Does early stress prepare individuals for a stressful future? Stress during adolescence improves foraging under threat

Adolescent exposure to adverse environmental conditions can cause lasting changes in behaviour, cognition and physiology. One explanation for why such changes occur is that they allow organisms to adjust aspects of their phenotype to enhance function in an unfavourable environment. This concept has been investigated for stress during gestation (e.g. thrifty phenotype hypothesis, maternal mismatch hypothesis). Here, we apply these ideas within an individual's lifetime as a possible explanation for long-term phenotypic changes in response to stress during adolescence. To test whether stress during adolescence can cause phenotypic changes that prepare an animal for future threat, we exposed laboratory rats to either chronic stress or unstressed control conditions during adolescent development. After a 5-week delay, rats were assessed in a timed-foraging task under both low-threat and high-threat conditions. Chronic stress during adolescence caused long-term changes in foraging behaviours and foraging performance. In low-threat conditions, stress-exposed rats had a longer latency to begin foraging but consumed the same number of rewards as unstressed rats. However, under high-threat conditions, rats exposed to stress during adolescence began foraging sooner, made more transitions between foraging patches and consumed more rewards than unstressed rats. These results indicate that stress exposure enabled rats to forage more effectively under later novel threat, and that phenotypic changes resulting from stressful experiences during adolescence may enhance function in future high-threat environments.