PhD Defense by Miguel G. Zornoza

Title: Bacteria, mosquitoes and beyond: some studies on spatial and environmental ecology

 Abstract: 

 Part 1: Microorganisms are ubiquitous in Nature and constitute key pieces in global energy and nutrient cycles. An important yet insufficiently understood interplay is that constituted by bacteria and their most common predator, the bacteriophages (short: phages). In this study we investigate predation, competition and diversity in a phage-bacteria spatially structured ecosystem shaped by intermittent biomass dispersal. Predatory dynamics between a single phage species and its bacterial host are characterized as a function of the dispersal parameters. Competition among phages is then studied by considering the presence of a secondary and less competitive phage species preying on the same bacterial host. The study reveals that the environmental context, in the form of habitat connectivity, significantly impacts the competitive outcome, allowing the “weaker” phage to coexist or even dominate under certain conditions. This research provides insights into the ecological complexity and potential coexistence mechanisms in microbial communities, underlining the role of environmental factors, such as dispersal, in shaping microbial diversity.

 Part 2: The Asian tiger mosquito, Aedes albopictus, is known for its status as invasive species and capable vector of diseases such as dengue, Zika and chikungunya. Originating from southeast Asia, this species has spread worldwide due to globalization, adapting to various climates. Our research uses a climate-aware dynamical model to analyse the mosquito’s life cycle and distribution in Italy, from 1980 to 2023. The study’s objectives include calibrating and validating the model with field data, understanding the mosquito’s geographical distribution and activity duration, and assessing the impact of heatwaves on its population dynamics. Simulated mosquito hotspots coincide with highly populated areas like Rome and Milan, with climate change extending the mosquito’s activity season, especially in the southern Italian coastal regions. The model’s predictive capabilities have the potential to help guide public health interventions and improve surveillance and risk assessment of mosquitoes and, with further model development effort, mosquito-borne diseases.

 Part 3: The mosquito Anopheles gambiae s.s. is a major vector of malaria in sub-Saharan Africa. As an ectothermic arthropod, its life cycle is susceptible to local climate variables, the magnitude of which change at a wide range of time scales, from sub-daily to seasonal and decadal. Using a climate-aware dynamical model, we investigate how variations in daily air temperature affect mosquito population by performing a “knock out” experiment, where the daily variability in air temperature at two-metre height is suppressed. Preliminary results allow us to i) estimate the seasonal effect of this variability and the regions where these effects will increase mosquito population and ii) ascertain a net change in the vector activity duration driven by variability at daily time scale. Ultimately, this project aims to provide insight into the effects of climate change on malaria spread.