Abstract
Phenotypic plasticity is a vital strategy for plants to deal with changing conditions by inducing phenotypes favourable in different environments. Understanding how natural selection acts on variation in phenotypic plasticity in plants is therefore a central question in ecology, but is often ignored in modelling studies. Here we present a new modelling approach that allows for the analysis of selection for variation in phenotypic plasticity as a response strategy. We assess selection for shade avoidance strategies of Arabidopsis thaliana in response to future neighbour shading signalled through a decrease in red:far-red (R:FR) ratio. For this, we used a spatially explicit 3D virtual plant model that simulates individual Arabidopsis plants competing for light in different planting densities. Plant structure and growth were determined by the organ-specific interactions with the light environment created by the vegetation structure itself. Shade avoidance plastic responses were defined by a plastic response curve relating petiole elongation and lamina growth to R:FR perceived locally. Different plasticity strategies were represented by different shapes of the response curve that expressed different levels of R:FR sensitivity. Our analyses show that the shape of the selected shade avoidance strategy varies with planting density. At higher planting densities, more sensitive response curves are selected for than at lower densities. In addition, the balance between lamina and petiole responses influences the sensitivity of the response curves selected for. Combining computational virtual plant modelling with a game theoretical analysis represents a new step towards analysing how natural selection could have acted upon variation in shade avoidance as a response strategy, which can be linked to genetic variation and underlying physiological processes.
Highlights
In the course of evolution, plants have evolved traits often specific to a certain environment
Plant growth in monomorphic populations without petiole or lamina plastic responses To illustrate how plant growth in the virtual Arabidopsis model depends on planting density (Fig 3), we simulated the growth of plants within monomorphic vegetation stands consisting of plants that do not exhibit R:FR induced plasticity related to petiole elongation or lamina growth reduction at different densities
Organ-level plasticity was induced by changes in the locally perceived R:FR ratio by using a plastic response curve, and allowed plants to dynamically change their phenotype during the growing season, depending on the distance, size and plasticity strategy of neighbour plants
Summary
In the course of evolution, plants have evolved traits often specific to a certain environment. Evolutionary and ecological population models are widely used to explain genetic variation and species composition in different environments, and these models are often based on evolutionary game theoretical principles [13,14,15,16,17]. These models implicitly assume that variation in trait values is entirely due to genetic variation among genotypes. If plasticity would be considered in evolutionary game theoretical models as the ability of a genotype to change its trait value in response to environmental conditions, selection for different trait values in different environments would not necessarily lead to selection for different genotypes. Considering plasticity as a trait in itself and considering variation in plasticity across genotypes is required to analyse to which extent natural selection may have acted on variation in plastic responses
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