Modeling phenological and physiological responses to climate warming in a hypothetical migratory songbird-mosquito system

Given the strong temperature-dependence of ectothermic vector physiology, climate warming is expected to profoundly impact many vector-borne diseases. Notably, endothermic hosts can also respond to warming by altering the timing of life history events like seasonal migration and reproduction, but relatively few predictive models of vector-borne disease have considered both phenological and physiological responses to climate warming. Here, we extend the Ross-MacDonald model for a vector-borne disease to incorporate temperature effects on host and vector phenology and physiology. We use this model to understand how projections of moderate and severe warming influence the emergence of a hypothetical vector-borne disease in a migratory bird. Modeled vector and host infection prevalence always increased under warming, and the increase was amplified when hosts failed to update their arrival phenology to keep pace with breeding site resources. While extreme warming scenarios yielded the highest infection prevalence, reduced vector survival in the hottest months caused late-season declines in transmission, altering seasonal patterns of infection. By considering host, vector, and parasite responses to temperature together, our modeling framework could be employed to help decipher otherwise non-intuitive wildlife infection outcomes under current and future climate conditions.

Methods
We use differential equations to track population and infection dynamics of a migratory avian host and mosquito vector over a single host breeding season, following the first introduction of a novel pathogen (i.e., assuming no pre-existing immunity in the host). We incorporate climate warming impacts on host and vector phenology and vital rates, assessing outcomes under moderate and severe warming scenarios. Warming affects mosquito emergence timing and, in some scenarios, the arrival date of birds (which in turn influences reproductive success). At the same time, temperature dependence in transmission traits is incorporated by linking mosquito mortality rate, bite rate, and pathogen development rate to daily temperature data. For tractability, we assume that only the focal host species can acquire and transmit the pathogen, and that mosquitoes preferentially bite this host.