Browsing by Author "Jorde, Per Erik"
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- Climate change and genetic structure of leading edge and rear end populations in a northwards shifting marine fish species, the corkwing wrasse (Symphodus melops)Publication . Knutsen, Halvor; Jorde, Per Erik; Gonzalez, Enrique Blanco; Robalo, Joana Isabel; Albretsen, Jon; Almada, Vítor CarvalhoOne mechanism by which marine organisms may respond to climate shifts is range shifts. The corkwing wrasse (Symphodus melops) is a temperate fish species, inhabiting the coasts of Europe, that show strong indications of current as well as historical (ice-age) range shifts towards the north. Nine neutral microsatellite DNA markers were screened to study genetic signatures and spatial population structure over the entire geographic and thermal gradient of the species from Portugal to Norway. A major genetic break (FST = 0.159 average among pairs) was identified between Scandinavian and more southern populations, with a marked reduction (30% or more) in levels of genetic variability in Scandinavia. The break is probably related to bottleneck(s) associated with post-glacial colonization of the Scandinavian coasts, and indicates a lack of present gene flow across the North Sea. The lack of gene flow can most likely be attributed to the species’ need for rocky substrate for nesting and a relatively short pelagic larval phase, limiting dispersal by ocean currents. These findings demonstrate that long-distance dispersal may be severely limited in the corkwing wrasse, and that successful range-shifts following present climate change may be problematic for this and other species with limited dispersal abilities, even in the seemingly continuous marine environment.
- Demographic history has shaped the strongly differentiated corkwing wrasse populations in Northern EuropePublication . Mattingsdal, Morten; Jorde, Per Erik; Knutsen, Halvor; Jentoft, Sissel; Stenseth, Nils Christian; Sodeland, Marte; Robalo, Joana I; Hansen, Michael M.; André, Carl; Gonzalez, Enrique BlancoUnderstanding the biological processes involved in genetic differentiation and divergence between populations within species is a pivotal aim in evolutionary biology. One particular phenomenon that requires clarification is the maintenance of genetic barriers despite the high potential for gene flow in the marine environment. Such patterns have been attributed to limited dispersal or local adaptation, and to a lesser extent to the demographic history of the species. The corkwing wrasse (Symphodus melops) is an example of a marine fish species where regions of particular strong divergence are observed. One such genetic break occurred at a surprisingly small spatial scale (FST ~0.1), over a short coastline (<60 km) in the North Sea-Skagerrak transition area in southwestern Norway. Here, we investigate the observed divergence and purported reproductive isolation using genome resequencing. Our results suggest that historical events during the post-glacial recolonization route can explain the present population structure of the corkwing wrasse in the northeast Atlantic. While the divergence across the break is strong, we detected ongoing gene flow between populations over the break suggesting recent contact or negative selection against hybrids. Moreover, we found few outlier loci and no clear genomic regions potentially being under selection. We concluded that neutral processes and random genetic drift e.g., due to founder events during colonization have shaped the population structure in this species in Northern Europe. Our findings underline the need to take into account the demographic process in studies of divergence processes.
- Interbreeding between local and translocated populations of a cleaner fish in an experimental mesocosm predicts risk of disrupted local adaptationPublication . Gonzalez, Enrique Blanco; Espeland, Sigurd H.; Jentoft, Sissel; Hansen, Michael M.; Robalo, Joana Isabel; Stenseth, Nils Christian; Jorde, Per ErikTranslocation of organisms within or outside its native range carries the risk of modifying the community of the recipient ecosystems and induces gene flow between locally adapted populations or closely related species. In this study, we evaluated the genetic consequences of large‐scale translocation of cleaner wrasses that has become a common practice within the salmon aquaculture industry in northern Europe to combat sea lice infestation. A major concern with this practice is the potential for hybridization of escaped organisms with the local, recipient wrasse population, and thus potentially introduce exogenous alleles and breaking down coadapted gene complexes in local populations. We investigated the potential threat for such genetic introgressions in a large seminatural mesocosm basin. The experimental setting represented a simulated translocation of corkwing wrasse (Symphodus melops) that occurs on a large scale in the Norwegian salmon industry. Parentage assignment analysis of mesocosm's offspring revealed 30% (195 out of 651 offspring) interbreeding between the two populations, despite their being genetically (FST = 0.094, p < 0.05) and phenotypically differentiated. Moreover, our results suggest that reproductive fitness of the translocated western population doubled that of the local southern population. Our results confirm that human translocations may overcome the impediments imposed by natural habitat discontinuities and urge for immediate action to manage the genetic resources of these small benthic wrasses.
- Northern refugia and recent expansion in the North Sea: The case of the wrasse Symphodus melops (Linnaeus, 1758)Publication . Robalo, Joana Isabel; Castilho, Rita; Francisco, Sara Martins; Almada, Frederico José Oliveira de; Knutsen, Halvor; Jorde, Per Erik; Pereira, Ana Martins; Almada, Vítor CarvalhoPleistocene climate changes have imposed extreme conditions to intertidal rocky marine communities, forcing many species to significant range shifts in their geographical distributions. Phylogeographic analyses based on both mitochondrial and nuclear genetic markers provide a useful approach to unravel phylogeographic patterns and processes of species after this time period, to gain general knowledge of how climatic changes affect shifts in species distributions.We analyzed these patterns on the corkwing wrasse (Symphodus melops, Labridae), a rocky shore species inhabiting North Sea waters and temperate northeastern Atlantic Ocean from Norway toMorocco including theAzores, using a fragment of the mitochondrial control region and the first intron of the nuclear S7 ribosomal protein gene.We found that S. melops shows a clear differentiation between the Atlantic and the Scandinavian populations and a sharp contrast in the genetic diversity, high in the south and low in the north. Within each of these main geographic areas there is little or no genetic differentiation. The species may have persisted throughout the last glacial maximum in the southern areas as paleotemperatures were not lower than they are today in North Scandinavia. The North Sea recolonization most likely took place during the current interglacial and is dominated by a haplotype absent from the south of the study area, but present in Plymouth and Belfast. The possibility of a glacial refugium in or near the English Channel is discussed.