Evolution of phenotypic plasticity during environmental fluctuations

Evolution in variable environments is predicted to disfavour genetic canalization and instead select for alternative strategies, such as phenotypic plasticity or possibly bet-hedging, depending on the accuracy of environmental cues and type of variation. While these two alternatives are often contrasted in theoretical studies, their evolution are seldom studied together in empirical work. We used experimental evolution for 30 generations in the nematode worm Caenorhabditis remanei to simultaneously study the evolution of plasticity and bet-hedging in environments differing only in their temperature variability, where one regime is exposed to faster temperature cycles between 20 and 25 °C, with little autocorrelation between parent and offspring environment, while the other regime had slowly increasing temperature with high autocorrelation in temperature between parent and offspring. These two environments had the same average temperature over evolutionary time, but one varied with larger magnitude on a shorter time scale. After experimental evolution, we scored adult size and fitness in full siblings reared in two different temperatures, optimal 20 °C and mildly stressful 25 °C. Experimental evolution in fast temperature cycles resulted in the evolution of increased body size plasticity but not increased bet-hedging, compared to evolution in the slowly changing environment. Plasticity followed the temperature-size rule as size decreased with increasing temperature and this plastic response was adaptive. In addition, we documented substantial standing genetic variation in body size, which represents a potential for further evolutionary change.