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Chinook salmon (Oncorhynchus tshawytscha) are migratory fish that are highly valued for subsistence, sport, and commercial fisheries throughout their native range. Populations of Chinook salmon in western Alaska have exhibited long-term declines, leading to restrictions on harvests. Management priorities require greater resolution for genetic stock identification (GSI) than is available with current methods. We leveraged RADseq, TaqMan, and GT-seq data originating from multiple sources, collected through time, to develop a set of GT-seq panels containing 1092 single nucleotide polymorphisms (SNPs) that improved GSI resolution in western Alaska for at-sea and in-river sampling. We generated a dense linkage map to ensure that markers selected for panels spanned the entire genome. In addition, we identified multiple RADseq markers that were associated with sex; these aligned to a 5-centimorgan (cM) region on the sex chromosome. Finally, we developed a bioinformatic pipeline to streamline analysis of GT-seq data that is capable of genotyping microhaplotypes and paralogs, both of which can improve GSI resolution over traditional single-SNP data. Our panels and pipeline provide tools for management agencies to rapidly and easily analyze large-scale genotyping projects.

Pink salmon (Oncorhynchus gorbuscha) adults are the smallest of the five Pacific salmon native to the western Pacific Ocean. Pink salmon are also the most abundant of these species and account for a large proportion of the commercial value of the salmon fishery worldwide. A strict two-year life-history of most pink salmon generates temporally isolated populations that spawn either in even-years or odd-years. To uncover the influence of this genetic isolation, reference genome assemblies were generated for each year-class and whole genome re-sequencing data was collected from salmon of both year-classes. The salmon were sampled from six Canadian rivers and one Japanese river. At multiple centromeres we identified peaks of Fst between year-classes that were millions of base-pairs long. The largest Fst peak was also associated with a million base-pair chromosomal polymorphism found in the odd-year genome near a centromere. These Fst peaks may be the result of centromere drive or a combination or reduced recombination and genetic drift, and they could influence speciation. Other regions of the genome influenced by odd-year and even-year temporal isolation and tentatively under selection were mostly associated with genes related to immune function, organ development/maintenance, and behaviour.

As the conservation challenges increase, new approaches are needed to help combat losses in biodiversity and slow or reverse the decline of threatened species. Genome-editing technology is changing the face of modern biology, facilitating applications that were unimaginable only a decade ago. The technology has the potential to make significant contributions to the fields of evolutionary biology, ecology, and conservation, yet the fear of unintended consequences from designer ecosystems containing engineered organisms has stifled innovation. To overcome this gap in the understanding of what genome editing is and what its capabilities are, more research is needed to translate genome-editing discoveries into tools for ecological research. Emerging and future genome-editing technologies include new clustered regularly interspaced short palindromic repeats (CRISPR) targeted sequencing and nucleic acid detection approaches as well as species genetic barcoding and somatic genome-editing technologies. These genome-editing tools have the potential to transform the environmental sciences by providing new noninvasive methods for monitoring threatened species or for enhancing critical adaptive traits. A pioneering effort by the conservation community is required to apply these technologies to real-world conservation problems.Transformación de la Ecología y la Biología de la Conservación por medio de la Edición Genómica Resumen Conforme aumentan los retos de conservación, se necesitan nuevas estrategias para ayudar a combatir las pérdidas de biodiversidad y para disminuir o revertir la declinación de especies. La tecnología de edición genómica está cambiando el rostro de la biología moderna, facilitando aplicaciones que eran inimaginables hace una década. Esta tecnología tiene el potencial de contribuir significativamente en los campos de la biología evolutiva, la ecología y la conservación, aun así, el miedo a las consecuencias accidentales de los ecosistemas planeados que contienen organismos diseñados ha sofocado a la innovación. Para sobreponerse a este vacío en el entendimiento de lo que es la edición genómica y cuáles son sus capacidades se requiere de mayor investigación para traducir los descubrimientos de la edición genómica a herramientas para la investigación ecológica. Las tecnologías de edición genómica emergentes y futuras incluyen nuevas estrategias CRISPR enfocadas en la secuenciación y detección de ácidos nucleicos, así como tecnologías de definición del código de barras genético de las especies y de edición somática de genes. Estas herramientas de edición genómica tienen el potencial para transformar las ciencias ambientales al proporcionar nuevos métodos no invasivos para el monitoreo de especies amenazadas o para mejorar las características adaptativas más importantes. Se requiere de un esfuerzo vanguardista por parte de la comunidad conservadora para aplicar esta tecnología a los problemas de conservación en el mundo real.随着生物多样性保护面临越来越多的挑战, 我们需要新的方法来对抗生物多样性丧失、减缓或逆转受胁迫物种的种群下降。基因组编辑技术推动了十年前人们还无法想象的应用, 正在改变着现代生物学的面貌。这项技术能为进化生物学、生态学和保护生物学领域做出重大贡献。然而, 对含有被工程改造过的生物有机体的生态系统是否会产生意外后果的担忧, 限制了这个方向的创新。为了帮助理解基因组编辑的概念及其功能, 还需要更多的研究将基因组编辑发现转变为生态学研究的工具。新兴及未来的基因组编辑技术包括新的 CRISPR 靶向测序和核酸检测方法、物种遗传条形码和体细胞基因组编辑技术等。这些基因组编辑工具可以通过提供新的非损伤性方法来监测受胁迫物种, 或改进关键的适应性性状, 为环境科学带来重大改变。因此, 要将这些技术应用于现实中的保护问题, 需要保护领域努力进行开拓。【翻译: 胡怡思; 审校: 聂永刚】.

