“Influencers” in Mixed-Species Fruit Fly Groups: Interspecific Behavioral Synchronization Determines Group Characteristics

Kaiya Hamamichi (doctoral student at the time) and Professor Yuma Takahashi of Chiba University Graduate School of Advanced Science and Engineering discovered "interspecific conformity" in mixed groups of different fruit fly species. Specifically, they found that a particular species (Takahashi fruit fly) acts as an "influencer," dramatically increasing the activity level of surrounding species (e.g., Kihada fruit fly) while being largely unaffected itself. This research suggests that animal behavior, previously understood on a species-by-species basis, is flexibly shaped by the composition of the community, indicating that "who they spend time with" is a crucial factor. The findings were published on March 17, 2026, in the international scientific journal Ecology and Evolution (DOI: 10.1002/ece3.73149). The study's background notes that while synchronized behavior in single-species groups is known, little was understood about interspecies influence in temporary aggregations like insects at feeding sites. Key findings include: 1) First confirmation of interspecific conformity in temporary groups, demonstrating that cross-species behavioral synchronization occurs and forms group characteristics. 2) Identification of an asymmetric mechanism where behavioral convergence is unilaterally driven by influential species, rather than mutual adjustment. 3) Identification of the Takahashi fruit fly as an "influencer" that significantly boosts the activity of other species like the Kihada fruit fly, while its own activity remains largely unchanged. Researchers comment that this study shows behavioral traits are determined by social factors (coexisting species) in addition to genetic and physical environmental factors. This warns of potential cascading effects from invasive species or extinction on other species' behavior and ecosystem functions. It also encourages re-evaluating interspecies interactions beyond predation and competition to include behavioral synchronization, which is expected to deepen the understanding of wild animal foraging efficiency and survival strategies. The research was supported by Chiba University's FY2025 "All-directional, Challenging Integrated Innovator Doctoral Human Resource Development Project," KAKENHI (22H05646, 23H03840), and the FY2023 Sasakawa Scientific Research Grant (Project No.: 2023-5051).