Phenotypic plasticity and trans-generational plasticity can dampen or amplify the effects of environmental fluctuations on population dynamics. As the pattern of environmental fluctuations shift and become more extreme due to anthropogenic climate change it is increasingly important to be able to predict population and meta-population persistence. In particular, adaptive trans-generational plasticity has been found to improve long-term population persistence in the face of a novel pattern of environmental heterogeneity. We used a genetically diverse population of nematode worms (Caenorhabditis elegans) that had been previously adapted to high salt conditions to explore how the combined effects of environmental fluctuations, trans-generational plasticity and environmental cues on the population growth rates. We exposed replicate populations of nematodes to an uncorrelated sequence of juvenile environments (normoxia/anoxia), measured the per-generation population growth rate, and culled populations to a fixed population size of 10^4. Replicate populations also experienced a weakly stressful “cue” in the form of blue light that was provided in either a reliable or unreliable fashion. This provided us with 2,160 measurements of population growth rate. Our aim was to understand how trans-generational effects, cue, and cue reliability related to the environment-dependent population growth rate.
Results/Conclusions
We analyzed our data using both GLM methods and Bayesian modeling. Our GLM analysis indicated that the reliability of the cue had a significant effect on population growth rate, and also that maternal or other deeper trans-generational effects must be present. To account for this, we defined a series of hierarchical models and used DIC to perform model selection. We found that both maternal environment and the presence of the weak stress cue influenced population growth rate in a non-additive manner (maternal environment has ~15% effect on growth rate). This affect was asymmetric, indicating that mothers who experienced deleterious environments were less able to utilize the weak stress cue (cue has ~25% effect on growth rate). Overall, our results suggest that an increase in the frequency of minor stressful events can weaken a population’s ability to dampen the effects of environmental variability. This implies that the fate of populations experiencing increasing levels of environmental stressors may be worse than previously understood.