propagule pressure from relatively wet maternal habitats to dry recipient habitats. Possible implications of these environmentally induced phenotypes are discussed with respect to ecological distribution, persistence under novel environments, and evolution in natural populations.