Earthworm individualities when facing a conflict between turn alternation and aversive learning

An individual’s personality develops through a combination of experiences and parental inheritance. When faced with a conflict, will an individual take an innate behavior or a learned one? In such situations, individuality will manifest itself. Here, we focused on turn alternation behavior, which is a habitual tendency to turn in the direction opposite the preceding turn, in earthworms (Eisenia fetida) and examined how this behavior is affected by an aversive stimulus. Of 10 earthworms, 3 were affected by the stimulus. Turn alternation deteriorated in two worms, one of which showed anti-turn alternation behavior, whereas the remaining worm showed an enhanced tendency toward turn alternation. Earthworms have a relatively simple nervous system. This study opens the door to investigate the neuronal basis for individuality that emerges between nature and nurture.