Skúli Skúlason - Academia.edu (original) (raw)

Papers by Skúli Skúlason

Research paper thumbnail of Resource polymorphisms in vertebrates

Trends in Ecology & Evolution, 1995

Research paper thumbnail of Egg size–related traits during the first year of growth and smolting in hatchery and wild juveniles of steelhead trout Oncorhynchus mykiss

Environmental Biology of Fishes

Research paper thumbnail of Variation in egg size and offspring phenotype among and within seven Arctic charr morphs

Ecology and Evolution

This is a self-archived version of an original article. This version may differ from the original... more This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details.

Research paper thumbnail of The use of aquatic organisms in ecosystem evaluation and how they are affected by potential hydropower development

Research paper thumbnail of Quick divergence but slow convergence during ecotype formation in lake and stream stickleback pairs of variable age

Journal of evolutionary biology, 2014

When genetic constraints restrict phenotypic evolution, diversification can be predicted to evolv... more When genetic constraints restrict phenotypic evolution, diversification can be predicted to evolve along so-called lines of least resistance. To address the importance of such constraints and their resolution, studies of parallel phenotypic divergence that differ in their age are valuable. Here, we investigate the parapatric evolution of six lake and stream threespine stickleback systems from Iceland and Switzerland, ranging in age from a few decades to several millennia. Using phenotypic data, we test for parallelism in ecotypic divergence between parapatric lake and stream populations and compare the observed patterns to an ancestral-like marine population. We find strong and consistent phenotypic divergence, both among lake and stream populations and between our freshwater populations and the marine population. Interestingly, ecotypic divergence in low-dimensional phenotype space (i.e. single traits) is rapid and seems to be often completed within 100 years. Yet, the dimensionali...

Research paper thumbnail of Phenotypic plasticity, heterochrony and ontogenetic repatterning during juvenile development of divergent Arctic charr (Salvelinus alpinus)

Journal of Evolutionary Biology, 2011

Research paper thumbnail of Feeding pattern of planktivorous Arctic charr: Int. mountain watershed symp. Subalpine processes and water quality

Research paper thumbnail of Resource polymorphism and diversity of Arctic charr Salvelinus alpinus in a series of isolated lakes

Journal of Fish Biology, 2013

Morphological, dietary and life-history variation in Arctic charr Salvelinus alpinus were charact... more Morphological, dietary and life-history variation in Arctic charr Salvelinus alpinus were characterized from three geographically proximate, but isolated lakes and one large lake into which they drain in south-western Alaska. Polymorphism was predicted to occur in the first three lakes because S. alpinus tend to become polymorphic in deep, isolated lakes with few co-occurring species. Only one morph was evident in the large lake and two of the three isolated lakes. In the third isolated lake, Lower Tazimina Lake, small and large morphs were found, the latter including two forms differing in growth rate. The small morph additionally differed from the two large forms by having more gill rakers and a deeper body than same-sized individuals of the large morph, consuming more limnetic and fewer benthic resources, having a greater gonado-somatic index and maturing at a smaller size. The two large forms consumed only slightly different foods (more terrestrial insects were consumed by the medium-growth form; more snails by the high-growth form). Trends in consumption of resources with body shape also differed between lakes. Variability in life history of S. alpinus in these Alaskan lakes was as broad as that found elsewhere. This variability is important for understanding lake ecosystems of remote regions where this species is commonly dominant.

Research paper thumbnail of Additional file 6 of Differences among families in craniofacial shape at early life-stages of Arctic charr (Salvelinus alpinus)

Additional file 6 Figure S3. Principal components analysis (PCA) plots showing both relative gene... more Additional file 6 Figure S3. Principal components analysis (PCA) plots showing both relative gene expression (for growth and skeletal related genes) and ventral size-free craniofacial shapes attributed to family in the brown Arctic charr morph from lake Vatnshlíðarvatn, at a) hatching (H), and b) first feeding (FF). Coloured shapes and associated standard error bars correspond to mean shape of offspring within a family. For gene expression only, green and red arrows show the top three genes (listed from highest to lowest) with the highest PCA loadings driving divergence towards the positive (green) and negative (red) extremes of the PC axes. Deformation grids at the extremes of both axes represent the amount of shape change, with two-fold magnification.

