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The HoloFood project used a hologenomic approach to understand the impact of host-microbiota interactions on salmon and chicken production by analysing multiomic data, phenotypic characteristics, and associated metadata in response to novel feeds. The project's raw data, derived analyses, and metadata are deposited in public, open archives (BioSamples, European Nucleotide Archive, MetaboLights, and MGnify), so making use of these diverse data types may require access to multiple resources. This is especially complex where analysis pipelines produce derived outputs such as functional profiles or genome catalogues. The HoloFood Data Portal is a web resource that simplifies access to the project datasets. For example, users can conveniently access multiomic datasets derived from the same individual or retrieve host phenotypic data with a linked gut microbiome sample. Project-specific metagenome-assembled genome and viral catalogues are also provided, linking to broader datasets in MGnify. The portal stores only data necessary to provide these relationships, with possible linking to the underlying repositories. The portal showcases a model approach for how future multiomics datasets can be made available. Database URL:  https://www.holofooddata.org., (© The Author(s) 2025. Published by Oxford University Press.)

Large scale production of insect larvae is considered a sustainable way to upcycle various organic waste- and by-products into more valuable food and feed products. The sustainability of insect larvae production depends on the substrates and species being used, but comparative studies that include both growth and efficiency are lacking. Here we compare larval fitness, including survival, development time, weight, substrate conversion efficiency, substrate reduction, and metabolic parameters across different combinations of densities and waste- and by-product-based substrates on the two fly species, the house fly (Musca domestica) and the black soldier fly (Hermetia illucens). The waste- and by-product-based substrates were a brewer's spent grain-based substrate, a digested sludge-based substrate, and a wheat bran/deproteinized grass-based substrate all highly abundant and of low value. Substrate and density significantly impacted on most larval growth and metabolic performance traits, but dependent on species. The brewer's spent grain-based substrate generally gave the highest performance in terms of larval weight, larval yield, and substrate conversion efficiency for both species, while a high density gave a higher larval yield and substrate conversion efficiency, but lower larval weight. Generally, black soldier fly larvae showed lower metabolic costs and higher net growth efficiency than house fly larvae. Altogether, our results demonstrate that both larval species, substrate, and larval densities affect larval growth and metabolic performance, and subsequently the scope for valorizing waste- or by-products to achieve a sustainable production of food and feed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Recent studies of dynamic interactions between epigenetic modifications of a host organism and the composition or activity of its associated gut microbiota suggest an opportunity for the host to shape its microbiome through epigenetic alterations that lead to changes in gene expression and noncoding RNA activity. We use insights from microbiota-induced epigenetic changes to review the potential of the host to epigenetically regulate its gut microbiome, from which a bidirectional 'epigenome-microbiome axis' emerges. This axis embeds environmentally induced variation, which may influence the adaptive evolution of host-microbe interactions. We furthermore present our perspective on how the epigenome-microbiome axis can be understood and investigated within a holo-omic framework with potential applications in the applied health and food sciences., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The canonical view of DNA methylation, a pivotal epigenetic regulation mechanism in eukaryotes, dictates its role as a suppressor of gene activity, particularly within promoter regions. However, this view is being challenged as it is becoming increasingly evident that the connection between DNA methylation and gene expression varies depending on the genomic location and is therefore more complex than initially thought. We examined DNA methylation levels in the gut epithelium of Atlantic salmon ( Salmo salar ) using whole-genome bisulfite sequencing, which we correlated with gene expression data from RNA sequencing of the same gut tissue sample (RNA-seq). Assuming epigenetic signals might be pronounced between distinctive phenotypes, we compared large and small fish, finding 22 significant associations between 22 differentially methylated regions and 21 genes. We did not detect significant methylation differences between large and small fish. However, we observed a consistent signal of methylation levels around the transcription start sites (TSS), being negatively correlated with the expression levels of those genes. We found both negative and positive associations of methylation levels with gene expression further upstream or downstream of the TSS, revealing a more unpredictable pattern. The 21 genes showing significant methylation-expression correlations were involved in biological processes related to salmon health, such as growth and immune responses. Deciphering how DNA methylation affects the expression of such genes holds great potential for future applications. For instance, our results suggest the importance of genomic context in targeting epigenetic modifications to improve the welfare of aquaculture species like Atlantic salmon.

To ensure sustainable aquaculture, it is essential to understand the path 'from feed to fish', whereby the gut microbiome plays an important role in digestion and metabolism, ultimately influencing host health and growth. Previous work has reported the taxonomic composition of the Atlantic salmon (Salmo salar) gut microbiome; however, functional insights are lacking. Here we present the Salmon Microbial Genome Atlas consisting of 211 high-quality bacterial genomes, recovered by cultivation (n = 131) and gut metagenomics (n = 80) from wild and farmed fish both in freshwater and seawater. Bacterial genomes were taxonomically assigned to 14 different orders, including 35 distinctive genera and 29 previously undescribed species. Using metatranscriptomics, we functionally characterized key bacterial populations, across five phyla, in the salmon gut. This included the ability to degrade diet-derived fibres and release vitamins and other exometabolites with known beneficial effects, which was supported by genome-scale metabolic modelling and in vitro cultivation of selected bacterial species coupled with untargeted metabolomic studies. Together, the Salmon Microbial Genome Atlas provides a genomic and functional resource to enable future studies on salmon nutrition and health., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Microbiome-directed dietary interventions such as microbiota-directed fibers (MDFs) have a proven track record in eliciting responses in beneficial gut microbes and are increasingly being promoted as an effective strategy to improve animal production systems. Here we used initial metataxonomic data on fish gut microbiomes as well as a wealth of a priori mammalian microbiome knowledge on α-mannooligosaccharides (MOS) and β-mannan-derived MDFs to study effects of such feed supplements in Atlantic salmon (Salmo salar) and their impact on its gut microbiome composition and functionalities. Our multi-omic analysis revealed that the investigated MDFs (two α-mannans and an acetylated β-galactoglucomannan), at a dose of 0.2% in the diet, had negligible effects on both host gene expression, and gut microbiome structure and function under the studied conditions. While a subsequent trial using a higher (4%) dietary inclusion of β-mannan significantly shifted the gut microbiome composition, there were still no biologically relevant effects on salmon metabolism and physiology. Only a single Burkholderia-Caballeronia-Paraburkholderia (BCP) population demonstrated consistent and significant abundance shifts across both feeding trials, although with no evidence of β-mannan utilization capabilities or changes in gene transcripts for producing metabolites beneficial to the host. In light of these findings, we revisited our omics data to predict and outline previously unreported and potentially beneficial endogenous lactic acid bacteria that should be targeted with future, conceivably more suitable, MDF strategies for salmon., (© 2024. The Author(s).)

