Biology subjects

Koop, B. F.

Publications and source records attributed to Koop, B. F..

17 recordsLinked to original sources

bioRxiv2024

The genome assembly of the westslope cutthroat trout, Oncorhynchus lewisi, reveals interspecific chromosomal rearrangements with the rainbow trout

Cutthroat trout (Oncorhynchus clarkii) are popular among anglers throughout their native range along the West Coast and interior of North America. As they colonized the interior of North America, cutthroat trout diverged into several genetically distinct groups. Many of these groups are now threatened by habitat destruction, hybridization with rainbow trout (O. mykiss), and competition from introduced species. These groups were previously classified as subspecies, but recent research suggests they may represent distinct species. In this study, we produced a chromosomal-level genome assembly and a genetic map for one of the species in the cutthroat trout species complex, the westslope cutthroat trout (O. lewisi--formerly O. clarki lewisi). We also constructed haplotype-resolved assemblies from a westslope cutthroat-rainbow trout F1 hybrid. We used the new genome assemblies to identify major interspecific chromosomal rearrangements between the two sister species, including fusions, fissions, and inversions. These genome assemblies and chromosome data provide valuable insights regarding genetic variation within cutthroat trout and in hybrids between rainbow and cutthroat trout. Article SummaryWestslope cutthroat trout inhabit bodies of water in several states and provinces near the Rocky Mountains and are well-known among anglers. In this study, we produced the first publicly available genome assemblies and a high-density genetic map for this species. These are research tools that allow detailed genetic analyses, including identifying differences among the genomes of related species. These comparisons allow researchers to understand the evolution of these species better and may provide insight into why successful interbreeding is possible among cutthroat and rainbow trout.

genomics↗

bioRxiv2024

Revealing the evolutionary history and contemporary population structure of Pacific salmon in the Fraser River through genome resequencing

The Fraser River once supported massive salmon returns, but now years with half of the recorded historical maximum are considered good. There is substantial interest from surrounding communities, governments, and other groups to increase salmon returns for both human use and for functional ecosystems. To help generate resources for this endeavour, we resequenced hundreds of genomes at moderate coverage ([~]16x) of Chinook (Oncorhynchus tshawytscha), coho (O. kisutch), and sockeye salmon (O. nerka) from the Fraser River. The resequenced genomes are an important resource that can give us new insights. In this study, we found evidence that Chinook salmon have 1.5-2x more polymorphic loci than coho or sockeye salmon. Using principal component analysis (PCA) and admixture analysis, we also identified genetic groups similar to those previously identified with only a few microsatellite markers. As the higher density data supports these previous genetic groups, it suggests that the identity of these groups is not overly sensitive to the number of genetic markers or when the groups were sampled. With the increased resolution from resequenced genomes, we were able to further identify factors influencing these genetic groups, including isolation-by-distance, migration barriers, recolonization from different glacial refugia, and environmental factors like precipitation. We were also able to identify 20 potentially adaptive loci among the genetic groups by analyzing runs of homozygosity. All of the resequenced genomes have been submitted to a public database where they can be used as a reference for the contemporary genomics of Fraser River salmon. Article SummaryConcerns over Fraser River salmon declines led us to generate resources to better understand the genetics of these salmon. Our findings were similar to previous studies that examined a very small fraction of the genetic markers examined here. We expanded upon previous studies by identifying possible influences on the genetics of Fraser River salmon. These included environmental factors, historical differences, and a lack of connectivity in the river caused by the Fraser Canyon.

