Background & Aims

Animals are typically presented with a plethora of threats, such as predators. Responses to such stressors are known as fear responses, which involve physiological and behavioural reactions. Physiologically, there is the activation of the sympathetic system and the inhibition of the automatic one. Behaviourally, individuals can display passive responses, such as freezing, or active responses, such as fighting or flying. Type and magnitude of fear responses can vary among individuals.

Variation in fear responses has been linked to cognition, personality, and monoamines.

Regarding cognition, the ability to learn from previous experiences and adapt to new environments, changing the response to specific stimuli, can be a key strategy to survive. Two examples of learning are habituation and sensitisation, which are respectively the gradual decrease and increase of the magnitude of the response to a repeated stimulus. These learning processes can increase the fitness of an individual. Learning that a stimulus is dangerous can lead an individual to react faster to it, increasing its survival rate. On the other hand, when a stimulus is not threatening, reacting to it numerous times implies a useless use of energy and can be detrimental in the long run since the immune and reproductive systems are inhibited.

Regarding personality, variation in fear responses has been associated with boldness and locomotor activity. Boldness is a personality gradient that refers to an individual’s willingness to take risks. An individual can be defined as ‘shy or ‘bold’, with bold individuals taking more risks than shy individuals.
Locomotor activity (hereafter referred to as activity) refers to the amount of movement an individual does in a familiar environment. An individual can be less or more active.   
Bolder and more active animals tend to shift to a dynamic reaction (e.g., fight or flight) faster than shyer and less active individuals.

Regarding monoamines, they are neurotransmitters that have been linked to a broad range of animal behaviours. Specifically, in situations of stress and danger, noradrenaline and octopamine are respectively released in vertebrates and invertebrates. These neurohormones modulate processes such as learning, and behaviours such as aggression and fear responses. They have also been correlated to elicitability, increasing an individual’s reactivity in stressful situations.

Though, how these factors inter-relate with each other is still unclear.

Therefore, I aimed to investigate the variation in fear responses, both initial and repeated, to understand if there is a link with personality and octopamine.