The highly proliferative gut tissue exhibits rapid telomere shortening with systemic effects on the host organism. Recent studies have demonstrated a bidirectionality in interactions between intestinal telomere length dynamics and the composition and activity of the gut microbiome thus linking processes of inflammation, dysbiosis and aging across different vertebrate species., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

As most life-forms exist as holobionts, reduction of host-level biodiversity drives parallel habitat losses to their host-adapted microorganisms. The holobiont concept helps us to understand how species are habitats for - often ignored - coevolved microorganisms also worthy of conservation. Indeed, loss of host-associated microbial biodiversity may accelerate the extinction risks of their host., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Despite a surge in microbiota-focused studies in teleosts, few have reported functional data on whole metagenomes as it has proven difficult to extract high biomass microbial DNA from fish intestinal samples. The zebrafish is a promising model organism in functional microbiota research, yet studies on the functional landscape of the zebrafish gut microbiota through shotgun based metagenomics remain scarce. Thus, a consensus on an appropriate sampling method accurately representing the zebrafish gut microbiota, or any fish species is lacking. Addressing this, we systematically tested four methods of sampling the zebrafish gut microbiota: collection of faeces from the tank, the whole gut, intestinal content, and the application of ventral pressure to facilitate extrusion of gut material. Additionally, we included water samples as an environmental control to address the potential influence of the environmental microbiota on each sample type. To compare these sampling methods, we employed a combination of genome-resolved metagenomics and 16S metabarcoding techniques. We observed differences among sample types on all levels including sampling, bioinformatic processing, metagenome co-assemblies, generation of metagenome-assembled genomes (MAGs), functional potential, MAG coverage, and population level microdiversity. Comparison to the environmental control highlighted the potential impact of the environmental contamination on data interpretation. While all sample types tested are informative about the zebrafish gut microbiota, the results show that optimal sample type for studying fish microbiomes depends on the specific objectives of the study, and here we provide a guide on what factors to consider for designing functional metagenome-based studies on teleost microbiomes., Competing Interests: The authors have no competing interests to declare., (© 2024 The Author(s). Ecology and Evolution published by John Wiley & Sons Ltd.)

Rainbow trout ( Oncorhynchus mykiss ) is a dominant aquaculture species of the Salmonidae family, native only to the North Pacific. Recently, the gut microbiome has been shown to reflect the health status and responses to environmental changes in farmed fish. In this analysis we investigated the microbiome composition of the intestinal tract in 20 wild-caught rainbow trout specimens sampled in Alaska, USA. The targeted 16S rRNA gene (V3-V4 region) was sequenced on the Illumina NovaSeq 6000 platform. After quality control, demultiplexing and adapter trimming reads were analyzed using the DADA2 pipeline to obtain Amplicon Sequencing Variants (ASVs) which were subsequently taxonomically assigned. We found two phyla dominating the gut ecosystem present in every sample, Firmicutes and Fusobacteria, followed by lower abundances of Cyanobacteria, Proteobacteria and Bacteroidetes. At the genus level, we found high relative abundances of Cetobacterium and Clostridium sensu stricto 1. Interestingly, we did not identify often dominant genera Mycoplasma, Pseudomonas or Weisella which were prevalent in numerous studies previously, in cultured rainbow trout. Wild fish are exposed to a plethora of unpredictable environmental challenges, ranging from fluctuating water temperatures to variable food availability, as opposed to controlled conditions in production facilities. Examining and comparing the gut ecosystem of wild and reared individuals holds great potential in optimizing management practices for commercially important species. Microbiome studies can provide novel ways to enhance the overall welfare of fish, strengthen disease prevention and increase sustainability in aquaculture production., (© 2024 The Author(s).)

Holo-omics refers to the joint study of non-targeted molecular data layers from host-microbiota systems or holobionts, which is increasingly employed to disentangle the complex interactions between the elements that compose them. We navigate through the generation, analysis, and integration of omics data, focusing on the commonalities and main differences to generate and analyze the various types of omics, with a special focus on optimizing data generation and integration. We advocate for careful generation and distillation of data, followed by independent exploration and analyses of the single omic layers to obtain a better understanding of the study system, before the integration of multiple omic layers in a final model is attempted. We highlight critical decision points to achieve this aim and flag the main challenges to address complex biological questions regarding the integrative study of host-microbiota relationships., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