evolutionary biology↗

bioRxiv2022

Allele surfing causes maladaptation in a Pacific salmon of conservation concern

How various factors, including demography, recombination or genome duplication, may impact the efficacy of natural selection and the burden of deleterious mutations,is a central question in evolutionary biology and genetics. In this study, we show that key evolutionary processes, including variations in i) effective population size (Ne) ii) recombination rates and iii) chromosome inheritance, have influenced the genetic load and efficacy of selection in Coho salmon (Oncorhynchus kisutch), a widely distributed salmonid species on the west coast of North America. Using whole genome resequencing data from 14 populations at different migratory distances from their southern glacial refugium, we found evidence supporting gene surfing, wherein reduced Ne at the postglacial recolonization front, leads to a decrease in the efficacy of selection and a surf of deleterious alleles in the northernmost populations. Furthermore, our results indicate that recombination rates play a prime role in shaping the load along the genome. Additionally, we identified variation in polyploidy as a contributing factor to within-genome variation of the load. Overall, our results align remarkably well with expectations under the nearly neutral theory of molecular evolution. We discuss the fundamental and applied implications of these findings for evolutionary and conservation genomics. Author SummaryUnderstanding how historical processes, such as past glaciations, may have impacted variations in population size and genetic diversity along the genome is a fundamental question in evolution. In this study, we investigated how recent postglacial demographic expansion has affected the distribution of deleterious genetic variants and the resulting deleterious mutation load in Coho salmon (Oncorhynchus kisutch), throughout its native range in North America. By sequencing the entire genome of 71 Coho salmon, we reveal that postglacial expansion has led to allele surfing, a process where alleles increase in frequency in populations that are expanding or colonizing new environments. Here, allele surfing resulted in an increased deleterious mutation load at the colonization front. Furthermore, we demonstrated that the efficacy of natural selection scales with variation in effective population size among populations. We showed that the specific genomic features of Coho salmon, namely variation in local recombination rate and variation in chromosomal inheritance, strongly impacted the segregation of deleterious mutations.

evolutionary biology↗

bioRxiv2022

Effects of ancient anthropogenic clam gardens on the growth, survival, and transcriptome of Pacific littleneck clams (Leukoma staminea)

Clam gardens traditionally established and maintained by coastal Indigenous Peoples of northwest North America are habitat modifications to enhance intertidal clam productivity for reliable local food production. In this study, phenotypic and transcriptomic responses of Pacific littleneck clams (Leukoma staminea) were evaluated 16 weeks after transplantation to either unmaintained clam gardens or reference (unmodified) clam beaches. Beach sediment characteristics including grain size and organic content were examined across all beaches. Large differences in abiotic characteristics and phenotypic responses were observed among beaches; however, differences were not related to the clam garden/reference beach effect. Clam survival and growth were negatively associated with small rocks, very fine sand, and silt, along with carbonate and organic content, and positively associated with coarse sand, sand, and fine sand. To investigate molecular responses to unmaintained clam gardens, a de novo transcriptome containing 52,000 putative transcripts was assembled for L. staminea and was used to test for differential expression between transplanted clams in unmaintained clam gardens or on reference beaches. As expected, given the lack of significant phenotypic differences between treatments, transcriptomic responses to unmaintained clam gardens were minor, although several weakly-associated transcripts were identified. By contrast, the strong survival gradient across beaches was used to identify genes associated with survival and, combined with characterization of tissue-specific expression in the gill and digestive gland, contributes to our understanding of molecular processes in this non-model species.

ecology↗

bioRxiv2022

Isolation-by-distance and population-size history inferences from the coho salmon (Oncorhynchus kisutch) genome

Coho salmon (Oncorhynchus kisutch) are a culturally and economically important species that return from multiyear ocean migrations to spawn in rivers that flow to the Northern Pacific Ocean. Southern stocks of coho salmon have significantly declined over the past quarter century, and unfortunately, conservation efforts have not reversed this trend. To assist in stock management and conservation efforts, we generated two chromosome-level genome assemblies and sequenced 24 RNA-seq libraries to better annotate the coho salmon genome assemblies. We also resequenced the genomes of 83 coho salmon across their North American range to identify nucleotide variants, characterize the broad effects of isolation-by-distance using a genome-wide association analysis approach, and understand the demographic histories of these salmon by modeling population size from genome-wide data. We observed that more than 13% of all SNPs were associated with latitude (before multiple test correction), likely an affect of isolation-by-distance. From demographic history modeling, we estimated that the SNP latitudinal gradient likely developed as recently as 8,000 years ago. In addition, we identified four genes each harboring multiple SNPs associated with latitude; all of these SNPs were also predicted to modify the function of the gene. Three of these genes have roles in cell junction maintenance and may be involved in osmoregulation. This signifies that ocean salinity may have been a factor influencing coho salmon recolonization after the last glaciation period - generating the current pattern of variation in these three genes.

