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Map of the Mediterranean Sea with the name of the sub-basins, main currents (white lines) and oceanographic fronts analysed (red lines). The name of the fronts and the acronym used (in black) is as follows: GS (Gibraltar Strait), AOF (Almeria-Oran Front), IC (Ibiza Channel), BF (Balearic Front), SC (Sicily Channel), ADR (Otranto Channel), AEG (southern margin of the Aegean Sea).
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Background
Marine species can demonstrate strong genetic differentiation and population structure despite the hypothesis of open seas and high connectivity. Some suggested drivers causing the genetic breaks are oceanographic barriers and the species’ biology. We assessed the relevance of seven major oceanographic fronts on species connectivity whi...
Citations
... This is consistent with the tagging studies of blue sharks that, despite a low recapture rate, have shown no evidence of blue shark migration between the Atlantic and the Mediterranean [57][58][59][60][61]. Other pelagic or migratory fishes also exhibit genetic differentiation between Atlantic and Mediterranean populations at microsatellite and mtDNA loci, such as the meagre (Argyrosomus regius) [62] and the strait of Gibraltar serves as a barrier to gene flow for many species regardless of their spatial ecology [63]. ...
The blue shark, Prionace glauca, is the most abundant pelagic shark in the open ocean but its vulnerability remains poorly understood while being one of the most fecund sharks. In the Mediterranean Sea, the blue shark is listed as Critically Endangered (CR) by the International Union for Conservation of Nature. The species is facing a strong decline due to fishing, and scientific data regarding its genetic structure and vulnerability are still lacking. Here, we investigated the genetic diversity, demographic history, and population structure of the blue shark within the Mediterranean Sea, from samples of the Gulf of Lion and Malta, using sequences of the mtDNA control region and 22 microsatellite markers. We also compared our mitochondrial data to previous studies to examine the Atlantic-Mediterranean population structure. We assessed the blue shark’s genetic vulnerability in the Mediterranean basin by modelling its effective population size. Our results showed a genetic differentiation between the Atlantic and the Mediterranean basins, with limited gene flow between the two areas, and distinct demographic histories making the Mediterranean population an independent management unit. Within the Mediterranean Sea, no sign of population structure was detected, suggesting a single population across the Western and Central parts of the sea. The estimated effective population size was low and highlighted the high vulnerability of the Mediterranean blue shark population, as the estimated size we calculated might not be sufficient to ensure the long-term persistence of the population. Our data also provide additional evidence that the Gulf of Lion area acts as a nursery for P. glauca, where protection is essential for the conservation strategy of the species in the Mediterranean.
... The pattern of differentiation between Atlantic populations and West and East Mediterranean populations has been reported in many species and is usually interpreted as the result of a secondary contact between Atlantic and Mediterranean subpopulations that were separated once or more times in the Pleistocene, when the sea level dropped because of the glaciations, cutting the connection between the Atlantic Ocean, the West Mediterranean Sea, and the East Mediterranean Sea. Present day oceanographic features such as the Almeria-Oran oceanographic front (AOOF) (Figure 1) and the patterns of marine circulation past the Siculo-Tunisian Strait are thought to contribute to the persistence of the genetic differentiation [8,9]. The effect of natural selection could favor the coincidence of allele frequency changes with oceanographic barriers [10,11]. ...
... Firstly, Cordero et al. found a strong genetic differentiation between the eastern and the western Mediterranean basins. This is a common observation in genetic studies of populations of many species of marine organisms [8][9][10]. There are several aspects of the previous studies that require more detailed scrutiny. ...
... Firstly, Cordero et al. found a strong genetic differentiation between the eastern and the western Mediterranean basins. This is a common observation in genetic studies of populations of many species of marine organisms [8][9][10]. However, in the study by Cordero et al., only populations from the northern coasts of the eastern Mediterranean (Adriatic and Aegean seas) were included. ...
