# Evolution of phenotypic plasticity owing to migration

## TL;DR

The paper shows how migration between populations can maintain phenotypic plasticity even in stable environments where it's not directly beneficial.

## Contribution

The study reveals that migration can sustain costly phenotypic plasticity in stable environments, even when it's not linked to the fittest genotype.

## Key findings

- Low migration rates between populations can promote phenotypic plasticity in stable environments.
- Plasticity can persist even when it's costly and not tied to the fittest genotype.
- Migration enables plasticity to invade adapted populations through introduced maladapted phenotypes.

## Abstract

Phenotypic plasticity enables organisms to produce better-suited phenotypes when the environment changes, improving fitness under adverse conditions. Yet responding to environmental cues may provide little use in a constant environment, where organisms already express optimal phenotypes. The forces that sustain plasticity and account for its widespread presence, thus, remain unclear, as plasticity must remain advantageous to persist. Although typically associated with changing environments, maintenance of plasticity requires generational turnover such that parents and offspring regularly encounter different conditions. Here, we demonstrate that even a low number of migrants between locally adapted populations, in constant environments, can promote the emergence and persistence of phenotypic plasticity even when plasticity is costly and never associated with the fittest genotype, independent of its genetic architecture. We support this conclusion by exploring the parameter space of a two-locus, two-deme model using stochastic simulations and analytical approximations. We derive analytical conditions under which plasticity is adaptively maintained as a function of selection strength, migration, and fitness trade-offs. These findings reveal new potential evolutionary origins of plasticity and offer insight into how maladaptive traits can invade adapted populations in stable environments.

Phenotypes can change without alterations in the underlying genotype—a phenomenon known as phenotypic plasticity—the evolution of which is typically triggered by adverse environmental conditions. Consequently, when we observe adapted populations in stable habitats, we do not expect phenotypic plasticity to be maintained by selection. Here, we show that migration introducing maladapted phenotypes, which may be rapidly removed by selection, can enable plasticity to invade adapted populations in stable environments. This holds even when plasticity is costly, not associated with the fittest genotype, and regardless of its genetic architecture. Migration contributes to the long-term maintenance of plasticity and may explain seemingly maladaptive plastic responses in stable habitats.