Development of Complex Behavior

Animal Personality

Anybody who has extensive interactions with individual animals knows that there is a degree of behavioral idiosyncrasy, much like what we experience with friends and relatives. In

Figure 9.13 S. T. Emlen photographed in the planetarium during an experiment involving exposure of indigo buntings to different stellar configurations in a planetarium.

Source: Planetarium photo courtesy of S. T. Emlen; indigo bunting photo from Creative Commons, https://search. creativecommons.org, by melissaleighpeck, license CC BY 2.0.

psychology, these idiosyncrasies relate to the concept of personality. A personality trait is a characteristic style of individual reaction in a variety of situations (Box 9.2). In one study (Gosling, Kwan, & John, 2003), owners judged both their own personality and the personality of their dogs; independently, a peer judged the personalities of both owners and dogs. Judgments were based on a questionnaire that included four traits defined by a set of statements adjusted so that they could be applied to both humans and dogs. The four general traits and example statements that judges had to agree/disagree on a 1-5 scale were the following:

• • Extraversion/energy: “Is full of energy.”
• • Agreeableness/affection: “Is cooperative.”
• • Neuroticism/emotional reactivity: “Can be tense.”
• • Openness/intelligence: “Is curious about many different things.”

The results suggested that judgments about these four traits were as consistently made about the dog’s personality as they were about the owner’s personality.

Box 9.2 Animal Personality

The idea that people can be classified according to their personality or temperament has its roots in Greco-Roman medicine. Hippocrates (ca. 460-370 BCE) is credited with the theory that the human body contains four fluids that he called humors: blood, yellow bile, black bile, and phlegm. Galen (131-200 CE) then took these basic elements and developed a typology of temperaments: sanguine, choleric, melancholic, and phlegmatic.

In modern times, Pavlov was among the first to adapt this typology to nonhuman animals. In his pioneering research on conditioning, Pavlov (1928) noticed that dogs (Cams vulgaris) could be classified along the lines of these four classic types. For example, the dogs that he classified as “sanguine” were quick to learn, but became drowsy and inactive if left undisturbed. In the other extreme were the “melancholic” dogs, which showed restraint in a new environment but exhibited an impressive stability in their conditioned reflexes. Pavlov mentions a melancholic dog nicknamed “Brains” because of its impressive conditioning skills.

In Belding ground squirrels (Urocitellus beldingi), common behavioral styles were observed in response to changes in predation, foraging, and mating parameters (Dosmann & Mateo, 2014). Behavioral style was initially assessed in terms of the use of a refuge area when changes in predatory risk were implemented under laboratory conditions. Whereas there are individual differences in refuge use in the predatory context, individuals tended to exhibit similar refuge use style in response to changes in foraging and mating contexts.

In a group of zoo chimpanzees (Pan troglodytes), well-being was associated with dominance, extraversion, and dependability, as rated by observers. Because the genetic relatedness of these chimpanzees was known, the heritability of well-being and these personality traits could be estimated using quantitative genetic techniques (Weiss, King, & Enns, 2002). This analysis indicated that well-being and dominance are dependent on the same genes. Dominance is related to such features as decisiveness, independence, and bullying behavior. Thus, dominance likely reflects the ability of a chimpanzee to obtain resources and, ultimately, the individual’s inclusive fitness. In fact, well-being could actually be used by a reproductively receptive animal as a proxy of the inclusive fitness of a potential mate.

There is more direct evidence that some personality traits are linked to reproductive success. In bighorn sheep rams (Olds canadensis), individuals high in both docility and boldness survive longer than their alternatives (indocile and shy) and produce more offspring (Réale, Martin, Coltman, Poissant, & Festa-Bianchet, 2009). Docile animals are risk-prone, whereas bold animals tend to be aggressive. In great tits (Pams major), a stronger tendency to explore new environments (boldness) is positively correlated with aggressive behavior, competitive ability, and social learning. Exploratory behavior is linked to dispersal and foraging efficiency. Still, when the reproductive success of male-female pairs of great tits was assessed in years with scanty food and strong competition from conspecifics, it turned out that pairs that were either both low or both high in exploratory behavior had higher success than mixed pairs (Both, Dingemanse, Drent, & Tinbergen, 2005). Apparently, parents with extreme exploratory phenotypes have different skills that independently increase reproductive success. For example, high-exploring males are better at defending territories, but low-exploring individuals have more efficient parental skills and produce larger fledglings.

These examples suggest that personality traits can be understood within an evolutionary framework, since they are likely to arise from an interplay between genetic and environmental factors (Hengartner, 2017).