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.

A fundamental question in evolutionary biology is how repeatable evolutionary trajectories are when species adapt to a new environment: will similar evolutionary solutions be found, or will alternative routes be followed? Does evolution repeatability depend on the scale considered (phenotype, molecular determinants, genetic changes) and on the trait considered? We propose to study these questions taking advantage of Ostrinia pests as a model system. Following the introduction of maize from the Americas 500 years ago, into Europe and Asia, two maize-specialized species have independently emerged in this moth geneus, one on each side of the Eurasian continent: the Asian Corn Borer and the European Corn Borer. Both species have developed very similar adaptations to maize, that distinguish them from their presumed ancestor the Adzuki Bean Borer. Both have become major agricultural pests. But to what extent did history repeat itself in Asia and in Europe? The Ostrinia system offers an ideal opportunity to study the convergent evolution of complex traits in natural populations, the two synchronous host-shifts to maize constituting two replicates of a giant evolution experiment, starting from a similar Dicot-feeding ancestor. We will systematically study several key traits known to be involved in host-plant adaptation: female oviposition preference (host choice), larval physiological adaptation, and larval geotaxis. Using a combination of approaches at different levels, from genomics to phenotypes and association studies, we will decipher the evolutionary changes that underlie the emergence of these pests and the genetic architecture of each of these adaptive traits. By systematically comparing the evolutionary changes that occurred in Asia and in Europe, we will determine the degree of evolutionary repeatability in these host-shifts, and its consistency across scales and traits. This will provide important insights into the mechanisms of species formation, the genetic architecture of pest adaptation, and a unique glance into evolution acting in natura at continent scale.

The POLADAPT project aims at unravelling the phenotypic and genomic determinants underlying tolerance to pollution in the eastern mosquitofish Gambusia holbrooki, an invasive teleost fish found both in freshwater and transitional mesohaline ecosystems. This project will first use an in-situ comparative approach in ten pairs of sites along different Mediterranean freshwater-seawater continuums, characterised by contrasted pollution profiles in terms of concentration levels, pollutant diversity and contamination sources (agricultural, domestic, industrial). The chemical exposome will be characterised using integrative samplers to describe the diversity of emerging polar organic pollutants in the water column and specific candidate molecules will be measured in gambusia tissues to quantify accumulation levels. The ecotoxicological responses, the life history traits and population structures will be measured in each site to characterize the phenotype associated with tolerance to pollution. Genomic signatures of local adaptation and evolutive divergence caused by pollution will be looked for between differentially exposed populations. We will use a mesocosms experiment to study the long-term consequences of chronic exposure to a cocktail of pollutants, and the ecological implications of adaptation to pollutants regarding population dynamics, prey communities and ecosystem functions.

Adaptation of organisms to contrasting environmental conditions is a major driver of species diversification. However we know very little on the genetic basis underlying ecologically-relevant traits, and on how and at what speed adaptive divergence leads to genetic differentiation. Here, we will use the pea aphid, a well-suited system for adaptive genomics, which conveniently shows a complex of plant-specialized biotypes, ranging from sympatric host races to incipient species, and resulting from a recent adaptive radiation. By combining novel phylogenetic and population genetic analyses of massive genomic dataset, innovative tools for functional analysis and unique biological resources, we will 1) reconstruct the evolutionary history of plant specialization and biotype formation, 2) identify genomic regions under divergent selection and characterize the genomic architecture underlying plant-based differentiation, and 3) identify genes and functions involved in plant specialization in the pea aphid complex. This project relies on a consortium of 3 French partners and 2 associate partners from other European countries who will bring complementary skills and know-how for the development of multidisciplinary approaches and combination of methods needed to reach project's objectives. This project will allow testing whether multiple independent events of adaptation to different environments involve the same genomic regions and the same set of genes and how genetic divergence accumulates along the genome through time in reproductive isolation. It will also increase knowledge on how insects overcome plant defenses and acquire new hosts on which they may become adapted, paving the way for the development of sustainable control strategies against aphids as important crop pests, based on enhanced plant defenses.