The grooved carpet-shell clam is one of the most economically relevant shellfish species living in the Mediterranean and nearby Atlantic coasts. Previous studies using different types of genetic markers showed a remarkable genetic divergence of the eastern Mediterranean, western Mediterranean, and Atlantic populations, but important details remained unclear. Here, data from six nuclear introns scored for restriction fragment size polymorphisms in eight populations that have not been studied before have been pooled for the analysis with data scattered through three previous studies, totaling 32 samples from 29 locations. The results show lower levels of heterozygosity, higher mean number of alleles, and alleles with restricted distribution in the Mediterranean populations, suggesting the existence of a large, isolated population in the eastern Mediterranean at the middle Pleistocene. The data also confirm the similarity of populations from Tunisia to Western Mediterranean populations. Finally, a genetic mosaic is apparent in the Atlantic coasts of the Iberian Peninsula, with a divergence of Rias Baixas populations from more northern populations and Central Portugal populations. The effects of oceanic fronts, seasonal upwellings, river plumes, and/or fishery management operations could explain this and other features of the Atlantic populations.
... After passing through the Strait of Sicily, one current branches towards the Tyrrhenian Sea, forming cyclonic currents along the coast, whereas another current flows through the Sicilian Channel and reaches the northern coasts of the Mediterranean Sea and the Levantine Basin. It forms surface, intermediate, and deep currents [38]. ...
In recent years, investments in renewable energy sources have been increasing in order to reduce fossil fuel consumption and mitigate the effects of global warming on the marine ecosystem. Recent studies have shown that marine current energy, which is one of the renewable energy sources, can provide very high energy gains. This study focuses on the Mediterranean region, which is one of the areas where the impacts of climate change are most clearly felt. The annual and seasonal analysis of the current velocity in the study area between 2016 and 2018 was carried out using remote sensing technology, and potential energy production was calculated using an underwater turbine system we selected. As a result of the study, it was determined that the maximum current velocities were 2.2 m/s in 2016 and 2017 and 2.7 m/s in 2018. In addition, it was observed that the current speed was approximately 2.7 m/s in the spring months and 2.0 m/s in the summer months. In the fall and winter months, it was 2.1 m/s and 2.2 m/s, respectively. Research has shown that the study area, especially in the eastern coastal areas, has the capacity to generate approximately 10 GWh of energy per year with the use of underwater turbine systems.
... The pattern of differentiation between Atlantic populations and West and East Mediterranean populations has been reported in many species and is usually interpreted as the result of a secondary contact between an Atlantic and Mediterranean subpopulations that were separated once or more times in the Pleistocene, when the sea level dropped because of the glaciations, cutting the connection between the Atlantic Ocean, the West Mediterranean Sea and the East Mediterranean Sea. Present day oceanographic features such as the Almeria -Oran oceanographic front (AOOF) ( Figure 1) and the patterns of marine circulation past the Siculo-Tunisian Strait are thought to contribute to the persistence of the genetic differentiation [8,9]. The effect of natural selection could favor the coincidence of allele frequency changes with oceanographic barriers [10,11]. ...
... Firstly, Cordero et al. found a strong genetic differentiation between the Eastern and the Western Mediterranean basins. This is a common observation in genetic studies of populations of many species of marine organisms [8][9][10]. However, in the study by Cordero et al. ...
... The results of this study agree with previous studies using intron-RFLP and microsatellite markers in showing a subdivision of the species in an Atlantic and two Mediterranean groups, corresponding to the Western and Eastern basins [6,12]. The genetic differentiation found between the Atlantic and the Mediterranean populations is consistent with many other studies showing the same result in other species using several types of genetic markers (enzyme polymorphisms, 13 mitochondrial DNA, microsatellites, SNP), and have been related to the Pleistocene glacialinterglacial cycles and present-day restriction to gene flow at some points ( [8,9]). ...
