A metabolic modeling framework to predict geographical and temporal changes in parasite fitness under climate change

Background/Question/Methods

Climate change is expected to alter disease dynamics around the world, and predictive models are needed to quantify future risk and proactively determine control strategies for parasites of humans, wildlife and domestic animals. Here, we provide a mechanistic modeling framework that can be used to address some of the central questions concerning the impacts of climate change on host-parasite systems, such as which systems are most sensitive to change, or at which geographical locations climate change will have the greatest impact.

Results/Conclusions

Specifically, we link the ‘Metabolic Theory of Ecology’ with traditional host-macroparasite models to predict parasite fitness, quantified through the basic reproductive number R₀, as a function of the environment. While our models are based on the Van’t Hoff-Arrhenius relation of metabolic theory (to describe exponential relationships between temperature, parasite development and parasite mortality), we show that this relationship needs to be modified in the context of host-parasite models to account for low and high temperature thresholds of development and mortality. This methodological framework can be used to estimate the fundamental niche of a parasite under novel conditions, and we show that the fitness response to temperature that determines this niche (and thus whether a parasite may experience a range contraction, a range shift, or a range expansion) depends on the relative strengths of the respective thermal sensitivities of larval development and mortality. Further, we apply the model to seasonal environments to quantify temporal dependencies in parasite fitness. In particular, the models show that climate warming can lead to a summer fitness trough in some parasites, effectively splitting a continuous spring-to-fall transmission season into two separate transmission seasons, in spring and fall, respectively. Finally, we use the framework to show that parasites with an indirect life cycle may adapt more easily to such changes than parasites with a direct life cycle by benefitting from behavioral thermoregulation of their intermediate host. In its current form, our models are strategic and thus most suitable to evaluate broad-scale patterns of climate change impacts. However, we also show that model predictions conform closely to empirical data from several arctic parasites, indicating model applicability at the species level. Furthermore, all results are qualitatively robust to changes in the model parameters, indicating generality and applicability to a wide variety of parasites around the globe.