Personality Diversity in Fly Groups Improves Trade-offs: Differences in Activity Between Individuals Enhance the Compatibility of Exploration and Vigilance

A research group consisting of Takahira Okuyama, a second-year doctoral student in the Graduate School of Science and Engineering at Chiba University, Daiki X. Sato, a specially appointed assistant professor at the International Center for Advanced Research, and Professor Yuma Takahashi of the Graduate School of Science, investigated the effects of grouping and diverse personalities on the exploration-vigilance trade-off (Note 2) in adult flies from approximately 80 strains of Drosophila melanogaster (Note 1). The results showed that in groups of individuals with the same personality, a trade-off emerged where "more active exploration led to reduced vigilance." Conversely, in groups with diverse personalities among individuals, this trade-off relationship was partially overcome, enhancing the compatibility of exploration and vigilance.

These research results were published in the international academic journal iScience on June 8, 2026 (JST).

(Paper here: 10.1016/j.isci.2026.116171)

■ Research Background

You can't have your cake and eat it too. Animals live with a trade-off: the more they move to explore for food, the less vigilant they are against predators, and if they are constantly vigilant against predators, their food exploration suffers. While it has been independently reported that grouping allows for efficient exploration and effective predator avoidance, the impact of group behavior on this trade-off was unknown (Figure 1).

■ Research Results

In this study, for Drosophila melanogaster, approximately 80 strains with different personalities, such as morphology and behavior, were prepared, and exploration and vigilance behaviors were measured under the following conditions where group composition was artificially manipulated:

- Single individual: Condition with one individual from each strain
- Homogeneous group: Condition with six individuals from the same strain, creating a group with uniform personalities
- Diverse group: Condition with three individuals each from two different strains, creating a group with personality diversity

① Analysis results showed that in single individuals, both exploration and vigilance levels were low, and no trade-off relationship appeared. However, in homogeneous groups, performance improved, and the exploration-vigilance trade-off became apparent. That is, groups that explored more actively showed a pattern of reduced vigilance.

② In diverse groups, the compatibility of exploration and vigilance increased, showing a tendency to improve the trade-off relationship observed in homogeneous groups (Figure 2).

③ To investigate the mechanism of trade-off improvement associated with diversity, an analysis called PheHAS (Note 3) was conducted using a vast amount of trait data. This revealed that diversity in activity levels among individuals contributes to the compatibility of exploration and vigilance.

These results demonstrate the possibility that trade-offs, which generally constrain animal behavior, can be improved or mitigated by diversity, providing a valuable research example.

■ Future Outlook (Researcher Comments)

This study shows the potential for groups containing diverse personalities to overcome antagonistic situations and is expected to contribute to understanding the relationship between "diversity and innovation." In the future, by focusing on behaviors other than exploration and vigilance and investigating how biological diversity overcomes familiar dilemmas, we aim to clarify the function of diversity in groups and how it can be utilized.

■ Glossary

Note 1) Strain: A breeding population maintained by repeated interbreeding among the descendants of a single individual (female) collected in the wild. Since each strain originates from a single female, it is thought to maintain that female's genetic characteristics and phenotype. Individuals of the same strain have extremely small genetic variation and can be considered clonal individuals.

Note 2) Trade-off: A relationship where increasing one element simultaneously leads to the loss of another element. In ecology, it is broadly divided into two types: allocation trade-offs and acquisition trade-offs. The former is a dilemma that arises when allocating finite resources, such as lifespan and reproduction. The exploration-vigilance trade-off addressed in this study falls into the latter category, referring to a relationship where actions to maximize resources cause disadvantages in another context.

Note 3) PheHAS: An abbreviation for Phenome-wide Higher-level Association Study, an analytical method that comprehensively investigates the relationship between group-level phenomena (e.g., improvement of trade-offs) and variations among individuals composing that group (e.g., trait distances). In this study, this analysis was used to examine individual variations contributing to the improvement of the exploration-vigilance trade-off across approximately 190 types of trait data, including locomotor characteristics and morphological information of the flies.

■ Paper Information

Title: Genetic heterogeneity alleviates behavioral trade-off between exploration and vigilance in Drosophila

Authors: Takahira Okuyama, Daiki X. Sato and Yuma Takahashi

Journal: iScience

DOI: 10.1016/j.isci.2026.116171

■ Reference 1)

Title: Big houses, big cars, superfleas and the costs of reproduction

Journal: Trends in Ecology & Evolution

DOI: 10.1016/S0169-5347(00)01941-8

■ Reference 2)

Title: Genetic heterogeneity induces non-additive behavioural changes in Drosophila

Journal: Journal of Experimental Biology

DOI: 10.1242/jeb.249449

■ About the Research Project

This research was conducted with the support of the following grants:

- Grants-in-Aid for Scientific Research "Social and ecological effects of contrarian behavior on groups and its genetic basis" (JP23H03840)
- Grants-in-Aid for Scientific Research "Multifunctionality of group behavior brought about by individual heterogeneity: Higher-order genetic basis and control of group behavior" (JP22H05646)