The behavioural ecology of optimism: exploring potential consequences of judgement bias in mice

Abstract

Abstract When confronted with ambiguous information, some individuals respond as expecting positive and others as expecting negative outcomes. Based on such decisions in ambiguous situations, a behavioural test was developed in animal welfare science that allows researchers to characterise animals as more “optimistic” or “pessimistic”. Recent studies using this judgement bias test detected consistent individual differences in “optimism levels”. However, the ecological and evolutionary relevance of these differences is not yet clear. In this proof-of-principle study with laboratory mice, we aimed to explore the potential ecological consequences of being more optimistic or pessimistic. Specifically, we investigated whether “optimists” make different foraging choices under predation risk than “pessimists”. To address this, we first characterised female mice (C57BL/6J) as more optimistic or pessimistic by using two established judgement bias tests. Then we assessed individual differences in the tendency to choose high-risk/high-reward or low-risk/low-reward conditions by using a newly developed test based on predator cues (rat odour). We show that this novel test is a suitable tool to investigate individual differences in ecologically relevant risk-taking: First, the test imposed a risk-foraging trade-off for mice because the risky condition clearly induced more avoidance and risk assessment. Second, individuals showed highly repeatable differences in their choice of the risky or safe option. Considering our main aim, we did not find evidence that optimistic and pessimistic mice make different foraging decisions under predation risk. A potential explanation is that optimists, although expecting positive outcomes, might not take more risks when it can jeopardise their survival.