Evidence of personality in migratory behavior of clonal Daphnia magna

Abstract: We re-examined raw data from the experiment conducted at the Max Planck Institute for Limnology, Plön, Germany, in 1992, in which individual Daphnia magna from a clonal cohort were observed while migrating freely for 4 consecutive nights and days in a set of thermally stratified vertical tubes (“plankton organ”) filled either with water enriched with fish kairomone or fish cues-free control water. Using somatic growth rate as a measure of fitness, we selected 5 individuals with the lowest fitness and 5 with the highest fitness from both the kairomone and control groups (20 individuals total). We then reconstructed their time-depth trajectories throughout the experi- ment to analyze the variation within and between individuals in two behavioral traits: depth selection and mobility. The variation in individual fitness in the control group was small and no consistent differences in behavior were found. However, the kairomone-treated Daphnia individuals differed significantly in fitness and this variation was accompanied by consistent, repeatable differences in both behavioral traits. The finding of this variation leads us to conclude that vertically migrating clonal individuals of Daphnia magna reveal distinct behavioral types, or personalities.