FIASCO - Illuminating range shifts through evolutionary FIASCO: contrasting FaIling And Successful ColOnizations in replicated wild populations

Understanding the processes shaping the uneven spatial and temporal distribution of biodiversity can inform how and when populations or species may have evolved. Recently, this knowledge has become of prime importance to face the ongoing redistribution of biodiversity, which includes both extinctions and biological invasions characterised by small population size. Why do some populations fail to survive changing environmental challenges while others thrive and even spread outside their historical range? Can we predict whether a population facing a new environment will contract, displace, or expand? Much remains unclear about why species are present where they are and how they will respond to environmental changes. We propose to explore the evolutionary mechanisms underlying range shifts by contrasting failing and successful colonisations in Littorina saxatilis (Figure 1). This marine snail represents an excellent and easily accessible study system to elucidate evolution at range edges in naturally replicated dispersal events. We will focus on the recent introduction in the Mediterranean Sea (Venetian Lagoon, Italy), where the snail represents the first confirmed alien species and yet is becoming extinct. This failing population will be compared to the recent establishment in San Francisco (California, USA), which, conversely, is flourishing. Additionally, we will contrast a historical pair of successful and failing post-glacial range expansions: northern Norway (Bodø) and the Baltic Sea (Bornholm, Denmark). Multidimensional data from genes to environments will be collected, generated, integrated, and analysed in these four introductions and their source populations. We will leverage information from whole genomes, which contain key signatures of populations’ evolutionary history and diversity including genomic structural variants; phenotypic traits including behaviour, that can be related to survival advantage; and local habitat, which can inform on novel ecological pressures and abiotic constraints experienced by these groups. Such diverse and unprecedented insights will clarify colonisation histories, demographic trajectories, and the interaction among evolutionary background, erosion of genetic diversity, fast-track adaptation, and environmental changes in shaping the fate of small populations. These findings will illuminate why some range shifts succeeded while others ended in a fiasco, advancing our understanding of ecological success. They will contribute to the urgently needed improvement of knowledge of the fundamental mechanisms that originate and maintain biodiversity to inform effective actions in wildlife management. Our results will be disseminated to the scientific community, stakeholders, and citizens to draw attention to biodiversity research, increase social trust and build resilience against the global decline of biodiversity, economy, and society.