Nils Ryman

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Verified

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• Professor
• Professor (Full) at Stockholm University

Translocations are carried out either unintentionally or intentionally for conservation or management reasons. In both cases, translocated populations may genetically impact natural populations via introgression. Understanding how genetic background may affect an establishment in a novel environment and the potential risks for native populations is...

Salmonids have a remarkable ability to form sympatric morphs after postglacial colonization of freshwater lakes. These morphs often exhibit differences in morphology, feeding, and spawning behaviour. Here we explore the genetics of morph differentiation by establishing a high-quality, annotated reference genome for the Arctic charr and use this as...

There are two primary measures of the amount of genetic variation in a population at a locus: heterozygosity and the number of alleles. Effective population size (Ne) provides both an expectation of the amount of heterozygosity in a population at drift‐mutation equilibrium and the rate of loss of heterozygosity because of genetic drift. In contrast...

Genetic diversity is fundamental to the adaptive potential and survival of species. Although its importance has long been recognized in science, it has a history of neglect within policy, until now. The new Global Biodiversity Framework recently adopted by the Convention on Biological Diversity, states that genetic diversity must be maintained at l...

International policy recently adopted commitments to maintain genetic diversity in wild populations to secure their adaptive potential, including metrics to monitor temporal trends in genetic diversity – so‐called indicators. A national programme for assessing trends in genetic diversity was recently initiated in Sweden. Relating to this effort, we...

Ungulate species have experienced severe declines over the past centuries through over-harvesting and habitat loss. Even if many game species have recovered thanks to strict hunting regulation, the genome-wide impacts of overharvesting are still unclear. Here, we examine the temporal and geographical differences in genome-wide diversity in moose (A...

The variance effective population size ([Formula: see text]) is frequently used to quantify the expected rate at which a population's allele frequencies change over time. The purpose of this paper is to find expressions for the global [Formula: see text] of a spatially structured population that are of interest for conservation of species. Since [F...

Measurement of allele frequency shifts between temporally spaced samples has long been used for assessment of effective population size (Ne), and this ‘temporal method’ provides estimates of Ne referred to as variance effective size (NeV). We show that NeV of a local population that belongs to a sub‐structured population (a metapopulation) is deter...

Fred Utter died in his sleep during the night of 5 March 2023 at the age of 91. In this paper, three friends and colleagues of Fred describe the important role that his genetics research has played in the management and conservation of fish populations.

Population extinction is ubiquitous in all taxa. Such extirpations can reduce intraspecific diversity, but the extent to which genetic diversity of surviving populations are affected remains largely unclear. A key concept in this context is the effective population size (Ne), which quantifies the rate at which genetic diversity within populations i...

Genetic diversity is the basis for population adaptation and long‐term survival, yet rarely considered in biodiversity monitoring. One key issue is the need for useful and straightforward indicators of genetic diversity. We monitored genetic diversity over 40 years (1970–2010) in metapopulations of brown trout (Salmo trutta) inhabiting 27 small mou...

Population translocations occur for a variety of reasons, from displacement due to climate change to human-induced transfers. Such actions have adverse effects on genetic variation and understanding their microevolutionary consequences requires monitoring. Here, we return to an experimental release of brown trout (Salmo trutta) in order to monitor...

Understanding the consequences of human induced translocations on natural populations requires genetic monitoring. Salmonid fishes represent a group of species experiencing several such large-scale perturbations expected to affect microevolutionary processes. Here, two genetically separate brown trout populations with divergent life history traits...

Genetic diversity is the basis for population adaptation and long-term survival, yet rarely considered in biodiversity monitoring. One key issue is the need for useful and straightforward indicators of genetic diversity. To test newly proposed indicators, we monitored genetic diversity over 40 years (1970-2010) in metapopulations of brown trout inh...

The sympatric existence of genetically distinguishable populations of the same species remains a puzzle in ecology. Coexisting salmonid fish populations are known from over 100 freshwater lakes. Most studies of sympatric populations have used limited numbers of genetic markers making it unclear if genetic divergence involves certain parts of the ge...

A correction to this paper has been published: https://doi.org/10.1007/s10592-021-01376-9

The sympatric existence of genetically distinct populations of the same species remains a puzzle in ecology. Coexisting salmonid fish populations are known from over 100 freshwater lakes. Most studies of sympatric populations have used limited numbers of genetic markers making it unclear if genetic divergence involves only certain parts of the geno...

