Data and code from: Direction and progression of thermal acclimation effects on ciliated protist populations both depend on direction of thermal change

Organisms acclimate to environmental temperatures to maintain
physiological homeostasis. Acclimation can alter demographic rates,
thereby affecting population dynamics. Previous research has demonstrated
that acclimation can have positive or negative effects on population
growth rates in variable thermal environments, depending on the amount of
time acclimation takes. A clear picture of the timescale of acclimation
may help identify the most consequential frequencies of thermal
fluctuations for population dynamics. However, the progression of
population-level effects of acclimation over time has not been explored.
We used experimental microcosms to test the effects of acclimation on
population dynamics of the ciliated protist Colpidium striatum in various
thermal regimes. We also observed the progression of these effects over
the course of acclimation. Prior acclimation to cooler conditions
increased intrinsic growth rates in warm trial conditions relative to the
growth rates of warm-acclimated populations. In contrast, prior
acclimation to warm conditions decreased intrinsic growth rates in cool
trial conditions relative to the growth rates of cold-acclimated
populations. These results are consistent with an overcompensatory
acclimation response and either the “colder is better” or “optimal
acclimation temperature” hypothesis, though we cannot distinguish between
these two possibilities without an intermediate acclimation temperature
treatment. The observed patterns may be due to resource uptake dynamics
and/or increased stress at high temperatures with increased exposure
duration. The progression of these effects over the course of acclimation
also differed in trajectory, and perhaps duration, for populations
acclimating to warmer versus cooler conditions. Differences in the effects
and progress of thermal acclimation depending on the direction of thermal
change suggest that different physiological mechanisms may be driving
acclimation to warmer versus cooler conditions.