Signals of heterogeneous selection at an MHC locus in geographically proximate ecotypes of sockeye salmon.

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Signals of heterogeneous selection at an MHC locus in geographically proximate ecotypes of sockeye salmon.

Mol Ecol. 2014 Oct 5;

Authors: Larson WA, Seeb JE, Dann TH, Schindler DE, Seeb LW

Abstract
The genes of the major histocompatibility complex (MHC) are an important component of the vertebrate immune system and can provide insights into the role of pathogen-mediated selection in wild populations. Here we examined variation at the MHC class II peptide binding region in 27 populations of sockeye salmon (Oncorhynchus nerka), distributed among three distinct spawning ecotypes, from a complex of interconnected rivers and lakes in southwestern Alaska. We also obtained genotypes from 90 putatively neutral SNPs for each population to compare the relative roles of demography and selection in shaping the observed MHC variation. We found that MHC divergence was generally partitioned by spawning ecotype (lake beaches, rivers, and streams) and was 30 times greater than variation at neutral markers. Additionally, we observed substantial differences in modes of selection and diversity among ecotypes, with beach populations displaying higher levels of directional selection and lower MHC diversity than the other two ecotypes. Finally, the level of MHC differentiation in our study system was comparable to that observed over much larger geographic ranges, suggesting that MHC variation does not necessarily increase with increasing spatial scale and may instead be driven by fine-scale differences in pathogen communities or pathogen virulence. The low levels of neutral structure and spatial proximity of populations in our study system indicates that MHC differentiation can be maintained through strong selective pressure even when ample opportunities for gene flow exist. This article is protected by copyright. All rights reserved.

PMID: 25283474 [PubMed – as supplied by publisher]

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Detection and mapping of QTL for temperature tolerance and body size in Chinook salmon (Oncorhynchus tshawytscha) using genotyping by sequencing.

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Detection and mapping of QTL for temperature tolerance and body size in Chinook salmon (Oncorhynchus tshawytscha) using genotyping by sequencing.

Evol Appl. 2014 Apr;7(4):480-92

Authors: Everett MV, Seeb JE

Abstract
Understanding how organisms interact with their environments is increasingly important for conservation efforts in many species, especially in light of highly anticipated climate changes. One method for understanding this relationship is to use genetic maps and QTL mapping to detect genomic regions linked to phenotypic traits of importance for adaptation. We used high-throughput genotyping by sequencing (GBS) to both detect and map thousands of SNPs in haploid Chinook salmon (Oncorhynchus tshawytscha). We next applied this map to detect QTL related to temperature tolerance and body size in families of diploid Chinook salmon. Using these techniques, we mapped 3534 SNPs in 34 linkage groups which is consistent with the haploid chromosome number for Chinook salmon. We successfully detected three QTL for temperature tolerance and one QTL for body size at the experiment-wide level, as well as additional QTL significant at the chromosome-wide level. The use of haploids coupled with GBS provides a robust pathway to rapidly develop genomic resources in nonmodel organisms; these QTL represent preliminary progress toward linking traits of conservation interest to regions in the Chinook salmon genome.

PMID: 24822082 [PubMed]

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Parallel signatures of selection in temporally-isolated lineages of pink salmon.

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Parallel signatures of selection in temporally-isolated lineages of pink salmon.

Mol Ecol. 2014 Apr 25;

Authors: Seeb LW, Waples RK, Limborg MT, Warheit KI, Pascal CE, Seeb JE

Abstract
Studying the effect of similar environments on diverse genetic backgrounds has long been a goal of evolutionary biologists with studies typically relying on experimental approaches. Pink salmon, a highly-abundant and widely-ranging salmonid, provide a naturally-occurring opportunity to study the effects of similar environments on divergent genetic backgrounds due to a strict two-year semelparous life-history. The species is composed of two reproductively-isolated lineages with overlapping ranges that share the same spawning and rearing environments in alternate years. We used restriction site-associated DNA (RAD) sequencing to discover and genotype approximately 8,000 SNP loci in three population pairs of even- and odd-year pink salmon along a latitudinal gradient in North America. We found greater differentiation within the odd-year than the even-year lineage and greater differentiation in the southern pair from Puget Sound than in the northern Alaskan population pairs. We identified 15 SNPs reflecting signatures of parallel selection using both a differentiation-based method (BAYESCAN) and an environmental correlation method (BAYENV). These SNPs represent genomic regions that may be particularly informative in understanding adaptive evolution in pink salmon and exploring how differing genetic backgrounds within a species respond to selection from the same natural environment. This article is protected by copyright. All rights reserved.

