Differing components of plasticity in threshold traits cause diverging eco-evolutionary responses to spatio-seasonal environmental deterioration

Eco-evolutionary responses to long-term environmental deteriorations will fundamentally depend on interactions between plasticity and evolution of life-history traits that shape population dynamics. Counter-intuitive evolutionary and (meta)population dynamics could arise when different components of individual-specific and/or shared site-specific developmental and labile plasticity affect traits with intrinsically non-linear genotype-environment-phenotype relationships, especially given density-dependent fitness outcomes. Frequency-dependent evolutionary responses could then emerge, but resulting eco-evolutionary dynamics and outcomes have rarely been considered. By modelling a partially-migratory metapopulation encompassing facultative seasonal migration versus residence formulated as a quantitative genetic threshold trait, we show how different forms of plasticity in liability to migrate interact with spatio-seasonal metapopulation dynamics to generate divergent eco-evolutionary responses to spatially restricted environmental deterioration. Temporary and permanent individual-specific environmental effects induced faster evolutionary recovery than might simply be expected, by revealing cryptic genetic variation and allowing adaptive phenotypic changes through repeated episodes of selective disappearance. Conversely, shared subpopulation-specific environmental effects caused among-year variation in phenotype frequencies, impeding evolutionary responses to the extent that migratory metapopulation connectivity was ultimately eradicated. We thereby reveal key principles of how structurally different forms of plasticity in a dichotomous quantitative genetic trait can induce complex eco-evolutionary dynamics, culminating in differing degrees of evolutionary rescue versus constraint.