Migratory behaviour patterns in animals are controlled by a complex genetic architecture. Rainbow trout (Oncorhynchus mykiss) is a salmonid fish that spawns in streams but exhibits three primary life history pathways: stream-resident (fluvial), lake-migrant (adfluvial) and ocean-migrant (anadromous). Previous studies examining fluvial and anadromous O. mykiss have identified several genes associated with life history divergence including the presence of an inversion complex within chromosome 5 (Omy05) that appears to maintain a suite of linked genes controlling migratory behaviour. However, adfluvial trout are migratory without being anadromous, and the genetic basis for this life history has not been investigated from evolutionary perspectives. We sampled wild, native nonanadromous rainbow trout occupying connected stream and lake habitats in a southwest Alaskan watershed to determine whether these fish exhibit genetic divergence between fluvial and adfluvial ecotypes, and whether that divergence parallels that documented in fluvial and anadromous O. mykiss. Data from restriction site-associated DNA (RAD) sequencing revealed an association between frequencies of both the Omy05 inversion complex and other single nucleotide polymorphisms (SNPs) with habitat type (stream or lake), supporting the genetic divergence of fluvial and adfluvial individuals in sympatry. The presence of a genetic basis for migration into lakes, analogous to that documented for anadromy, indicates that the adfluvial ecotype must be recognized separately from the fluvial form of O. mykiss even though neither is anadromous. These results highlight the genetic architecture underlying migration and the importance of chromosomal inversions in promoting and sustaining intraspecific diversity.

Natural-origin steelhead trout (Oncorhynchus mykiss (Walbaum, 1792)) in the Pacific Northwest, USA, are threatened by a number of factors including habitat destruction, disease, decline in marine survival, and a potential erosion of genetic viability due to introgression from hatchery strains. Our major goal was to use a recently developed SNP array containing ∼57 000 SNPs to identify a subset of SNPs that differentiate hatchery and natural-origin populations. We analyzed 35 765 polymorphic SNPs in nine populations of steelhead trout sampled from Puget Sound, Washington, USA. We then conducted two outlier tests and found 360 loci that were candidates for divergent selection between hatchery and natural-origin populations (mean FCT = 0.29, maximum = 0.65) and 595 SNPs that were candidates for selection among natural-origin populations (mean FST = 0.25, maximum = 0.51). Comparisons with a linkage map revealed that two chromosomes (Omy05 and Omy25) contained significantly more outliers than other chromosomes, suggesting that regions on Omy05 and Omy25 may be of adaptive significance. Our results highlight several advantages of the 57 000 SNP array as a tool for population and conservation genomics studies.

Pink salmon, the most abundant Pacific salmon, have an obligate 2-year life cycle that leads to reproductively isolated even- and odd-year lineages. Using new and existing data, we examined the genetic structure of both lineages across their distributional range by genotyping 16 681 single-nucleotide polymorphisms for 383 individuals originating from seven pairs of even- and odd-year populations. Distinct differences in standing pools of genetic variation were identified between the lineages; we observed higher levels of heterozygosity, allelic richness, and significantly more private alleles in the odd-year lineage. However, the patterns of population structure were concordant between lineages: the Asian and northern Alaska populations displayed little differentiation but differed significantly from populations in southcentral Alaska and the Pacific Northwest. Our population structure results, in the context of known paleoecological information, suggest that both lineages occupied a northern Beringial refugium as well as a Cascadian refugium in North America during the Last Glacial Maximum. These results highlight the influence of historical patterns of habitat availability on contemporary population structure and support the hypothesis of a pre-glacial origin of the lineages.

Understanding population-specific spawner–recruit relationships is necessary for sustainable salmon management. Where multiple populations are harvested together, run reconstruction methods partition mixed-stock catches and allocate recruits back to their populations of origin. Traditional run reconstruction methods often use age composition data to inform catch partitioning. However age-only methods do not account for stock-specific differences in the availability of fish to harvest within fishing areas or the incidental harvest of nontarget stocks in nearby fishing areas. Advances in molecular genetic techniques permit genetic stock identification (GSI) of both contemporary and historical catch samples. We present a statistical model for salmon run reconstruction that utilizes both age composition and GSI data to estimate differences in the availability of stocks within, and interception rates among, terminal fisheries. When applied to the commercial sockeye salmon (Oncorhynchus nerka) fishery in Bristol Bay, Alaska, new estimates of population productivity differed from those generated using previous age-only methods by 0.1%–155.1%, with stock-specific mean absolute percent differences of 9.7%–38.7% across years, underscoring the value of genetic data for run reconstruction. With more accurate run reconstruction methods, spawner–recruit relationships can be identified more precisely, thus providing more accurate management targets for salmon fisheries.

Different pathways of propagation and dispersal of non‐native species into new environments may have contrasting demographic and genetic impacts on established populations. Repeated introductions of rainbow trout (Oncorhynchus mykiss) to Chile in South America, initially through stocking and later through aquaculture escapes, provide a unique setting to contrast these two pathways. Using a panel of single nucleotide polymorphisms, we found contrasting genetic metrics and patterns among naturalized trout in Lake Llanquihue, Chile's largest producer of salmonid smolts for nearly 50 years, and Lake Todos Los Santos (TLS), a reference lake where aquaculture has been prohibited by law. Trout from Lake Llanquihue showed higher genetic diversity, weaker genetic structure, and larger estimates for the effective number of breeders (Nb) than trout from Lake TLS. Trout from Lake TLS were divergent from Lake Llanquihue and showed marked genetic structure and a significant isolation‐by‐distance pattern consistent with secondary contact between documented and undocumented stocking events in opposite shores of the lake. Multiple factors, including differences in propagule pressure, origin of donor populations, lake geomorphology, habitat quality or quantity, and life history, may help explain contrasting genetic metrics and patterns for trout between lakes. We contend that high propagule pressure from aquaculture may not only increase genetic diversity and Nb via demographic effects and admixture, but also may impact the evolution of genetic structure and increase gene flow, consistent with findings from artificially propagated salmonid populations in their native and naturalized ranges.