Research paper thumbnail of Data from: Gene expression in the phenotypically plastic Arctic charr (Salvelinus alpinus): a focus on growth and ossification at early stages of development

Gene expression during development shapes the phenotypes of individuals. Although embryonic gene ... more 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 across embryonic development in Arctic charr (Salvelinus alpinus). We test to what extent their relative expression is correlated with egg size and size at early life‐stages within the study population. We predict smaller individuals to have higher expression of growth and skeletal promoting genes, due to less maternal resources (i.e., yolk) and prioritization of energy toward ossification. We found expression levels to vary across developmental stages and only three genes (Mmp9, Star, and Sgk1) correlated with individual size at a given developmental stage. Contrary to our hypothesis, expression of Mmp9 and Star showed a non‐linear relationship with size (at post fertilization and hatching, respectively), whilst Sgk1 was higher in larger embryos at hatching. Interestingly, these genes are also associated with craniofacial divergence of Arctic charr morphs. Our results indicate that early life‐stage variation in gene expression, concomitant to maternal effects, can influence developmental plasticity and potentially the evolution of resource polymorphism in fishes

Research paper thumbnail of Morphological & genetic data for threespine sticklebacks from Switzerland and Iceland

Research paper thumbnail of Table 1) Physicochemical properties of 35 Icelandic lakes housing a single morph of Arctic charr (Salvelinus alpinus)

Research paper thumbnail of Trout and Char of the North Atlantic Isles

Research paper thumbnail of The Relationship between Egg Size and the Rate of Early Development in Arctic charr, Salvelinus alpinus

Environmental Biology of Fishes, 2002

Previous studies have found no consistent relationship between egg size and the rate of developme... more Previous studies have found no consistent relationship between egg size and the rate of development in fish. This is surprising since there are several hypothesis as to why such a relationship should exist. By using eggs from Arctic charr, Salvelinus alpinus, we examined several developmental features repeatedly on live individuals. In all measured parameters except date of hatching, embryos from smaller eggs were found to develop faster. Time of hatching has often been used as a principal measurement for rate of development in fish, but our results suggest that this should be discontinued, since it is poorly correlated with the rates of development of other early life history features.

Research paper thumbnail of Hidden genetic variation evolves with ecological specialization: the genetic basis of phenotypic plasticity in Arctic charr ecomorphs

Evolution & development

The genetic variance that determines phenotypic variation can change across environments through ... more The genetic variance that determines phenotypic variation can change across environments through developmental plasticity and in turn play a strong role in evolution. Induced changes in genotype-phenotype relationships should strongly influence adaptation by exposing different sets of heritable variation to selection under some conditions, while also hiding variation. Therefore, the heritable variation exposed or hidden from selection is likely to differ among habitats. We used ecomorphs from two divergent populations of Arctic charr (Salvelinus alpinus) to test the prediction that genotype-phenotype relationships would change in relation to environment. If present over several generations this should lead to divergence in genotype-phenotype relationships under common conditions, and to changes in the amount and type of hidden genetic variance that can evolve. We performed a common garden experiment whereby two ecomorphs from each of two Icelandic lakes were reared under conditions ...

Research paper thumbnail of Segregation in spawning and early life history among polymorphic Arctic charr, Salvelinus alpinus, in Thingvallavatn, Iceland

Journal of Fish Biology, 2006

Research paper thumbnail of Does Breeding Site Fidelity Drive Phenotypic and Genetic Sub-Structuring of a Population of Arctic Charr?

Evolutionary Ecology, 2006

There is now increasing acceptance that divergence of phenotypic traits, and the genetic structur... more There is now increasing acceptance that divergence of phenotypic traits, and the genetic structuring that underlie such divergence, can occur in sympatry. Here we report the serendipitous discovery of a sympatric polymorphism in the upper Forth catchment, Scotland, in a species for which high levels of phenotypic variation have been reported previously, the Arctic charr, Salvelinus alpinus. Attempting to determine the proximate mechanisms through which this pattern of phenotypic variation is maintained, we examine the use of the available feeding resource and the genotypic and phenotypic structure of charr in this system. We show clear differences in head morphology between charr from three very closely connected lakes with no barrier to movement (Lochs Doine, Voil and Lubnaig) and also differences in muscle stable isotope signatures and in stomach contents. There were significant differences at 6 microsatelite loci (between Lubnaig and the other two lochs) and very low estimates of effective migration between populations. We conclude that, despite living in effective sympatry, strong genetic and phenotypic sub-structuring is likely maintained by very high levels of site fidelity, especially during spawning, resulting in functional allopatric divergence of phenotype.

