Vector host choice and the environmental context of mosquito-borne virus transmission
The present thesis explored ethological and geographical approaches for the investigation of vector-borne parasites. In the first part, the role of associative learning on vector preferences for hosts was investigated through a comprehensive series of behavioural experiments using the vector of dengue and yellow fever diseases, the mosquito Aedes aegypti. To this end, the possibility that the mosquitoes were able to associate unconditional stimuli with particular odours and visual patterns to which they were responsive was explored, but no evidence supporting the hypothesis that associative learning abilities are present in adults of this species was found. A critical review of the literature on learning in mosquitoes conducted afterward allowed the reinterpretation of findings in the field, narrowing the scope of evidence suggesting the existence of these cognitive abilities in some species. In the second part of the thesis, the distribution and evolution of mosquito-borne viruses was investigated with the use of geo-coded environmental data and spatial statistics. Initially, the eco-climates associated with the distribution of Japanese encephalitis virus were described and modelled, allowing the production of a worldwide predictive map defining the probability of each region to develop this disease in the future. Predominating amongst those areas shown to be under high risk were the equatorial regions of South America and Africa. The methodology used to infer such patterns – non-linear discriminant analysis – was subsequently explored with a number of simulations. Overall, differences in the choice of parameters required for the analysis were shown to lead to differences in the final outputs produced, basically in those cases where the environmental range for which predictions are generated is not rigorously limited. Finally, eco-climate surrogates for the evolution of the Japanese encephalitis serocomplex were investigated, but the current environmental distances between the viruses did not seem to be associated with the events leading to their speciation.