Exercise changes behaviour

Summary Exercise, which may be defined as bodily movement produced by the contraction of skeletal muscle and which increases energy expenditure above basal levels, is essential for fitness-related activities such as foraging, migration and dispersal. The frequency with which individuals engage in exercise depends on a range of intrinsic and environmental factors. Exercise itself can modify behaviour by inducing endocrine changes and by a training effect that increases physiological capacities. Here, we test the hypothesis that exercise changes behaviour and that there is positive feedback so that performing exercise increases the likelihood of performing exercise-related behaviours. We show that there was a training effect that improved sustained swimming performance of mosquitofish (Gambusia holbrooki) exposed to chronic exercise in flowing water for 4 weeks compared to sedentary controls. Exercised fish also became bolder and were quicker to leave a refuge, showed an increasing tendency to explore unfamiliar environments, and were more aggressive than sedentary fish. These physiological and behavioural changes reverted back to control levels when exercised fish assumed a sedentary lifestyle again. We used the calcium channel blocker nifedipine to decrease swimming performance of exercised fish to control levels, which allowed us to determine whether increased locomotor capacity per se influences behaviour. We show that reducing the swimming performance of exercised fish also reduced exploration and aggression, but it did not affect the latency to leave a refuge (boldness). Our data show that behavioural phenotypes are not fixed. Exercise changes behaviour and may thereby alter interactions between individuals and dispersal. Environmental changes that demand increased levels of exercise induce behavioural responses that are likely to increase the success of individuals under these changed conditions.