Research paper thumbnail of Characterisation and expression of the paired box protein 7 (Pax7) gene in polymorphic Arctic charr (Salvelinus alpinus)

Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2006

Research paper thumbnail of Habitat use of arctic charrSalvelinus alpinus in Thingvallavatn, Iceland

Environmental Biology of Fishes, 1987

... However, the dietary segregation of sympatric morphs may to some extent be interactive (sensu... more ... However, the dietary segregation of sympatric morphs may to some extent be interactive (sensuBrian 1956) as the niche overlap is high in ... 6°C and no classically defined thermocline is de-veloped (Lindegaard 1980), although a thermal stratification does exist (Lastein 1983 ...

Research paper thumbnail of Adaptive Speciation in Northern Freshwater Fishes

Research paper thumbnail of Resource polymorphisms in vertebrates

Trends in Ecology & Evolution, 1995

Research paper thumbnail of Egg size–related traits during the first year of growth and smolting in hatchery and wild juveniles of steelhead trout Oncorhynchus mykiss

Environmental Biology of Fishes

Research paper thumbnail of Variation in egg size and offspring phenotype among and within seven Arctic charr morphs

Ecology and Evolution

This is a self-archived version of an original article. This version may differ from the original... more This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details.

Research paper thumbnail of The use of aquatic organisms in ecosystem evaluation and how they are affected by potential hydropower development

Research paper thumbnail of Quick divergence but slow convergence during ecotype formation in lake and stream stickleback pairs of variable age

Journal of evolutionary biology, 2014

When genetic constraints restrict phenotypic evolution, diversification can be predicted to evolv... more When genetic constraints restrict phenotypic evolution, diversification can be predicted to evolve along so-called lines of least resistance. To address the importance of such constraints and their resolution, studies of parallel phenotypic divergence that differ in their age are valuable. Here, we investigate the parapatric evolution of six lake and stream threespine stickleback systems from Iceland and Switzerland, ranging in age from a few decades to several millennia. Using phenotypic data, we test for parallelism in ecotypic divergence between parapatric lake and stream populations and compare the observed patterns to an ancestral-like marine population. We find strong and consistent phenotypic divergence, both among lake and stream populations and between our freshwater populations and the marine population. Interestingly, ecotypic divergence in low-dimensional phenotype space (i.e. single traits) is rapid and seems to be often completed within 100 years. Yet, the dimensionali...

Research paper thumbnail of Phenotypic plasticity, heterochrony and ontogenetic repatterning during juvenile development of divergent Arctic charr (Salvelinus alpinus)

Journal of Evolutionary Biology, 2011

Research paper thumbnail of Feeding pattern of planktivorous Arctic charr: Int. mountain watershed symp. Subalpine processes and water quality

Research paper thumbnail of Resource polymorphism and diversity of Arctic charr Salvelinus alpinus in a series of isolated lakes

Journal of Fish Biology, 2013

Morphological, dietary and life-history variation in Arctic charr Salvelinus alpinus were charact... more Morphological, dietary and life-history variation in Arctic charr Salvelinus alpinus were characterized from three geographically proximate, but isolated lakes and one large lake into which they drain in south-western Alaska. Polymorphism was predicted to occur in the first three lakes because S. alpinus tend to become polymorphic in deep, isolated lakes with few co-occurring species. Only one morph was evident in the large lake and two of the three isolated lakes. In the third isolated lake, Lower Tazimina Lake, small and large morphs were found, the latter including two forms differing in growth rate. The small morph additionally differed from the two large forms by having more gill rakers and a deeper body than same-sized individuals of the large morph, consuming more limnetic and fewer benthic resources, having a greater gonado-somatic index and maturing at a smaller size. The two large forms consumed only slightly different foods (more terrestrial insects were consumed by the medium-growth form; more snails by the high-growth form). Trends in consumption of resources with body shape also differed between lakes. Variability in life history of S. alpinus in these Alaskan lakes was as broad as that found elsewhere. This variability is important for understanding lake ecosystems of remote regions where this species is commonly dominant.

