Interspecific Conformity and Asymmetric Behavioral Convergence in Drosophila

Many animals form mixed-species groups. Interactions among individuals within a group often induce behavioral conformity, forming group-level characteristics. However, mixed-species groups are often studied with a focus on specific species, and it remains unclear whether conformity emerges or group-level characteristics form in passive aggregations, such as insects patchily distributed on food sources. Here we focused on four sympatric Drosophila species, i.e., D. simulans, D. suzukii, D. lutescens, and D. takahashii, and revealed interspecific conformity in activity and the formation of group-level characteristics. Within each species' solitary group, activity levels increased in other individuals when the focal individual began walking, indicating that activity conforms among individuals in all species. Experiments were conducted with D. lutescens in mixed groups that combined the other three species. Convergence in activity levels due to conformity was observed across all species. Interestingly, D. takahashii exhibited smaller behavioral changes in mixed groups than the other species. Conversely, D. lutescens showed the greatest change in activity levels when mixed with this species. These results suggest that D. takahashii exerts disproportionate influence on the formation of group-level characteristics. Understanding intraspecific behavioral variation and intergroup variation may require considering the impact of such influential species within the same guild.