genomics↗

bioRxiv2021

Genome assembly, transcriptome and SNP database for chum salmon (Oncorhynchus keta)

Chum salmon (Oncorhynchus keta) is the species with the widest geographic range of the anadromous Pacific salmonids. Chum salmon is the second largest of the Pacific salmon, behind Chinook salmon, and considered the most plentiful Pacific salmon by overall biomass. This species is of significant commercial and economic importance: on average the commercial chum salmon fishery has the second highest processed value of the Pacific salmon within British Columbia. The aim of this work was to establish genomic baseline resources for this species. Our first step to accomplish this goal was to generate a chum salmon reference genome assembly from a doubled-haploid chum salmon. Gene annotation of this genome was facilitated by an extensive RNA-seq database we were able to create from multiple tissues. Range-wide resequencing of chum salmon genomes allowed us to categorize genome-wide geographic variation, which in turn reinforced the idea that genetic differentiation was best described on a regional, rather than at a stock-specific, level. Within British Columbia, chum salmon regional groupings were described at the conservation unit (CU) level, and there may be substructure within particular CUs. Genome wide associations of phenotypic sex to SNP genetic markers identified two clear peaks, a very strong peak on Linkage Group 15, and another on Linkage Group 3. With these new resources, we were better able to characterize the sex-determining region and gain further insights into sex determination in chum salmon and the general biology of this species.

genomics↗

bioRxiv2021

Long distance migration is a major factor driving local adaptation at continental scale in Coho Salmon

Inferring the genomic basis of local adaptation is a long-standing goal of evolutionary biology. Beyond its fundamental evolutionary implications, such knowledge can guide conservation decisions for populations of conservation and management concern. Here, we investigated the genomic basis of local adaptation in the Coho salmon (Oncorhynchus kisutch) across its entire North American range. We hypothesized that extensive spatial variation in environmental conditions and the species homing behavior may promote the establishment of local adaptation. We genotyped 7,829 individuals representing 217 sampling locations at more than 100,000 high-quality RADseq loci to investigate how recombination might affect the detection of loci putatively under selection and took advantage of the precise description of the demographic history of the species from our previous work to draw accurate population genomic inferences about local adaptation. Results indicated that genetic differentiation scans and genetic-environment association analyses were both significantly affected by variation in recombination rate as low recombination regions displayed an increased number of outliers. By taking these confounding factors into consideration, we revealed that migration distance was the primary selective factor driving local adaptation and partial parallel divergence among distant populations. Moreover, we identified several candidates SNP associated with long distance migration and altitude including a gene known to be involved in adaptation to altitude in other species. The evolutionary implications of our findings are discussed along with conservation applications.

evolutionary biology↗

bioRxiv2021

The pink salmon genome: uncovering the genomic consequences of a strict two-year life-cycle

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.

genomics↗

bioRxiv2021

The salmon louse genome: copepod features and parasitic adaptations.

Copepods encompass a range of ecological roles from parasites to phytoplankton grazers linking primary producers to higher trophic levels. Despite these important roles, copepod genome assemblies are scarce. Lepeophtheirus salmonis is an economically and ecologically important ectoparasitic copepod. We present the 695.4 Mbp L. salmonis genome assembly containing {approx}60% repetitive regions and 13081 annotated protein-coding genes. The genome comprises 14 autosomes and a ZZ-ZW sex chromosome system. Assembly assessment identified 92.4% of the expected arthropod genes. Transcriptomics validated annotation and revealed a marked shift in gene expression after host attachment, including downregulation of genes related to circadian rhythm coinciding with abandoning diurnal migration. The genome shows evolutionary signatures including loss of peroxisomes, numerous FNII domains, and an incomplete heme homeostasis pathway suggesting heme proteins to be obtained from the host. Despite large capacity to develop resistance against chemical treatments L. salmonis exhibits low numbers of many genes involved in detoxification.

genomics↗

bioRxiv2020

Detection of selection signatures in farmed coho salmon (Oncorhynchus kisutch) using dense genome-wide information

