Grégory Charrier

Populations of Haliotis tuberculata tuberculata declined sharply over the last two decades, mainly due to pathogenic bacteria, Vibrio Harveyi. In this context, restocking or stock-enhancement operations based on hatchery juveniles might be relevant to restore populations and ensure sustainable fisheries. Maintaining the genetic diversity of wild populations and hatchery individuals is a primary concern in supplementation programs. Here, the genetic diversity of 14 hatchery samples and 10 wild populations was assessed using 158 nuclear SNPs. Genetic diversity was comparable between wild and hatchery samples, and even slightly higher in the hatchery. However, high genetic differentiation and small effective population sizes suggested strong genetic drift in the hatchery. Pooling hatchery samples decreased differentiation levels with wild samples, suggesting that released juveniles should be composed of several cohorts and/or generations to limit the genetic heterogeneity between seed and wild populations. Moreover, reduced connectivity was detected between northwestern and southeastern populations, suggesting that restocking broodstock should be chosen depending on the locality where it would be released. Overall, this study provides useful guidelines for future restocking programs.

Swordfish (Xiphias gladius) is of significant economic importance as it is the second most exploited billfish in the Indian Ocean. While the Indian Ocean Tuna Commission (IOTC) considers swordfish to be a single panmictic population in the Indian Ocean, several studies have examined the potential for spatial variations within this highly migratory species with conflicting results, including emerging evidence that population structuring does indeed exist within swordfish. These findings therefore raise questions about the current guidelines for management adopted by the IOTC. In the present study, we address questions about the genetic structuring of swordfish in the Indian Ocean through the analysis of three datasets: (i) neutral SNPs, (ii) with, and (iii) only SNPs under potential selection identified from 1694 swordfish originating from 24 distinct locations across the Indian Ocean. A discriminant analysis of principal components showed the presence of two swordfish subpopulations in the Indian Ocean in the north and the south and was confirmed by admixture methods. This genetic differentiation may be explained by a chromosomal inversion, indicating that both populations could be demographically connected but remain differentiated by this structural variant.

Ocean acidification and warming are key stressors for many marine organisms. Some organisms display physiological acclimatization or plasticity, but this may vary across species ranges, especially if populations are adapted to local climatic conditions. Understanding how acclimatization potential varies among populations is therefore important in predicting species responses to climate change. We carried out a common garden experiment to investigate how different populations of the economically important great scallop (Pecten maximus) from France and Norway responded to variation in temperature and PCO2 concentration. After acclimation, post-larval scallops (spat) were reared for 31 days at one of two temperatures (13°C or 19°C) under either ambient or elevated PCO2 (pH 8.0 and pH 7.7). We combined measures of proteomic, metabolic and phenotypic traits to produce an integrative picture of how physiological plasticity varies between the populations. The proteome of French spat showed significant sensitivity to environmental variation, with 12 metabolic, structural and stress-response proteins responding to temperature and/or PCO2. Principal component analysis revealed seven energy metabolism proteins in French spat that were consistent with countering ROS stress under elevated temperature. Oxygen uptake in French spat did not change under elevated temperature but increased under elevated PCO2. In contrast, Norwegian spat reduced oxygen uptake under both elevated temperature and PCO2. Metabolic plasticity allows French scallops to maintain greater energy availability for growth compared with Norwegian spat. However, increased physiological plasticity and growth in French spat may come at a cost, as they showed reduced survival compared with Norwegian scallops under elevated temperature.

Ocean acidification and warming are key stressors for many marine organisms. Some organisms display physiological acclimatisation or plasticity, but this may vary across species ranges, especially if populations are adapted to local climatic conditions. Understanding how acclimatisation potential varies among populations is therefore important in predicting species responses to climate change. We carried out a common garden experiment to investigate how different populations of the economically important great scallop ( Pecten maximus ) from France and Norway responded to variation in temperature and p CO ₂ concentration. After acclimation, post-larval scallops (spat) were reared for 31 days at one of two temperatures (13°C and 19°C) under either ambient or elevated p CO ₂ (pH 8.0 and pH 7.7). We combined measures of proteomic, metabolic, and phenotypic traits to produce an integrative picture of how physiological plasticity varies between the populations. The proteome of French spat showed significant sensitivity to environmental variation, with 12 metabolic, structural and stress-response proteins responding to temperature and/or p CO ₂ . Principal component analysis revealed seven energy metabolism proteins in French spat that were consistent with countering ROS stress under elevated temperature. Oxygen uptake in French spat did not change under elevated temperature, but increased under elevated p CO ₂ . In contrast, Norwegian spat reduced oxygen uptake under both elevated temperature and p CO ₂ . Metabolic plasticity seemingly allowed French scallops to maintain greater energy availability for growth than Norwegian spat. However, increased physiological plasticity and growth in French spat may come at a cost, as French (but not Norwegian) spat showed reduced survival under elevated temperature. Summary Statement: Juvenile scallops from France and Norway differ in their response to warming and acidification. French scallops show more physiological plasticity, adjusting their proteome and metabolism in order to maintain growth.

The objective of this study was to develop an integrative approach in ecotoxicology (from biomarkers to population genetics) to assess the ecological status of fish populations. Flounders (Platichthys flesus) collected after the spawning season in the heavily polluted Seine estuary were compared with the moderately polluted Bay of Douarnenez. The muscle energetic reserves were highly depleted in Seine vs. Douarnenez fish. The Seine fish displaying a reduced capacity to manage the oxidative stress and a higher energetic metabolism. An increase in the content of muscle membrane phospholipids (sphingomyelin, phosphatidylserine, free sterols) was detected in the Seine vs. Douarnenez fish. The data integration allowed to hypothesize relationships between membrane phospholipids, xenobiotic metabolism, bioenergetics, and antioxidant defence. The genetic diversity considering neutral markers was maintained in the heavily polluted Seine population compared with the Douarnenez population. Finally, we suggest that the high physiological cost of tolerance to toxicants in the Seine flounder population could compromise its capacity to respond in the future to an additional stressor like warming waters in shallow depth. Thus, this population could be submitted to an ecological risk.

The soft-shell clam Mya arenaria is one of the most ancient invaders of European coasts and is present in many coastal ecosystems, yet little is known about its genetic structure in Europe. We collected 266 samples spanning a latitudinal cline from the Mediterranean to the North Sea and genotyped them at 12 microsatellite loci. In parallel, geometric morphometric analysis of shell outlines was used to test for associations between shell shape, latitude and genotype, and for a selection of shells we measured the thickness and organic content of the granular prismatic (PR), the crossed-lamellar (CL) and the complex crossed-lamellar (CCL) layers. Strong population structure was detected, with Bayesian cluster analysis identifying four groups located in the Mediterranean, Celtic Sea, along the continental coast of the North Sea and in Scotland. Multivariate analysis of shell shape uncovered a significant effect of collection site but no associations with any other variables. Shell thickness did not vary significantly with either latitude or genotype, although PR thickness and calcification were positively associated with latitude, while CCL thickness showed a negative association. Our study provides new insights into the population structure of this species and sheds light on factors influencing shell shape, thickness and microstructure.

An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.