Impacts of climate change on tsetse (Diptera: Glossinidae) : water balance physiology and mechanistic modelling

[摘要] ENGLISH ABSTRACT: Climate change will alter both temperature and moisture availability in the future and therefore willlikely affect vector borne disease prevalence. Organisms faced with changes in weather can respondin a variety of ways and this complicates any predictions and inferences for these organisms withclimate change. Cause-and-effect links between climate change, insect vector responses, andchanges in risk of disease transmission are poorly established for most vector borne diseases. Tsetse(Diptera, Glossinidae) are important vectors of trypanosome parasites posing a major threat tohuman health and socio-economic welfare in Africa. Water balance plays an important role indetermining activity patterns, energy budgets, survival and population dynamics and, hence,geographic distribution and abundance of insects. Glossina species occupy a wide range of habitatsin Africa and are notable for their desiccation resistance in xeric environments. Yet, whether or notthe different species, subgroups or ecotype groups differ in susceptibility to changes in weatherremain undetermined.The first main focus of my thesis was to test the effects of climate change on water balance traits(water loss rate, body water content and body lipid content) of adult tsetse flies. Four species fromxeric and mesic habitats were exposed to a range of temperature (20 – 30 °C) and relative humidity(0 – 99 %) combinations. Water loss rates were significantly affected by measurement treatments,while body water content, body lipid content and mass were less affected and less variable acrosstreatment combinations. The results provide support for mass-independent inter- and intra-specificvariation in water loss rate and survival times. Therefore, water balance responses to variation intemperature and relative humidity are complex in Glossina, and this response varies within andamong species, sub-groups and ecotypes in terms of magnitude and the direction of effect change.Secondly, I apply a mechanistic distribution model for G. pallidipes to predict potential populationresponses to climate change. I validate the mechanistic model (NicheMapperTM) results spatiallyand temporally using two methods. Both tests of the model showed that NicheMapper‟s predictedresting metabolic rate has great potential to capture various aspects of population dynamics andbiogeography in G. pallidipes. Furthermore, I simulate the effect of phenotypic plasticity underdifferent climate change scenarios and solve for the basic reproductive number of thetrypanosomiasis disease (R0) under a future climate scenario.This integrated thesis provides strong evidence for a general decrease in optimal habitat for G.pallidipes under future climate change scenarios. However, it also provides strong support for a 1.85 fold increase in R0 based on changes in biting frequency as a result of higher predictedmetabolic rates in the future. This might suggest that the reduction in optimal habitat could beoutweighed by the increase in R0. The results demonstrate that an understanding of thephysiological mechanism(s) influencing vectors of disease with climate change can provide insightinto forecasting variation in vector abundance and disease risk.

[发布机构] Stellenbosch University