Bjarni Kristófer Kristjánsson

Hólar University · Department of Aquaculture and Fish Biology

Adaptive genetic divergence occurs when selection imposed by the environment causes the genomic component of the phenotype to differentiate. However, genomic signatures of natural selection are usually identified without information on which trait is responding to selection by which selective agent(s). Here we integrate whole‐genome‐sequencing with...

Given the threat of climate change to biodiversity, a growing number of studies are investigating the potential for organisms to adapt to rising temperatures. Earlier work has predicted that physiological adaptation to climate change will be accompanied by a shift in temperature preferences, but empirical evidence for this is lacking. Here, we test...

The analysis of phylogeographic patterns has often been based on mitochondrial DNA variation, but recent analyses dealing with nuclear DNA have in some instances revealed mito-nuclear discordances and complex evolutionary histories. These enigmatic scenarios, which may involve stochastic lineage sorting, ancestral hybridization, past dispersal and...

Within-clutch variation in the size or the amount of yolk in the egg has been widely studied because of its importance for both maternal and ofspring ftness. In particular, egg size has been used as a proxy for survival in first-feeding salmonids alevins. We tested the hypothesis that egg size has implications for the phenotypes (development, physi...

Gaining the ability to predict population responses to climate change is a pressing concern. Using a "natural experiment," we show that testing for divergent evolution in wild populations from contrasting thermal environments provides a powerful approach, and likely an enhanced predictive power for responses to climate change. Specifically, we used...

The costs and benefits of being social vary with environmental conditions, so individuals must weigh the balance between these trade-offs in response to changes in the environment. Temperature is a salient environmental factor that may play a key role in altering the costs and benefits of sociality through its effects on food availability , predato...

David Lloyd George Noakes (1942–2020) is best known for his insatiable curiosity, his quick wit and dry sense of humor, his scientific contributions to the field of animal behaviour, and his ability to form and maintain long-lasting connections. His research interests were vast but remained grounded in early life history, behaviour, social behaviou...

Maternal effects have the potential to alter early developmental processes of offspring and contribute to adaptive diversification. Egg size is a major contributor to offspring phenotype, which can influence developmental trajectories and potential resource use. However, to what extent intraspecific variation in egg size facilitates evolution of re...

Uncovering the demographic basis of population fluctuations is a central goal of population biology. This is particularly challenging for spatially structured populations, which require disentangling synchrony in demographic rates from coupling via movement between locations. In this study, we fit a stage-structured metapopulation model to a 29-yea...

Adaptive genetic divergence occurs when selection imposed by the environment causes the genomic component of the phenotype to differentiate. However, genomic signatures of natural selection are usually identified without information on which trait is responding to selection by which selective agent(s). Here, we integrate whole-genome-sequencing wit...

In many respects, freshwater springs can be considered as unique ecosystems on the fringe of aquatic habitats. This integrates their uniqueness in terms of stability of environmental metrics. The main objective of our study was to evaluate how environmental variables may shape invertebrate diversity and community composition in different freshwater...

Genetic variation in resistance against parasite infections is a predominant feature in host–parasite systems. However, mechanisms maintaining genetic polymorphism in resistance in natural host populations are generally poorly known. We explored whether differences in natural infection pressure between resource‐based morphs of Arctic charr (Salveli...

The ability to re-identify individuals is fundamental to the individual-based studies that are required to estimate many important ecological and evolutionary parameters in wild populations. Traditional methods of marking individuals and tracking them through time can be invasive and imperfect, which can affect these estimates and create uncertaint...

Many life-history events in aquatic invertebrates are triggered by seasonal changes in water temperature, but other ecological factors may be important as well. To rule out the confounding effects of changing water temperature, we studied the seasonal dynamics of an aquatic invertebrate community and their effect on a top fish predator in a thermal...

Background Organismal fitness can be determined at early life-stages, but phenotypic variation at early life-stages is rarely considered in studies on evolutionary diversification. The trophic apparatus has been shown to contribute to sympatric resource-mediated divergence in several taxa. However, processes underlying diversification in trophic tr...

