Playing smart vs. playing safe: the joint expression of phenotypic plasticity and potential bet hedging across and within thermal environments

Adaptive phenotypic plasticity evolves when cues reliably predict fitness consequences of life-history decisions, whereas bet hedging evolves when environments are unpredictable. These modes of response should be jointly expressed, because environmental variance is composed of both predictable and unpredictable components. However, little attention has been paid to the joint expression of plasticity and bet hedging. Here, I examine the simultaneous expression of plasticity in germination rate and two potential bet-hedging traits - germination fraction and within-season diversification in timing of germination - in seeds from multiple seed families of five geographically distant populations of Lobelia inflata (L.) subjected to a thermal gradient. Populations differ in germination plasticity to temperature, in total germination fraction and in the expression of potential diversification in the timing of germination. The observation of a negative partial correlation between the expression of plasticity and germination variance (potential diversification), and a positive correlation between plasticity and germination fraction is suggestive of a trade-off between modes of response to environmental variance. If the observed correlations are indicative of those between adaptive plasticity and bet hedging, we expect an optimal balance to exist and differ among populations. I discuss the challenges involved in testing whether the balance between plasticity and bet hedging depends on the relative predictability of environmental variance.