Diversitat genètica de la truita comuna (Salmo trutta L.) a la Península Ibèrica: biogeografia i gestió

L'estudi de la diversitat i la diferenciació genètiques de les poblacions de truita comuna (Salmo trutta L.) a la Península Ibèrica ha confirmat l'elevada diferenciació observada en treballs previs i la divergència, ja descrita, entre les poblacions de la vessant atlàntica i la mediterrània. El resultats obtinguts, però, ens permeten observar patrons d'estructura poblacional tant en les poblacions atlàntiques com les mediterrànies. A l'Atlàntic s'observa un marcat patró hidrogràfic en la distribució de la diferenciació genètica, que contrasta fortament amb la distribució d'aquesta diferenciació en les poblacions mediterrànies, caracteritzades pels contactes secundaris entre llinatges durant les expansions pleniglacials i una forta divergència local conseqüència de la seva marginalitat i aïllament en els períodes interglacials. El manteniment d'aquesta diferenciació i individualitat descrites en les poblacions de truita de la Península, es veu seriosament compromès per les contínues repoblacions dels rius amb exemplars exògens d'origen nord europeu. La substitució dels genomes autòctons per la introducció de gens al.lòctons provoca una erosió dels patrimonis genètics natius i una homogeneïtzació de les poblacions, destruint els patrons de diferenciació existents. Al mateix temps, els nostres resultats indiquen que les conseqüències de les repoblacions no són sempre les mateixes. Concretament, es constata un fracàs de les repoblacions en rius intensament repoblats i sotmesos a pesca intensiva, que contrasta amb una enorme erosió de les poblacions quan les repoblacions s'efectuen sobre àrees protegides i sense cap mena de pressió pesquera. Això suggereix que múltiples factors com la gestió dels rius posterior a les repoblacions, l'estat de les poblacions o les condicions de l'hàbitat són determinants de la introducció efectiva dels exemplars alliberats; fet que dificulta la predicció sobre actuacions particulars. Malgrat aquesta introgressió de gens exògens que es detecta en moltes de les poblacions analitzades, els gens natius predominen en gairebé tots els rius de la Península. La conservació d'aquesta elevada riquesa genètica que encara resta en les poblacions de truita de la Península Ibèrica ha de ser l'objectiu final de qualsevol programa de gestió. Per això, defensem una gestió basada en el propi riu mitjançant una pesca sostinguda per la reproducció natural de les poblacions salvatges, acompanyada d'una millora i recuperació d'hàbitats adequats per la truita, i evitant, per sobre de tot, la introducció en els rius d'exemplars exògens, degut als efectes nocius i incontrolables que comporta aquest procés.Our study on the genetic diversity and differentiation of brown trout (Salmo trutta L.) population of the Iberian Peninsula confirmed the high levels of differentiation and the divergence between Atlantic and Mediterranean populations previously described. However, additional substructuring among Atlantic rivers and among Mediterranean ones has been detected. In the Atlantic, genetic diversity is related with the river network, producing a marked hydrographical pattern in sharp contrast with a mosaic distribution of genetic variation among the Mediterranean collections. In this later area, genetic resources distributed as a result of distinct colonization episodes during pleniglacial expansions, secondary contacts, and local divergence due to its marginality and isolation in the interglacial periods. Continuous stocking with hatchery-reared fish of north European origin, seriously compromises the conservation of this differentiation and individuality described in brown trout populations of the Iberian Peninsula. Replacement of the autochthonous genome due to introduction of exogenous genes is leading to an erosion of the native gene pools, a homogenisation of populations, and a destruction of the ancestral patterns of differentiation. At the same time, our results indicated that successful stocking appears to be limited to wild populations subjected to occasional releases in protected or unfished areas. Extensive stocking in fished areas result in a more limited impact on the recipient native population. These results suggest that stocking success is unpredictable and controlled by different factors including habitat and population conditions at the time of stocking, as well as post-release management actuations. Although many of the analysed populations are introgressed with exogenous genes, native gene pools predominate in almost all the Iberian rivers. Conservation of this high genetic richness that still remains in brown trout Iberian populations must be the final goal of any management program. So, our management proposal is based on fisheries sustained by natural reproduction of the respective wild populations, coupled with an improvement and recovery of habitat suitable for brown trout; avoiding stocking with exogenous fish due to the harmful and incontrollable risks that this process involves for the genetic resources of the species

Anàlisi genètica de la truita comuna, Salmo trutta L., a la conca alta de la Noguera Ribagorçana