One third of the food produced for human consumption is currently lost or wasted. Insects have a high potential for converting organic waste- and by-products into food and feed for a growing human population due to symbiosis with microorganisms. These symbioses provide an untapped reservoir of functional microbiomes that can be used to improve industrial insect production but are poorly studied in most insect species. Here we review the most current understanding and challenges of valorizing organic waste- and by-products through insects and their microbiomes for food and feed, and emerging novel food technologies that can be used to investigate and manipulate host(insects)-microbiome interactions. We further construct a holistic framework, by integration of novel food technologies including holo-omics, genome editing, breeding, phage therapy, and administration of prebiotics and probiotics to investigate and manipulate host(insects)-microbiome interactions, and solutions for achieving stakeholder acceptance of novel food technologies for a sustainable food production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Animals and their associated microbiota share long evolutionary histories. However, it is not always clear how host genotype and microbiota interact to affect phenotype. We applied a hologenomic approach to explore how host-microbiota interactions shape lifetime growth and parasite infection in farmed Atlantic salmon ( Salmo salar ). Multi-omics data sets were generated from the guts of 460 salmon, 82% of which were naturally infected with an intestinal cestode. A single Mycoplasma bacterial strain, MAG01, dominated the gut metagenome of large, non-parasitized fish, consistent with previous studies showing high levels of Mycoplasma in the gut microbiota of healthy salmon. While small and/or parasitized salmon also had high abundance of MAG01, we observed increased alpha diversity in these individuals, driven by increased frequency of low-abundance Vibrionaceae and other Mycoplasma species that carried known virulence genes. Colonization by one of these cestode-associated Mycoplasma strains was associated with host individual genomic variation in long non-coding RNAs. Integrating the multi-omic data sets revealed coordinated changes in the salmon gut mRNA transcriptome and metabolome that correlated with shifts in the microbiota of smaller, parasitized fish. Our results suggest that the gut microbiota of small and/or parasitized fish is in a state of dysbiosis that partly depends on the host genotype, highlighting the value of using a hologenomic approach to incorporate the microbiota into the study of host-parasite dynamics.IMPORTANCEStudying host-microbiota interactions through the perspective of the hologenome is gaining interest across all life sciences. Intestinal parasite infections are a huge burden on human and animal health; however, there are few studies investigating the role of the hologenome during parasite infections. We address this gap in the largest multi-omics fish microbiota study to date using natural cestode infection of farmed Atlantic salmon. We find a clear association between cestode infection, salmon lifetime growth, and perturbation of the salmon gut microbiota. Furthermore, we provide the first evidence that the genetic background of the host may partly determine how the gut microbiota changes during parasite-associated dysbiosis. Our study therefore highlights the value of a hologenomic approach for gaining a more in-depth understanding of parasitism., Competing Interests: H.S. is employed at Lerøy Seafood Group, who produces, markets, and sells farmed Atlantic salmon, including the fish used in the current investigation. Furthermore, Lerøy Seafood Group provided parts of the funding for this study. All other authors declare they have no competing interests.

In nature, secondary metabolites mediate interactions between microorganisms residing in complex microbial communities. However, the degree to which community dynamics can be linked to secondary metabolite potential remains largely unknown. In this study, we address the relationship between community succession and secondary metabolism variation. We used 16S and 18S rRNA gene and adenylation domain amplicon sequencing, genome-resolved metagenomics, and untargeted metabolomics to track the taxons, biosynthetic gene clusters, and metabolome dynamics in situ of microorganisms during marine biofilm succession over 113 days. Two phases were identified during the community succession, with a clear shift around Day 29, where the alkaloid secondary metabolites, pseudanes, were also detected. The microbial secondary metabolite potential changed between the phases, and only a few community members, including Myxococotta spp., were responsible for the majority of the biosynthetic gene cluster potential in the early succession phase. In the late phase, bryozoans and benthic copepods were detected, and the microbial nonribosomal peptide potential drastically decreased in association with a reduction in the relative abundance of the prolific secondary metabolite producers. Conclusively, this study provides evidence that the early succession of the marine biofilm community favors prokaryotes with high nonribosomal peptide synthetase potential. In contrast, the late succession is dominated by multicellular eukaryotes and a reduction in bacterial nonribosomal peptide synthetase potential., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the International Society for Microbial Ecology.)

Alternative feed ingredients for farmed salmon are warranted due to increasing pressure on wild fish stocks. As locally farmed blue mussels may represent an environmentally sustainable substitute with a lower carbon footprint, we aimed to test the potential and safety of substituting fish meal with blue mussel meal in feed for Atlantic salmon. Salmon were fed diets in which fish meal was partially replaced with blue mussel meal in increments, accounting for up to 13.1 % of the ingredients. Fillets from the salmon were subsequently used to prepare obesity-promoting western diets for a 13-weeks mouse feeding trial. In a second mouse trial, we tested the effects of inclusion of up to 8% blue mussel meal directly in a meat-based western diet. Partial replacement of fish meal with blue mussel meal in fish feed preserved the n-3 polyunsaturated fatty acid (PUFA) content in salmon fillets. The observed blue mussel-induced changes in the fatty acid profiles in salmon fillets did not translate into similar changes in the livers of mice that consumed the salmon, and no clear dose-dependent responses were found. The relative levels of the marine n-3 fatty acids, EPA, and DHA were not reduced, and the n-3/n-6 PUFA ratios in livers from all salmon-fed mice were unchanged. The inclusion of blue mussel meal in a meat-based western diet led to a small, but dose-dependent increase in the n-3/n-6 PUFA ratios in mice livers. Diet-induced obesity, glucose intolerance, and hepatic steatosis were unaffected in both mice trials and no blue mussel-induced adverse effects were observed. In conclusion, our results suggest that replacing fish meal with blue mussel meal in salmon feed will not cause adverse effects in those who consume the salmon fillets., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

