Plastic proteans: reduced predictability in the face of predation risk in hermit crabs

Abstract

Variation in behaviour occurs at multiple levels, including between individuals (personality) and between situations (plasticity). Behaviour also varies within individuals, and intra-individual variation (IIV) in behaviour describes within-individual residual variance in behaviour that remains after the effects of obvious external and internal influences on behaviour have been accounted for. IIV thus describes how predictable an individual's behaviour is. Differences in predictability, between individuals and between situations, might be biologically significant. For example, behaving unpredictably under predation threat might reduce the chance of capture. Here, we investigated the duration of startle responses in hermit crabs, in the presence and absence of a predator cue. Individuals differed in startle response duration (personality) and while individuals also varied in their sensitivity to risk, mean response time was greater in the presence of a predator (plasticity). Moreover, IIV was greater in the presence of a predator, providing some of the first evidence that the facultative injection of unpredictability into behaviour might represent a strategy for dealing with risk.

Keywords: boldness; hermit crab; intra-individual variation; personality; risk.

Figure 1.

Inter-individual variation in reaction norms across situations. For each crab, a line links the mean startle response durations in the presence and absence of the predator cue.

Figure 2.

Mean riSD (±s.e.) of startle response durations in the presence and absence of the predator cue. In the presence of the predator cue, riSD was greater, meaning that startle response durations were less predictable.