“Should I change or should I go? Phenotypic plasticity and matching habitat choice in the adaptation to environmental heterogeneity”

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Pim Edelaar, Roger Jovani, and Ivan Gomez-Mestre

A new model explains when to expect matching habitat choice and when phenotypic plasticity given environmental variation

Top (photos by Pim Edelaar), two Azure Sand Grasshoppers (Sphingonotus azurescens), and two distinct natural substrates: one substrate that matches a grasshopper´s color and therefore provides protective crypsis, and another one that does not. Grasshoppers could increase crypsis by changing their color (adaptive phenotypic plasticity), or by moving to a suitable substrate (matching habitat choice). Bottom (photo by Ivan Gomez-Mestre): two sibling tadpoles of the Western Spadefoot Toad (Pelobates cultripes) with widely divergent phenotypes. The tadpole on the left was raised in the presence of chemical cues from a predatory dragonfly, and developed a rounder body, a deeper tail fin and a more anterior insertion of the tail than its sibling raised in clean water (plasticity). In their paper, Edelaar et al. model and discuss the simultaneous evolution of habitat choice and plasticity as adaptations to cope with such environmental variation.

Wouldn’t it be nice if the environment was just perfect wherever you are? Unfortunately this is not the case, so all organisms have to somehow cope with environmental variation, or suffer the consequences. For example, when grasshoppers resemble the color of their environment, they are harder to find by predators. How then do grasshoppers that live in environments of different colors improve their camouflage? Perhaps via genetic divergence in color among grasshopper populations living in distinct environments? Or do individual grasshoppers change their color (phenotypic plasticity)? Or do they move to color matching environments (matching habitat choice)? Or all of the above? Surprisingly few studies consider so many possible solutions at the same time. In their simulation study, Pim Edelaar, Roger Jovani, and Ivan Gomez-Mestre investigate which solutions might evolve, and what this may depend on. When phenotypic plasticity and matching habitat choice are not allowed, populations evolve through differential survival of individuals, resulting in adaptive genetic divergence. However, if environments change too fast, natural selection is too strong and genetic variation insufficient, and populations go extinct. Phenotypic plasticity that allows organisms to improve their match with the environment can avoid this extinction, and in fact evolves under most circumstances. The ability of individuals to purposefully move to a matching environment can similarly prevent extinction, but provides a less perfect solution when the set of environments available is limiting. Hence, only when phenotypic plasticity does not evolve (e.g. because it is too costly) does habitat choice evolve. Overall, this study shows the diverse ways in which organisms cope with variation among environments. It also predicts when we should expect different solutions to occur in nature. At the same time, it promotes the simultaneous study of multiple solutions to this key challenge to all living organisms. Read the Article