Trade-offs in resource access and health by avoidance of self-fouling, motivated via disgust

The landscape of disgust framework emphasizes the trade-off of satisfying critical needs against environmental cues of putative disease risk. For animals that revisit areas, repeated exposures to infectious disease through self-fouling are a potential threat that can be averted through the mechanism of fecal avoidance, motivated by disgust. Here we present an agent-based, spatially explicit, network model, where simulated animal groups move along edges connecting network nodes representing waterholes. These water resources dynamically shift via evaporation, drinking, and rainfall. We parameterize our model with the case study of buffalo and their intestinal parasites. Buffaloes defecate near (and are then motivated to avoid) waterholes and we simulate parasite aggregation as a measure of contamination and potential disease risk. Though disgust (intolerance of fecal contamination) reduced maximum environmental parasite density at waterholes, strong disgust resulted in a marked increase of traveling, incurring energetic or other costs. We calculated an optimum trade-off in which fecal avoidance provides a reduction in expected environmental parasite density, but travel to obtain new water resources was not markedly increased. We recalculated this optimum varying assumptions of water influx and prioritization biases. Given the necessity of water, even when contaminated, it is theoretically justified that disgust would have some temporal and spatial variability via habituation. Thus, we included a cumulative modifier to disgust based on local conditions and travel burden; we observed pronounced habituation during periods of higher water availability and groups acclimated to conditions before low water availability. We present this model to encourage similar expansive approaches using a network-based model and to stimulate discussion, modeling, and experimental approaches which continue to develop the landscape of disgust.