Copycat cannibals witnessing cannibalism early in life affects adult behaviour

Cannibalism is ubiquitous in the animal kingdom. The evolution and causation of cannibalistic behaviour have been amply investigated, but the ontogeny has received less attention. Here, we studied the ontogeny of cannibalistic behaviour in the tiny, blind predatory mite Amblyseius herbicolus. We found that individuals that were exposed to egg-cannibalizing adults when juvenile developed into cannibalistic adults more than 2.5 times as often as juveniles without such exposure. This was not due to their experience with eggs pierced by the adults: exposing juveniles to artificially pierced eggs did not result in increased cannibalism upon becoming adult. The exposure of juveniles to cannibalistic adults did not result in significant increases in juvenile mortality; hence, no selection against certain behavioural syndromes occurred during the juvenile stages. We therefore conclude that the experience with cannibalistic adults changed the behaviour of juveniles later in life. To the best of our knowledge, this is the first study showing that witnessing cannibalism as juvenile results in a higher tendency to cannibalize as adult.