Behavioural responses to stress in animals

Real or perceived threat in the environment, elicits stress response in animals, which disrupts the internal constant environment of the animal. There are different kinds of stressors that animals can be exposed to, and there are different kinds of stress responses that animals display as a result. Physiological changes that happen because of stress cause behavioural responses in animals. There are different types of behavioural responses: impairment of response inhibition and lack of motivation, changes in social, sexual, aggression and nurture behaviour in animals. The extent of the impact is dependent upon the type, and duration of the stress, as well as the past experiences of the animal. Behavioural responses to prolonged stress can also be transferred across generations.
Overview
Stress responses are any responses that an organism makes or goes through, in response to a stressor that is causing a stress. A stress in accordance to Walter Cannon (1871-1945), is any disturbance that imbalances the internal environment of an organism also known as homeostasis. There are two major types of stressors that cause stress to animals: abiotic stressors and biotic stressors. Abiotic stressors are any ecological, geological, or climatological changes, that causes stress to the animal such as increased temperatures, and natural disasters. Biotic stressors are living things-related complications that causes stress; these include dominance, pollution, infection social pressures and competition.
There are different types of stress responses in an animal in response to stressors: Physiological responses, Behavioural responses, Psychological responses, and/or Physical responses (fight or flight). The response depends on the choice the animal partakes in, when it is faced with danger that causes distress. Walter Canon (1871-1945), argues that there are two possible choices that an organism may choose when stress is encountered: fight or flight responses; the choice is based on careful evaluation of the situation that would derive a response.
Behavioural responses
Behavioural responses to stress, are evoked from some underlying complex physiological changes that arise consequently from stress. There are many different types of behavioural responses to stress:
Impairment of response inhibition and lack of motivation
According to a study conducted by Mika and his colleagues, prolonged stress in rats causes response inhibition. It was evident through their experiment that stressed rats had inhibited premature responses (decreased timing of intervals to food), along with decreased intrinsic motivation to initiate a response. They link the decreased motivation to the stress-associated reduction in incentive motivation, as presented by another study conducted by Kleen and his colleagues. Decreased motivation was also seen in a study conducted by Beery and Kaufer, where they explained that stressed rodents are less likely to be motivated to interact with one another.
Change in social behaviours
A study conducted by Beery and Kaufer, revealed that social behaviours in rodents change in response to stress. They explain that social withdrawal and general reduction in social interaction after an exposure to a stressor are evident in rodents. They argue that this is due to the underlying physiological changes that the rodent goes through in response to stress. For instance, the changes that occur to the hypothalamic-pituitary-adrenal (HPA) hormonal axis, is directly related to the changes in social behaviour. Social avoidance is another consequence of stress that can be seen in rodents. Rodents are more likely to avoid dominant rats and avoid social interactions amongst each other after the exposure to a stressor.
Sexual Behaviours
Sexual interests change in many species when exposed to stressors. For instance, stressed male and female rats express inhibited mating behaviour which is evident through the clear increase in the inhibitory hormone RF-amide. Another study suggests that masculine sexual behaviour in male rats is subject to changes in accordance to the type of stressors that the rats were subjected to. Female Zebra Finches mating choice is determined by the stressors that they are exposed to early in life, which remains consistent throughout adulthood. A study about stress effects on female songbird's response to sexual signal for mating, indicated that the response to this specific signal can be impaired if the female is exposed to developmental stress. Behavioural changes as a result from developmental stress impairs neural responses to sexual signal, which reduces mating:
Aggressive behaviours and Anti-predator responses
Stressed animals would choose to avoid a novel situation rather than confront it. Aggressive behaviour is associated with sex hormones, such as testosterone, and specific brain regions and systems such as the medial preoptic nucleus, prefrontal cortex-dependent response inhibition, and anterior hypothalamus. Stress negatively impacts sex hormones, which results in an imbalance and reduction in aggression related hormones and function. Also, chronic stress results in prefrontal cortex-dependent response inhibition. This results in reduction in aggression, thus promoting anti-predator responses.
Prolonged stress reduces parental behaviour toward offspring
Prolonged stress alters parental behaviour toward offspring and promotes parental neglect. According to a study performed by Tilgar and associates, predation stress alters parents' behaviours such as the reduction in provisioning rates, which negatively impacts the offspring's performance. Oxytocin and vasopressin hormones are generally responsible for affiliative and pair-bonding behaviours in many species. Stress alters the level of both hormones resulting in an abnormal behaviour from parents towards offspring. For instance, levels of oxytocin decrease as a result of prolonged stress, which has been shown to reduce pair bonding behaviour and increase withdrawal behaviour. Also, prolactin is another important hormone that is associated with nurture by parents to offspring, and levels of this hormone can be altered as a result of stress. Reduced levels of prolactin as a result of stress decreases behaviours such as suckling, licking, and brooding.
Transgenerational behavioural response to stress
Behavioural response to stress can be transmitted from parents to offspring. When an offspring observes the expression of behaviour such as fear in response to a stress stimulus, the same response would be elicited in the offspring when the stimulus is presented. Using Rodent model, Debeik and associates illustrated that fear is transferred from mother to infant in response to a certain odour stimulus. They further proved that the neural activity, such as the basal amygdala activity of the offspring's brain, illustrated fear response. Therefore, parents' behavioural response to stress can be transgenerational and can be proven via neural activity.
References
Ethology