Cold groundwater springs at the edges of lava fields along the volcanic active zone in Iceland are an interesting habitat, presenting an ecotone between groundwater, surface water and the terrestrial ecosystems. They are categorized as fennoscandian mineral-rich springs according to the European Nature Information System (EUNIS) classification (C2....

The aim of this study was to characterize the Trichoptera fauna of freshwater springs in Iceland and to relate distribution of caddis larvae to environmental properties of the springs. Out of a total of 48 springs sampled, Trichoptera larvae were found in only eleven. Larval densities were low, as was species diversity. Only three of the 12 species...

1. Ecological damage by scuba divers has been extensively studied in marine ecosystems, particularly coral reefs, whereas the impacts on freshwater environments such as groundwater springs is unknown. In the Silfra groundwater fissure in Iceland, a vast increase in diver entries has occurred during the last decade, prompting concerns over potential...

Background Organismal fitness can be determined at early life-stages, but phenotypic variation at these early life-stages has rarely been considered in studies on evolutionary diversification. The trophic apparatus has been shown to contribute to sympatric resource-mediated divergence in several taxa. However, processes underlying this diversificat...

Background Organismal fitness can be determined at early life-stages, but phenotypic variation at early life-stages is rarely considered in studies on evolutionary diversification. The trophic apparatus has been shown to contribute to sympatric resource-mediated divergence in several taxa. However, processes underlying diversification in trophic tr...

In light of global climate change, there is a pressing need to understand and predict the capacity of populations to respond to rising temperatures. Metabolic rate is a key trait that is likely to influence the ability to cope with climate change. Yet, empirical and theoretical work on metabolic rate responses to temperature changes has so far prod...

Crangonyx islandicus is a groundwater amphipod endemic to Iceland, considered to have survived the Ice Ages in subglacial refugia. Currently the species is found in spring sources in lava fields along the tectonic plate boundary of the country. The discovery of a groundwater species in this inaccessible habitat indicates a hidden ecosystem possibly...

The repeatability of adaptive radiation is expected to be scale-dependent, with determinism decreasing as greater spatial separation among "replicates" leads to their increased genetic and ecological independence. Threespine stickleback (Gasterosteus aculeatus) provide an opportunity to test whether this expectation holds for the early stages of ad...

In light of global climate change, there is a pressing need to understand and predict the capacity of populations to respond to rising temperatures. Metabolic rate is a key trait that is likely to influence the ability to cope with climate change. Yet, empirical and theoretical work on metabolic rate responses to temperature changes has so far prod...

Abstract Divergence in phenotypic traits is facilitated by a combination of natural selection, phenotypic plasticity, gene flow, and genetic drift, whereby the role of drift is expected to be particularly important in small and isolated populations. Separating the components of phenotypic divergence is notoriously difficult, particularly for multiv...

A major goal of evolutionary science is to understand how biological diversity is generated and altered. Despite considerable advances, we still have limited insight into how phenotypic variation arises and is sorted by natural selection. Here we argue that an integrated view, which merges ecology, evolution and developmental biology (eco evo devo)...

Iceland has an abundance of fissures that are parallel to the Mid‐Atlantic Ridge where bedrock cracks as a result of continental rifting. Some fissures penetrate the aquifer and expose the groundwater within the bedrock, becoming springs. As such, groundwater fissures have uniform and constant physical and chemical environment but they can differ g...

Given the threat of climate change to biodiversity, a growing number of studies are investigating the potential for organisms to adapt to rising temperatures through changes in their physiology, morphology, and behaviour. Earlier work has predicted that evolutionary adaptation to climate change will be accompanied by a shift in temperature preferen...

In light of climate change, the ability to predict evolutionary responses to temperature changes is of central importance for conservation efforts. Studying parallel evolution in natural populations inhabiting contrasting thermal environments presents a powerful approach for understanding and predicting responses to increasing temperatures. In this...

The repeatability of adaptive radiation is expected to be scale dependent, with determinism decreasing as greater spatial separation among ″replicates″ leads to their increased genetic and ecological independence. Threespine stickleback ( Gasterosteus aculeatus ) provide an opportunity to test whether this expectation holds for the early stages of...