Background Numerous megafauna species from northern latitudes went extinct during the Pleistocene/Holocene transition as a result of climate-induced habitat changes. However, several ungulate species managed to successfully track their habitats during this period to eventually flourish and recolonise the holarctic regions. So far, the genomic impac...

Population census size (N C) and effective population sizes (N e) are two crucial parameters that influence population viability, wildlife management decisions , and conservation planning. Genetic estimators of both N C and N e are increasingly widely used because molecular markers are increasingly available, statistical methods are improving rapid...

Developing genomic insights is challenging in nonmodel species for which resources are often scarce and prohibitively costly. Here, we explore the potential of a recently established approach using Pool-seq data to generate a de novo genome assembly for mining exons, upon which Pool-seq data are used to estimate population divergence and diversity....

Estimation of effective population size (Ne) from genetic marker data is a major focus for biodiversity conservation because it is essential to know at what rates inbreeding is increasing and additive genetic variation is lost. But are these the rates assessed when applying commonly used Ne estimation techniques? Here we use recently developed anal...

Sympatric populations are conspecific populations that co‐exist spatially. They are of interest in evolutionary biology by representing the potential first steps of sympatric speciation and are important to identify and monitor in conservation management. Reviewing the literature pertaining to sympatric populations, we find that most cases of sympa...

The majority of herbivorous insects are specialized in host use. Even among insects that use many hosts, local specialization is common with a single host plant often being used in any given locality. Here, we establish such a pattern for the European swallowtail butterfly, Papilio machaon. We sampled larvae on five different natural hosts at eight...

Intraspecific genetic variation can have similar effects as species diversity on ecosystem function; understanding such variation is important, particularly for ecological key species. The brown trout plays central roles in many northern freshwater ecosystems, and several cases of sympatric brown trout populations have been detected in freshwater l...

Atlantic herring is an excellent species for studying the genetic basis of adaptation in geographically distant populations because of its characteristically large population sizes and low genetic drift. In this study we compared whole-genome resequencing data of Atlantic herring populations from both sides of the Atlantic Ocean. An important findi...

Atlantic herring is an excellent species for studying the genetic basis of adaptation in geographically distant populations because of its characteristically large population sizes and low genetic drift. In this study we compared whole-genome resequencing data of Atlantic herring populations from both sides of the Atlantic Ocean. An important findi...

The genetically effective population size (Ne) is of key importance for quantifying rates of inbreeding and genetic drift, and is often used in conservation management to set targets for genetic viability. The concept was developed for single, isolated populations and the mathematical means for analyzing the expected Ne in complex, subdivided popul...

Sympatric populations occur in many freshwater fish species; such populations are typically detected through morphological distinctions that are often coupled to food niche and genetic separations. In salmonids, trophic and genetically separate sympatric populations have been reported in landlocked Arctic char, whitefish and brown trout. In Arctic...

Understanding spatiotemporal population genetic patterns is important for conservation management of ecologically and socioeconomically important species. This is particularly so in species-poor environments such as the brackish Baltic Sea. We examined over 600 northern pike (Esox lucius), a coastal predator and treasured sport fish, collected over...

The Scandinavian wolf population descends from only five individuals, is isolated, highly inbred and exhibits inbreeding depression. To meet international conservation goals, suggestions include managing subdivided wolf populations over Fennoscandia as a metapopulation; a genetically effective population size of Ne⩾ 500, in line with the widely acc...

(A) Summary of sequencing data used to generate the herring genome assembly. (B) Statistics of the herring genome assembly developed using SOAPdenovo. v1.0 to v1.4 refer to different versions of the assembly. Full description of the assembly process is provided within the Methods section. (C) Statistics for genome completeness based on 248 annotate...

Endogenous retroviruses detected with RetroTector. DOI: http://dx.doi.org/10.7554/eLife.12081.022

(A) List of loci showing strong genetic differentiation between Atlantic and Baltic herring (p<10-10). (B) List of structural changes associated with genetic differentiation between Atlantic and Baltic herring. (C) List of loci showing strong genetic differentiation between spring- and autumn-spawning herring (p<10-10). (D) List of structural chang...

Ecological adaptation is of major relevance to speciation and sustainable population management, but the underlying genetic factors are typically hard to study in natural populations due to genetic differentiation caused by natural selection being confounded with genetic drift in subdivided populations. Here, we use whole genome population sequenci...