A common challenge for fisheries management is resolving the relative contribution of closely related populations where accuracy of genetic assignment may be limited. An overlooked method for increasing assignment accuracy is the use of multi-SNP (single nucleotide polymorphism) haplotypes rather than single-SNP genotypes. Haplotypes increase power for detecting population structure, and loci derived from next-generation sequencing methods often contain multiple SNPs. We evaluated the utility of multi-SNP haplotyping for mixture analysis in western Alaska Chinook salmon (Oncorhynchus tshawytscha). Multi-SNP haplotype data increased the accuracy of mixture analysis for closely related populations by up to seven percentage points relative to single-SNP genotype data for a set of 500 loci; 90% accuracy was achievable with as few as 150 loci with multi-SNP haplotypes but required at least 300 loci with single-SNP genotypes. Individual assignment to reporting groups showed an even greater increase in accuracy of up to 17 percentage points when multi-SNP haplotypes were used. Haplotyping multiple SNPs shows promise to improve the accuracy of assigning unknown fish to population of origin whenever haplotype data are available.

Humans by their very nature alter the distribution of species. Be it introduction of exotic species, habitat alterations or construction of barriers, anthropogenic changes provide novel experimental systems for the molecular ecologist to study evolutionary change. These events often provide a contradiction. Effective population sizes are generally low, and introduced populations are typically characterized by reduced diversity consistent with theoretical predictions of population bottlenecks and founder effects. However, despite reduced diversity, rapid change sometimes occurs. Identification of genomic regions associated with these rapid adaptive responses to novel selection pressures provides a window into genomic regions important in adaptive diversity, both in the novel and native ranges. These studies also provide an important means to estimate the pace of evolutionary change. In this issue, Willoughby et al. () compared the heterozygosity of steelhead (the anadromous form of rainbow trout Oncorhynchus mykiss) introduced into Lake Michigan in the late 1880s to the putative source population from the ancestral California range. After 25 generations of isolation in Lake Michigan, Willoughby et al. () found consistent genomewide reductions in genetic diversity as estimated by a measure of pooled heterozygosity. Despite this overall reduction in heterozygosity, three chromosomal regions showed signals of rapid adaptation and contained genes associated with osmoregulatory and wound-healing functions.

Invasive species with migratory behavior and complex life cycle represent a challenge for evaluating natal sites among individuals. Private and government-sponsored initiatives resulted in the successful introduction and naturalization of Chinook salmon (Oncorhynchus tshawytscha) throughout northern and southern Patagonia in South America. These migratory fish breed in freshwater, but spend most of their life at sea feeding, forming abundant populations in several watersheds draining into the southeast Pacific Ocean. We used single nucleotide polymorphisms (SNPs) combined with genetic structure and mixed-stock analyses to evaluate natal sites of Chinook salmon at-sea caught in one estuary and two coastal locations compared to reference populations from breeding sites in freshwater. Firstly, Bayesian individual-assignment analyses revealed no genetic structure among adults caught off the coast of the Toltén River and migrating (maturing) adults caught in Toltén River estuary, suggesting they likely belong to a single population. Secondly, mixed-stock genetic analyses revealed that most at-sea Chinook salmon caught in one estuary and two coastal locations likely originated from spawners from the nearest river (90-95%), with a small contribution from adjacent watersheds (5-10%). This appears consistent with Chinook salmon populations in their native range in which juveniles migrate short distances (100-200 km) from their river of origin to coastal feeding grounds, some of which became donor of propagules for non-native Chinook salmon populations under study. Mixed-stock genetic analyses provide considerable potential to identify the population of origin of Chinook salmon mixtures caught off the coast. They also seem an appropriate proof of concept to help identify potential immigrants from other watersheds as well as migration patterns and invasion pathways in a non-native species.

Many studies exclude loci exhibiting linkage disequilibrium (LD); however, high LD can signal reduced recombination around genomic features such as chromosome inversions or sex-determining regions. Chromosome inversions and sex-determining regions are often involved in adaptation, allowing for the inheritance of co-adapted gene complexes and for the resolution of sexually antagonistic selection through sex-specific partitioning of genetic variants. Genomic features such as these can escape detection when loci with LD are removed; in addition, failing to account for these features can introduce bias to analyses. We examined patterns of LD using network analysis to identify an overlapping chromosome inversion and sex-determining region in chum salmon. The signal of the inversion was strong enough to show up as false population substructure when the entire dataset was analyzed, while the signal of the sex-determining region was only obvious after restricting genetic analysis to the sex chromosome. Understanding the extent and geographic distribution of inversions is now a critically important part of genetic analyses of natural populations. The results of this study highlight the importance of analyzing and understanding patterns of LD in genomic dataset and the perils of ignoring or excluding loci exhibiting LD.

Whole genome duplications have occurred in the recent ancestors of many plants, fish, and amphibians, resulting in a pervasiveness of paralogous loci and the potential for both disomic and tetrasomic inheritance in the same genome. Paralogs can be difficult to reliably genotype and are often excluded from genotyping-by-sequencing (GBS) analyses; however, removal requires paralogs to be identified which is difficult without a reference genome. We present a method for identifying paralogs in natural populations by combining two properties of duplicated loci: 1) the expected frequency of heterozygotes exceeds that for singleton loci, and 2) within heterozygotes, observed read ratios for each allele in GBS data will deviate from the 1:1 expected for singleton (diploid) loci. These deviations are often not apparent within individuals, particularly when sequence coverage is low; but, we postulated that summing allele reads for each locus over all heterozygous individuals in a population would provide sufficient power to detect deviations at those loci. We identified paralogous loci in three species: Chinook salmon (Oncorhynchus tshawytscha) which retains regions with ongoing residual tetrasomy on eight chromosome arms following a recent whole genome duplication, mountain barberry (Berberis alpina) which has a large proportion of paralogs that arose through an unknown mechanism, and dusky parrotfish (Scarus niger) which has largely re-diploidized following an ancient whole genome duplication. Importantly, this approach only requires the genotype and allele-specific read counts for each individual, information which is readily obtained from most GBS analysis pipelines. This article is protected by copyright. All rights reserved.