It remains a challenge to obtain the desired phenotypic traits in aquacultural production of Atlantic salmon, and part of the challenge might come from the effect that host-associated microorganisms have on the fish phenotype. To manipulate the microbiota towards the desired host traits, it is critical to understand the factors that shape it. The bacterial gut microbiota composition can vary greatly among fish, even when reared in the same closed system. While such microbiota differences can be linked to diseases, the molecular effect of disease on host-microbiota interactions and the potential involvement of epigenetic factors remain largely unknown. The aim of this study was to investigate the DNA methylation differences associated with a tenacibaculosis outbreak and microbiota displacement in the gut of Atlantic salmon. Using Whole Genome Bisulfite Sequencing (WGBS) of distal gut tissue from 20 salmon, we compared the genome-wide DNA methylation levels between uninfected individuals and sick fish suffering from tenacibaculosis and microbiota displacement. We discovered >19,000 differentially methylated cytosine sites, often located in differentially methylated regions, and aggregated around genes. The 68 genes connected to the most significant regions had functions related to the ulcerous disease such as epor and slc48a1a but also included prkcda and LOC106590732 whose orthologs are linked to microbiota changes in other species. Although the expression level was not analysed, our epigenetic analysis suggests specific genes potentially involved in host-microbiota interactions and more broadly it highlights the value of considering epigenetic factors in efforts to manipulate the microbiota of farmed fish., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Understanding the evolutionary relationships between a host and its intestinal resident bacteria can transform how we understand adaptive phenotypic traits. The interplay between hosts and their resident bacteria inevitably affects the intestinal environment and, thereby, the living conditions of both the host and the microbiota. Thereby this co-existence likely influences the fitness of both bacteria and host. Whether this co-existence leads to evolutionary co-diversification in animals is largely unexplored, mainly due to the complexity of the environment and microbial communities and the often low host selection. We present the gut metagenome from wild Atlantic salmon (Salmo salar), a new wild organism model with an intestinal microbiota of low complexity and a well-described population structure, making it well-suited for investigating co-evolution. Our data reveal a strong host selection of a core gut microbiota dominated by a single Mycoplasma species. We found a clear co-diversification between the population structure of Atlantic salmon and nucleotide variability of the intestinal Mycoplasma populations conforming to expectations from co-evolution between host and resident bacteria. Our results show that the stable microbiota of Atlantic salmon has evolved with its salmonid host populations while potentially providing adaptive traits to the salmon host populations, including defence mechanisms, biosynthesis of essential amino acids, and metabolism of B vitamins. We highlight Atlantic salmon as a novel model for studying co-evolution between vertebrate hosts and their resident bacteria., (© 2023. The Author(s).)

Motivation: Machine learning (ML) methods are motivated by the need to automate information extraction from large datasets in order to support human users in data-driven tasks. This is an attractive approach for integrative joint analysis of vast amounts of omics data produced in next generation sequencing and other -omics assays. A systematic assessment of the current literature can help to identify key trends and potential gaps in methodology and applications. We surveyed the literature on ML multi-omic data integration and quantitatively explored the goals, techniques and data involved in this field. We were particularly interested in examining how researchers use ML to deal with the volume and complexity of these datasets., Results: Our main finding is that the methods used are those that address the challenges of datasets with few samples and many features. Dimensionality reduction methods are used to reduce the feature count alongside models that can also appropriately handle relatively few samples. Popular techniques include autoencoders, random forests and support vector machines. We also found that the field is heavily influenced by the use of The Cancer Genome Atlas dataset, which is accessible and contains many diverse experiments., Availability and Implementation: All data and processing scripts are available at this GitLab repository: https://gitlab.com/polavieja_lab/ml_multi-omics_review/ or in Zenodo: https://doi.org/10.5281/zenodo.7361807., Supplementary Information: Supplementary data are available at Bioinformatics online., (© The Author(s) 2023. Published by Oxford University Press.)

African swine fever virus (ASFV) has become a global threat to the pig production industry and has caused enormous economic losses in many countries in recent years. Peripheral blood mononuclear cells (PBMCs) from pigs infected with ASFV not only express ASFV genes (almost 200 in number) but have altered patterns of host gene expression as well. Both up- and down-regulation of host cell gene expression can be followed using RNAseq on poly(A)+ mRNAs harvested from the PBMCs of pigs collected at different times post-infection. Consistent with the time course of changes in viral gene expression, only few and limited changes in host gene expression were detected at 3 days post-infection (dpi), but by 6 dpi, marked changes in the expression of over 1300 host genes were apparent. This was co-incident with the major increase in viral gene expression. The majority of the changes in host gene expression were up-regulation, but many down-regulated genes were also identified. The patterns of changes in gene expression within the PBMCs detected by RNAseq were similar in each of the four infected pigs. Furthermore, changes in the expression of about twenty selected host genes, known to be important in host defence and inflammatory responses, were confirmed using high-throughput microfluidic qPCR assays.

Microbiomes provide key ecological functions to their host; however, most host-associated microbiomes are too complicated to allow a model of essential host-microbe-microbe interactions. The intestinal microbiota of salmonids may offer a solution since few dominating species often characterize it. Healthy fish coexist with a mutualistic Mycoplasma sp. species, while stress allows the spread of pathogenic strains, such as Aliivibrio sp. Even after a skin infection, the Mycoplasma does not recover; Aliivibrio sp. often remains the dominant species, or Mycoplasma - Aliivibrio coexistence was occasionally observed. We devised a model involving interactions among the host immune system, Mycoplasma sp. plus a toxin-producing pathogen. Our model embraces a complete microbiota community and is in harmony with experimental results that host- Mycoplasma mutualism prevents the spread of pathogens. Contrary, stress suppresses the host immune system allowing dominance of pathogens, and Mycoplasma does not recover after stress disappears., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Scheuring, Rasmussen, Bozzi and Limborg.)

The concept of a holobiont, a host organism and its associated microbial communities, encapsulates the vital role the microbiome plays in the normal functioning of its host. Parasitic infections can disrupt this relationship, leading to dysbiosis. However, it is increasingly recognized that multicellular parasites are themselves holobionts. Intestinal parasites share space with the host gut microbiome, creating a system of nested microbiomes within the primary host. However, how the parasite, as a holobiont, interacts with the host holobiont remains unclear, as do the consequences of these interactions for host health. Here, we used 16S amplicon and shotgun metagenomics sequencing to characterize the microbiome of the intestinal cestode Eubothrium and its effect on the gut microbiome of its primary host, Atlantic salmon. Our results indicate that cestode infection is associated with salmon gut dysbiosis by acting as a selective force benefiting putative pathogens and potentially introducing novel bacterial species to the host. Our results suggest that parasitic cestodes may themselves be holobionts nested within the microbial community of their holobiont host, emphasizing the importance of also considering microbes associated with parasites when studying intestinal parasitic infections. IMPORTANCE The importance of the parasite microbiome is gaining recognition. Of particular concern is understanding how these parasite microbiomes influence host-parasite interactions and parasite interactions with the vertebrate host microbiome as part of a system of nested holobionts. However, there are still relatively few studies focusing on the microbiome of parasitic helminths in general and almost none on cestodes in particular, despite the significant burden of disease caused by these parasites globally. Our study provides insights into a system of significance to the aquaculture industry, cestode infections of Atlantic salmon and, more broadly, expands our general understanding of parasite-microbiome-host interactions and introduces a new element, the microbiome of the parasite itself, which may play a critical role in modulating the host microbiome, and, therefore, the host response, to parasite infection.

