Data and code from: Experimental evolution of environmental tolerance, acclimation, and physiological plasticity in a randomly fluctuating environment

Environmental tolerance curves, representing absolute fitness against the
environment, are an empirical assessment of the fundamental niche, and
emerge from the phenotypic plasticity of underlying phenotypic traits.
Dynamic plastic responses of these traits can lead to acclimation effects,
whereby recent past environments impact current fitness. Theory predicts
that higher levels of phenotypic plasticity should evolve in environments
that fluctuate more predictably, but there have been few experimental
tests of these predictions. Specifically, will still lack experimental
evidence for evolution of acclimation effects in response to environmental
predictability. Here, we exposed 25 genetically diverse populations of the
halotolerant microalgae Dunaliella salina to different constant
salinities, or to randomly fluctuating salinities, for over 200
generations. The fluctuating treatments differed in their autocorrelation,
which determines the similarity of subsequent values, and thus
environmental predictability. We then measured acclimated tolerance
surfaces, mapping population growth rate against past (acclimation) and
current (assay) environments. We found that experimental mean and variance
in salinity caused the evolution of niche position (optimal salinity) and
breadth, with respect to not only current but also past (acclimation)
salinity. We also detected weak but significant evidence for evolutionary
changes in response to environmental predictability, with higher
predictability leading notably to an upwards shift in optimal salinities
and stronger acclimation effect of past environment on current fitness. We
further showed that these responses are related to the evolution of
plasticity for intracellular glycerol, the major osmoregulatory mechanism
in this species. However the direction of plasticity evolution did not
match simple theoretical predictions. Our results underline the need for a
more explicit consideration of the dynamics of environmental tolerance and
its underlying plastic traits to reach a better understanding of ecology
and evolution in fluctuating environments.