Loci that can be used to screen for sex in salmon can provide important information for study of both wild and cultured populations. Here, we tested for associations between sex and genotypes at thousands of loci available from a genotyping-by-sequencing (GBS) dataset to discover sex-associated loci in sockeye salmon (Oncorhynchus nerka). We discovered 7 sex-associated loci, developed high-throughput assays for 2 loci, and tested the utility of these 2 assays in 8 collections of sockeye salmon sampled throughout North America. We also screened an existing assay based on the master sex-determining gene in salmon (sdY) in these collections. The ability of GBS-derived loci to assign fish to their phenotypic sex varied substantially among collections suggesting that recombination between the loci that we discovered and the sex-determining gene has occurred. Assignment accuracy to phenotypic sex was much higher with the sdY assay but was still less than 100%. Alignment of sequences from GBS-derived loci to draft genomes for 2 salmonids provided strong evidence that many of these loci are found on chromosomes orthologous to the known sex chromosome in sockeye salmon. Our study is the first to describe the approximate location of the sex-determining region in sockeye salmon and indicates that sdY is also the master sex-determining gene in this species. However, discordances between sdY genotypes and phenotypic sex and the variable performance of GBS-derived loci warrant more research.

Local adaptation to heterogeneous environments generates population diversity within species, significantly increasing ecosystem stability and flows of ecosystem services. However, few studies have isolated the specific mechanisms that create and maintain this diversity. Here, we examined the relationship between water temperature in streams used for spawning and genetic diversity at a gene involved in immune function [the major histocompatibility complex (MHC)] in 14 populations of sockeye salmon (Oncorhynchus nerka) sampled across the Wood River basin in south-western Alaska. The largest influence on MHC diversity was lake basin, but we also found a significant positive correlation between average water temperature and MHC diversity. This positive relationship between temperature and MHC diversity appears to have been produced by natural selection at very local scales rather than neutral processes, as no correlation was observed between temperature and genetic diversity at 90 neutral markers. Additionally, no significant relationship was observed between temperature variability and MHC diversity. Although lake basin was the largest driver of differences in MHC diversity, our results also demonstrate that fine-scale differences in water temperature may generate variable selection regimes in populations that spawn in habitats separated by as little as 1 km. Additionally, our results indicated that some populations may be reaching a maximum level of MHC diversity. We postulate that salmon from populations in warm streams may delay spawning until late summer to avoid thermal stress as well as the elevated levels of pathogen prevalence and virulence associated with warm temperatures earlier in the summer.

Preservation of heritable ecological diversity within species and populations is a key challenge for managing natural resources and wild populations. Salmonid fish are iconic and socio-economically important species for commercial, aquaculture, and recreational fisheries across the globe. Many salmonids are known to exhibit ecological divergence within species, including distinct feeding ecotypes within the same lakes. Here we used 5559 SNPs, derived from RAD sequencing, to perform population genetic comparisons between two dietary ecotypes of sockeye salmon (Oncorhynchus nerka) in Jo-Jo Lake, Alaska (USA). We tested the standing hypothesis that these two ecotypes are currently diverging as a result of adaptation to distinct dietary niches; results support earlier conclusions of a single panmictic population. The RAD sequence data revealed 40 new SNPs not previously detected in the species, and our sequence data can be used in future studies of ecotypic diversity in salmonid species.

Understanding the genetic mechanisms that facilitate adaptive radiation is an important component of evolutionary biology. Here, we genotyped 82 neutral SNPs, seven SNPs in islands of divergence identified in a previous study (island SNPs), and a region of the major histocompatibility complex (MHC) in 32 populations of sockeye salmon to investigate whether conserved genes and genomic regions are involved in adaptive radiation. Populations representing three ecotypes were sampled from seven drainages with differing habitats and colonization histories spanning a range of 2,000 km. We found strong signatures of parallel selection across drainages at the island SNPs and MHC, suggesting that the same loci undergo divergent selection during adaptive radiation. However, patterns of differentiation at most island SNPs and the MHC were not associated with ecotypes, suggesting that these loci are responding differently to a mosaic of selective pressures. Our study provides some of the first evidence that conserved genomic islands may be involved in adaptive divergence of salmon populations. Additionally, our data provide further support for the hypothesis that sockeye salmon inhabiting rivers unconnected to lakes harbour similar genetic diversity across large distances, are likely the ancestral form of the species, and have repeatedly recolonized lake systems as they have become available after glacial recession. Finally, our results highlight the value and importance of validating outlier loci by screening additional populations and regions, a practice that will hopefully become more common in the future.

Genetics data have provided unprecedented insights into evolutionary aspects of colonization by non-native populations. Yet, our understanding of how artificial (human-mediated) and natural dispersal pathways of non-native individuals influence genetic metrics, evolution of genetic structure, and admixture remains elusive. We capitalize on the widespread colonization of Chinook salmon Oncorhynchus tshawytscha in South America, mediated by both dispersal pathways, to address these issues using data from a panel of polymorphic SNPs. First, genetic diversity and the number of effective breeders (Nb) were higher among artificial than natural populations. Contemporary gene flow was common between adjacent artificial and natural and adjacent natural populations, but uncommon between geographically distant populations. Second, genetic structure revealed four distinct clusters throughout the Chinook salmon distributional range with varying levels of genetic connectivity. Isolation by distance resulted from weak differentiation between adjacent artificial and natural and between natural populations, with strong differentiation between distant Pacific Ocean and Atlantic Ocean populations, which experienced strong genetic drift. Third, genetic mixture analyses revealed the presence of at least six donor geographic regions from North America, some of which likely hybridized as a result of multiple introductions. Relative propagule pressure or the proportion of Chinook salmon propagules introduced from various geographic regions according to government records significantly influenced genetic mixtures for two of three artificial populations. Our findings support a model of colonization in which high-diversity artificial populations established first; some of these populations exhibited significant admixture resulting from propagule pressure. Low-diversity natural populations were likely subsequently founded from a reduced number of individuals. Fil: Gomez Uchida, Daniel. Núcleo Milenio Invasal; Chile. Universidad de Concepción; Chile Fil: Cañas Rojas, Diego. Núcleo Milenio Invasal; Chile. Universidad de Concepción; Chile Fil: Riva Rossi, Carla Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Diversidad y Evolución Austral; Argentina Fil: Ciancio Blanc, Javier Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina Fil: Pascual, Miguel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina Fil: Ernst, Billy. Universidad de Concepción; Chile. Núcleo Milenio Invasal; Chile Fil: Aedo, Eduardo. Universidad Austral de Chile; Chile Fil: Musleh, Selim S.. Universidad de Concepción; Chile. Núcleo Milenio Invasal; Chile Fil: Valenzuela Aguayo, Francisca. Universidad de Concepción; Chile Fil: Quinn, Thomas P.. Núcleo Milenio Invasal; Chile. University of Washington; Estados Unidos Fil: Seeb, James E.. Núcleo Milenio Invasal; Chile. University of Washington; Estados Unidos Fil: Seeb, Lisa W.. Núcleo Milenio Invasal; Chile. University of Washington; Estados Unidos