Research on animal-microbiota interactions has become a central topic in biological sciences because of its relevance to basic eco-evolutionary processes and applied questions in agriculture and health. However, animal hosts and their associated microbial communities are still seldom studied in a systemic fashion. Hologenomics, the integrated study of the genetic features of a eukaryotic host alongside that of its associated microbes, is becoming a feasible - yet still underexploited - approach that overcomes this limitation. Acknowledging the biological and genetic properties of both hosts and microbes, along with the advantages and disadvantages of implemented techniques, is essential for designing optimal studies that enable some of the major questions in biology to be addressed., (© 2021. Springer Nature Limited.)

Aims: Given the pivotal role played by the gut microbiota in regulating the host immune system, great interest has arisen in the possibility of controlling fish health by modulating the gut microbiota. Hence, there is a need to better understand of the host-microbiota interactions after disease responses to optimize the use of probiotics to strengthen disease resilience and recovery., Methods and Results: We tested the effects of a probiotic feed additive in rainbow trout and challenged the fish with the causative agent for enteric red mouth disease, Yersinia ruckeri. We evaluated the survival, host immune gene expression and the gut microbiota composition. Results revealed that provision of probiotics and exposure to Y. ruckeri induced immune gene expression in the host, which were associated with changes in the gut microbiota. Subsequently, infection with Y. ruckeri had very little effect on microbiota composition when probiotics were applied, indicating that probiotics increased stabilisation of the microbiota. Our analysis revealed potential biomarkers for monitoring infection status and fish health. Finally, we used modelling approaches to decipher interactions between gut bacteria and the host immune gene responses, indicating removal of endogenous bacteria elicited by non-specific immune responses., Conclusions: We discuss the relevance of these results emphasizing the importance of host-microbiota interactions, including the protective potential of the gut microbiota in disease responses., Significance and Impact of the Study: Our results highlight the functional consequences of probiotic-induced changes in the gut microbiota post infection and the resulting host immune response., (© 2022 The Society for Applied Microbiology.)

Plastic pollution has become a major concern on a global scale. The plastic is broken down into minuscule particles, which have an impact on the biosystems, however long-term impacts through an entire generation is largely unknown. Here, we present the first whole generation study exposing fish to a 500 nm polystyrene plastic particle at environmentally relevant concentrations. Short- and long-term adverse effects were investigated in the zebrafish model organism using a holistic multi-omics approach. The particles accumulated in the yolk sac of young larvae and short-term biological impacts included immune-relevant gene regulation related to inflammation and tolerance as well as disruption of metabolic processes, such as the fatty acid and lipid pathways. The long-term effects comprised gene regulations pointing towards skin and/or gill inflammation, dysbiosis of the gut microbiota, a tendency towards decreased condition factor in adult males as well as a lowered reproductive capability. From this study, it can be concluded that exposures to plastic nanoparticles have an impact on population as well as ecosystem level in fish and likely also in other vertebrates., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Background: Animal protein production is increasingly looking towards microbiome-associated services such as the design of new and better probiotic solutions to further improve gut health and production sustainability. Here, we investigate the functional effects of bacteria-based pro- and synbiotic feed additives on microbiome-associated functions in relation to growth performance in the commercially important rainbow trout (Oncorhynchus mykiss). We combine complementary insights from multiple omics datasets from gut content samples, including 16S bacterial profiling, whole metagenomes, and untargeted metabolomics, to investigate bacterial metagenome-assembled genomes (MAGs) and their molecular interactions with host metabolism., Results: Our findings reveal that (I) feed additives changed the microbiome and that rainbow trout reared with feed additives had a significantly reduced relative abundance of the salmonid related Candidatus Mycoplasma salmoninae in both the mid and distal gut content, (II) genome resolved metagenomics revealed that alterations of microbial arginine biosynthesis and terpenoid backbone synthesis pathways were directly associated with the presence of Candidatus Mycoplasma salmoninae, and (III) differences in the composition of intestinal microbiota among feed types were directly associated with significant changes of the metabolomic landscape, including lipids and lipid-like metabolites, amino acids, bile acids, and steroid-related metabolites., Conclusion: Our results demonstrate how the use of multi-omics to investigate complex host-microbiome interactions enable us to better evaluate the functional potential of probiotics compared to studies that only measure overall growth performance or that only characterise the microbial composition in intestinal environments. Video Abstract., (© 2022. The Author(s).)

Invasion rates have increased in the past 100 y irrespective of international conventions. What characterizes a successful invasion event? And how does genetic diversity translate into invasion success? Employing a whole-genome perspective using one of the most successful marine invasive species world-wide as a model, we resolve temporal invasion dynamics during independent invasion events in Eurasia. We reveal complex regionally independent invasion histories including cases of recurrent translocations, time-limited translocations, and stepping-stone range expansions with severe bottlenecks within the same species. Irrespective of these different invasion dynamics, which lead to contrasting patterns of genetic diversity, all nonindigenous populations are similarly successful. This illustrates that genetic diversity, per se, is not necessarily the driving force behind invasion success. Other factors such as propagule pressure and repeated introductions are an important contribution to facilitate successful invasions. This calls into question the dominant paradigm of the genetic paradox of invasions, i.e., the successful establishment of nonindigenous populations with low levels of genetic diversity., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

African swine fever virus (ASFV) has become widespread in Europe, Asia and elsewhere, thereby causing extensive economic losses. The viral genome includes nearly 200 genes, but their expression within infected pigs has not been well characterized previously. In this study, four pigs were infected with a genotype II strain (ASFV POL/2015/Podlaskie); blood samples were collected before inoculation and at both 3 and 6 days later. During this period, a range of clinical signs of infection became apparent in the pigs. From the blood, peripheral blood mononuclear cells (PBMCs) were isolated. The transcription of the ASFV genes was determined using RNAseq on poly(A)+ mRNAs isolated from these cells. Only very low levels of virus transcription were detected in the PBMCs at 3 days post-inoculation (dpi) but, at 6 dpi, extensive transcription was apparent. This was co-incident with a large increase in the level of ASFV DNA within these cells. The pattern of the virus gene expression was very reproducible between the individual pigs. Many highly expressed genes have undefined roles. Surprisingly, some genes with key roles in virus replication were expressed at only low levels. As the functions of individual genes are identified, information about their expression becomes important for understanding their contribution to virus biology.

