Effects of resource availability on the temperature dependence of mosquito population fitness

Mosquitoes are a major global public health concern because they vector pathogens that cause multiple human diseases. Recent reports of local vector-borne disease transmission in temperate suburban and urban populations have raised concerns over how global environmental change will affect the spatiotemporal distribution of vector-borne disease transmission. However, our understanding of the ecological processes that regulate vector population growth and, therefore abundance is incomplete. This limits our capacity to reliably predict and effectively manage any shifts in vector-borne disease risk that may arise from different environmental change scenarios. The life history traits that determine population growth (survival, development, reproduction) in cold-blooded organisms (ectotherms), such as mosquitoes, respond to environmental temperature in predictable ways. This provides a mechanistic basis for predicting how climatic warming will affect vector-borne disease dynamics, partially through the temperature dependence of the abundance dynamics of the vector population. Furthermore, the effects of temperature on abundance should also be affected by other environmental factors; for instance, ecological theory predicts that variation in resource availability should also affect vector traits. However, while this may seem an obvious source of additional variation, this problem remains largely unresolved in vector-borne disease research, and in thermal ecology in general. In this thesis, I address this issue using laboratory experiments to investigate how realistic variation in resource availability in larval environments directly impacts the temperature dependence of life history traits that determine fitness in the mosquito vector, Aedes aegypti. Then, using mathematical population modelling, I use datasets from these experiments to assess how resource variation in the larval environment can affect the temperature dependence of the species’ maximal population growth rate (rm). I also use the results from this experimental and modelling work to assess the ability of a general analytic rm model based on the Euler-Lotka equation to provide reliable estimates of temperature- and resource-dependent rm. I found that resource limitation and larval competition in depleting resource environments can both significantly mediate the shape of rm’s ¬unimodal thermal response. These findings provide compelling evidence that variation in resource availability should be considered when predicting how vector-borne disease dynamics will respond to environmental change. I also show that, except when populations are constrained by resource availability below a certain threshold, analytic rm models based on the Euler-Lotka equation can be used to incorporate the effects of temperature and resource availability on vector fitness into existing vector-borne disease transmission model frameworks. This provides a novel avenue towards improving the reliability of predictions derived from these frameworks. Overall, the strong potential for variation in resource availability in the larval environment to profoundly affect the temperature dependence of population fitness means that future research effort should be invested in developing novel methods to measure effective temperature- and resource-dependent fitness and abundance in the field.Open Acces