We examined genetic diversity patterns among 55 collections of Chum Salmon from the northeastern Pacific Ocean using 89 single nucleotide polymorphisms (SNPs). The distribution of Chum Salmon samples extended from the Nass River along the coast of British Columbia and along the coast of Washington as far south as the Columbia River. Chum Salmon represented three previously defined run-groups: fall (primarily), summer, and winter. Genetic variation at SNP loci, as measured by FST, ranged from 0.002 to 0.279 over all collections and averaged 0.062 over all loci. Similar to the genetic patterns detected with microsatellites and allozymes, genetic variation followed a regional structure along geographic distance, with genetic diversity being highest in the north and decreasing southward, then increasing in and near the Columbia River. Within Puget Sound, Washington, genetic variation was structured further according to run timing (fall, summer, and winter) and shared ancestry. Simulations indicated th...

Meiotic recombination is fundamental for generating new genetic variation and for securing proper disjunction. Further, recombination plays an essential role during the rediploidization process of polyploid-origin genomes because crossovers between pairs of homeologous chromosomes retain duplicated regions. A better understanding of how recombination affects genome evolution is crucial for interpreting genomic data; unfortunately, current knowledge mainly originates from a few model species. Salmonid fishes provide a valuable system for studying the effects of recombination in nonmodel species. Salmonid females generally produce thousands of embryos, providing large families for conducting inheritance studies. Further, salmonid genomes are currently rediploidizing after a whole genome duplication and can serve as models for studying the role of homeologous crossovers on genome evolution. Here, we present a detailed interrogation of recombination patterns in sockeye salmon (Oncorhynchus nerka). First, we use RAD sequencing of haploid and diploid gynogenetic families to construct a dense linkage map that includes paralogous loci and location of centromeres. We find a nonrandom distribution of paralogs that mainly cluster in extended regions distally located on 11 different chromosomes, consistent with ongoing homeologous recombination in these regions. We also estimate the strength of interference across each chromosome; results reveal strong interference and crossovers are mostly limited to one per arm. Interference was further shown to continue across centromeres, but metacentric chromosomes generally had at least one crossover on each arm. We discuss the relevance of these findings for both mapping and population genomic studies.

Whole-genome duplications have occurred in the recent ancestors of many plants, fish and amphibians. Signals of these whole-genome duplications still exist in the form of paralogous loci. Recent advances have allowed reliable identification of paralogs in genotyping-by-sequencing (GBS) data such as that generated from restriction-site-associated DNA sequencing (RADSeq); however, excluding paralogs from analyses is still routine due to difficulties in genotyping. This exclusion of paralogs may filter a large fraction of loci, including loci that may be adaptively important or informative for population genetic analyses. We present a maximum-likelihood method for inferring allele dosage in paralogs and assess its accuracy using simulated GBS, empirical RADSeq and amplicon sequencing data from Chinook salmon. We accurately infer allele dosage for some paralogs from a RADSeq data set and show how accuracy is dependent upon both read depth and allele frequency. The amplicon sequencing data set, using RADSeq-derived markers, achieved sufficient depth to infer allele dosage for all paralogs. This study demonstrates that RADSeq locus discovery combined with amplicon sequencing of targeted loci is an effective method for incorporating paralogs into population genetic analyses.

Different pathways of propagation and dispersal of non‐native species into new environments may have contrasting demographic and genetic impacts on established populations. Repeated introductions of rainbow trout (Oncorhynchus mykiss) to Chile in South America, initially through stocking and later through aquaculture escapes, provide a unique setting to contrast these two pathways. Using a panel of single nucleotide polymorphisms, we found contrasting genetic metrics and patterns among naturalized trout in Lake Llanquihue, Chile's largest producer of salmonid smolts for nearly 50 years, and Lake Todos Los Santos (TLS), a reference lake where aquaculture has been prohibited by law. Trout from Lake Llanquihue showed higher genetic diversity, weaker genetic structure, and larger estimates for the effective number of breeders (N b) than trout from Lake TLS. Trout from Lake TLS were divergent from Lake Llanquihue and showed marked genetic structure and a significant isolation‐by‐distance pattern consistent with secondary contact between documented and undocumented stocking events in opposite shores of the lake. Multiple factors, including differences in propagule pressure, origin of donor populations, lake geomorphology, habitat quality or quantity, and life history, may help explain contrasting genetic metrics and patterns for trout between lakes. We contend that high propagule pressure from aquaculture may not only increase genetic diversity and N b via demographic effects and admixture, but also may impact the evolution of genetic structure and increase gene flow, consistent with findings from artificially propagated salmonid populations in their native and naturalized ranges.

Puritz et al. provide a review of several RADseq methodological approaches in response to our 'Population Genomic Data Analysis' workshop (Sept 2013) review (Andrews & Luikart 2014). We agree with Puritz et al. on the importance for researchers to thoroughly understand RADseq library preparation and data analysis when choosing an approach for answering their research questions. Some of us are currently using multiple RADseq protocols, and we agree that the different methods may offer advantages in different cases. Our workshop review did not intend to provide a thorough review of RADseq because the workshop covered a broad range of topics within the field of population genomics. Similarly, neither the response of Puritz et al. nor our comments here provide sufficient space to thoroughly review RADseq. Nonetheless, here we address some key points that we find unclear or potentially misleading in their evaluation of techniques.

