Temporal dynamics of selection on early-life phenotypic plasticity in seasonal migration versus residence

The form, magnitude and temporal dynamics of selection on phenotypic plasticity will fundamentally shape eco-evolutionary responses to environmental variation, but such attributes have not been fully conceptualized or quantified in nature. We provide a general framework that conceptualizes the dynamics of selection on phenotypic plasticity in labile dichotomous traits, which commonly shape behaviour and life history. Specifically, we highlight distinctions between selection on expressed plasticity and selection on resulting phenotypes, effects of phenotypic switches in opposite directions, and the full selection dynamics emerging across temporal sequences of environmental conditions. To enact this framework, we quantified selection on early-life plasticity in the ecologically critical trait of seasonal migration versus residence, by fitting a novel multi-state model to spatio-seasonal resighting data from 13 newly fledged cohorts of partially migratory European shags (Gulosus aristotelis). We demonstrate strong and consistent directional selection against early-life plasticity, manifested as substantially lower juvenile survival after phenotypic switches from resident to migrant, but not after reverse switches from migrant to resident. Yet, evident short-term costs translated into weaker and fluctuating selection on plasticity given sequences of phenotypes expressed throughout initial months. We thereby reveal how complex forms of selection against early-life plasticity can arise yet be rapidly attenuated in nature.