In this project we will study how self-fertilization evolves and its evolutionary consequences in hermaphroditic animals . A strong limitation of the theory of mating system evolution is that it has been tested quasi exclusively in flowering plants. This poses problems of generality (to what extent do the arguments made depend on specificities of this group ?) and feasibility (most plants are not easily amenable to multi-generation experiments such as experimental evolution). For these two reasons it is urgent to develop animal models. We will here focus on a group of freshwater snails (basommatophorans) with highly diverse mating systems, presenting a suite of advantages making them ideal to address hitherto unsolved questions. We will focus on evolutionary transitions between outcrossing and selfing, how and when they occur, and their consequences. In particular we will test the long-standing hypothesis that selfing is an evolutionary dead-end in two ways. First we will characterize the number and unidirectionality of transitions in the phylogeny; second, we will empirically test the key steps of the most plausible scenario describing how an outcrossing species can become a preferential selfer (but not the reverse). The main components of this scenario are (i) constraints on mate or pollen availability resulting in a selection for selfing as a reproductive insurance. (ii) the existence of an intermediate state of preferential outcrossing with delayed, optional selfng when mates are lacking. (iii) the purging of inbreeding depression, resulting in runaway selection for selfing and even less inbreeding depression. (iv) the lack of adaptive potential in selfers, resulting in high extinction rates. All these aspects will be tested experimentally by looking at experimental evolution under elevated contraints on mating (frequent lack of mates), by measuring response to artificial and natural selection in pairs of outcrossing/selfing species living in the same environment, and by comparing their ability to colonize empty sites, estimated from metapopulation studies in the field This project is very ambitious in terms of (i) gathering molecular polymorphism data from many hitherto unstudied species, (ii) the number of size of experiments, and (iii) the requirement for long-term field data. It brings together a highly qualified consortium with previous experience of common work and complementary skills. Among the expected breakthroughs of this project will be the first experimental-evolution study of mating system evolution; and the first unbiased estimates of the frequency of mixed-mating in animals, and why it seems to be lower than in plants. All this will serve our ambition to establish animals, and especially basommatophoran snails, as essential models for mating system theory.

Chemical pollutants from industrial and agricultural sources are significant ecological stressors of the freshwater environment, with more than half of all European waterbodies negatively impacted. Whilst catastrophic discharge events are an obvious threat to biodiversity, they are relatively rare. Long-term effects may be less evident, but frequently pose a more significant impact. One such impact is their influence on the evolutionary trajectories of species, a subject of growing concern in ecotoxicology and environmental risk management. My research will address this problem in the waterflea (cladoceran microcrustaceans of the genus Daphnia), planktonic animals that are critical to the proper functioning of freshwater ecosystems. Daphnia are important models in ecotoxicological risk assessment, and can easily be cultured over many generations, thereby facilitating studies designed to simulate evolution within a laboratory setting. They are also characterized by an interesting reproductive cycle alternating between clonal and sexual reproduction, providing an ideal model to explore the effects of chemical contaminants against a variety of genetic backgrounds. However, one of their most unique properties is the producing of resting eggs (ephippia) that may lay dormant for centuries, yet be resuscitated when exposed to the proper stimuli. This provides an incredibly rare opportunity to study changes in molecular function in a deep historical context, to a time pre-dating the Industrial Revolution and the first exposure of populations to anthropogenic chemical contaminants. Using contemporary and resurrected populations of Daphnia from natural ponds and marshes in western France, an area of important agricultural production, I will explore the effects that pesticide drift has had on the evolutionary history of this important species. I will sample Daphnia currently inhabiting sites located in protected areas with those from neighbouring waters impacted by the unintentional diffusion of agricultural chemicals, contrasting the effects of pesticide exposure on survival and reproduction in multiple independent lines. I will also use the latest advances in sequencing technology to search for genomic signals of natural selection in wild populations, and attempt to validate these results experimentally by comparing functional/physiological differences between groups in the genes identified as under selection. In these same populations, as well as in resurrected historical lines, I will explore how exposure to agricultural contaminants affects the expression of genes at the transcriptional level, both immediately and over many generations of evolution. These results will also be used to identify lineages that differ in their immediate stress response to a chemical contaminant, which will then be used to address an area of fundamental importance in current discussions of evolution: the role of plasticity. Contrasting lines will be subjected to multiple generations of contaminant-induced selection to determine if/how an inherently increased sensitivity in one of key molecular pathways affected by pesticide exposure (the oxidative stress response) influences the evolutionary response to life in a contaminated environment.

FishNess investigates individual fish robustness as a determinant of population vulnerability and aquaculture sustainability in the face of major global change stressors, warming and hypoxia. Robustness is a core concern for agricultural sustainability in the face of global change. It is measured as the ability to allocate energy towards growth and reproduction under prevailing environmental conditions, and the extent to which this ability is resilient to perturbation by extreme climatic events. Robustness in fishes requires intensive study because it has important implications for both wild and farmed populations. FishNess combines experimental biology, genomics and modelling, in a case study on a valuable species for fisheries and farming, the European sea bass. The species has three genetically distinct populations, in the Atlantic, Western Mediterranean and Eastern Mediterranean. FishNess will reproduce these in captivity from existing broodstock and rear them over two years, under three seasonal thermal regimes that reflect each population’s range, in a full-factorial design. Individual and populational diversity in robustness will be investigated, as temperature-related allocation of energy to growth, reproduction and physiological performance; and as resilience to summer heatwaves and hypoxic events. The heritable component of variation in traits of robustness will be evaluated with a 57K SNP chip for sea bass, to investigate genotype by environment interactions in each population and existence of local adaptation. Integration of phenotypic information into the dynamic energy budget (DEB) paradigm will be used to project individual outcomes for life history traits such as growth, maturation and reproduction, while accounting for costs of coping with environmental stress. Outputs from individual DEB models, and estimates of their genomic heritability, will be used in evolutionary models to predict robustness to various future scenarios in wild and domesticated populations, across multiple generations. The results will help preserve fish stocks by revealing population short-term coping capacity and long-term adaptability, and consequences for future stock productivity. They will promote sustainable aquaculture by identifying robust populations, starting genomic selection on robustness, and projecting productivity in future climates.