L'anàlisi genètica de cinquanta loci proteics ha permès estudiar l'estructura poblacional de la truita comuna a l'alta Noguera Ribagorçana, incloent-hi part del Parc Nacional d'Aigüestortes i Estany de Sant Maurici. Els resultats obtinguts indiquen una important diferenciació genètica entre les mostres, que és conseqüència dels diferents graus d'introducció de peixos originaris de repoblació. La incidència de les repoblacions és menor fora del Parc Nacional, en àrees explotades i intensament repoblades. Sembla que en aquestes àrees la pesca extreu els exemplars repo-blats abans que aquests s'incorporin al grup reproductor de la població receptora. En el Parc Nacional la incidència de les repoblacions és més elevada. Aquí, l'establiment d'una població al'lòctona al barranc de Morrano, representa el principal perill per a la conservació de la diversitat genètica de l'espècie i la integritat de tot l'ecosistema. Aquests resultats posen de manifest importants errades de gestió tant en les àrees de pesca com en el Parc Nacional.El análisis genético de 50 loci codificadores de proteínas ha permitido estudiar la estructura poblacional de la trucha común en el alto Noguera Ribagorçana, incluyendo parte del Parque Nacional de Aigüestortes y Estany de Sant Maurici. Los resultados obtenidos indican una diferenciación genética importante entre las muestras, que es conse-cuencia de los distintos grados de introducción de peces originarios de repoblación. La incidencia de las repoblacio-nes es menor fuera del Parque Nacional, en áreas explotadas e intensamente repobladas. Parece ser que en estas áreas la pesca extrae los ejemplares repoblados antes de que éstos se incorporen al grupo reproductor de la pobla-ción receptora. En el Parque Nacional, la incidencia de las repoblaciones es más elevada y se ha establecido una población exógena en el barranc de Morrano, que representa el principal peligro para la conservación de la diversi-dad genética de la especie y la integridad de todo el ecosistema. Estos resultados indican errores de gestión impor-tantes tanto en las áreas de pesca como en el Parque Nacional.The population structure of brown trout in the upper Noguera Ribagorçana, including areas within the «Aigüestortes i Estany de Sant Maurici» National Park, was assessed by electrophoretic variation at 50 protein coding loci. An important genetic differentiation was detected among samples, basically due to the different genetic impact of the released exogenous hatchery fish. The occurrence of fish of hatchery ancestry is lower in the fished and heavily stocked areas outside the National Park. Apparently, the capture of hatchery fish prior to sexual maturity permits the perpetuation of a predominantly native population in this area. The occurrence of fish of hatchery origin is higher within the National Park, where almost complete displacement of native fish has occurred at Barranc de Morrano. This population represents the main risk for the conservation of the genetic diversity of the specie and the ecosystem. These data suggest important errors in the management undertaken in both fished and protected areas

Genetic risks of supplementing trout populations with native stocks: A simulation case study from current pyrenean populations

The risks of supplementation must be examined to assess the genetic effects to native wild populations before full implementation or exclusion of programs that involve captive breeding and release. Real genetic data can be applied to simulations of genetic changes in populations of interest and subsequently used in risk assessment. Ancestral Mediterranean brown trout (Salmo trutta) lineages exhibit complex population structure among native populations. Genetically divergent Atlantic stocks were maintained and released in the Mediterranean rivers as recreational fish, which resulted in hybridization and introgression with local populations. Therefore, we designed a new supplementation program based on native stocks and evaluated the genetic risks associated with releasing native fish in recreational fisheries. Our simulation was delimited by the observed population genetic structure and available hatchery facilities in the study region. Supplementation with native stocks maintained estimates of gene diversity indexes (total diversity (HT), local diversity (HS), and population differentiation (GST)). However, simulations indicated that long-term supplementation significantly reduced genetic diversity among locations because of a homogenizing effect of populations along each management unit. Therefore, such reinforcements compromised the conservation of local genetic variation. Nevertheless, replacement of current foreign stocks with native stocks can be an important step towards promoting the value of preserving local diversity among anglers

Using Massive Parallel Sequencing for the Development, Validation, and Application of Population Genetics Markers in the Invasive Bivalve Zebra Mussel (Dreissena polymorpha)

The zebra mussel (Dreissena polymorpha, Pallas, 1771) is one of the most invasive species of freshwater bivalves, due to a combination of biological and anthropogenic factors. Once this species has been introduced to a new area, individuals form dense aggregations that are very difficult to remove, leading to many adverse socioeconomic and ecological consequences. In this study, we identified, tested, and validated a new set of polymorphic microsatellite loci (also known as SSRs, Single Sequence Repeats) using a Massive Parallel Sequencing (MPS) platform. After several pruning steps, 93 SSRs could potentially be amplified. Out of these SSRs, 14 were polymorphic, producing a polymorphic yield of 15.05%. These 14 polymorphic microsatellites were fully validated in a first approximation of the genetic population structure of D. polymorpha in the Iberian Peninsula. Based on this polymorphic yield, we propose a criterion for establishing the number of SSRs that require validation in similar species, depending on the final use of the markers. These results could be used to optimize MPS approaches in the development of microsatellites as genetic markers, which would reduce the cost of this proces

Current status of the brown trout (Salmo trutta) populations within eastern Pyrenees genetic refuges

