Abstract
Chronic stress is known to enhance mammals’ emotional reactivity and alters several of their cognitive functions, especially spatial learning. Few studies have investigated such effects in birds. We investigated the impact of a two-week stress on Japanese quail’s emotional reactivity and spatial learning. Quail is an avian model widely used in laboratory studies and for extrapolation of data to other poultry species. As sensitivity to chronic stress can be modulated by intrinsic factors, we tested juvenile female Japanese quail from three lines, two of them divergently selected on tonic immobility duration, an indicator of general fearfulness. The different emotional reactivity levels of quail belonging to these lines can be revealed by a large variety of tests. Half of the birds were submitted to repeated unpredictable aversive events for two weeks, whereas the other half were left undisturbed. After this procedure, two tests (open field and emergence tests) evaluated the emotional reactivity of treated and control quails. They were then trained in a T-maze for seven days and their spatial learning was tested. The chronic stress protocol had an impact on resting, preening and foraging in the home cage. As predicted, the emotional reactivity of treated quails, especially those selected for long tonic immobility duration, was higher. Our spatial learning data showed that the treatment enhanced acquisition but not memorization. However, intrinsic fearfulness did not seem to interact with the treatment in this test. According to an inverted U-shaped relationship between stress and cognition, chronic stress can improve the adaptability of birds to a stressful environment. We discussed the mechanisms possibly implied in the increase of emotional reactivity and spatial abilities.
Highlights
Whether natural or experimental, chronic stress has numerous influences on the physiology and behaviour in various species [1,2]
Previous studies on starlings, zebra finches (Taeniopygia guttata) and Japanese quail report a decrease of basal corticosterone levels after exposure to unpredictable and repetitive mild stressors [3,17,22] and chronically stressed birds’ cognitive abilities vary between studies [21,26]
Treatment only affected this parameter in control line (CTI) quail: treated quail emitted more calls than did control quail (Mann-Whitney U-test, CTI, treated group: 18.261.4, control group: 3.161.4 calls, U = 23.0, P = 0.007; STI, treated group: 24.463.7, control group: 21.362.5, U = 149.0, P = 0.91; LTI, treated group: 6.162.0, control group: 4.362.1, U = 85.5, P = 0.63)
Summary
Chronic stress has numerous influences on the physiology and behaviour in various species [1,2]. Chronic stress can affect growth, hypothalamus-pituitary-adrenal (HPA) axis response and emotional reactivity, and can induce several brain and cognitive alterations [4,5,6]. Whereas reports show that chronic stress procedures can influence birds’ physiological parameters Previous studies on starlings, zebra finches (Taeniopygia guttata) and Japanese quail report a decrease of basal corticosterone levels after exposure to unpredictable and repetitive mild stressors [3,17,22] and chronically stressed birds’ cognitive abilities vary between studies [21,26]. Regardless of the species studied, these results raised the possibility of an inverted
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