Biology subjects

Bekkevold, D.

Publications and source records attributed to Bekkevold, D..

4 recordsLinked to original sources

bioRxiv2020

The genetic architecture underlying ecological adaptation in Atlantic herring is not consistent with the infinitesimal model

Atlantic herring is widespread in North Atlantic and adjacent waters and is one of the most abundant vertebrates on earth. This species is well suited to explore genetic adaptation due to minute genetic differentiation at selectively neutral loci. Here we report hundreds of loci underlying ecological adaptation to different geographic areas and spawning conditions. Four of these represent megabase inversions confirmed by long read sequencing. The genetic architecture underlying ecological adaptation in the herring is in conflict with the infinitesimal model for complex traits because of the large shifts in allele frequencies at hundreds of loci under selection.

evolutionary biology↗

bioRxiv2019

Beyond parallel evolution: when several species colonize the same environmental gradient

Genomic signatures associated with population divergence, speciation and the evolutionary mechanisms responsible for these are key research topics in evolutionary biology. Evolutionary radiations and parallel evolution have offered opportunities to study the role of the environment by providing replicates of ecologically driven speciation. Here, we apply an extension of the parallel evolution framework to study replicates of ecological speciation where multiple species went through a process of population divergence during the colonization of a common environmental gradient. We used the conditions offered by the North Sea - Baltic Sea environmental transition zone and found clear evidence of population structure linked to the Baltic Sea salinity gradient in four flatfish species. We found highly heterogeneous signatures of population divergence within and between species, and no evidence of parallel genomic architecture across species associated with the divergence. Analyses of demographic history suggest that Baltic Sea lineages are older than the age of the Baltic Sea itself. In most cases, divergence appears to involve reticulated demography through secondary contact, and our analyses revealed that genomic patterns of divergence were likely the result of a combination of effects from past isolation and subsequent adaptation to a new environment. In one case, we identified two large structural variants associated with the environmental gradient, where populations were inferred to have diverged in the presence of gene flow. Our results highlight the heterogeneous genomic effects associated with complex interplays of evolutionary forces, and stress the importance of genomic background for studies of parallel evolution.

evolutionary biology↗

bioRxiv2019

Evolution at two-time frames shape structural variants and population structure of European plaice (Pleuronectes platessa)

Changing environmental conditions can lead to population diversification through differential selection on standing genetic variation. Structural variant (SV) polymorphisms provide examples of ancient alleles that in time become associated with novel environmental gradients. The European plaice (Pleuronectes platessa) is a marine flatfish showing large allele frequency differences at two putative SVs associated with environmental variation. In this study, we explored the contribution of these SVs to population structure across the North East Atlantic. We compared genome wide population structure using sets of RAD sequencing SNPs with the spatial structure of the SVs. We found that in contrast to the rest of the genome, the SVs were only weakly associated with an isolation-by-distance pattern. Indeed, both SVs showed important allele frequency differences associated with two different environmental gradients, with the same allele increasing both along the salinity gradient of the Baltic Sea, and the latitudinal gradient along the Norwegian coast. Nevertheless, both SVs were found to be polymorphic across most sampling sites, even in the Icelandic population inferred to originate from a different glacial refuge than the remaining populations from the European continental shelf. Phylogenetic analyses suggested that the SV alleles are much older than the age of the Baltic Sea itself. These results suggest that the SVs are older than the age of the environmental gradients with which they currently co-vary. Interestingly, both SVs shared similar phylogenetic and genetic diversity, suggesting that they have a common origin. Altogether, our results suggest that the plaice SVs were shaped by evolutionary processes occurring at two time-frames, firstly following their common origin and secondly related to their current association with more recent environmental gradients such as those found in the North Sea - Baltic Sea transition zone.

evolutionary biology↗

bioRxiv2019

Fine scale population structure linked to neutral divergence in the common sole (Solea solea), a marine fish with high dispersal capacity

The Baltic Sea provides a classical example of how an environmental gradient is associated with the distribution of marine species. Here, numerous genetic studies have revealed clear patterns of population structuring linked to the physical features of the gradient itself. Nevertheless, it remains difficult to distinguish clearly between the different micro-evolutionary processes that shape these structured populations in situ. The common sole (Solea solea) is a benthic flatfish that rarely occurs within the Baltic Sea, but that exhibits a clear genetic break between populations from the North Sea - Baltic Sea transition zone and the remainder of the Atlantic Ocean. Here, we aim to evaluate the extent to which natural selection is involved in the observed patterns of divergence of sole populations occurring in the transition zone by comparing them with population structures of other flatfish species that have successfully colonized the Baltic Sea. By using several thousand of ddRAD-derived SNPs, we identified a fine-scale pattern of isolation-by-distance (IBD) of sole populations in the region. However, despite strong biological similarities among the flatfishes compared here, the sole IBD was, by far, the lowest detected across the transition zone. While selection was inferred to strongly influence all other flatfishes evolutionary histories, the analytical inference on the sole demographic history suggests that this fine-scale IBD is mainly maintained by neutral processes due to low effective population size of sole in the transition zone and asymmetrical gene flow. Our work contributes to a growing body of evidence suggesting that the strength of the different micro-evolutionary processes is species-specific, even when species occur in the same environment.

evolutionary biology↗