Using an Agent-Based Model to Explore the Effectiveness of Strategies Used by Ants to Mitigate the Spread of the Fungus Ophiocordyceps camponoti-rufipedis

Abstract

Scientists have long studied the unexpected resistance of eusocial insect colonies to pathogen and parasitic threats. Despite having many closely related individuals living in proximity, these colonies have shown the ability to persist for long periods of time without epidemic collapse. Previous studies have theorized a variety of reasons for their ability to withstand chronic infections including the conveyor belt model and task specialization. The impact of each of these different strategies and the synergy between them is unknown. Testing the impact of each strategy experimentally may be difficult and time consuming. This paper examines the impact of five (5) strategies used by Camponotus rufipes to endure a chronic infection from Ophiocordyceps camponoti-rufipedis, a fungal infection which results in “zombie ants.” These five strategies are to avoid areas with increased numbers of spores, prevent completion of the fungal lifecycle within the nest, use specialized workers, separate groups within the nest, and invest less in forager immune response. A full factorial analysis of the strategies is performed through an agent-based model by selectively turning “off” each of the strategies. The contribution of this work is two-fold. First, a conceptual model for C. rufipes is presented. Synthesizing the current literature, the result is a tool for modeling colony behavior. Secondly, the output of the model indicates the role of each strategy in preventing fungal disease propagation in the colony and the interaction effects between the strategies. Analysis includes a 5-way ANOVA with interaction effects, post-hoc testing, and effect size measurements. Significant findings include that the strategy of minimizing the chance of fungal infection and preventing the fungus from completing its life cycle within the nest are the most important. When these strategies were disabled, 100% of colony collapse occurred. Additionally, the use of the conveyor belt approach (the use of older ants to forage) had a negligible effect on colony survival. Interaction effects between the five strategies are also presented. The results of this work highlight the synergies between the strategies used to prevent O. camponoti-rufipedis propagation, guide future experimentation on this species, and provide additional information for those seeking to use this species as a source of biologically inspired design.