Salmonids are important sources of protein for a large proportion of the human population. Mycoplasma species are a major constituent of the gut microbiota of salmonids, often representing the majority of microbiota. Despite the frequent reported dominance of salmonid-related Mycoplasma species, little is known about the phylogenomic placement, functions and potential evolutionary relationships with their salmonid hosts. In this study, we utilise 2.9 billion metagenomic reads generated from 12 samples from three different salmonid host species to I) characterise and curate the first metagenome-assembled genomes (MAGs) of Mycoplasma dominating the intestines of three different salmonid species, II) establish the phylogeny of these salmonid candidate Mycoplasma species, III) perform a comprehensive pangenomic analysis of Mycoplasma, IV) decipher the putative functionalities of the salmonid MAGs and reveal specific functions expected to benefit the host. Our data provide a basis for future studies examining the composition and function of the salmonid microbiota.

Background: Infectious diseases cause significant production losses in aquaculture every year. Since the gut microbiota plays an essential role in regulating the host immune system, health and physiology, altered gut microbiota compositions are often associated with a diseased status. However, few studies have examined the association between disease severity and degree of gut dysbiosis, especially when the gut is not the site of the primary infection. Moreover, there is a lack of knowledge on whether bath treatment with formalin, a disinfectant commonly used in aquaculture to treat external infections, might affect the gut microbiome as a consequence of formalin ingestion. Here we investigate, through 16S rRNA gene metabarcoding, changes in the distal gut microbiota composition of a captive-reared cohort of 80 Atlantic salmon (Salmo salar L.), in consequence of an external bacterial skin infection due to a natural outbreak and subsequent formalin treatment., Results: We identified Tenacibaculum dicentrarchi as the causative disease pathogen and we show that the distal gut of diseased salmon presented a different composition from that of healthy individuals. A new, yet undescribed, Mycoplasma genus characterized the gut of healthy salmon, while in the sick fish we observed an increase in terms of relative abundance of Aliivibrio sp., a strain regarded as opportunistic. We also noticed a positive correlation between fish weight and Mycoplasma sp. relative abundance, potentially indicating a beneficial effect for its host. Moreover, we observed that the gut microbiota of fish treated with formalin was more similar to those of sick fish than healthy ones., Conclusions: We conclude that external Tenacibaculum infections have the potential of indirectly affecting the host gut microbiota. As such, treatment optimization procedures should account for that. Formalin treatment is not an optimal solution from a holistic perspective, since we observe an altered gut microbiota in the treated fish. We suggest its coupling with a probiotic treatment aimed at re-establishing a healthy community. Lastly, we have observed a positive correlation of Mycoplasma sp. with salmon health and weight, therefore we encourage further investigations towards its potential utilization as a biomarker for monitoring health in salmon and potentially other farmed fish species.

From ontogenesis to homeostasis, the phenotypes of complex organisms are shaped by the bidirectional interactions between the host organisms and their associated microbiota. Current technology can reveal many such interactions by combining multi-omic data from both hosts and microbes. However, exploring the full extent of these interactions requires careful consideration of study design for the efficient generation and optimal integration of data derived from (meta)genomics, (meta)transcriptomics, (meta)proteomics, and (meta)metabolomics. In this perspective, we introduce the holo-omic approach that incorporates multi-omic data from both host and microbiota domains to untangle the interplay between the two. We revisit the recent literature on biomolecular host-microbe interactions and discuss the implementation and current limitations of the holo-omic approach. We anticipate that the application of this approach can contribute to opening new research avenues and discoveries in biomedicine, biotechnology, agricultural and aquacultural sciences, nature conservation, as well as basic ecological and evolutionary research., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

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., (© 2019 John Wiley & Sons Ltd.)