Since the end of the 20th century, some headwaters of rivers in the eastern Pyrenees have been designated as genetic refuges to protect remaining native brown trout (Salmo trutta) diversity. The declaration was based on limited or no evidence of genetic impact from released non-native Atlantic hatchery fish. Hatchery releases were completely banned into the genetic refuges, but pre-existing fishing activities were maintained. Specific locations in each refuge have been monitored every 2–3 trout generations to update genetic information to accurately assess the contribution of these reservoirs to the preservation of native brown trout gene pools. This work updates genetic information to year 2014 in three of these locations (in Ter, Freser and Flamisell rivers). Previous studies identified hatchery introgressed populations within refuges and suggested discrepancies between the underlying intention of the genetic refuges and the gene pools detected. Therefore, we also examined genetic divergences among locations inside refuge river segments. Combined information at five microsatellite and the lactate dehydrogenase C (LDH-C*) loci showed reduced but significant temporal native allele frequency fluctuations in some of the above specific locations that did not modify overall levels of local diversity and river divergences. Bayesian clustering analyses confirmed the presence of differentiated native units within each genetic refuge. Some locations of the Freser River within the genetic refuge area showed high hatchery impact of non-native fish (over 20%). We discuss additional local actions (releases of native fish, selective removals and fishery reinforcement with sterile individuals) to improve the conservation objective of genetic refuge

Temporal genetic dynamics among mosquitofish (Gambusia holbrooki) populations in invaded watersheds

The temporal components of genetic diversity and geographical structure of invasive mosquitofish populations are poorly known. Through the genetic monitoring of four consecutive cohorts of Gambusia holbrooki from three different river basins we aimed to determine temporal patterns of regional genetic variation and dispersal rates within invasive populations. Despite showing evidence of strong population size fluctuations, genetic diversity levels were maintained among local cohorts. We only detected temporal allele frequency changes associated with seasonal flooding that did not modify major trends on population structure among cohorts. Downstream gene flow coupled with increased connectivity at lowland locations to increase genetic diversity levels in these areas. A large proportion of local fish (up to 50 %) were dispersers, often originated from locations within the same river basin. High dispersal capability, ecological tolerance, and reproductive traits likely promote river colonization. Finally, our results also confirmed that human-assisted translocations promote within and among basin gene flow and maintained levels of genetic diversity, particularly in upstream locationsThis work has been possible thank to the financial support of the former Spanish Ministry of Economy and Competitiveness (MINECO, CGL2009-12877-C02-02). DDM held a Ph.D. scholarship from the University of Girona (UdG, BR10/12

Validated methodology for quantifying infestation levels of dreissenid mussels in environmental DNA (eDNA) samples

The zebra mussel (Dreissena polymorpha Pallas, 1771) and the quagga mussel (D. rostriformis Deshayes, 1838) are successful invasive bivalves with substantial ecological and economic impacts in freshwater systems once they become established. Since their eradication is extremely difficult, their detection at an early stage is crucial to prevent spread. In this study, we optimized and validated a qPCR detection method based on the histone H2B gene to quantify combined infestation levels of zebra and quagga mussels in environmental DNA samples. Our results show specific dreissenid DNA present in filtered water samples for which microscopic diagnostic identification for larvae failed. Monitoring a large number of locations for invasive dreissenid species based on a highly specific environmental DNA qPCR assay may prove to be an essential tool for management and control plans focused on prevention of establishment of dreissenid mussels in new locationsWe are indebted to different colleagues for zebra mussel sample collections: Concha Durán (Ebro Hydrografic Confederation, Spain) for the logistic advice; Anna Terrats and Carolina Solà (Catalan Water Agency from the Government of Catalonia, Spain) for the filtered-water environmental samples. We would thank to Mariona Palacios for her collaboration in the analysis into her Final Master Project. This research was carried out within the objectives of the research project CGL200909407 of the Spanish Ministerio de Ciencia e Innovación (MICINN

Gene Flow and Maintenance of Genetic Diversity in Invasive Mosquitofish (Gambusia holbrooki)

Genetic analyses contribute to studies of biological invasions by mapping the origin and dispersal patterns of invasive species occupying new territories. Using microsatellite loci, we assessed the genetic diversity and spatial population structure of mosquitofish (Gambusia holbrooki) that had invaded Spanish watersheds, along with the American locations close to the suspected potential source populations. Mosquitofish populations from the Spanish streams that were studied had similar levels of genetic diversity to the American samples; therefore, these populations did not appear to have undergone substantial losses of genetic diversity during the invasion process. Population structure analyses indicated that the Spanish populations fell into four main clusters, which were primarily associated with hydrography. Dispersal patterns indicated that local populations were highly connected upstream and downstream through active dispersal, with an average of 21.5% fish from other locations in each population. After initially introducing fish to one location in a given basin, such dispersal potential might contribute to the spread and colonization of suitable habitats throughout the entire river basin. The two-dimension isolation-by-distance pattern here obtained, indicated that the human-mediated translocation of mosquitofish among the three study basins is a regular occurrence. Overall, both phenomena, high natural dispersal and human translocation, favor gene flow among river basins and the retention of high genetic diversity, which might help retain the invasive potential of mosquitofish population