Description du sujet de thèse

Human activities contribute to increased environmental pollution and stress on associated communities. These pressures have dramatic repercussions on both biodiversity and the dynamics of infectious disease transmission, including zoonotic diseases. Complex ecological processes link biodiversity, ecosystem stress, host physiology, and pathogen circulation, with varying effects depending on the species interacting in these disturbed environments. A given ecosystem disturbance can, depending on the context, either inhibit or promote parasite transmission.
This thesis will explore the extent to which certain anthropogenic pressures, particularly aquatic pollution, select for host species or populations that are more tolerant to pollutants but potentially more susceptible to parasitic infections. A central eco-evolutionary hypothesis will postulate the existence of an evolutionary trade-off between tolerance/resistance to pollutants and the effectiveness of the immune response. We will therefore seek to answer the following question: does the use of pollutants favor the emergence of hosts that are highly tolerant to pollutants but more permissive towards parasites?
We will answer this question by focusing on the interactions between freshwater gastropod mollusks and trematodes in the Camargue, a region rich in wetlands and subject to increasing anthropogenic pressure. These organisms are particularly relevant in the context of this thesis because: i. freshwater aquatic environments are receptacles for many chemicals through leaching and drainage of contaminated soil and water; ii. Aquatic mollusks are capable of accumulating a significant amount of pollutants compared to most invertebrates (3,4), particularly through complex detoxification pathways that are therefore potentially energy-intensive (5,6); iii. These organisms are intermediate hosts for many parasites, particularly trematodes (7). Furthermore, empirical studies have already highlighted the immunotoxicological effects of several anthropogenic pollutants on several species of aquatic molluscs, suggesting links between certain pollutants and the regulatory pathways of immune functions in these organisms. Together, these elements support the central hypothesis formulated in this thesis. To test this hypothesis, the project will integrate field approaches, controlled environment experiments, and functional approaches.
This thesis fits into the “One Health” context, which recognizes the interdependence between human, animal, and environmental health. In fact, this thesis will provide an overview of the aquatic environments of the Camargue in terms of biotic (communities of mollusks, vertebrates, and trematodes) and abiotic (quantification of the pressure exerted by phytosanitary, pharmaceutical, and industrial pollutants) factors. Furthermore, it will also provide a better understanding of the mechanisms linking the health of these aquatic ecosystems and the risks of local transmission of infectious diseases in humans and animals through the prism of evolutionary ecology.

Contexte de travail

The thesis will mainly be carried out at the IHPE laboratory on the Perpignan site within the campus of the University of Perpignan Via Domitia (UPVD). This unit is composed of staff affiliated with UPVD, CNRS, IFREMER, and the University of Montpellier 2. This laboratory focuses on interactions between hosts, pathogens, and the environment, from molecules to ecosystems. It is structured into three teams that interact closely with each other. The candidat will be integrated into the MIA team, to which Olivier Rey is attached, but will also participate in the meetings of the 2MAP team, to which Annia Alba is attached. During this thesis, the candidat will have access to the various facilities of the IHPE laboratory (molecular biology platform, invertebrate animal facility) and to the services of the UPVD's BioEnvironnement platform. Short/medium-term assignments will be necessary to ensure field monitoring in the Camargue. This thesis project is part of the ZOOCAM project (PEPR PREZODE 2024-2029).
Supervision will be provided through weekly meetings with the doctoral student and participation in biweekly team meetings. The candidate will also participate in the “Doctoriales,” a scientific meeting of UMR 5244 dedicated to doctoral students in the unit who present the progress of their thesis work to all members of our laboratory. The student will also have the opportunity to present their research work at meetings of the PEPR ZOOCAM project, which brings together several partners working together on issues related to the circulation of zoonotic parasites in the Camargue region. Finally, each year, the doctoral student will also have to organize their CSI with a report sent to ED305 UPVD.

Contraintes et risques

Our laboratory is composed of two sites (Perpignan and Montpellier), and travel between sites is expected.
The thesis will involve experiments in the invertebrate animal facility (molluscarium), classified as a P2 containment level laboratory, due to the handling of pathogens that are moderately dangerous to humans, fauna, flora, or the environment (e.g., Fasciola hepatica, Schistosoma sp.). These biological agents do not pose a serious danger to healthy adults, and effective prevention and treatment measures exist. Compliance with biosafety protocols and hygiene rules is imperative.
This thesis also includes the handling of certain pollutants as part of the experiments, according to strict protocols that guarantee personal and environmental safety. The student will be trained and assisted by the staff in charge of invertebrate breeding in the laboratory throughout the thesis.
With regard to fieldwork, occasional trips to the Camargue are to be expected. These trips may involve time constraints (early morning departures, late returns) and temporary on-site accommodation to limit travel. In this context, it is also important to strictly follow the health and safety rules related to this fieldwork. The student will also be trained in best practices to limit the risks associated with fieldwork.