PMID: 24762204 [PubMed – as supplied by publisher]

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Genotyping by sequencing resolves shallow population structure to inform conservation of Chinook salmon (Oncorhynchus tshawytscha).

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Genotyping by sequencing resolves shallow population structure to inform conservation of Chinook salmon (Oncorhynchus tshawytscha).

Evol Appl. 2014 Mar;7(3):355-69

Authors: Larson WA, Seeb LW, Everett MV, Waples RK, Templin WD, Seeb JE

Abstract
Recent advances in population genomics have made it possible to detect previously unidentified structure, obtain more accurate estimates of demographic parameters, and explore adaptive divergence, potentially revolutionizing the way genetic data are used to manage wild populations. Here, we identified 10 944 single-nucleotide polymorphisms using restriction-site-associated DNA (RAD) sequencing to explore population structure, demography, and adaptive divergence in five populations of Chinook salmon (Oncorhynchus tshawytscha) from western Alaska. Patterns of population structure were similar to those of past studies, but our ability to assign individuals back to their region of origin was greatly improved (>90% accuracy for all populations). We also calculated effective size with and without removing physically linked loci identified from a linkage map, a novel method for nonmodel organisms. Estimates of effective size were generally above 1000 and were biased downward when physically linked loci were not removed. Outlier tests based on genetic differentiation identified 733 loci and three genomic regions under putative selection. These markers and genomic regions are excellent candidates for future research and can be used to create high-resolution panels for genetic monitoring and population assignment. This work demonstrates the utility of genomic data to inform conservation in highly exploited species with shallow population structure.

PMID: 24665338 [PubMed]

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Secondary contact and changes in coastal habitat availability influence the nonequilibrium population structure of a salmonid (Oncorhynchus keta).

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Secondary contact and changes in coastal habitat availability influence the nonequilibrium population structure of a salmonid (Oncorhynchus keta).

Mol Ecol. 2013 Dec;22(23):5848-60

Authors: Petrou EL, Hauser L, Waples RS, Seeb JE, Templin WD, Gomez-Uchida D, Seeb LW

Abstract
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.

PMID: 24118255 [PubMed – indexed for MEDLINE]

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Secondary contact and changes in coastal habitat availability influence the nonequilibrium population structure of a salmonid (Oncorhynchus keta).

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Secondary contact and changes in coastal habitat availability influence the nonequilibrium population structure of a salmonid (Oncorhynchus keta).

Mol Ecol. 2013 Oct 1;

Authors: Petrou EL, Hauser L, Waples RS, Seeb JE, Templin WD, Gomez-Uchida D, Seeb LW

Abstract
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 likely 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. This article is protected by copyright. All rights reserved.

PMID: 24118255 [PubMed – as supplied by publisher]

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Meiotic maps of sockeye salmon derived from massively parallel DNA sequencing.

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Meiotic maps of sockeye salmon derived from massively parallel DNA sequencing.

