Individuals differ in the way they judge ambiguous information: some individuals interpret ambiguous information in a more optimistic, and others in a more pessimistic way. Over the past two decades, such “optimistic” and “pessimistic” cognitive judgment biases (CJBs) have been utilized in animal welfare science as indicators of animals’ emotional states. However, empirical studies on their ecological and evolutionary relevance are still lacking. We, therefore, aimed at transferring the concept of “optimism” and “pessimism” to behavioral ecology and investigated the role of genetic and environmental factors in modulating CJB in mice. In addition, we assessed the temporal stability of individual differences in CJB. We show that the chosen genotypes (C57BL/6J and B6D2F1N) and environments (“scarce” and “complex”) did not have a statistically significant influence on the responses in the CJB test. By contrast, they influenced anxiety-like behavior with C57BL/6J mice and mice from the “complex” environment displaying less anxiety-like behavior than B6D2F1N mice and mice from the “scarce” environment. As the selected genotypes and environments did not explain the existing differences in CJB, future studies might investigate the impact of other genotypes and environmental conditions on CJB, and additionally, elucidate the role of other potential causes like endocrine profiles and epigenetic modifications. Furthermore, we show that individual differences in CJB were repeatable over a period of seven weeks, suggesting that CJB represents a temporally stable trait in laboratory mice. Therefore, we encourage the further study of CJB within an animal personality framework.

Touchscreen-based procedures are increasingly used in experimental animal research. They not only represent a promising approach for translational research, but have also been highlighted as a powerful tool to reduce potential experimenter effects in animal studies. However, to prepare the animals for a touchscreen-based test, an often time-consuming training phase is required that has itself been shown to cause increased adrenocortical activity and anxiety-like behavior in mice. While these findings point at a potentially negative effect of touchscreen training at first glance, results have also been discussed in light of an enriching effect of touchscreen training. The aim of the present study was therefore to shed more light on recently reported touchscreen training effects, with a particular focus on the termination of the training routine. Specifically, we investigated whether the termination of regular touchscreen training could constitute a loss of enrichment for mice. Thus, we assessed fecal corticosterone metabolites (FCMs), exploratory-, anxiety-like and home cage behavior in touchscreen-trained mice in comparison to food restricted and ad libitum fed mice, as a restricted diet is an integral part of the training process. Furthermore, we compared these parameters between mice that were continuously trained and mice whose training was terminated 2 weeks earlier. Our results confirm previous findings showing that a mild food restriction increases the animals' exploratory behavior and shifts their activity rhythm. Moreover, touchscreen training was found to increase FCM levels and anxiety-like behavior of the mice. However, no effect of the termination of touchscreen training could be detected, a finding which contradicts the enrichment loss hypothesis. Therefore, we discuss two alternative explanations for the findings. Yet, the current state of knowledge is not sufficient to draw final conclusions at this stage. In compliance with the refinement endeavors for laboratory animals, further research should assess the severity of touchscreen procedures to ensure a responsible and well-founded use of animals for experimental purposes.

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.