The moose (Alces alces) is the most intensely managed game species in Fennoscandia; approximately one-third of the population, ca. 160,000 animals, is harvested annually. Despite the species’ biological and socioeconomic importance, there are knowledge gaps with respect to its intraspecific diversity and genetic structure. Recent studies of moose i...

Motivated by problems in conservation biology we study genetic dynamics in structured populations of diploid organisms (monoecious or dioecious). Our analysis provides an analytical framework that unifies substantial parts of previous work in terms of exact identity by descent (IBD) and identity by state (IBS) recursions. We provide exact condition...

The main purpose of this paper is to develop a theoretical framework for assessing effective population size and genetic divergence in situations with structured populations that consist of various numbers of more or less interconnected subpopulations. We introduce a general infinite allele model for a diploid, monoecious and subdivided population,...

The world faces a global fishing crisis. Wild marine fisheries comprise nearly 15% of all animal protein in the human diet, but, according to the U.N. Food and Agriculture Organization, nearly 60% of all commercially important marine fish stocks are overexploited, recovering, or depleted (FAO ; Fig. ). Some authors have suggested that the large pop...

Information on spatial and temporal patterns of genetic diversity is a prerequisite to understanding the demography of populations, and is fundamental to successful management and conservation of species. In the sea, it has been observed that oceanographic and other physical forces can constitute barriers to gene flow that may result in similar pop...

In this paper, we develop a method for computing the variance effective size [Formula: see text], the fixation index [Formula: see text] and the coefficient of gene differentiation [Formula: see text] of a structured population under equilibrium conditions. The subpopulation sizes are constant in time, with migration and reproduction schemes that c...

The variance effective population size (NeV) is a key concept in population biology, because it quantifies the microevolutionary process of random genetic drift, and understanding the characteristics of NeV is thus of central importance. Current formulas for NeV for populations with overlapping generations weight age classes according to their repr...

Many empirical studies estimating effective population size apply the temporal method that provides an estimate of the variance effective size through the amount of temporal allele frequency change under the assumption that the study population is completely isolated. This assumption is frequently violated, and the magnitude of the resulting bias i...

Appendix S1 Derivations and mathematical expressions for expected estimates of variance effective population size (NeV) when sampling from a population system assuming an island model of migration.

Appendix S2 Computer simulations to verify analytical results.

Detecting population subdivision when apparent barriers to gene flow are lacking is important in evolutionary and conservation biology. Recent research indicates that intraspecific population complexity can be crucial for maintaining a species′ evolutionary potential, productivity, and ecological role. We monitored the genetic relationships at 14 a...

Use of genetic methods to estimate effective population size (Ne) is rapidly increasing, but all approaches make simplifying assumptions unlikely to be met in real populations. In particular, all assume a single, unstructured population, and none has been evaluated for use with continuously distributed species. We simulated continuous populations w...

The wolf (Canis lupus) is classified as endangered in Sweden by the Swedish Species Information Centre, which is the official authority for threat classification. The present population, which was founded in the early 1980s, descends from 5 individuals. It is isolated and highly inbred, and on average individuals are more related than siblings. Hun...

The fixation index F(ST) and the coefficient of gene differentiation G(ST) are analyzed for the finite island model under short time spans, ignoring mutations. Dividing the reproduction cycle into the three steps-gamete formation, fertilization, and migration-we develop a new approach for computing quasi equilibrium formulas for F(ST) (and G(ST))....

The Atlantic herring (Clupea harengus), one of the most abundant marine fishes in the world, has historically been a critical food source in Northern Europe. It is one of the few marine species that can reproduce throughout the brackish salinity gradient of the Baltic Sea. Previous studies based on few genetic markers have revealed a conspicuous la...

Knowledge of the degree of temporal stability of population genetic structure and composition is important for understanding microevolutionary processes and addressing issues of human impact of natural populations. We know little about how representative single samples in time are to reflect population genetic constitution, and we explore the tempo...

Interspecific hybridization between Atlantic salmon and brown trout is well documented, but why it should vary so much among populations is not clear. Determining the maternal origin of hybrids can provide insights into the mechanisms underlying interspecific hybridization, but this information is lacking in many studies. Here we present a species-...

a b s t r a c t Stocks of whitefish (Coregonus maraena) in the northern part of the Baltic Sea have in many areas declined drastically during recent years. Causes for the decline are yet not fully understood, but knowledge on the genetic population structure of the species is pivotal for future conservation measures. In this study we analyse the ge...

