Individual Variation of Diel Vertical Migration: Theory, Empirical Evidence, and Research Perspectives

Diel vertical migrations (DVM) of freshwater organisms have traditionally been described as population-wide behaviour. Evolutionary explanations for DVM in fish consider predation avoidance, feeding opportunities and bioenergetics, all of these processes being sensitive to phenotypical differences between individuals within a population, for example with respect to size, sex, or reproductive status. The unit of selection is likewise the individual, and therefore we have to expect that the selective forces causing the evolution of DVM are individual-specific. Consequently, I predict that highly variable migration patterns and trajectories coexist in populations performing DVM. In this keynote lecture, I will show conceptual models on how the adaptive value of DVM is shaped by phenotypic variance within populations, and how individuals may modify their migrations to achieve highest relative fitness. I will combine the models with empirical evidence of individual migration trajectories and partial migration patterns. I will close the presentation by highlighting a few promising research questions which will foster understanding of the evolutionary origin of DVM.