The evolutionary ecology of disease transmission: how will vector control programmes change parasite life histories?

Parasites live in inside the bodies of others, with whom they are engaged in a life-and-death struggle. The Reece lab uncovers the strategies parasites have evolved to cope with the challenges and opportunities of their lifestyle by asking “what makes a successful parasite and what are the evolutionary limits to their success?”. Specifically, we investigate how parasites maximise "survival" and "reproduction". These fitness components underpin the symptoms and transmission of diseases.
Most disease research focuses on interactions between parasites and their hosts. Analogous studies of interactions between parasites and vectors have been largely neglected, despite the fact that vectors are responsible for spreading disease. Clearly, to fully understand the evolution of vector-born parasites it is necessary to ask how they solve the challenges of living in hosts and in vectors. This is especially important for malaria parasites whose vectors are changing in response to vector-control programs (e.g., bed nets, insecticides). Whilst the evolutionary responses of malaria-transmitting mosquitoes to vector-control are being monitored, the knock-on consequences for parasite evolution have been overlooked. Just like drugs or vaccines administered to hosts, vector-control represents an ecological perturbation aimed at reducing parasite fitness. History clearly illustrates that attempts to reduce the survival and/or transmission of malaria parasites is usually met with counter-evolution (e.g., drug resistance mutations and phenotypic tolerance). Parasite counter evolution to vector-control may be constrained or facilitated, depending on the amount of genetic variation and plasticity underpinning parasite phenotypes. Anticipating parasite evolution will inform monitoring strategies for current control programs as well as uncovering novel new vector-control strategies.
Malaria is transmitted by Anopheline mosquitoes and their control centres on long-lasting insecticide treated bed nets and indoor residual spraying. Insecticides are implicated in causing: the evolution of resistance mutations to target sites and detoxification mechanisms, shifts in feeding schedule and location, altered host preference, changes in the relative importance of different mosquito species as vectors, and shorter lifespan. Predicting how parasites will respond to such changes in vector populations requires knowledge of: (a) The impacts of interventions on parasites directly (e.g. do insecticides kill parasites?). (b) How parasite fitness is affected by changes in vector genotypes and phenotypes (e.g. insecticide resistance, biting time-of-day, lifespan, vector species). (c) How much plasticity and genetic variation exist in parasite populations for heritable traits, including fitness, that are affected by vector-control. (d) Whether parasite traits affected by vector-control are governed by trade-offs or co-variances that affect responses to selection.

This PhD will open the black box of what life inside mosquito vectors is like and develop a novel field by revealing the genetic and environmental drivers of parasite transmission to, and from, the vector. This project will use malaria parasites of rodents and mosquitoes to integrate developments from different biological disciplines into an evolutionary framework. Malaria parasites are an ideal model system because well-controlled laboratory experiments that perturb the environments parasites experience within mosquito vectors can easily be carried out. The experiments will reveal the genetic and environmental drivers of parasite transmission to, and from, the vector.

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The PhD student will be joining a well-resourced lab with a technician, graduate research assistant and lab manager, 3 other PhD students, and 3 postdocs. Thus, the student will receive considerable intellectual and practical support to develop their research project. Our work to date suggests there are multiple novel and tractable directions for this PhD project to take and the student will be encouraged to decide which lines of enquiry to follow and to develop their own interests during the PhD.