The link between stress, personality and infection
The project 'The role of host personality and stress responses in parasite dynamics' (PARA-PEST) used a fish (guppy) host–parasite model. Personality was determined from behavioural trials. Stress levels were determined via stress hormones (cortisol) collected and extracted from the water before and after fish had experienced stressful events. These events were designed to mimic an unsuccessful predation attempt. Researchers then compared hormonal and behavioural responses after a stressful event, as well as after repeated stressful events, to test long-term responses and physiological adaptation to stress. Parasite susceptibility studies involved infecting individual fish of known personality and stress responses, and tracking the progression of the infection. Transmission studies involved infecting single fish within a pair or group, and then tracking the spread of infection among individuals. Researchers also looked at whether infection had an effect on personality. The results showed that stress hormone release and personality were correlated: Fish that released more cortisol were more cautious and explored less. All fish responded to stressful events by increasing cortisol release and changing their behaviour. Neither cortisol release nor personality, however, were predictors of which fish died or survived a parasite infection. Instead, body size and condition determined susceptibility. At non-lethal levels, infection did not cause a change in personality. Personality did have an effect on transmission rates. The personality of individuals was influenced by the personality of other individuals within their group, and both personality and body size affected how long individuals spent together. In general, the longer fish spent together, the greater the likelihood of infection. To investigate the long-term effects of stress during development on adults, the researchers raised juvenile guppies under both stressful and non-stressful conditions. Surprisingly, the guppies raised under stress did not show an increase in stress hormones, a change in behaviour, or a difference in susceptibility to infection, suggesting that animals can adapt to stress as they grow. This work has implications for understanding how parasite infections spread among animals in captivity, as well as in wild populations. By understanding stressors, especially those caused by humans, it becomes possible to improve conditions for animals. This includes those raised for agriculture and aquaculture, as well those being bred in captivity for conservation purposes.
Keywords
Stress, personality, host–parasite model, cortisol, parasite infection, animals in captivity