Determining spatio-temporal distributions of fish populations is of interest to marine ecology, in general, and to fisheries science in particular. Genetic mixed-stock analysis is routinely applied in several anadromous fishes for determining migratory routes and timing but has rarely been used for marine fishes, for which population differentiatio...

Census (N(C)) and effective population size (N(e)) were estimated for a lake-resident population of brown trout Salmo trutta as 576 and 63, respectively. The point estimate of the ratio of effective to census population size (N(e):N(C)) for this population is 0.11 with a range of 0.06-0.26, suggesting that N(e):N(C) ratio for lake-resident populati...

In this study, the genetic variation of perch Perca fluviatilis from 18 different sites along the Swedish coast of the Baltic Sea was assessed. There was a relative strong support for isolation by distance and the results suggest an overall departure from panmixia. The level of genetic divergence was moderate (global F(ST) = 0·04) and indications o...

Intraspecific planting and introduction of new species of fish has been much more restricted in northern Scandinavia than in many other parts of the world. Further, the general geography, with a large number of independent drainages and numerous impassable waterfalls, often prevented extensive spread of planted freshwater fish. Therefore, the genet...

Examples of desired genetic changes produced in fish by selective breeding are contrasted with those of unintentional and often harmful genetic changes resulting from artificial propagation over prolonged periods, e.g. reduced longevity and reduced temperature tolerance. Evidence for undesired effects caused by the hatchery environment on captive f...

The amount of genetic differentiation between stocks of Atlantic cod (Gadus morhua) was estimated from electrophoretically detectable protein loci expressed in skeletal muscle and liver. Variant alleles at 13 of these loci were detected among nine samples covering most of the species range: North America, Greenland, Iceland, Barents Sea, Norwegian...

In many marine fish species, genetic population structure is typically weak because populations are large, evolutionarily young and have a high potential for gene flow. We tested whether genetic markers influenced by natural selection are more efficient than the presumed neutral genetic markers to detect population structure in Atlantic herring (Cl...

ABSTRACT  The moose (Alces alces) is the most intensely managed game species in Sweden. Despite the biological and socioeconomical importance of moose, little is known of its population genetic structure. We analyzed 132 individuals from 4 geographically separate regions in Sweden for genetic variability at 6 microsatellite loci. We found evidence...

Large-scale exploitation of wild animals and plants through fishing, hunting and logging often depends on augmentation through releases of translocated or captively raised individuals. Such releases are performed worldwide in vast numbers. Augmentation can be demographically and economically beneficial but can also cause four types of adverse genet...

Population census size (N C) and effective population sizes (N e) are two crucial parameters that influence population viability, wildlife management decisions, and conservation planning. Genetic estimators of both N C and N e are increasingly widely used because molecular markers are increasingly available, statistical methods are improving rapidl...

During the Late Pleistocene, the woolly mammoth (Mammuthus primigenius) experienced a series of local extinctions generally attributed to human predation or environmental change. Some small and isolated populations did however survive far into the Holocene. Here, we investigated the genetic consequences of the isolation of the last remaining mammot...

Genetic diversity is the foundation for all biological diversity; the persistence and evolutionary potential of species depend on it. World leaders have agreed on the conservation of genetic diversity as an explicit goal of the Convention on Biological Diversity (CBD). Nevertheless, actions to protect genetic diversity are largely lacking. With onl...

“Favourable Conservation Status” (FCS) is a central concept in the biodiversity conservation legislation of the European Union (EU). Here, we highlight the importance of incorporating aspects of conservation genetics in interpretation of this concept. Recent documents from the EU Commission indicate that knowledge of conservation genetics has so fa...

Statistical power is critical in conservation for detecting genetic differences in space or time from allele frequency data. Organelle and nuclear genetic markers have fundamentally different transmission dynamics; the potential effect of these differences on power to detect divergence have been speculated on but not investigated. We examine, analy...

Information on the temporal stability of genetic structures is important to permit detection of changes that can constitute threats to biological resources. Large-scale harvesting operations are known to potentially alter the composition and reduce the variability of populations, and Atlantic herring (Clupea harengus) has a long history of heavy ex...

At the Army Dog Training Center - ADTC -, Sollefteå, Sweden, a test of mentality has been designed to judge eight “components of behaviour” in working dogs. The test is used to choose dogs suitable for training in different military and civil tasks. Furthermore the test results are also important in the breeding-planning at the ADTC as well as in t...