The grooved carpet-shell clam is one of the most economically relevant shellfish species living in the Mediterranean and nearby Atlantic coasts. Previous studies using different types of genetic markers showed a remarkable genetic divergence of the Eastern Mediterranean, Western Mediterranean and Atlantic populations, but important details remained unclear. Here, data from six nuclear introns scored for restriction fragment size polymorphisms in eight populations that have not been studied before have been pooled for the analysis with data scattered through three previous studies, totaling 32 samples from 29 locations. The results show lower levels of heterozygosity, higher mean number of alleles, and alleles with restricted distribution in the Mediterranean populations, suggesting the existence of a large isolated population in the eastern Mediterranean at the middle Pleistocene. The data also confirm the similarity of populations from Tunisia to western Mediterranean populations. Finally, a genetic mosaic is apparent in the Atlantic coasts of the Iberian Peninsula, with a divergence of Rias Baixas populations from more northern populations and Central Portugal populations. The effects of oceanic fronts, seasonal upwellings, river plumes and/or fishery management operations could explain this and other features of the Atlantic populations.
... Historical paleogeographic changes at ocean levels may have contributed to the isolation of populations, leaving a genetic fingerprint that can currently be detected genetically (Allaya et al., 2015;Forde et al., 2023). Furthermore, species life history traits and strategies, such as the duration of larval stages combined with phylogeographic discontinuities caused by oceanic fronts or gyres, could promote local retention and self-recruitment of larvae, contributing to the genetic differentiation of populations (Pascual et al., 2017;Van Wyngaarden et al., 2017). ...
... Thus, and putting all the results together, Atlantic bonito stands out as a canonical example of population structure in a marine pelagic species, where the combination of the assumed absence of barriers is expected to produce a population structure of isolation by distance. However, it does not exclude the formation of discrete genetic groups, probably as a consequence of the combination of elusive biogeographic barriers with philopatric behavior (Pascual et al., 2017). ...
... Several barriers influence the connectivity and distribution of Mediterranean marine species [43]. Monitoring larvae in the water column is highly challenging; therefore, detailed observations have not been reported for most benthic invertebrates. ...
The population genetics of Patella ferruginea Gmelin, 1791, an endangered limpet endemic to the western Mediterranean, has been analysed using 11 polymorphic microsatellite markers on 533 individuals from 18 localities throughout its distribution area. The results showed a deficit of heterozygotes, denoting a certain degree of inbreeding, and, with an overall FST of 0.004, a low level of genetic variability among localities. These data indicate that the species is distributed as a metapopulation (an assemblage of discrete local populations with migration among them) along most of the species’ range. Moreover, 99% of the variability observed was within populations, with only 0.41% accounting for between-population variability. No pattern of isolation-by-distance was found, and 35.5% of the individuals were recognised as migrants. Altogether, the findings indicate that most of the populations studied are connected to each other to some extent and that larvae of the species show a higher dispersal capacity than previously assumed. The exchange network does not follow a clear direction but rather shows a chaotic pattern attributed to stochastic factors resulting from the complex interaction of biotic and abiotic factors. This pattern indicates the lack of strong barriers to dispersal in the study area and permeable barriers that do not limit population connectivity. A relatively high level of self-recruitment and occasional stochastic dispersal events at variable distances are also evidenced by the analyses. Currently, marine protected areas (MPAs) safeguard the benthic adults but not the larval phase of the species. Considering our results, the conservation of P. ferruginea should be based on a holistic approach in which the protection of its habitats extends from the benthic to the pelagic zones, which will help maintain the larval pool and promote larval dispersal and settlement and, ultimately, gene flow. Lastly, conservation efforts must prioritise the survival of the extant populations of P. ferruginea, both within and outside MPAs, over measures that require the manipulation or translocation of specimens.
... Within Lake Constance, quagga mussel populations revealed no population structure and there was no detectable genetic differentiation across populations from different sampling sites or depth (all pairwise F st < 0). The observed lack of any population genetic patterns is comparable to patterns observed for a range of marine broadcast spawners (reviewed in Pascual et al., 2017). In general, their longer planktonic larval phase allows long-distance dispersal and can hinder the evolution of population differentiation and prevent signals of isolation by distance (e.g., Charrier et al., 2006;Pascual et al., 2017). ...
... The observed lack of any population genetic patterns is comparable to patterns observed for a range of marine broadcast spawners (reviewed in Pascual et al., 2017). In general, their longer planktonic larval phase allows long-distance dispersal and can hinder the evolution of population differentiation and prevent signals of isolation by distance (e.g., Charrier et al., 2006;Pascual et al., 2017). In particular, marine species with high fecundity, large population sizes, and larvae with long-distance dispersal can show low genetic structures (Palumbi, 1994). ...
