The behavioural ecology of optimism: judgement bias and foraging under predation risk in mice

Abstract

When confronted with ambiguous information, some individuals respond expecting positive outcomes and others expect negative outcomes. Based on such decisions under ambiguous situations, a behavioural paradigm has been developed in animal welfare science that allows researchers to characterize animals as more ‘optimistic’ or ‘pessimistic’. Using this judgement bias test, recent studies have detected consistent individual differences in ‘optimism levels’. However, the potential ecological and evolutionary causes and consequences of these differences are not yet clear. We aimed to explore the ecological relevance of being more optimistic or pessimistic. Specifically, we investigated the correlation between optimism levels and foraging choices under predation risk in laboratory mice, Mus musculus f. domestica. To address this, we first characterized female mice (C57BL/6J) as more optimistic or pessimistic by using an established judgement bias test. 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 showed that this novel test is a suitable tool to investigate individual differences in foraging under predation risk. 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 could be that the consequences of individual differences in optimism levels are context specific and might not be relevant in the face of predation risk.