The role of grooming in regulating biomass growth of ants and symbiotic fungi under entomopathogenic fungal infection: experiments and mathematical modelling

This study presents an extended mathematical model, originally developed to explore biomass dynamics in Acromyrmex ants and their symbiotic fungus, which has been adapted to investigate biomass growth in Atta sexdens and its fungal partner. The model incorporates ant grooming as a defence against entomopathogenic fungi, building on experimental data where self-grooming and allogrooming were quantified across three groups: Metarhizium anisopliae , Escovopsis phialicopiosa , and a control. A second chamber was introduced to simulate biomass transfer between compartments. Inflection points in growth curves were identified to detect shifts in population dynamics, and bifurcation diagrams explored key parameters affecting system stability, namely worker allocation to fungal cultivation, ant mortality, and fungal mortality. Metarhizium anisopliae significantly reduced both ant and fungal biomass, even under optimal grooming conditions, owing to its direct virulence to workers. In contrast, E. phialicopiosa , an opportunistic pathogen, had minimal impact unless fungal mortality exceeded a critical threshold. Self-grooming proved more effective than allogrooming in mitigating M. anisopliae effects, likely owing to prioritisation of individual defences under high pathogen pressure. Spatial dynamics enhanced resilience: one-way transfer between chambers redistributed biomass, delaying inflection points and bolstering structural stability. Bifurcation analysis revealed that extreme proportions of workers cultivating the symbiotic fungus reduced the biomass for both partners, whilst ant and fungal mortality rates led to non-linear declines in most simulations. These findings underscore the role of multi-chamber architecture in mitigating pathogen impacts in Atta colonies and suggest potential applications for biological control strategies by identifying behavioural and structural factors that may limit or enhance the effectiveness of pathogenic fungi in field settings. The model provides a useful framework for understanding epidemiological dynamics in natural nests, integrating behavioural defences and spatial strategies to safeguard this mutualism.