Abstract
Understanding how eco-evolutionary processes and environmental factors drive population differentiation and adaptation are key challenges in evolutionary biology of relevance for biodiversity protection. Differentiation requires at least partial reproductive separation, which may result from different modes of isolation such as geographic isolation (allopatry) or isolation by distance (IBD), resistance (IBR), and environment (IBE). Despite that multiple modes might jointly influence differentiation, studies that compare the relative contributions are scarce. Using RADseq, we analyse neutral and adaptive genetic diversity and structure in 11 pike (Esox lucius) populations from contrasting environments along a latitudinal gradient (54.9-63.6°N), to investigate the relative effects of IBD, IBE and IBR, and to assess whether the effects differ between neutral and adaptive variation, or across structural levels. Patterns of neutral and adaptive variation differed, probably reflecting that they have been differently affected by stochastic and deterministic processes. The importance of the different modes of isolation differed between neutral and adaptive diversity, yet were consistent across structural levels. Neutral variation was influenced by interactions among all three modes of isolation, with IBR (seascape features) playing a central role, wheares adaptive variation was mainly influenced by IBE (environmental conditions). Taken together, this and previous studies suggest that it is common that multiple modes of isolation interactively shape patterns of genetic variation, and that their relative contributions differ among systems. To enable identification of general patterns and understand how various factors influence the relative contributions, it is important that several modes are simultaneously investigated in additional populations, species and environmental settings.
Highlights
Understanding how eco-evolutionary processes and environmental factors drive population differentiation and adaptation remain key challenges in evolutionary biology
Differentiation requires at least partial reproductive separation, which may result from different modes of isolation such as geographic isolation or isolation by distance (IBD), resistance (IBR), and environment (IBE)
The results show that in addition to distance, both the environment and landscape/seascape can play important roles in shaping patterns of genetic variation, and exemplify how a combination of analyses of neutral and adaptive variation can help disentangle the complex interplay of different stochastic and deterministic contributing processes
Summary
Understanding how eco-evolutionary processes and environmental factors drive population differentiation and adaptation remain key challenges in evolutionary biology. We report on the results of a population genetic study utilizing the RADseq method to investigate genetic structure and decipher the roles of different ecological and evolutionary processes for differentiation and adaptation in pike. For this we used 11 populations representing the three ecotypes and spanning 8.7 degrees in latitude, from Denmark in the south to Umeå in northern Sweden (Figure 1, Table 1), that experience different environmental conditions. We performed outlier analyses to identify loci putatively under selection and to pinpoint specific environmental factors contributing to evolutionary divergence
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