Immediate freezing is perhaps the most preferred method used for preserving gut microbial samples, but research on sample preservation has been principally based around samples from mammalian species, and little is known about the advantages or disadvantages relating to different storage methods for fish guts. Fish gut samples may pose additional challenges due to the different chemical and enzymatic profile, as well as the higher water content, which might affect the yield and purity of DNA recovered. To explore this, we took gut content and mucosal scrape samples from 10 rainbow trout (Oncorhynchus mykiss), and tested whether different preservation methods have any effect on the ability to construct high quality genomic libraries for shotgun and 16S rRNA gene sequencing. Four different storage methods were compared for the gut content samples (immediate freezing on dry ice, 96% ethanol, RNAlater and DNA/RNA shield), while two different methods were compared for mucosal scrape samples (96% ethanol and RNAlater). The samples were thereafter stored at -80 °C. Our findings concluded that 96% ethanol outperforms the other storage methods when considering DNA quantity, quality, cost and labor. Ethanol works consistently well for both gut content and mucosal scrape samples, and enables construction of DNA sequencing libraries of sufficient quantity and with a fragment length distribution suitable for shotgun sequencing. Two main conclusions from our study are i) sample storage optimisation is an important part of establishing a microbiome research program in a new species or sample type system, and ii) 96% ethanol is the preferred method for storing rainbow trout gut content and mucosal scrape samples., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Deciphering the mechanisms governing population genetic divergence and local adaptation across heterogeneous environments is a central theme in marine ecology and conservation. While population divergence and ecological adaptive potential are classically viewed at the genetic level, it has recently been argued that their microbiomes may also contribute to population genetic divergence. We explored whether this might be plausible along the well-described environmental gradient of the Baltic Sea in two species of sand lance (Ammodytes tobianus and Hyperoplus lanceolatus). Specifically, we assessed both their population genetic and gut microbial composition variation and investigated not only which environmental parameters correlate with the observed variation, but whether host genome also correlates with microbiome variation., Results: We found a clear genetic structure separating the high-salinity North Sea from the low-salinity Baltic Sea sand lances. The observed genetic divergence was not simply a function of isolation by distance, but correlated with environmental parameters, such as salinity, sea surface temperature, and, in the case of A. tobianus, possibly water microbiota. Furthermore, we detected two distinct genetic groups in Baltic A. tobianus that might represent sympatric spawning types. Investigation of possible drivers of gut microbiome composition variation revealed that host species identity was significantly correlated with the microbial community composition of the gut. A potential influence of host genetic factors on gut microbiome composition was further confirmed by the results of a constrained analysis of principal coordinates. The host genetic component was among the parameters that best explain observed variation in gut microbiome composition., Conclusions: Our findings have relevance for the population structure of two commercial species but also provide insights into potentially relevant genomic and microbial factors with regards to sand lance adaptation across the North Sea-Baltic Sea environmental gradient. Furthermore, our findings support the hypothesis that host genetics may play a role in regulating the gut microbiome at both the interspecific and intraspecific levels. As sequencing costs continue to drop, we anticipate that future studies that include full genome and microbiome sequencing will be able to explore the full relationship and its potential adaptive implications for these species.

Aquaculture will play an essential role in feeding a growing human population, but several biological challenges impede sustainable growth of production. Emerging evidence across all areas of life has revealed the importance of the intimate biological interactions between animals and their associated gut microbiota. Based on challenges in aquaculture, we leverage current knowledge in molecular biology and host microbiota interactions to propose an applied holo-omic framework that integrates molecular data including genomes, transcriptomes, epigenomes, proteomes, and metabolomes for analyzing fish and their gut microbiota as interconnected and coregulated systems. With an eye towards aquaculture, we discuss the feasibility and potential of our holo-omic framework to improve growth, health, and sustainability in any area of food production, including livestock and agriculture., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A whole-genome duplication (WGD) doubles the entire genomic content of a species and is thought to have catalysed adaptive radiation in some polyploid-origin lineages. However, little is known about general consequences of a WGD because 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 nonduplicated 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 nondiverged 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., (© 2017 John Wiley & Sons Ltd.)

Marine ecosystems occupy 71% of the surface of our planet, yet we know little about their diversity. Although the inventory of species is continually increasing, as registered by the Census of Marine Life program, only about 10% of the estimated two million marine species are known. This lag between observed and estimated diversity is in part due to the elusiveness of most aquatic species and the technical difficulties of exploring extreme environments, as for instance the abyssal plains and polar waters. In the last decade, the rapid development of affordable and flexible high-throughput sequencing approaches have been helping to improve our knowledge of marine biodiversity, from the rich microbial biota that forms the base of the tree of life to a wealth of plant and animal species. In this review, we present an overview of the applications of genomics to the study of marine life, from evolutionary biology of non-model organisms to species of commercial relevance for fishing, aquaculture and biomedicine. Instead of providing an exhaustive list of available genomic data, we rather set to present contextualized examples that best represent the current status of the field of marine genomics., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Regions of the genome displaying elevated differentiation (genomic islands of divergence) are thought to play an important role in local adaptation, especially in populations experiencing high gene flow. However, the characteristics of these islands as well as the functional significance of genes located within them remain largely unknown. Here, we used data from thousands of SNPs aligned to a linkage map to investigate genomic islands of divergence in three ecotypes of sockeye salmon (Oncorhynchus nerka) from a single drainage in southwestern Alaska. We found ten islands displaying high differentiation among ecotypes. Conversely, neutral structure observed throughout the rest of the genome was low and not partitioned by ecotype. One island on linkage group So13 was particularly large and contained six SNPs with F ST  > 0.14 (average F ST of neutral SNPs = 0.01). Functional annotation revealed that the peak of this island contained a nonsynonymous mutation in a gene involved in growth in other species (TULP4). The islands that we discovered were relatively small (80-402 Kb), loci found in islands did not show reduced levels of diversity, and loci in islands displayed slightly elevated linkage disequilibrium. These attributes suggest that the islands discovered here were likely generated by divergence hitchhiking; however, we cannot rule out the possibility that other mechanisms may have produced them. Our results suggest that islands of divergence serve an important role in local adaptation with gene flow and represent a significant advance towards understanding the genetic basis of ecotypic differentiation., (© 2016 John Wiley & Sons Ltd.)

Salmonids are an important cultural and ecological resource exhibiting near worldwide distribution between their native and introduced range. Previous research has generated linkage maps and genomic resources for several species as well as genome assemblies for two species. We first leveraged improvements in mapping and genotyping methods to create a dense linkage map for Chinook salmon Oncorhynchus tshawytscha by assembling family data from different sources. We successfully mapped 14 620 SNP loci including 2336 paralogs in subtelomeric regions. This improved map was then used as a foundation to integrate genomic resources for gene annotation and population genomic analyses. We anchored a total of 286 scaffolds from the Atlantic salmon genome to the linkage map to provide a framework for the placement 11 728 Chinook salmon ESTs. Previously identified thermotolerance QTL were found to colocalize with several candidate genes including HSP70, a gene known to be involved in thermal response, as well as its inhibitor. Multiple regions of the genome with elevated divergence between populations were also identified, and annotation of ESTs in these regions identified candidate genes for fitness related traits such as stress response, growth and behaviour. Collectively, these results demonstrate the utility of combining genomic resources with linkage maps to enhance evolutionary inferences., (© 2015 John Wiley & Sons Ltd.)

