Stress relief may promote the evolution of greater phenotypic plasticity in exotic invasive species: a hypothesis

Abstract

Invasion ecologists have often found that exotic invaders evolve to be more plastic than conspecific populations from their native range. However, an open question is why some exotic invaders can even evolve to be more plastic given that there may be costs to being plastic. Investigation into the benefits and costs of plasticity suggests that stress may constrain the expression of plasticity (thereby reducing the benefits of plasticity) and exacerbate the costs of plasticity (although this possibility might not be generally applicable). Therefore, evolution of adaptive plasticity is more likely to be constrained in stressful environments. Upon introduction to a new range, exotic species may experience more favorable growth conditions (e.g., because of release from natural enemies). Therefore, we hypothesize that any factors mitigating stress in the introduced range may promote exotic invaders to evolve increased adaptive plasticity by reducing the costs and increasing the benefits of plasticity. Empirical evidence is largely consistent with this hypothesis. This hypothesis contributes to our understanding of why invasive species are often found to be more competitive in a subset of environments. Tests of this hypothesis may not only help us understand what caused increased plasticity in some exotic invaders, but could also tell us if costs (unless very small) are more likely to inhibit the evolution of adaptive plasticity in stressful environments in general.

Exotic plant species are locally adapted but not to high ultraviolet‐B radiation: a reciprocal multispecies experiment

“…Evolution of greater phenotypic plasticity during plant invasions is generally assumed to be costly for species and even more likely constrained in stressful environments, whereas any relief from stressful factors (e.g., enemy release) in the exotic range may facilitate evolution of phenotypic plasticity (Huang et al. ). Regarding UV‐B, Suchar and Robberecht (, ) did not find an indication for a direct link between cost for epidermal UV‐B absorbing compounds and inhibition of growth.…”

“…However, the relative importance of phenotypic plasticity to local adaptation is often assumed to decrease in the course of the colonization process (Dietz and Edwards 2006, Si et al 2014, Zenni et al 2014, Lamarque et al 2015, and may largely depend also on the cost of plasticity, the mean variance and predictability of the new environment and on whether the novel range actually requires a new optimal phenotype (Lande 2015). Evolution of greater phenotypic plasticity during plant invasions is generally assumed to be costly for species and even more likely constrained in stressful environments, whereas any relief from stressful factors (e.g., enemy release) in the exotic range may facilitate evolution of phenotypic plasticity (Huang et al 2015). Regarding UV-B, Robberecht (2014, 2016) did not find an indication for a direct link between cost for epidermal UV-B absorbing compounds and inhibition of growth.…”

Non-native populations of an invasive tree outperform their native conspecifics

“…It remains to be tested in future studies if these genetic shifts in non-native U. pumila populations are reflective of an adaptive evolutionary change. Therefore, reciprocal transplantation experiments under heterogeneous environmental conditions in both native and non-native ranges should be conducted to definitively infer the role of local adaptation in explaining performance differences (Huang et al 2015; Gibson et al 2016). Moreover, our results may be biased due to the sampling design representing relatively few geographical regions per range (Keller and Taylor 2008).…”

Adjusting phenotypes via within‐ and across‐generational plasticity

“…Second, plasticity may reflect an inability to maintain adaptive phenotypes across diverse environments rather than adaptive responses to cues (Sultan, 1995;Wright & McConnaughay, 2002;van Kleunen & Fischer, 2005). In particular, plasticity may be a passive response to stress or lack of resources (Valladares et al, 2007;Huang et al, 2015). Parents and offspring may differ in the degree of stress experienced because of differences in resource requirements or environmental tolerances.…”