Implications of dispersal in Atlantic salmon: lessons from a demo-genetic agent-based model

Despite growing evidence of spatial dispersal and gene flow between salmonid populations, the implications of connectivity for adaptation, conservation, and management are still poorly appreciated. Here, we explore the influence of a gradient of dispersal rates on portfolio strength and eco-evolutionary dynamics in a simulated population network of Atlantic salmon (Salmo salar) by extending a demo-genetic agent-based model to a spatially explicit framework. Our model results highlight a nonlinear relationship between dispersal rates and the stability of the metapopulation, resulting in an optimal portfolio effect for dispersal rates around 20%. At local population scale, we also demonstrate phenotypic changes induced by density-dependent effects modulated by dispersal, and a dispersal-induced increase in genetic diversity. We conclude that it is critical to account for complex interactions between dispersal and eco-evolutionary processes and discuss future avenues of research that could be addressed by such modeling approaches to more fully appreciate responses of Atlantic salmon to environmental changes and investigate management actions accordingly. Key words: Atlantic salmon, demo-genetic agent-based model, dispersal, eco-evolutionary dynamics, metapopulation, portfolio effect, synchrony Malgre des preuves de plus en plus abondantes de dispersion spatiale et de flux genetique entre populations de salmonides, les consequences de la connectivite en ce qui concerne l'adaptation, la conservation et la gestion demeurent mal comprises. Nous explorons l'influence d'un gradient de taux de dispersion sur la force du portefeuille et les dynamiques eco-evolutives d'un reseau de populations simule de saumon atlantique (Salmo salar) en elargissant un modele demo-genetique base sur les agents a un cadre spatialement explicite. Les resultats du modele font ressortir une relation non lineaire entre les taux de dispersion et la stabilite de la metapopulation, qui se traduit par un effet de portefeuille optimal pour des taux de dispersion d'environ 20 %. Nous demontrons aussi la presence de changements phenotypiques a l'echelle de la population locale induits par des effets dependants de la densite modules par la dispersion, ainsi qu'une augmentation de la diversite genetique induite par la dispersion. Nous concluons qu'il est d'importance capitale de tenir compte des interactions complexes entre la dispersion et les processus eco-evolutifs et abordons des avenues de recherche future pouvant etre explorees a l'aide de telles approches de modelisation pour mieux comprendre les reponses du saumon atlantique aux changements environnementaux et examiner differentes mesures de gestion. [Traduit par la Redaction] Mots-cles : saumon atlantique, modele demo-genetique base sur les agents, dispersion, dynamique eco-evolutive, metapopulation, effet de portefeuille, synchronie
1. Introduction Rapid environmental changes and associated selection pressures are affecting the adaptive capacity and persistence of many species globally (Ceballos et al. 2015). Consequently, there is considerable interest in [...]