Gene expression during development shapes the phenotypes of individuals. Although embryonic gene expression can have lasting effects on developmental trajectories, few studies consider the role of maternal effects, such as egg size, on gene expression. Using qPCR, we characterize relative expression of 14 growth and/or skeletal promoting genes acro...

Although numerous methods have been developed for SCUBA diver-operated sampling, few are suitable for sampling complex physical substrates. Sites such as groundwater springs sometimes have narrow sections along with uneven vertical and horizontal rock substrates at various depths. Here we developed a SCUBA diver-operated suction pump sampling syste...

Two endemic subterranean freshwater amphipod species have been discovered in groundwater of the volcanic active zone in Iceland, Crangonyx islandicus and Crymostygius thingvallensis. At least five different ciliate sequences were isolated from C. islandicus and the analysis of variation at the 18S ribosomal DNA gene suggests that they present previ...

In 1937, S. L. Tuxen studied the animal community of hot springs in Iceland, and classified springs according to their relative temperature into cold, tepid, and hot. Eighty years after Tuxen’s study, we revisited some of the hot springs in Skagafjörður, Northern Iceland. Our aim was to compare the invertebrate community of 1937 and today, and to a...

Phenotypic differences between closely related taxa or populations can arise through genetic variation or be environmentally induced, leading to altered transcription of genes during development. Comparative developmental studies of closely related species or variable populations within species can help to elucidate the molecular mechanisms related...

Results from differential expression analysis. Multiple testing corrected p-values (q-values) and overall log fold change between morphs from the full model for each transcript are shown (Model FM in methods). TransID:Trinity transcript identification code q_MxT: Q-value for the Morph × Time interaction term from likelihood ratio test between model...

The results of gene ontology analyses of the transcripts with significant expression difference between morphs (or morph by time interaction) in the Arctic charr developmental transcriptome. The enrichment was tested for transcripts and genes (SalmoBase) GO.ID: Identification number for Gene Ontology categories Term: The Gene Ontology term or descr...

Supplementary material Sequencing effort, quality trimming, mapping and estimated insert size for each sample.

Information about genes used in qPCR. Detailed gene names, primer sequence, amplicon size and transcripts in the assembly used for comparison Gene Symbol: The symbol or short gene name used in figures and text Description: Full name of each gene Forward primer:Sequence for the forward qPCR primer in 5’-3’ orientation Reverse primer: Sequence for th...

Developmental events in the LB-charr at relative ages 100–200τs (A) Developmental events in the LB-charr at relative ages 100–200τs (dorsal views of 6 time points). By 100τs heart contractions have begun and second gill fissures have started to form. By 140τs all somites are formed and eye pigmentation has started to appear. Between 150–200τs the u...

Principal component analysis (PCA) of expression data for all transcripts (A) shows the first and second PCA-axis and (B) the third and fourth PCA-axis. The first PCA-axis correlates with developmental time. Samples from 2011 (SB100, SB140 and PL140) do not deviate largely from other samples for any of the PCA-axis. Standardized expression normaliz...

Effect of 3’-bias correction on the number of transcripts differently expressed by developmental timepoint (time), morph and interaction of morph and time (int) Each figure shows the intersection size (upper barplot) - the number of transcripts significant for each one or a combination of two or more factors (indicated by dots), while the set size...

The invertebrate fauna from 22 lava spring sources throughout Iceland’s volcanically active zone was studied to investigate the role of spring type and environmental variables in shaping invertebrate communities. Springs were selected based on the ability to identify a discrete source, which was discharging water that appeared to be geothermally un...

The early stages of intraspecific diversity are important for the evolution of diversification and speciation. Early stages of diversification can be seen in individual specialization, where individuals consume only a portion of the diet of the population as a whole, and how such specialization is related to phenotypic diversity within populations....

Polymorphism, the occurrence of two or more distinct phenotypes of a same species, is the result of evolutionary and ecological processes. Arctic charr, a Northern freshwater fish, is a good model to study resource polymorphism due to its high level of intra-specific diversity. Pairs of sympatric resource-based morphs are commonly found within lake...