We estimated the genetic structure and diversity of Japanese Chum Salmon Oncorhynchus keta populations using single-nucleotide polymorphism (SNP) markers to support the management and assessment of the Japanese salmon hatchery program. A total of 5,571 individuals from 57 Japanese Chum Salmon populations were genotyped with 52 markers. A neighbor-joining tree, principal coordinate analysis, analysis of molecular variance, and average pairwise FST values indicated the existence of eight regional groups, six in Hokkaido and two in Honshu. Weak but significant isolation by distance was found within the populations of Hokkaido and the Pacific Ocean coast of Honshu. These results suggest that the genetic differentiation among the eight regional groups is small but distinct and occurred through low or restricted gene flow. Furthermore, our results also suggest the persistence of the historical genetic structure (or remnants of it) in extant populations in Japan despite the operation of a hatchery progra...

Members of the genus Salvelinus often occur sympatrically, exhibit a high degree of phenotypic plasticity, and commonly hybridize. These factors often complicate species identification and hybrid detection based solely on morphology. Many species and populations of Salvelinus are threatened or endangered and accurate species identification and hybrid detection are important for conservation. Single nucleotide polymorphism (SNP) markers offer several advantages over other classes of genetic markers for species identification. We used DNA sequences from six species of Salvelinus to identify 16 SNPs that exhibited fixed differences among species and 16 additional SNPs that were variable within different species. These markers were used for species identification of putative Bull Trout Salvelinus confluentus that were misidentified as Lake Trout S. namaycush in a recreational fishery in Lake Pend Oreille, Idaho. The markers developed in this study will be useful for Salvelinus species identification a...

The emerging field of next-generation sequencing (NGS) is rapidly expanding capabilities for cutting edge genomic research, with applications that can help meet marine conservation challenges of food security, biodiversity loss, and climate change. Navigating the use of these tools, however, is complex at best. Furthermore, applications of marine genomic questions are limited in developing nations where both marine biodiversity and threats to marine biodiversity are most concentrated. This is particularly true in Southeast Asia. The first Pan-Pacific Advanced Studies Institute (PacASI) entitled "Genomic Applications to Marine Science and Resource Management in Southeast Asia" was held in July 2012 in Dumaguete, Philippines, with the intent to draw together leading scientists from both sides of the Pacific Ocean to understand the potential of NGS in helping address the aforementioned challenges. Here we synthesize discussions held during the PacASI to provide perspectives and guidance to help scientists new to NGS choose among the variety of available advanced genomic methodologies specifically for marine science questions.

Numerous empirical studies have reported lack of migration–drift equilibrium in wild populations. Determining the causes of nonequilibrium population structure is challenging because different evolutionary processes acting at a variety of spatiotemporal scales can produce similar patterns. Studies of contemporary populations in northern latitudes suggest that nonequilibrium population structure is probably caused by recent colonization of the region after the last Pleistocene ice age ended ~13 000 years ago. The chum salmon's (Oncorhynchus keta) range was fragmented by dramatic environmental changes during the Pleistocene. We investigated the population structure of chum salmon on the North Alaska Peninsula (NAP) and, using both empirical data and simulations, evaluated the effects of colonization timing and founder population heterogeneity on patterns of genetic differentiation. We screened 161 single nucleotide polymorphisms and found evidence of nonequilibrium population structure when the slope of the isolation-by-distance relationship was examined at incremental spatial scales. In addition, simulations suggested that this pattern closely matched models of recent colonization of the NAP by secondary contact. Our results agree with geological and archaeological data indicating that the NAP was a dynamic landscape that may have been more recently colonized than during the last deglaciation because of dramatic changes in coastal hydrology over the last several thousand years.

A whole genome duplication (WGD) doubles the entire genomic content of a species and is thought to have catalyzed adaptive radiation in some polyploid-origin lineages. However, little is known about general consequences of a WGD since gene duplicates (i.e. paralogs) are commonly filtered in genomic studies; such filtering may remove substantial portions of the genome in data sets from polyploid-origin species. We demonstrate a new method that enables genome-wide scans for signatures of selection at both non-duplicated and duplicated loci by taking locus-specific copy number into account. We apply this method to RAD sequence data from different ecotypes of a polyploid-origin salmonid (Oncorhynchus nerka) and reveal signatures of divergent selection that would have been missed if duplicated loci were filtered. We also find conserved signatures of elevated divergence at pairs of homeologous chromosomes with residual tetrasomic inheritance suggesting that joint evolution of some non-diverged gene duplicates may affect the adaptive potential of these genes. These findings illustrate that including duplicated loci in genomic analyses enables novel insights into the evolutionary consequences of WGDs and local segmental gene duplications. This article is protected by copyright. All rights reserved.

Whole-genome duplications are major evolutionary events with a lasting impact on genome structure. Duplication events complicate genetic analyses as paralogous sequences are difficult to distinguish; consequently, paralogs are often excluded from studies. The effects of an ancient whole-genome duplication (approximately 88 MYA) are still evident in salmonids through the persistence of numerous paralogous gene sequences and partial tetrasomic inheritance. We use restriction site-associated DNA sequencing on 10 collections of chum salmon from the Salish Sea in the USA and Canada to investigate genetic diversity and population structure in both tetrasomic and rediploidized regions of the genome. We use a pedigree and high-density linkage map to identify paralogous loci and to investigate genetic variation across the genome. By applying multivariate statistical methods, we show that it is possible to characterize paralogous loci and that they display similar patterns of population structure as the diploidized portion of the genome. We find genetic associations with the adaptively important trait of run-timing in both sets of loci. By including paralogous loci in genome scans, we can observe evolutionary signals in genomic regions that have routinely been excluded from population genetic studies in other polyploid-derived species.