Human activities have facilitated the invasion of freshwater ecosystems by various organisms. Especially, invasive bivalves such as the quagga mussels, Dreissena bugensis, have the potential to alter ecosystem function as they heavily affect the food web. Quagga mussels occur in high abundance, have a high filtration rate, quickly spread within and between waterbodies via pelagic larvae, and colonize various substrates. They have invaded various waterbodies across the Northern Hemisphere. In Central Europe, they have invaded multiple large and deep perialpine lakes with first recordings in Lake Geneva in 2015 and 2016 in Lake Constance. In the deep perialpine lakes, quagga mussels quickly colonized the littoral zone but are also abundant deeper (>80 m), where they are often thinner and brighter shelled. We analysed 675 quagga mussels using ddRAD sequencing to gain in‐depth insights into the genetic population structure of quagga mussels across Central European lakes and across various sites and depth habitats in Lake Constance. We revealed substantial genetic differentiation amongst quagga mussel populations from three unconnected lakes, and all populations showed high genetic diversity and effective population size. In Lake Constance, we detected no genetic differentiation amongst quagga mussels sampled across different sites and depth habitats. We also did not identify any convincing candidate loci evidential for adaptation along a depth gradient and a transplant experiment showed no indications of local adaptation to living in the deep based on investigating growth and survival. Hence, the shallow‐water and the deep‐water morphotypes seem to be a result of phenotypic plasticity rather than local adaptation to depth. In conclusion, our ddRAD approach revealed insight into the establishment of genetically distinct quagga mussel populations in three perialpine lakes and suggests that phenotypic plasticity and life history traits (broadcast spawner with high fecundity and dispersing pelagic larvae) facilitate the fast spread and colonization of various depth habitats by the quagga mussel.
... The marked genetic isolation of the Black Sea population based on haplotype networks and phylogenetic trees are in agreement with the expectations based on geographic barriers that limit the gene flow (Firidin et al. 2020;Öztürk and Altınok 2021). The duration of the planktonic egg and/or larval stages tends to correlate positively with the species distribution range (Macpherson and Raventos 2006;Walsh et al. 2015;Öztürk, 2023;Pereira et al. 2023) and correlate negatively with spatial genetic differentiation level (Marko and Hart 2018;Pascual et al. 2017;Veli et al., 2021). Restriction of egg and or larval transportation has important demographic and evolutionary consequences. ...
In this study, the genetic structure and phylogeny of the European flounder (Platichthys flesus L.) was investigated through the analysis of three mitochondrial gene sequences: COI, 16S rRNA, and cyt-b with specimens collected from the Black Sea and the Baltic Sea. In addition, available mtDNA sequences of P. flesus with known geographic information (from the Baltic Sea, the North Sea, the White Sea, the Atlantic Ocean, and the Mediterranean Sea) were retrieved from the GenBank database and included in phylogenetic analysis to increase resolution. The Black Sea is comprised of a geographically isolated European flounder population. Among analyzed mtDNA sequences, cyt-b sequence appeared to be more informative for detecting genetic differentiation at population level whereas 16S rRNA sequence was the less informative. The maximum likelihood trees generated based on COI, 16S rRNA, and cyt-b sequences suggested the presence of distinct European flounder population in the Black Sea, separating it from the European flounder populations from the rest of the geographic regions. Similarly, the highest genetic distances were obtained between the Black Sea population and the rest of the populations. The low salinity level of the Black Sea and narrow straits that connect the Black Sea to the Mediterranean Sea may function as an effective barrier that restrict gene flow and larval dispersal. We suggest designation of the Black Sea European flounder population as an evolutionary significant unit.
... The marked genetic isolation of the Black Sea population based on haplotype networks and phylogenetic trees are in agreement with the expectations based on geographic barriers that limit the gene flow (Firidin et al. 2020;Öztürk and Altınok 2021). The duration of the planktonic egg and/or larval stages tends to correlate positively with the species distribution range (Macpherson and Raventos 2006;Walsh et al. 2015;Öztürk, 2023;Pereira et al. 2023) and correlate negatively with spatial genetic differentiation level (Marko and Hart 2018;Pascual et al. 2017;Veli et al., 2021). Restriction of egg and or larval transportation has important demographic and evolutionary consequences. ...