Phenotypic differences between closely related taxa or populations can arise through genetic variation or be environmentally induced, in both cases leading to altered transcription of genes during the structural and functional development of the body. Comparative developmental studies of closely related species or variable populations of the same s...

Phenotypic differences between closely related taxa or populations can arise through genetic variation or be environmentally induced, in both cases leading to altered transcription of genes during the structural and functional development of the body. Comparative developmental studies of closely related species or variable populations of the same s...

Intraspecific phenotypic diversity is the raw material for evolution, so understanding its origin and maintenance is critically important for conservation of biodiversity. Intraspecific diversity in a trait or a suite of traits can result from genetic diversity and/or phenotypic plasticity. The two are, however, not independent as plasticity has be...

In 1937, the Danish biologist S. L. Tuxen visited Iceland and dedicated a couple of months to the study of the hot spring fauna of the country. His description of hot spring communities set a cornerstone for crenobiology and is still cited nowadays. He classified springs according to their relative temperature into cold, tepid, and hot springs, and...

Species and populations with parallel evolution of specific traits can help illuminate how predictable adaptations and divergence are at the molecular and developmental level. Following the last glacial period, dwarfism and specialized bottom feeding morphology evolved rapidly in several landlocked Arctic charr Salvelinus alpinus populations in Ice...

Experiments using natural populations have provided mixed support for thermal adaptation models, probably because the conditions are often confounded with additional environmental factors like seasonality. The contrasting geothermal environments within Lake Mývatn, northern Iceland, provide a unique opportunity to evaluate thermal adaptation models...

Cases of evolutionary diversification can be characterized along a continuum from weak to strong genetic and phenotypic differentiation. Several factors may facilitate or constrain the differentiation process. Comparative analyses of replicates of the same taxon at different stages of differentiation can be useful to identify these factors. We esti...

A key question in evolutionary biology is to understand which factors shape biological diversity. This is especially true at the intra-specific level, where evolutionary and ecologically processes interact to shape the phenotypic and genetic structure of natural populations. Long-term monitoring studies on highly replicated wild populations are par...

The impressive diversity in the feeding apparatus often seen among related fish species clearly reflects differences in feeding modes and habitat utilization. Such variation can also be found within species. One example of such intraspecific diversity is the Arctic charr in Lake Thingvallavatn, where four distinct morphs coexist: two limnetic, with...

Species and populations with parallel evolution of specific traits can help illuminate how predictable adaptations and divergence are at the molecular and developmental level. Following the last glacial period, dwarfism and specialized bottom feeding morphology evolved rapidly in several landlocked Arctic charr Salvelinus alpinus populations in Ice...

The file is tab-delimited and the columns are; “Unigene.Description”: the annotation for that gene/paralog group. “NR.contigs”: number of contigs with this annotation. “logCPM”: count per million, log-scale. “logFC.morph”: Mean fold change between the morphs, log-scale. “logFC.T163”, “logFC.T200”, “logFC.T433”: Mean fold change for each timepoints...

“Gene Type”: Designates the reference and candidate genes. “Gene”: Name of the gene. “Morph”: Which charr type the sample came from. “Relative age”: Developmental timepoint, and also indicates the samples from adult fish. “Biological replicate”: The two or more biological replicates used. “cDNA No”: Marks the cDNA isolation used. “Ct value”: Estima...

“Gene Type”: Designates the reference and candidate genes. “Gene”: Name of the gene. “Morph”: Which charr type the sample came from. “Relative age”: Developmental timepoint. “Biological replicate”: The two or more biological replicates used. “cDNA No”: Marks the cDNA isolation used. “Ct value”: Estimate of gene expression. “Tissue”: Indicates the m...

Species showing repeated evolution of similar traits can help illuminate the molecular and developmental basis of diverging traits and specific adaptations. Following the last glacial period, dwarfism and specialized bottom feeding morphology evolved rapidly in several landlocked Arctic charr (Salvelinus alpinus) populations in Iceland. To initiate...