Intrinsic strain-specific behaviour predicts emergent collective aggregation in heterogeneous C. elegans groups

Collective animal behaviour research to date typically specifies members of the group as identical individuals, even though within group heterogeneity is commonplace. We exploit the tractable C. elegans study system to explicitly define and manipulate heterogeneity to investigate how individuals with different behavioural phenotypes interact and aggregate in heterogeneous group settings. Using controlled mixing experiments between pairs of strains that have defined aggregation tendencies, we apply a quantitative behavioural analysis framework and show that individuals maintain their intrinsic movement patterns and interaction rules regardless of group composition. Notably, neither behavioural differences nor distant genetic relatedness between strains lead to a modulation of individual behaviour; instead, distinct strains behave and coexist without influencing each others intrinsic behavioural tendencies. Using a simulation model, we further show that aggregation in mixed C. elegans groups can be accurately predicted from strain-specific individual-level parameters measured in homogeneous settings. Our integrated approach provides a generalised framework for understanding collective behaviour in diverse heterogeneous systems, which may offer insights into population-level consequences of phenotypic variation and broader ecological processes.