In their recently corrected manuscript, "Breaking RAD: An evaluation of the utility of restriction site associated DNA sequencing for genome scans of adaptation", Lowry et al. argue that genome scans using RADseq will miss many loci under selection due to a combination of sparse marker density and low levels of linkage disequilibrium in most species. We agree that marker density and levels of LD are important considerations when designing a RADseq study; however, we dispute that RAD-based genome scans are as prone to failure as Lowry et al. suggest. Their arguments ignore the flexible nature of RADseq; the availability of different restriction enzymes and capacity for combining restriction enzymes ensures that a well-designed study should be able to generate enough markers for efficient genome coverage. We further believe that simplifying assumptions about linkage disequilibrium in their simulations are invalid in many species. Finally, it is important to note that the alternative methods proposed by Lowry et al. have limitations equal to or greater than RADseq. The wealth of studies with positive impactful findings that have used RAD genome scans instead supports the argument that properly conducted RAD genome scans are an effective method for gaining insight into ecology and evolution, particularly for non-model organisms and those with large or complex genomes.

Identifying the spatial distribution of genetic variation across the landscape is an essential step in informing species conservation. Comparison of closely related and geographically overlapping species can be particularly useful in cases where landscape may similarly influence genetic structure. Congruent patterns among species highlight the importance that landscape heterogeneity plays in determining genetic structure whereas contrasting patterns emphasize differences in species-specific ecology and life-history or the importance of species-specific adaptation to local environments. We examined the interacting roles of demography and adaptation in determining spatial genetic structure in two closely related and geographically overlapping species in a pristine environment. Using single nucleotide polymorphism (SNP) loci exhibiting both neutral and putative adaptive variation, we evaluated the genetic structure of sockeye salmon in the Copper River, Alaska; these data were compared to existing data for Chinook salmon from the same region. Overall, both species exhibited patterns of isolation by distance; the spatial distribution of populations largely determined the distribution of genetic variation across the landscape. Further, both species exhibited largely congruent patterns of within- and among-population genetic diversity, highlighting the role that landscape heterogeneity and historical processes play in determining spatial genetic structure. Potential adaptive differences among geographically proximate sockeye salmon populations were observed when high FST outlier SNPs were evaluated in a landscape genetics context. Results were evaluated in the context of conservation efforts with an emphasis on reproductive isolation, historical processes, and local adaptation.

We genotyped nuclear and mitochondrial single nucleotide polymorphisms (SNPs) in six paired archived and contemporary collections of Alaskan sockeye salmon ( Oncorhynchus nerka ) to evaluate the stability of allele frequencies over 25–42 years (4.9–8.4 generations). First, our results show that temporal changes were dramatically (between 40- and 250-fold) smaller than spatial differences in allele frequencies when based on nuclear SNPs. Second, the magnitude of temporal change was consistent with a model of genetic drift: (i) SNPs with high levels of differentiation (large θ) and candidates for diversifying selection were not more likely to show significant temporal changes than small-θ SNPs; and (ii) the fraction of single-locus significant tests was consistent with theoretical predictions relating sample size and the annual number of breeders (Nb). Third, estimates of Nbwere bound by infinitely large upper 95% confidence intervals, except for one paired collection with unique life-history attributes of both a smoltification phase and generation time shorter than the other paired collections. Use of multigenerational SNP data sets seems a safe practice in management of Alaska sockeye salmon that could be extended to other large, wild aquatic populations.

Recent advances in molecular interrogation techniques now allow unprecedented genomic inference about the role of adaptive genetic divergence in wild populations. We used high-throughput genotyping to screen a genome-wide panel of 276 single nucleotide polymorphisms (SNPs) for the economically and culturally important salmonid Oncorhynchus mykiss. Samples included 805 individuals from 11 anadromous and resident populations from the northwestern United States and British Columbia, and represented two major lineages including paired populations of each life history within single drainages of each lineage. Overall patterns of variation affirmed clear distinctions between lineages and in most instances, isolation by distance within them. Evidence for divergent selection at eight candidate loci included significant landscape correlations, particularly with temperature. High diversity of two nonsynonymous mutations within the peptide-binding region of the major histocompatibility complex (MHC) class II (DAB) gene provided signatures of balancing selection. Weak signals for potential selection between sympatric resident and anadromous populations were revealed from genome scans and allele frequency comparisons. Our results suggest an important adaptive role for immune-related functions and present a large genomic resource for future studies

Lacustrine sockeye salmon (Oncorhynchus nerka) are listed as an endangered species in Japan despite little genetic information on their population structure. In order to clarify the genetic diversity and structure of Japanese populations for evaluating on the bottleneck effect and an endangered species, we analyzed the ND5 region of mitochondrial DNA (mtDNA) and 45 single nucleotide polymorphisms (SNPs) in 640 lacustrine sockeye salmon in Japan and 80 anadromous sockeye salmon in Iliamna Lake of Alaska. The genetic diversity of the Japanese population in both mtDNA and SNPs was significantly less than that of the Iliamna Lake population. Moreover, all Japanese populations had SNP loci deviating from the HWE. In spite of low genetic diversity, the SNP analyses resulted that the Japanese population was significantly divided into three groups. These suggest that Japanese sockeye salmon populations should be protected as an endangered species and genetically disturbed by the hatchery program and transplantations.

We estimate patterns of nearshore migration in the eastern Bering Sea for out-migrating Bristol Bay sockeye salmon Oncorhynchus nerka in their first year at sea. Over 3,000 juveniles were collected during the late summer of 2005–2007 as part of the Bering–Aleutian Salmon International Survey and tested with a regional genetic baseline of 45 single-nucleotide polymorphisms. Population-specific and westward migrations from natal rivers were evident. Populations from Wood River and northwestward predominated in the northern latitudes of Bristol Bay and the eastern Bering Sea and populations from the Egegik River and southwestward in the southern latitudes, while the populations spawning at the head of Bristol Bay had the highest proportions in the middle latitudes. These patterns were stable across years, apparently unaffected by marine productivity and temperature. This continuum of marine migratory patterns most likely reflects stable and population-specific adaptations to buffer the distribution ...

