Dormant propagule banks (eggs, cysts, spores, etc.) are widespread in freshwater zooplankton, phytoplankton, and bacteria. Recent studies have found that these organisms evolve rapidly enough to affect ecological dynamics in the wild. Therefore, it is important to understand the effects of dormancy on microevolution. Here we examine the effects of dormant egg banks on microevolutionary dynamics by using theoretical models. Specifically, we considered evolution under directional selection with environmental fluctuations by using a standard egg bank model as well as a structured egg bank model that has shallowly and deeply buried egg banks.
Results/Conclusions
We found that dormancy has potentially conflicting effects on the speed of evolution: dormancy slows down evolution because a certain fraction of individuals is not visible to natural selection. On the other hand, it promotes the maintenance of genetic variation in temporally fluctuating environments (i.e., temporal storage effect). This may speed up contemporary evolution by providing standing genetic variation. Our analyses show that (1) when environmental stochasticity is low, a higher hatching fraction results in faster evolutionary response to environmental change because the storage effect is very weak; (2) when environmental stochasticity is high, an intermediate hatching fraction is the best at promoting contemporary evolution due to the double-edged effect of dormancy. In this case, a higher hatching fraction results in less generation overlap and a weak storage effect, while a smaller hatching fraction causes a “migration load” from the past. This pattern was further confirmed by a structured egg bank model, where separating shallowly and deeply buried egg banks makes it easy for the storage effect to work. Therefore, it is essential to understand both the hatching fraction and environmental stochasticity in order to predict the importance of rapid evolution and eco-evolutionary dynamics in the wild for organisms with dormant propagule banks.