"Influencers" in Mixed-Species Drosophila Populations: Interspecific Behavioral Synchronization Determines Overall Group Characteristics

Kaiya Hamamichi (then a doctoral student at Chiba University Graduate School of Advanced Science and Engineering) and Professor Yuma Takahashi of the Chiba University Graduate School of Science have revealed that "interspecific conformity" (Note 1), where different species of Drosophila synchronize their behavior, occurs in mixed populations of Drosophila with different characteristics. In particular, it was found that a specific species (*Drosophila takahashii*) is hardly affected by other species, while playing the role of an "influencer" that dramatically increases the activity levels of surrounding species. This research suggests that the behavior of organisms, which has conventionally been discussed for each species, is actually flexibly reshaped by the composition of the community, i.e., "what kind of neighbors they spend time with."

These research findings were published on March 17, 2026, in the international scientific journal Ecology and Evolution.

(Paper here: 10.1002/ece3.73149)

Figure: Influencers that increase the activity of other individuals

Background of the Research In nature, different species sometimes gather in the same place to form loose "mixed flocks." In such groups, "synchronous behavior" occurs due to interactions between individuals, and it is thought to play ecologically important roles such as information sharing and predator avoidance. However, previous research has focused only on single-species flocks. Therefore, in "haphazard" groups like insects gathering at a feeding ground, it was largely unknown whether different species influence each other's behavior and how the overall behavior of the group is formed.

Key Points of the Research Findings 1) First confirmation of "interspecific conformity" in temporary groups: Unlike groups such as bird flocks, it was first demonstrated that interspecific behavioral synchronization occurs even in "temporary groups" that accidentally gather at a food resource, and that group characteristics are formed. 2) Asymmetric behavioral convergence: It was identified that the convergence of behavior in mixed flocks does not occur through mutual compromise, but is unilaterally caused by specific "influential species" through an asymmetric mechanism. 3) Identification of "influencers": Among the species targeted in this study, *Drosophila takahashii* was shown to have a strong social influence that significantly increases the activity of other species (such as *Drosophila suzukii*), while its own activity level remains almost unchanged.

Future Outlook (Researcher's Comment) This research shows that the behavioral characteristics of organisms in a certain region are determined not only by genetic factors and physical environment, but also by social factors such as "which species coexist there." This warns of the possibility that the invasion of alien species or the extinction of specific species could have unexpected cascading effects (such as the loss of influencers) on the behavior of remaining species and ecosystem functions. Furthermore, by re-examining interspecific interactions not only from the perspective of "predation" or "competition" but also "behavioral synchronization," it is expected to deepen our understanding of foraging efficiency and survival strategies of wild animals.

Glossary (Note 1) Interspecific conformity: A phenomenon in which individuals of different species adjust their own behavior (e.g., activity level) to that of surrounding individuals.

Paper Information Title: Interspecific conformity and asymmetric behavioral convergence in Drosophila Authors: Kaiya Hamamichi and Yuma Takahashi Journal: Ecology and Evolution DOI: 10.1002/ece3.73149

About the Research Project This research was conducted with support from the Chiba University Reiwa 7th year "All-Directional, Challenging Integrated Innovator Doctoral Human Resource Development Project," KAKENHI (22H05646, 23H03840; Takahashi), and the 2023 Sasakawa Scientific Research Grant (Project No.: 2023-5051). We express our gratitude to Chiba University, the Japan Society for the Promotion of Science, and the Sasakawa Scientific Research Foundation.