The strict homing of sockeye salmon Oncorhynchus nerka results in reproductively isolated populations that often spawn in close proximity and share rearing habitat. High spawning fidelity enables these populations to adapt to local conditions, resulting in a wide range of life history characteristics and genetic variation within individual watersheds. The Wood River system in southwestern Alaska provides a pristine, well-studied system in which to examine fine-scale population structure and its influences on juvenile life histories. Adult sockeye salmon spawn in lake beaches, rivers, and small tributaries throughout this watershed, and juveniles rear in five nursery lakes. We genotyped 30 spawning populations and 6,066 migrating smolts at 45 single nucleotide polymorphism loci, two of which are candidates for positive selection in the study system. We show that there is significant genetic structure (F ST = 0.032) in the Wood River lakes and that divergence is generally related to spawning rather...

We establish a TaqMan-based assay panel for genotyping single-nucleotide polymorphisms in rainbow trout and steelhead (Oncorhynchus mykiss). We develop 22 novel single-nucleotide polymorphism markers based on new steelhead sequence data and on assays from sister taxa. Additionally, we adapt 154 previously developed markers to the TaqMan platform. At the beginning of this study, 59 SNPs with TaqMan assays were available to the scientific community. By adding 176 additional TaqMan assays to this number, we greatly expand the biological applications of TaqMan genotyping within both population genetics and quantitative genetics.

Incorporating historical tissues into the study of ecological, conservation and management questions can broaden the scope of population genetic research by enhancing our understanding of evolutionary processes and anthropogenic influences on natural populations. Genotyping historical and low-quality samples has been plagued by challenges associated with low amounts of template DNA and the potential for pre-existing DNA contamination among samples. We describe a two-step process designed to (i) accurately genotype large numbers of historical low-quality scale samples in a high-throughput format and (ii) screen samples for pre-existing DNA contamination. First, we describe how an efficient multiplex preamplification PCR of 45 single nucleotide polymorphisms (SNPs) can generate highly accurate genotypes with low failure and error rates in subsequent SNP genotyping reactions of individual historical scales from sockeye salmon (Oncorhynchus nerka). Second, we demonstrate how the method can be modified for the amplification of microsatellite loci to detect pre-existing DNA contamination. A total of 760 individual historical scale and 182 contemporary fin clip samples were genotyped and screened for contamination. Genotyping failure and error rates were exceedingly low and similar for both historical and contemporary samples. Pre-existing contamination in 21% of the historical samples was successfully identified by screening the amplified microsatellite loci. The advantages of automation, low failure and error rates, and ability to multiplex both the preamplification and subsequent genotyping reactions combine to make the protocol ideally suited for efficiently genotyping large numbers of potentially contaminated low-quality sources of DNA.

How practical is gene and SNP discovery in a nonmodel species using short read sequences? Next-generation sequencing technologies are being applied to an increasing number of species with no reference genome. For nonmodel species, the cost, availability of existing genetic resources, genome complexity and the planned method of assembly must all be considered when selecting a sequencing platform. Our goal was to examine the feasibility and optimal methodology for SNP and gene discovery in the sockeye salmon (Oncorhynchus nerka) using short read sequences. SOLiD short reads (up to 50 bp) were generated from single- and pooled-tissue transcriptome libraries from ten sockeye salmon. The individuals were from five distinct populations from the Wood River Lakes and Mendeltna Creek, Alaska. As no reference genome was available for sockeye salmon, the SOLiD sequence reads were assembled to publicly available EST reference sequences from sockeye salmon and two closely related species, rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar). Additionally, de novo assembly of the SOLiD data was carried out, and the SOLiD reads were remapped to the de novo contigs. The results from each reference assembly were compared across all references. The number and size of contigs assembled varied with the size reference sequences. In silico SNP discovery was carried out on contigs from all four EST references; however, discovery of valid SNPs was most successful using one of the two conspecific references.

Most information about Chinook salmon genetic diversity and life history originates from studies from the West Coast USA, western Canada and southeast Alaska; less is known about Chinook salmon from western and southcentral Alaska drainages. Populations in this large area are genetically distinct from populations to the south and represent an evolutionary legacy of unique genetic, phenotypic and life history diversity. More genetic information is necessary to advance mixed stock analysis applications for studies involving these populations. We assembled a comprehensive, open-access baseline of 45 single nucleotide polymorphisms (SNPs) from 172 populations ranging from Russia to California. We compare SNP data from representative populations throughout the range with particular emphasis on western and southcentral Alaska. We grouped populations into major lineages based upon genetic and geographic characteristics, evaluated the resolution for identifying the composition of admixtures and performed mixed stock analysis on Chinook salmon caught incidentally in the walleye pollock fishery in the Bering Sea. SNP data reveal complex genetic structure within Alaska and can be used in applications to address not only regional issues, but also migration pathways, bycatch studies on the high seas, and potential changes in the range of the species in response to climate change.

Because of their high variability, microsatellites are still considered the marker of choice for studies on parentage and kinship in wild populations. Nevertheless, single nucleotide polymorphisms (SNPs) are becoming increasing popular in many areas of molecular ecology, owing to their high-throughput, easy transferability between laboratories and low genotyping error. An ongoing discussion concerns the relative power of SNPs compared to microsatellites-that is, how many SNP loci are needed to replace a panel of microsatellites? Here, we evaluate the assignment power of 80 SNPs (H(E) = 0.30, 80 independent alleles) and 11 microsatellites (H(E) = 0.85, 192 independent alleles) in a wild population of about 400 sockeye salmon with two commonly used software packages (Cervus3, Colony2) and, for SNPs only, a newly developed software (SNPPIT). Assignment success was higher for SNPs than for microsatellites, especially for parent pairs, irrespective of the method used. Colony2 assigned a larger proportion of offspring to at least one parent than the other methods, although Cervus and SNPPIT detected more parent pairs. Identification of full-sib groups without parental information from relatedness measures was possible using both marker systems, although explicit reconstruction of such groups in Colony2 was impossible for SNPs because of computation time. Our results confirm the applicability of SNPs for parentage analyses and refute the predictability of assignment success from the number of independent alleles.