In this study, the genetic structure and phylogeny of the European flounder (Platichthys flesus L.) was investigated through the analysis of three mitochondrial gene sequences: COI, 16S rRNA, and cyt-b with specimens collected from the Black Sea and the Baltic Sea. In addition, available mtDNA sequences of P. flesus with known geographic information (from the Baltic Sea, the North Sea, the White Sea, the Atlantic Ocean, and the Mediterranean Sea) were retrieved from the GenBank database and included in phylogenetic analysis to increase resolution. The Black Sea is comprised of a geographically isolated European flounder population. Among analyzed mtDNA sequences, cyt-b sequence appeared to be more informative for detecting genetic differentiation at population level whereas 16S rRNA sequence was the less informative. The maximum likelihood trees generated based on COI, 16S rRNA, and cyt-b sequences suggested the presence of distinct European flounder population in the Black Sea, separating it from the European flounder populations from the rest of the geographic regions. Similarly, the highest genetic distances were obtained between the Black Sea population and the rest of the populations. The low salinity level of the Black Sea and narrow straits that connect the Black Sea to the Mediterranean Sea may function as an effective barrier that restrict gene flow and larval dispersal. We suggest designation of the Black Sea European flounder population as an evolutionary significant unit.
... Consistently with the Mediterranean pattern of diffusion already proposed in Sanna et al. (2013) for this species, this finding suggests that the already known oceanographic barriers at the Sicily Strait and at the Otranto Strait might be limiting the dispersal of the species and minimizing the gene flow (Čekovská et al., 2020). Due to its short pelagic larval duration stage, P. nobilis is a species which is considered to be rather affected by currents and fronts; at the same time, it could be less prone to gene flow from other locations (Pascual et al., 2017) and it could exhibit strong population structuring, as has been shown for other bivalves also characterized by a short planktonic larval stage (Ye, Wu & Li, 2015). eDNA and mtDNA marker sequencing eDNA has been used widely for biodiversity assessments (Pereira et al., 2021) and for the detection of cryptic, threatened (Hunter et al., 2018) and invasive species (Ardura et al., 2015). ...
The fan mussel Pinna nobilis Linnaeus, 1758 is an endemic species of the Mediterranean Sea, protected by international agreements. It is one of the largest bivalves in the world, playing an important role in the benthic communities; yet it has been recently characterized as Critically Endangered by the IUCN, due to mass mortality events. In this context, the assessment of the genetic variation of the remaining P. nobilis populations and the evaluation of connectivity among them are crucial elements for the conservation of the species. For this purpose, samples were collected from six regions of the Eastern Mediterranean Sea; the Islands of Karpathos, Lesvos and Crete; the Chalkidiki and Attica Peninsulas; and the Amvrakikos Gulf. Sampling was performed either by collecting tissue from the individuals or by using a non-invasive method, i.e. , by scraping the inside of their shells aiming to collect their mucus and thus avoid stress induction to them. Conventional molecular techniques with the use of the COI and 16S rRNA mitochondrial markers were selected for the depiction of the intra-population genetic variability. The analyses included 104 samples from the present study and publicly available sequences of individuals across the whole Mediterranean Sea. The results of this work (a) suggest the use of eDNA as an efficient sampling method for protected bivalves and (b) shed light to the genetic structure of P. nobilis population in the Eastern Mediterranean; this latter knowledge might prove to be fundamental for the species conservation and hence the ecosystem resilience. The haplotype analyses reinforced the evidence that there is a certain degree of connectivity among the distinct regions of the Mediterranean; yet there is evidence of population distinction within the basin, namely between the Western and the Eastern basins. The combination of both genetic markers in the same analysis along with the inclusion of a large number of individuals produced more robust results, revealing a group of haplotypes being present only in the Eastern Mediterranean and providing insights for the species’ most suitable conservation management.
