Absence of population structure of turbot (Psetta maxima) in the Baltic Sea

Abstract

We found low, albeit significant, genetic differentiation among turbot (Psetta maxima) in the Baltic Sea but in contrast to earlier findings we found no evidence of isolation by distance. In fact temporal variation among years in one locality exceeded spatial variation among localities. This is an unexpected result since adult turbot are sedentary and eggs are demersal at the salinities occurring in the Baltic. Our findings are most likely explained by the fact that we sampled fish that were born after/during a large influx of water to the Baltic Sea, which may have had the consequence that previously locally and relatively sedentary populations became admixed. These results suggest that populations that colonize relatively variable habitats, like the Baltic, face problems. Any adaptations to local conditions that may build up during stable periods may quickly become eroded when conditions change and/or when populations become admixed. Our results indicate that the ability of turbot to survive and reproduce at the low salinity in the Baltic is more likely due to phenotypic plasticity than a strict genetic adaptation to low salinity.

Parallel evolution and adaptation to environmental factors in a marine flatfish: Implications for fisheries and aquaculture management of the turbot (Scophthalmus maximus)

“…Very low genetic differentiation between samples was observed within the Atlantic region, supporting previous findings (Bouza et al., 2002; Coughlan et al., 1998; Florin & Höglund, 2007; Nielsen et al., 2004; Vandamme et al., 2014; Vilas et al., 2015), which indicates relatively high levels of gene flow. This is the case notwithstanding the presence of different well‐known current fronts inside the large marine ecosystems (LME) surveyed in this study, such as the Iberian Coastal, Irish and Biscay Shelf, and North Sea (Belkin & Cornillon, 2007; Belkin, Cornillon, & Sherman, 2009; Vandamme et al., 2014).…”

“…Differentiation due to selection (and genetic drift) may be favored by limited gene flow related to differences in salinity tolerance. It is known that Atlantic turbot eggs do not survive at the lower salinities of the Baltic Sea (Florin & Höglund, 2007), and, in addition, because turbot eggs are not buoyant at salinities below 20 PSU, eggs from the Baltic are demersal rather than pelagic (Nissling et al., 2006). Three of the five markers that were statistically significant in the ATL‐BAS comparison (1916_69 at LG9, 6850_51 and 7550_55 at LG2) were also significant in the comparison between ATL and BLS, strongly supporting that their divergence might be related to adaptation to differences in salinity.…”

“…It has a demersal lifestyle and inhabits sandy coastal habitats (Bouza et al., 2014). Postlarval stages are relatively sedentary, with generally short migration distances (<10 km) being reported for both juvenile and adults of the species (Florin & Höglund, 2007; Nielsen et al., 2004). In contrast, the high dispersal potential of pelagic larvae (until ~30 days posthatching) mediated by oceanic currents coupled with the high fecundity provides potential for gene flow on larger spatial scales (Johannesson & André, 2006).…”

“…Additionally, evidence suggestive of adaptation to temperature and salinity at a regional level has been reported (Vandamme et al., 2014; Vilas et al., 2015). Reproductive success and growth differences in turbot between the Atlantic Ocean and the Baltic Sea have been associated with salinity (Nissling, Johansson, & Jacobsson, 2006) and have been explained either by phenotypic plasticity (Florin & Höglund, 2007) or divergent selection (Vilas et al., 2010, 2015). Significant divergence at specific markers (SNPs or microsatellites) has been reported between turbot sampled from the Irish shelf and the North Sea, the English Channel and the Biscay Gulf, between southern and northern North Sea, and between Baltic and North Sea (Vandamme et al., 2014; Vilas et al., 2010, 2015).…”

Mitochondrial Control Region DNA Variation in Turbot Populations from the Bulgarian and Romanian Black Sea Coasts

“…the local turbot populations were studied using a wide range of morphological parameters, biochemical (3,7,18) and molecular markers (2,11,16,20). Several recent studies of natural turbot populations demonstrated a weak genetic structure among the populations from the northeast Atlantic and the low but significant genetic differentiation of turbot from the Baltic Sea (5,12,20). taken together the results from these studies suggest that turbot populations are related to high gene flow rate combined with low level of adaptive polymorphisms and genetic differentiation for some coastal areas.…”