Individual Differences in Electric Fishes: An Animal Model of Personality

Individual differences in animals have recently been described in behavioral ecology as behavioral syndromes: suites of correlated behaviors within individuals that are consistent across environmental situations. A central idea behind the behavioral syndromes approach is that behaviors do not occur in isolation; rather, they are integrated with other behaviors within the limited biological machinery of one individual. Electric fish are ideally suited for studies of behavioral syndromes because their behavior can be easily measured and tracked due to their unique electric organ discharges (EODs). It is also a good system to present realistic electric signals that mimic social interactions. Using a cohort of 22 Microsternarchus sp. a neotropical knifefish, we carried out a series of behavioral experiments, including (a) a free exploration experiment, (b) a terrestrial challenge, (c) a novelty response experiment, (d) a playback experiment with an aggressive sympatric species, and (e) a jamming avoidance experiment. With the exception of the playback experiment, all were performed twice on all available individuals over the course of two years. Behavioral responses including EOD rate, locomotor activity, responses to novel as well as threatening stimuli, and reaction times were measured. Through principal components analysis and correlational analysis we determined that Microsternarchus sp. exhibit behavioral syndromes in activity, reactivity, aggression/dominance and possibly behavioral flexibility, integrating electric signaling behaviors with components of exploratory behavior and responses to stimuli. For example, individuals with the highest EOD rates spent more time swimming around a novel environment, than individuals with lower EOD rates, thus these behaviors form part of an activity syndrome.