Genetic heterogeneity induces nonadditive behavioural changes in Drosophila

The formation and dynamics of group behaviours are important topics in ecology and evolution. Although several theoretical studies assume homogeneity among individuals, real-world organisms often display remarkable behavioural diversity within groups. This study investigated the synergistic impact of genetic heterogeneity on group behaviour and reveals the behavioural underpinnings of diversity effects using 83 genetically distinct strains of Drosophila melanogaster. Various indices of foraging behaviour, including movement speed, search comprehensiveness, spatial preference and stopping time, were measured using homogeneous (single strain) and heterogeneous (mixing two distinct strains) groups of flies. The heterogeneous groups exhibited significant increases in spatial preference and stopping time compared with the homogeneous groups, suggesting that genetic heterogeneity induces nonadditive changes in group behaviour. Furthermore, the magnitude and direction of the behavioural change varied among different combinations. Multiple regression analysis showed that the phenotypic distance in some traits between mixed strains could explain the emergence of diversity effects on group behaviour. Specifically, interindividual heterogeneity in the locomotor activity level showed a positive correlation with diversity effects. These results emphasise the importance of intraspecific diversity in group dynamics and suggest that genetic heterogeneity can improve group performance through the acquisition of novel behavioural traits.