Age-dependent genetic variation in aggression

Understanding the extent to which behavioural variance is underlain by genotypic, environmental and genotype-by-environment effects is important for predicting how behavioural traits might respond to selection and evolve. How behaviour varies both within and among individuals can change across ontogeny, leading to differences in the relative contribution of genetic and environmental effects to phenotypic variation across ages. We investigated among-individual and among-genotype variation in aggression across ontogeny by measuring, twice as juveniles and twice as adults, both approaches and attacks against a three-dimensional-printed model opponent in eight individuals from each of eight genotypes (N = 64). Aggression was only significantly repeatable and heritabile in juveniles. Additionally, how aggression changed between juvenile and adult life-history stages varied significantly among individuals and genotypes. These results suggest that juvenile aggression is likely to evolve more rapidly via natural selection than adult aggression and that the trajectory of behavioural change across the lifespan has the potential to evolve. Determining when genetic variation explains (or does not explain) behavioural variation can further our understanding of key life-history stages during which selection might drive the strongest or swiftest evolutionary response.

Automated summary

Understanding the factors underlying behavioural variance is crucial in predicting behavioural response to selection and evolution. Behavioural variation can change across ontogeny, with varying contributions of genetics and environment across ages. This study investigated variation in aggression among individuals and genotypes across development stages. Results showed that aggression was repeatable and heritable only in juveniles, and the changes in aggression between juvenile and adult stages varied significantly among individuals and genotypes. These findings suggest that juvenile aggression is more likely to evolve rapidly through natural selection and that the trajectory of behavioural change across lifespan has evolutionary potential. Determining when genetic variation explains behavioural variation can enhance our understanding of key life-history stages for strong evolutionary response.