Genetic Influences on Individual Variability in Western Lowland Gorilla (Gorilla gorilla gorilla) Social Behavior

While primates are considered highly social animals, the evolutionary origins and mechanisms underlying their social behaviors remain unclear. Not only do they exhibit an extensive range of behaviors, but individuals within the same species can also vary widely in their social interactions. Genetics play a significant role in shaping these individual variations in behavior; multiple genetic variants have been associated with differences in social behavior in mammals. Examples of these include MAOA and OXTR genes, which influence the expression of behaviors associated with antisocial and prosocial temperaments. Genetic polymorphisms affect primate interactions, impacting an individual’s ability to maintain its status in dominance hierarchies, compete for resources, and protect offspring. Therefore, diversity in social behavior also plays a crucial role in primate fitness. Socially adept individuals can form stronger bonds and have greater fitness than their antisocial counterparts. Current research focuses on polymorphisms in monkeys and humans, with few studies performed in nonhuman apes, such as gorillas. This thesis investigates the relationship between individual variation in social behavior and polymorphisms in the MAOA and OXTR genes in 11 western lowland gorillas (Gorilla gorilla gorilla). Using behavioral observation data collected across 25 ten-minute focal samples per subject, sociability was measured through social proximity scores, as well as affiliative and agonistic behaviors. DNA extracted from whole blood samples was then used to identify genotypes of these subjects at two candidate loci: the MAOA promoter VNTR region and the OXTR SNP rs35062132. Results indicate significant individual variation in social behavior, with social group as a significant predictor of social proximity scores. No variation was detected in the OXTR region among the sampled subjects, but divergence from other great apes at select nucleotide sites was identified. Multiple genotypes were observed in the gorilla MAOA promoter VNTR region, including novel 0-, 3-, and 5-repeat alleles not previously reported in published literature. However, due to statistical power being limited by the sample size, no conclusions were drawn from the MAOA genotyping results and their potential influence on the significant behavioral differences observed. These findings highlight the value of integrating behavioral and genetic approaches in great apes and underscore the need for further research into the biological basis of social variation in gorillas.