Animal domestication and artificial selection give rise to gradual changes at the genomic level in populations. Subsequent footprints of selection known as selection signatures or selective sweeps have been traced in the genomes of many animal livestock species by exploiting variations in linkage disequilibrium patterns and/or reduction of genetic diversity. Domestication of most aquatic species is recent in comparison with land animals, and salmonids are one of the most important fish species in aquaculture. Coho salmon (Oncorhynchus kisutch), cultivated primarily in Chile, has been subject to breeding programs to improve growth, disease resistance traits, and flesh color. This study aimed to identify selection signatures that may be involved in adaptation to culture conditions and traits of productive interest. To do so, individuals of two domestic populations cultured in Chile were genotyped with 200 thousand SNPs, and analyses were conducted using iHS, XP-EHH and CLR. Several signatures of selection on different chromosomal regions were detected across both populations. Some of the identified regions under selection contained genes such anapc2, alad, chp2 and myn that have been previously associated with body weight in Atlantic salmon or sec24d and robo1 that have been associated with disease resistance to Piscirickettsia salmonis in coho salmon. Findings in our study can contribute to an integrated genome-wide map of selection signatures, to help identify the genetic mechanisms of phenotypic diversity in coho salmon.

genetics↗

bioRxiv2020

Comparative regulomics reveals pervasive selection on gene dosage following whole genome duplication

Whole genome duplication (WGD) events have played a major role in eukaryotic genome evolution, but the consequence of these extreme events in adaptive genome evolution is still not well understood. To address this knowledge gap we used a comparative phylogenetic model and transcriptomic data from seven species to infer selection on gene expression in duplicated genes (ohnologs) following the salmonid WGD 80-100 million years ago. We find rare cases of tissue-specific expression evolution but pervasive expression evolution affecting many tissues, reflecting strong selection on maintenance of genome stability following genome doubling. Although ohnolog expression levels have evolved mostly asymmetrically, by diverting one ohnolog copy down a path towards pseudogenization, strong evolutionary constraints have frequently also favoured symmetric shifts in gene dosage of both copies, likely to achieve gene dose reduction while avoiding accumulation of toxic mutations. Mechanistically, ohnolog regulatory divergence is dictated by the number of bound transcription factors in promoters, with transposable elements being one source of novel binding sites driving tissue-specific gains in expression. Our results imply pervasive adaptive expression evolution following WGD to overcome the immediate challenges posed by genome doubling and to exploit the long-term genetic opportunities for novel phenotype evolution.

evolutionary biology↗

bioRxiv2020

Population genomics of North American northern pike: variation and sex-specific signals from a chromosome-level, long read genome assembly

The northern pike Esox lucius is a freshwater fish renowned for having low genetic diversity but ecological success throughout the Northern Hemisphere. Here we generate an annotated chromosome-level genome assembly of 941 Mbp in length with 25 chromosome-length scaffolds using long-reads and chromatin capture technology. We then align whole-genome resequencing data against this reference to genotype northern pike from Alaska through New Jersey (n = 47). A striking decrease in genetic diversity occurs along the sampling range, whereby samples to the west of the North American Continental Divide have substantially higher diversity than populations to the east. As an example, individuals from Interior Alaska in the west and St. Lawrence River in the east have on average 181K and 64K heterozygous SNPs per individual, respectively (i.e., a SNP variant every 3.2 kbp and 11.2 kbp, respectively). Even with such low diversity, individuals clustered with strong support within each population, and this may be related to numerous private alleles in each population. Evidence for recent population expansion was observed for a Manitoba hatchery and the St. Lawrence population (Tajimas D = -1.07 and -1.30, respectively). Non-uniform patterns of diversity were observed across the genome, with large regions showing elevated diversity in several chromosomes, including LG24. In populations with the master sex determining gene amhby still present in the genome, amhby is in LG24. As expected, amhby was largely male-specific in Alaska and the Yukon and absent southeast to these populations, but we also document some amhby(-) males in Alaska and amhby(+) males in the Columbia River. This indicates that rather than a discrete boundary after which amhby was lost in North America, there is a patchwork of presence of this system in the western region. These results support the theory that northern pike recolonized North America from refugia in Alaska and expanded following deglaciation from west to east, with probable founder effects resulting in loss of both neutral and functional diversity including the loss of the sex determination system.

