Short communication: Problems of classifying predator-induced prey immobility – an unexpected case of post-contact freezing

Abstract

Prey noticing predators may turn immobile to avert detection. Such “freezing” is generally thought to precede direct predator–prey contact and thus appears distinct from so-called “post-contact immobility”, or thanatosis. This distinction, however, may be inapplicable if predators lack long-distance senses or monitor their surroundings incompletely. The predatory sandy beach gastropod Agaronia propatula (Olividae) detects its prey, Pachyoliva semistriata of the same family, only when located within centimetres in front of the predator. Pachyoliva therefore reduces its risks by active flight when directly approached by an Agaronia, whereas it freezes to remain undetected when contacting Agaronia from the side. This unexpected “post-contact freezing” suggests that physical contact between prey and predator as such does not always help to distinguish freezing from other types of predator-induced prey immobility and highlights how our interpretations of predator–prey interactions depend critically on our understanding of the sensory capabilities involved.