Artificial evolution of behavioral and life history strategies of high-latitude copepods in response to bottom-up and top-down selection pressures

Strong seasonality of resources and predation risk act as bottom-up and top-down selection pressures in high-latitudes, under which numerous behavioral and life history strategies evolve. Although such seasonal strategies are well-documented among high-latitude marine zooplankton, it is difficult to separate the role of bottom-up and top-down selection pressures in the evolution of seasonal strategies. Here, we present a model that allows partitioning of bottom-up (i.e. food availability and temperature) and top-down (i.e. visual predation risk) selection pressures to study how behavioral and life history strategies of high-latitude copepods evolve. In the model, timing, amplitude and ontogenetic trajectories of diel and seasonal vertical migrations (DVM and SVM) were defined as behavioral strategies. Body size, generation time and birth time comprised the life history strategy. Numerous combinations of behavioral and life history strategies were hardwired to copepods representing three model species. In a given model environment, strategies were evaluated for growth, survival and reproductive performances using a fitness estimate, which was heuristically maximized using a Genetic Algorithm. Model simulations were performed in three seasonality regimes representing various levels of visual predation risk from low- to high-Arctic. At lower visual predation risk, species-specific behavioral and life history strategies were largely influenced by food availability and temperature. As visual predation risk increased, the influence of bottom-up selection pressures diminished, and irrespective of the modelled latitude, all model species employed largely similar strategies to counter the predation risk. Modest increase of visual predation risk stimulated the diel vertical migration behavior. Further increase of visual predation risk was associated with decrease of body size, which created a significant impact on the observed behavioral and life history strategies through allometric processes. Our findings suggest that top-down selection pressures play a significant role in the evolution of behavioral and life history strategies of high-latitude copepods.