Inteligencia Artificial (IA)

Animals generate physiological and behavioural responses to help cope with changes in their environments. Relatively benign environmental stimuli may require minor

adjustments in physiology and behaviour in order to maintain homeostasis, such as a slight change in wind direction prompting an animal to move into shelter. Other stimuli may require more robust responses in order for animals to survive. Two types of stimuli that animals may encounter are threatening stimuli and stimuli that pose physical

challenges. Threatening stimuli are stimuli from the environment that are likely to cause damage or danger and can elicit a state of fear and a fear response in animals. Fear can therefore be defined as a state or situation in which an animal is responding to an environmental threat (LeDoux, 1996; Rodrigues et al., 2009). Fear responses help animals to avoid the potentially deleterious consequences of exposure to danger, and involve both behavioural and physiological adjustments. The amygdala is a region of the brain responsible for detecting and responding to threatening stimuli, and fear arousal is one of the most potent activators of the HPA axis (Davis, 1997; Rodrigues et al., 2009). Auditory, visual, somatosensory, gustatory and olfactory stimuli are

processed by the sensory thalamus and cortex, and information about threatening stimuli is sent to the amygdala (Rodrigues et al., 2009). The amygdala has downstream

projections to the hypothalamus, and during a fear response amygdaloid signalling leads to activation of the HPA axis by stimulating the secretion of CRF by the hypothalamic paraventricular nucleus (Rodrigues et al., 2009). When a threatening stimulus leads to a state of fear in an animal and the HPA axis is activated, then the stimulus can be called an emotional stressor. Activation of the HPA axis in response to an emotional stressor, therefore, is synonymous with a fear response (LeDoux, 1996; Fendt and Fanselow, 1999; Labar and LeDoux, 2001; Walker et al., 2003). In contrast, when animals

experience stimuli that pose physical challenges and the HPA axis is activated, the stimulus can be called a physical stressor. An animal responding to a physical stressor is responding to an actual physical challenge, rather than a threat, so an animal

responding to a physical stressor will not be in a state of fear. An animal in a state of fear, therefore, will also be generating a stress response, whereas an animal generating a stress response will not necessarily be in a state of fear.

The term fear can be used to describe both the experience (i.e. state of fear) and expression (i.e. fear behaviour) of an emotional event (Davis, 1997). Although the experience of fear cannot be measured directly, the expression of fear behaviour can be used to infer an animal’s fear state, also known as its level of fearfulness. Changes in freezing, scanning and vigilance behaviours for example, can potentially be used as measures of fear behaviour (Davis, 1997). The tonic immobility test is a widely used measure of fear in birds, where tonic immobility is an “unlearned response easily induced by brief manual restraint in which an animal remains still and exhibits reduced responsiveness to external stimulation” (Jones, 1986). Tonic immobility may represent the final stage in anti-predator behaviour, and the duration of tonic immobility is considered to be proportional to fearfulness (Gallup, 1974). Other fear behaviour tests used in birds are open field tests, and to a lesser extent, novel object tests (Forkman et al., 2007). Studies of fear have invariably used domesticated rather than free-living species of birds, and have focused on finding methods to reduce the potentially detrimental effects of heightened fear on welfare and performance in poultry (Jones, 1996; Satterlee and Jones, 1997). In an ecological context, however, fear behaviour has evolved to help birds avoid danger, and so there is interest in fearfulness in birds from an evolutionary perspective as well.

Although relationships between fearfulness and the HPA axis have not been studied in wild free-living species of birds, knowledge of how birds respond to threatening events in their natural environments can be gained from studies in domesticated species like the Japanese quail. One interesting finding from studies in quail is that when birds are subjected to an emotional stressor their levels of fearfulness increase in subsequent behaviour tests of fear. For example, quail restrained for 5 min, either 0 or 55 min before tonic immobility or open field testing showed higher levels of fearfulness than control birds left undisturbed before behaviour testing (Satterlee et al., 1993; Satterlee

and Marin, 2006). When birds experience emotional stressors in their natural habitats, do their levels of fearfulness also increase, and what might this mean? Corticosterone is the primary glucocorticoid secreted when birds respond to emotional stressors such as restraint (Carsia and Harvey, 2000), and these findings raise important questions about whether or not elevated plasma corticosterone concentrations were responsible for the subsequent increase in fearfulness in these quail. Corticosterone secretion is considered to help animals cope with threatening situations, primarily through increasing

mobilisation of stored energy (Wingfield and Kitaysky, 2002), but can corticosterone also potentiate fear behaviour in birds? A study designed to address this question is presented in the current thesis (see section 1.7).