Behavioral Genetics

Genes are the basis of all life, and variations in the genetic code significantly affect a variety of physiological traits in animals, e.g., body confirmation traits, production and fertility, or the susceptibility to diseases. Behavior, in contrast, resembles rather an action or reaction than a physiological trait, so does the concept of a genetic contribution to trait variation between individuals also apply for behavior?

Probably one of the first evidence for a genetic background of animal behavior can be found in the evolution and breed history of the domestic dog (Canis familiaris). In the course of the domestication of dogs, the traits under selection, be it natural or artificial, were also of behavioral nature, e.g., tameness and attachment to humans and later hunting and herding behavior. Subsequently, in the formation of the different dog breeds, the modern dog as we know it today, was shaped among others by selecting dogs with favorable personalities.

Dmitry Belyaev demonstrated this process of behavioral selection in canid domestication in a similar species, the silver fox (Vulpes vulpes). In his selection experiment beginning in 1959, farm foxes were selected for tameness only in a standardized environmental setting: after birth and weaning, pups were caged with litter mates and kept under minimal contact to humans. In the first months of their lives, a pups’ tameness was evaluated in a series of behavior tests and only the ones with the highest scores for tameness were selected for breeding. The selection over multiple generations resulted in a shift towards tame behavior, with a growing percentage of animals within every generation that expressed docile behaviors. Based on these observations Belyaev concluded that behavior has a genetic background to some extent. After multiple decades of selection, experimenters refer to these animals as domesticated foxes, as they were eager to establish human contact, they whimper to attract attention and sniffing and licking experimenters like dogs (Trut 1999).

Now, the idea that genetic variations besides environmental factors and individual experiences contribute to the way an animal behaves in response to external stimuli and in certain situations is widely accepted. However, to which extend behavior variations are influenced by either genetic or non-genetic (environmental) factors is excessively discussed in the nature vs. nurture debate. More likely than exclusive influences of nature (genes) or nurture (environment) is an interaction between both factors: genetic variants can determine how environmental stimuli that trigger behaviors are received and processed (e.g., by modifying the sensory system) and the environment can alter the inner state of an animal (e.g., a lack of food leads to hunger) which in turn can regulate gene expression (Bendesky and Bargmann 2011).

In the era of molecular genetics, research on behavior genetics in animals can evolve from descriptive observations from selection experiments to the detection of causal variants and molecular mechanisms involved in the genetic architecture of behavior. Comprehensive data from various molecular levels, e.g., genome, transcriptome, and metabolome information, can now be used to meet the still growing interest in the genetic contribution to behavior variation in animals: dissecting the genetic background of animal behavior has its relevance in animal welfare in domesticated species (e.g., breeding for stress-resistance in livestock), can give insights into the evolutionary importance of behavior in wild populations, and finally, can provide general information which might be related to behavioral conditions or psychological disorders in humans.

In the following, the basis of the genetic architecture of animal behavior is described and relevant candidate mechanisms with known influence on behavior variation in animals are introduced. Then, methods for behavior phenotyping and the subsequent genetic analysis are presented and examples for the genetic contribution to specific behavior traits or patterns are given. Additionally, the interactions between non-genetic (environmental) and genetic factors in relation to behavior variation are presented. In the conclusion, the challenges and perspectives of animal behavior genetics are briefly discussed.