Many plants and animals of polyploid origin are currently enjoying a genomics explosion enabled by modern sequencing and genotyping technologies. However, routine filtering of duplicated loci in most studies using genotyping by sequencing introduces an unacceptable, but often overlooked, bias when detecting selection. Retained duplicates from ancient whole-genome duplications (WGDs) may be found throughout genomes, whereas retained duplicates from recent WGDs are concentrated at distal ends of some chromosome arms. Additionally, segmental duplicates can be found at distal ends or nearly anywhere in a genome. Evidence shows that these duplications facilitate adaptation through one of two pathways: neo-functionalization or increased gene expression. Filtering duplicates removes distal ends of some chromosomes, and distal ends are especially known to harbour adaptively important genes. Thus, filtering of duplicated loci impoverishes the interpretation of genomic data as signals from contiguous duplicated genes are ignored. We review existing strategies to genotype and map duplicated loci; we focus in detail on an overlooked strategy of using gynogenetic haploids (1N) as a part of new genotyping by sequencing studies. We provide guidelines on how to use this haploid strategy for studies on polyploid-origin vertebrates including how it can be used to screen duplicated loci in natural populations. We conclude by discussing areas of research that will benefit from better inclusion of polyploid loci; we particularly stress the sometimes overlooked fact that basing genomic studies on dense maps provides value added in the form of locating and annotating outlier loci or colocating outliers into islands of divergence., (© 2016 John Wiley & Sons Ltd.)

Linkage mapping is often used to identify genes associated with phenotypic traits and for aiding genome assemblies. Still, many emerging maps do not locate centromeres - an essential component of the genomic landscape. Here, we demonstrate that for genomes with strong chiasma interference, approximate centromere placement is possible by phasing the same data used to generate linkage maps. Assuming one obligate crossover per chromosome arm, information about centromere location can be revealed by tracking the accumulated recombination frequency along linkage groups, similar to half-tetrad analyses. We validate the method on a linkage map for sockeye salmon (Oncorhynchus nerka) with known centromeric regions. Further tests suggest that the method will work well in other salmonids and other eukaryotes. However, the method performed weakly when applied to a male linkage map (rainbow trout; O. mykiss) characterized by low and unevenly distributed recombination - a general feature of male meiosis in many species. Further, a high frequency of double crossovers along chromosome arms in barley reduced resolution for locating centromeric regions on most linkage groups. Despite these limitations, our method should work well for high-density maps in species with strong recombination interference and will enrich many existing and future mapping resources., (© 2015 The Authors. Molecular Ecology Resources published by John Wiley & Sons Ltd.)

Understanding the genetic architecture of phenotypic traits can provide important information about the mechanisms and genomic regions involved in local adaptation and speciation. Here, we used genotyping-by-sequencing and a combination of previously published and newly generated data to construct sex-specific linkage maps for sockeye salmon (Oncorhynchus nerka). We then used the denser female linkage map to conduct quantitative trait locus (QTL) analysis for 4 phenotypic traits in 3 families. The female linkage map consisted of 6322 loci distributed across 29 linkage groups and was 4082 cM long, and the male map contained 2179 loci found on 28 linkage groups and was 2291 cM long. We found 26 QTL: 6 for thermotolerance, 5 for length, 9 for weight, and 6 for condition factor. QTL were distributed nonrandomly across the genome and were often found in hotspots containing multiple QTL for a variety of phenotypic traits. These hotspots may represent adaptively important regions and are excellent candidates for future research. Comparing our results with studies in other salmonids revealed several regions with overlapping QTL for the same phenotypic trait, indicating these regions may be adaptively important across multiple species. Altogether, our study demonstrates the utility of genomic data for investigating the genetic basis of important phenotypic traits. Additionally, the linkage map created here will enable future research on the genetic basis of phenotypic traits in salmon., (© The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

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., (Copyright © 2015 Limborg et al.)

A whole genome duplication occurred in the ancestor of all salmonid fishes some 50-100 million years ago. Early inheritance studies with allozymes indicated that loci in the salmonid genome are inherited disomically in females. However, some pairs of duplicated loci showed patterns of inheritance in males indicating pairing and recombination between homeologous chromosomes. Nearly 20% of loci in the salmonid genome are duplicated and share the same alleles (isoloci), apparently due to homeologous recombination. Half-tetrad analysis revealed that isoloci tend to be telomeric. These results suggested that residual tetrasomic inheritance of isoloci results from homeologous recombination near chromosome ends and that continued disomic inheritance resulted from homologous pairing of centromeric regions. Many current genetic maps of salmonids are based on single nucleotide polymorphisms and microsatellites that are no longer duplicated. Therefore, long sections of chromosomes on these maps are poorly represented, especially telomeric regions. In addition, preferential multivalent pairing of homeologs from the same species in F1 hybrids results in an excess of nonparental gametes (so-called pseudolinkage). We consider how not including duplicated loci has affected our understanding of population and evolutionary genetics of salmonids, and we discuss how incorporating these loci will benefit our understanding of population genomics., (© The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

A species' genetic diversity bears the marks of evolutionary processes that have occurred throughout its history. However, robust detection of selection in wild populations is difficult and often impeded by lack of replicate tests. Here, we investigate selection in pink salmon (Oncorhynchus gorbuscha) using genome scans coupled with inference from a haploid-assisted linkage map. Pink salmon have a strict 2-year semelparous life history which has resulted in temporally isolated (allochronic) lineages that remain sympatric through sharing of spawning habitats in alternate years. The lineages differ in a range of adaptive traits, suggesting different genetic backgrounds. We used genotyping by sequencing of haploids to generate a high-density linkage map with 7035 loci and screened an existing panel of 8036 loci for signatures of selection. The linkage map enabled identification of novel genomic regions displaying signatures of parallel selection shared between lineages. Furthermore, 24 loci demonstrated divergent selection and differences in genetic diversity between lineages, suggesting that adaptation in the 2 lineages has arisen from different pools of standing genetic variation. Findings have implications for understanding asynchronous population abundances as well as predicting future ecosystem impacts from lineage-specific responses to climate change., (© The American Genetic Association 2014. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)