BMC Genomics. 2012;13:521

Authors: Everett MV, Miller MR, Seeb JE

Abstract
BACKGROUND: Meiotic maps are a key tool for comparative genomics and association mapping studies. Next-generation sequencing and genotyping by sequencing are speeding the processes of SNP discovery and the development of new genetic tools, including meiotic maps for numerous species. Currently there are limited genetic resources for sockeye salmon, Oncorhynchus nerka. We develop the first dense meiotic map for sockeye salmon using a combination of novel SNPs found in restriction site associated DNA (RAD tags) and SNPs available from existing expressed sequence tag (EST) based assays.
RESULTS: We discovered and genotyped putative SNPs in 3,430 RAD tags. We removed paralogous sequence variants leaving 1,672 SNPs; these were combined with 53 EST-based SNP genotypes for linkage mapping. The map contained 29 male and female linkage groups, consistent with the haploid chromosome number expected for sockeye salmon. The female map contains 1,057 loci spanning 4,896 cM, and the male map contains 1,118 loci spanning 4,220 cM. Regions of conservation with rainbow trout and synteny between the RAD based rainbow trout map and the sockeye salmon map were established.
CONCLUSIONS: Using RAD sequencing and EST-based SNP assays we successfully generated the first high density linkage map for sockeye salmon.

PMID: 23031582 [PubMed – indexed for MEDLINE]

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Rank and order: evaluating the performance of SNPs for individual assignment in a non-model organism.

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Rank and order: evaluating the performance of SNPs for individual assignment in a non-model organism.

PLoS One. 2012;7(11):e49018

Authors: Storer CG, Pascal CE, Roberts SB, Templin WD, Seeb LW, Seeb JE

Abstract
Single nucleotide polymorphisms (SNPs) are valuable tools for ecological and evolutionary studies. In non-model species, the use of SNPs has been limited by the number of markers available. However, new technologies and decreasing technology costs have facilitated the discovery of a constantly increasing number of SNPs. With hundreds or thousands of SNPs potentially available, there is interest in comparing and developing methods for evaluating SNPs to create panels of high-throughput assays that are customized for performance, research questions, and resources. Here we use five different methods to rank 43 new SNPs and 71 previously published SNPs for sockeye salmon: F(ST), informativeness (I(n)), average contribution to principal components (LC), and the locus-ranking programs BELS and WHICHLOCI. We then tested the performance of these different ranking methods by creating 48- and 96-SNP panels of the top-ranked loci for each method and used empirical and simulated data to obtain the probability of assigning individuals to the correct population using each panel. All 96-SNP panels performed similarly and better than the 48-SNP panels except for the 96-SNP BELS panel. Among the 48-SNP panels, panels created from F(ST), I(n), and LC ranks performed better than panels formed using the top-ranked loci from the programs BELS and WHICHLOCI. The application of ranking methods to optimize panel performance will become more important as more high-throughput assays become available.

PMID: 23185290 [PubMed – indexed for MEDLINE]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/pubmed/23185290?dopt=Abstract

Rank and Order: Evaluating the Performance of SNPs for Individual Assignment in a Non-Model Organism.

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Rank and Order: Evaluating the Performance of SNPs for Individual Assignment in a Non-Model Organism.

PLoS One. 2012;7(11):e49018

Authors: Storer CG, Pascal CE, Roberts SB, Templin WD, Seeb LW, Seeb JE

Abstract
Single nucleotide polymorphisms (SNPs) are valuable tools for ecological and evolutionary studies. In non-model species, the use of SNPs has been limited by the number of markers available. However, new technologies and decreasing technology costs have facilitated the discovery of a constantly increasing number of SNPs. With hundreds or thousands of SNPs potentially available, there is interest in comparing and developing methods for evaluating SNPs to create panels of high-throughput assays that are customized for performance, research questions, and resources. Here we use five different methods to rank 43 new SNPs and 71 previously published SNPs for sockeye salmon: F(ST), informativeness (I(n)), average contribution to principal components (LC), and the locus-ranking programs BELS and WHICHLOCI. We then tested the performance of these different ranking methods by creating 48- and 96-SNP panels of the top-ranked loci for each method and used empirical and simulated data to obtain the probability of assigning individuals to the correct population using each panel. All 96-SNP panels performed similarly and better than the 48-SNP panels except for the 96-SNP BELS panel. Among the 48-SNP panels, panels created from F(ST), I(n), and LC ranks performed better than panels formed using the top-ranked loci from the programs BELS and WHICHLOCI. The application of ranking methods to optimize panel performance will become more important as more high-throughput assays become available.

PMID: 23185290 [PubMed – in process]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/23185290?dopt=Abstract