genomics↗

bioRxiv2020

The rise and fall of the ancient northern pike master sex determining gene

Sexual reproduction is a ubiquitous basic feature of life and genetic sex determination is thus widespread, at least among eukaryotes. Understanding the remarkable diversity of sex determination mechanisms, however, is limited by the paucity of empirical studies. Here, we traced back the evolution of sex determination in an entire clade of vertebrates and uncovered that the northern pike (Esox lucius) master sex-determining gene initiated from a 65 to 90 million-year-old gene duplication and remained sex-linked on undifferentiated sex chromosomes for at least 56 million years. Contrasting with its ancient origin, we identified several independent species- or population-specific transitions of sex determination mechanisms in this lineage, including an unexpected complete and recent Y-chromosome loss in some North American northern pike populations. These findings highlight the diversity of the evolutionary fates of master sex-determining genes and raise the importance of careful considerations of population demographic history in sex determination studies. Our study also puts forward the hypothesis that occasional sex reversals and genetic bottlenecks provide a non-adaptive explanation for sex determination transitions.

evolutionary biology↗

bioRxiv2020

Estimates of autozygosity through runs of homozygosity in farmed coho salmon

The characterization of runs of homozygosity (ROH), using high-density single nucleotide polymorphisms (SNPs) allows inferences to be made about the past demographic history of animal populations and the genomic ROH has become a common approach to characterize the inbreeding. We aimed to analyze and characterize ROH patterns and compare different genomic and pedigree-based methods to estimate the inbreeding coefficient in two pure lines (POP A and B) and one recently admixed line (POP C) of coho salmon breeding nuclei, genotyped using a 200K Affymetrix Axiom(R) myDesign Custom SNP Array. A large number and greater mean length of ROH were found for the two "pure" lines and the recently admixed line (POP C) showed the lowest number and smaller mean length of ROH. The ROH analysis for different length classes suggests that all three coho salmon lines the genome is largely composed of a high number of short segments (<4 Mb), and for POP C no segment >16 Mb was found. A high variable number of ROH, mean length and inbreeding values across chromosomes; positively the consequence of artificial selection. Pedigree-based inbreeding values tended to underestimate genomic-based inbreeding levels, which in turn varied depending on the method used for estimation. The high positive correlations between different genomic-based inbreeding coefficients suggest that they are consistent and may be more accurate than pedigree-based methods, given that they capture information from past and more recent demographic events, even when there are no pedigree records available.

genomics↗

bioRxiv2018

Sex-dependent dominance maintains migration supergene in rainbow trout

Traits with different fitness optima in males and females cause sexual conflict when they have a shared genetic basis. Heteromorphic sex chromosomes can resolve this conflict and protect sexually antagonistic polymorphisms but accumulate deleterious mutations. However, many taxa lack differentiated sex chromosomes, and how sexual conflict is resolved in these species is largely unknown. Here we present a chromosome-anchored genome assembly for rainbow trout (Oncorhynchus mykiss) and characterize a 56 Mb double-inversion supergene that mediates sex-specific migration through sex-dependent dominance, a mechanism that reduces sexual conflict. The double-inversion contains key photosensory, circadian rhythm, adiposity, and sexual differentiation genes and displays frequency clines associated with latitude and temperature, revealing environmental dependence. Our results constitute the first example of sex-dependent dominance across a large autosomal supergene, a novel mechanism for sexual conflict resolution capable of protecting polygenic sexually antagonistic variation while avoiding the homozygous lethality and deleterious mutation load of heteromorphic sex chromosomes.

evolutionary biology↗

bioRxiv2017

Parallel epigenetic modifications induced by hatchery rearing in a Pacific Salmon

