Reciprocal phenotypic plasticity in a predator–prey system: inducible offences against inducible defences?

Abstract

AbstractWe describe one of the first examples of reciprocal phenotypic plasticity in a predator–prey system: the interaction between an inducible defence and an inducible offence. When confronted with the predatory ciliate Lembadion bullinum, the hypotrichous ciliate Euplotes octocarinatus develops protective lateral wings, which inhibit ingestion by the predator. We show that L. bullinum reacts to this inducible defence by expressing an inducible offence – a plastic increase in cell size and gape size. This counteraction reduced the effect of the defence, but did not completely neutralize it. Therefore, the defence remained beneficial for E. octocarinatus. From L. bullinum's point of view, the increase in feeding rate because of the offence was not larger than the increase in mean cell volume and apparently, did not increase the predator's fitness. Therefore, the inducible offence of L. bullinum does not seem to be an effective counter‐adaptation to the inducible defence of E. octocarinatus.