Personality is defined by four key elements: (i) it is manifested early in life, and is relatively stable throughout development, (ii) it is primarily biologically based (genetics and neurobiological mechanisms), (iii) it refers to characteristics of behavioral reactions such as intensity, speed, response threshold, latency and recovery time, and (iv) it is most clearly expressed in novel and unpredictable situations (Stamps and Groothuis, 2010). Previous research on animal personality suggests a relationship between certain traits and the formation and maintenance of social bonds (Massen and Koski, 2014), immunity strength (Bolhuis et al., 2003; Capitanio et al., 1999), the ability to cope with physiological stress (Carere et al., 2010), the performance of abnormal or stereotypic behaviors (Ijichi et al., 2013; Cussen and Mench, 2015), and the expression of pain (Ijichi et al., 2014).


Behavioral Experiments

Description

Behaviors recorded

Restraint Test Limit the movement of an animal for a brief period of time, for example by tethering, or by close confinement in a weighing crate. Vocalization, freezing, and escape attempts.
Open Field Test Separate animal from its pen or herd mates and place it in a novel arena for brief time. Vocalization, exploration, freezing, and activity.
Novel Object Test Animal is presented a species-relevant object in home pen/pasture or experimental arena. Latency to approach, duration of contact, and average distance from object.
Feeding Competition Measure aggression and social rank by placing a single highly-valued food source in a pen/pasture with a certain number of animals. Aggression, duration/rate of food access, latency to approach food resource, and displacement at food resource.
Resident-Intruder Test Single animal is confronted with unknown conspecific in their home pen/pasture. Aggression, tactile contact, and inter-animal distance.
Human Approach Test Animal is placed in solitary arena with an unfamiliar human. The location of experiment can be familiar (home pen) or unfamiliar (open field test). Latency to approach a human (Voluntary Approach), or the response to an approach by a human (Forced Approach), and frequency/duration of tactile contact.

 


Personality traits may also influence the affective state of an animal by shaping attentional and informational processing. These cognitive biases can elicit negative affective states, such as the perception of danger during exposure to an actual (fear state) or potential (anxiety state) threat. While fear is a highly functional and adaptive state, captive animals can be housed in environments that prevent the performance of adaptive behaviors, such as escape or shelter. These environmental constraints can exacerbate fear responses and elicit harmful side-effects including the development of maladaptive behaviors, an increased risk of injury, a decreased immune system, and/or reduced productivity (Boissy, 1995; Korte, 2001). Therefore, how an animal perceives social and environmental stimuli is influenced by their affective state, and how an animal responds to these stimuli is shaped by their personality.

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References

Boissy, A. (1995). Fear and fearfulness in animals. Quarterly Review of Biology, 70, 165-191.

Bolhuis, J. E., Parmentier, H. K., Schouten, W. G., Schrama, J. W., & Wiegant, V. M. (2003). Effects of housing and individual coping characteristics on immune responses of pigs.  Physiology & Behavior, 79, 289-296.

Capitanio, J. P., Mendoza, S. P., & Baroncelli, S. (1999). The relationship of personality dimensions in adult male rhesus macaques to progression of simian immunodeficiency virus disease. Brain, Behavior, and Immunity, 13, 138-154.

Carere, C., Caramaschi, D., & Fawcett, T. (2010). Covariation between personalities and individual differences in coping with stress: converging evidence and hypotheses. Current Zoology, 56, 728-740.

Cussen, V., & Mench, J. (2015). The relationship between personality dimensions and resiliency to environmental stress in orange-winged amazon parrots, as indicated by the development of abnormal behaviors. PloS one, 10, e0126170.

Ijichi, C., Collins, L., & Elwood, R. (2013). Evidence for the role of personality in stereotypy predisposition. Animal Behavior, 85, 1145–1151.

Ijichi, C., Collins, L., & Elwood, R. (2014). Pain expression is linked to personality in horses. Applied Animal Behavior Science, 152, 38–43.

Korte, S. (2001). Corticosteroids in relation to fear, anxiety and psychopathology. Neuroscience & Biobehavioral Reviews. 25, 117–142.

Massen, J., & Koski, S. (2014). Chimps of a feather sit together: chimpanzee friendships are based on        homophily in personality. Evolution and Human Behavior. 35, 1–8.

Stamps, J., & Groothuis, T. (2010). The development of animal personality: relevance, concepts and perspectives. Biological Review. 85, 301–325.