Highlights- First study to highlight parallel epigenetic modifications induced by hatchery rearing as a potential explanatory mechanism for rapid change in fitness\n\nSummaryA puzzling question in conservation biology is how to maintain overall fitness of individuals bred in captive environment upon release into the wild, especially for rehabilitating declining or threatened species [1,2]. For salmonid species, a heritable change in fitness related traits and gene expression has been reported to occur in a single generation of captivity in hatchery environment [3-5]. Such rapid changes are congruent with models of inadvertent domestication selection which may lead to maladaptation in the natural environment [4]. Arguably, the underlying mechanism by which captivity may induce fitness difference between wild and captive congeners is still poorly understood. Short-term selection on complex phenotypic traits is expected to induce subtle changes in allele frequency over multiple loci [7-9]. Yet, most studies investigating the molecular basis for rapid change in fitness related traits occurring in hatchery have concentrated their effort on finding evidence for selection at the genome level by identifying loci with large effect.\n\nNumerous wild stocks of Pacific anadromous salmon and trout (genus Oncorhynchus and Salmo) have experienced fluctuating abundance over the past century, with a series of sharp declines [6-8]. With the objectives of preserving ecosystem integrity, enhancing declining populations and sustaining fisheries, conservation hatcheries have been flourishing. This is particularly true along the North American Pacific coast where billions of salmonids, all species included, are released each year. Despite substantial improvement of production management, the beneficial ecological role of hatcheries in enhancing and restoring wild stocks is still debated, mainly because of the reduced fitness and maladaptation of hatchery-fish when released in the wild [3,5,9]. Although previous studies showed that domestication selection was involved in such fitness impairment, they also observed that different environmental conditions (e.g. reduced fish density) significantly modulated the physiological acclimation to hatchery environment [4].\n\nEnvironmental stimuli are especially relevant during early embryonic development, which also correspond to a sensitive methylation reprogramming window in vertebrates [10,11]. It is therefore plausible that differences in rearing environment during early development may result in epigenetic modifications that could in turn impact on fitness. However, the only epigenetic study to date pertaining to captive rearing in salmonids and performed using methylation-sensitive amplified fragments (MSAP) failed to identify significant changes in methylation profile associated with hatchery rearing [12]\n\nHere, we used a higher resolution approach to compare the genome-wide pattern of methylation in hatchery-reared juvenile (smolt) Coho Salmon with that of their wild counterparts in two geographically distant rivers in British Columbia, Canada. Using a reduced representation bisulfite sequencing (RRBS) approach covering an average per individual of about 70 million cytosines in CpG context, we identified 100 methylated regions (DMRs) that differed in parallel between hatchery and natural origin salmon in both rivers. The total variance of epigenetic variation among individuals explained by river or origin and rearing environment in a RDA model was 16% (adj.R2=0.16), and both variables equally explained about 8% of the variance after controlling for each other. The gene ontology analysis revealed that regions with different methylation levels between hatchery and natural origin salmon showed enrichment for ion homeostasis, synaptic and neuromuscular regulation, immune and stress response, and control of locomotion functions. We further identified 15,044 SNPs that allowed detection of significant differences between either rivers or sexes. However, no effect of rearing environment was observed, confirming that hatchery and natural origin fish of a given river belong to the same panmictic population, as expected based on the hatchery programs applied in these rivers (see Supplementary experimental procedures). Moreover, neither a standard genome-scan approach nor a polygenic statistical framework allowed detection of selective effects within a single generation between hatchery and natural origin salmon. Therefore, this is the first study to demonstrate that parallel epigenetic modifications induced by hatchery rearing during early development may represent a potential explanatory mechanism for rapid change in fitness-related traits previously reported in salmonids.

genomics↗

bioRxiv2016

Functional Analysis of All Salmonid Genomes (FAASG): an international initiative supporting future salmonid research, conservation and aquaculture

We describe an emerging initiative - the Functional Analysis of All Salmonid Genomes (FAASG), which will leverage the extensive trait diversity that has evolved since a whole genome duplication event in the salmonid ancestor, to develop an integrative understanding of the functional genomic basis of phenotypic variation. The outcomes of FAASG will have diverse applications, ranging from improved understanding of genome evolution, through to improving the efficiency and sustainability of aquaculture production, supporting the future of fundamental and applied research in an iconic fish lineage of major societal importance.

genomics↗