Temporal dynamics and adaptiveness of thermal phenotypic plasticity in a ciliate

Phenotypic plasticity is a widespread strategy used by organisms to cope with environmental fluctuations. Empirical studies have mostly focused on describing the amplitude of phenotypic change through reaction norms, which ignore the temporal dynamics of plasticity. Although the speed of plastic responses has recurrently been predicted to modulate their adaptiveness, it remains largely understudied. Here, we retraced the time course of plasticity across four traits in 12 isogenic strains of the ciliate Tetrahymena thermophila to test how the temporal dynamics of plasticity mediate its adaptiveness under fluctuations. We decomposed plastic responses into 3 parameters: a lag and a rate describing their temporal dimension and the canonical plastic capacity. All showed high intraspecific variability. We found the plastic capacity to be positively correlated to the rate of plasticity and not to the time required for plastic changes to be implemented. We then linked the dynamics of plasticity to how strains performed across a gradient of fluctuation periods. The temporal parameters of plasticity significantly explained performance in fluctuating conditions, more so than the plastic capacity alone. Interestingly, strains mounting morphological plasticity at a slower rate tended to be less sensitive to fluctuations. This study demonstrates that a better understanding of how organisms cope with environmental change requires us to consider and incorporate the temporal dynamics of plasticity in theories and experiments.