Research paper thumbnail of Additional file 6 of Differences among families in craniofacial shape at early life-stages of Arctic charr (Salvelinus alpinus)

Additional file 6 Figure S3. Principal components analysis (PCA) plots showing both relative gene... more Additional file 6 Figure S3. Principal components analysis (PCA) plots showing both relative gene expression (for growth and skeletal related genes) and ventral size-free craniofacial shapes attributed to family in the brown Arctic charr morph from lake Vatnshlíðarvatn, at a) hatching (H), and b) first feeding (FF). Coloured shapes and associated standard error bars correspond to mean shape of offspring within a family. For gene expression only, green and red arrows show the top three genes (listed from highest to lowest) with the highest PCA loadings driving divergence towards the positive (green) and negative (red) extremes of the PC axes. Deformation grids at the extremes of both axes represent the amount of shape change, with two-fold magnification.

Research paper thumbnail of Data from: Gene expression in the phenotypically plastic Arctic charr (Salvelinus alpinus): a focus on growth and ossification at early stages of development

Gene expression during development shapes the phenotypes of individuals. Although embryonic gene ... more 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 across embryonic development in Arctic charr (Salvelinus alpinus). We test to what extent their relative expression is correlated with egg size and size at early life‐stages within the study population. We predict smaller individuals to have higher expression of growth and skeletal promoting genes, due to less maternal resources (i.e., yolk) and prioritization of energy toward ossification. We found expression levels to vary across developmental stages and only three genes (Mmp9, Star, and Sgk1) correlated with individual size at a given developmental stage. Contrary to our hypothesis, expression of Mmp9 and Star showed a non‐linear relationship with size (at post fertilization and hatching, respectively), whilst Sgk1 was higher in larger embryos at hatching. Interestingly, these genes are also associated with craniofacial divergence of Arctic charr morphs. Our results indicate that early life‐stage variation in gene expression, concomitant to maternal effects, can influence developmental plasticity and potentially the evolution of resource polymorphism in fishes

Research paper thumbnail of Morphological & genetic data for threespine sticklebacks from Switzerland and Iceland

Research paper thumbnail of Table 1) Physicochemical properties of 35 Icelandic lakes housing a single morph of Arctic charr (Salvelinus alpinus)

Research paper thumbnail of Trout and Char of the North Atlantic Isles

Research paper thumbnail of The Relationship between Egg Size and the Rate of Early Development in Arctic charr, Salvelinus alpinus

Environmental Biology of Fishes, 2002

Previous studies have found no consistent relationship between egg size and the rate of developme... more Previous studies have found no consistent relationship between egg size and the rate of development in fish. This is surprising since there are several hypothesis as to why such a relationship should exist. By using eggs from Arctic charr, Salvelinus alpinus, we examined several developmental features repeatedly on live individuals. In all measured parameters except date of hatching, embryos from smaller eggs were found to develop faster. Time of hatching has often been used as a principal measurement for rate of development in fish, but our results suggest that this should be discontinued, since it is poorly correlated with the rates of development of other early life history features.

Research paper thumbnail of Hidden genetic variation evolves with ecological specialization: the genetic basis of phenotypic plasticity in Arctic charr ecomorphs

Evolution & development

The genetic variance that determines phenotypic variation can change across environments through ... more The genetic variance that determines phenotypic variation can change across environments through developmental plasticity and in turn play a strong role in evolution. Induced changes in genotype-phenotype relationships should strongly influence adaptation by exposing different sets of heritable variation to selection under some conditions, while also hiding variation. Therefore, the heritable variation exposed or hidden from selection is likely to differ among habitats. We used ecomorphs from two divergent populations of Arctic charr (Salvelinus alpinus) to test the prediction that genotype-phenotype relationships would change in relation to environment. If present over several generations this should lead to divergence in genotype-phenotype relationships under common conditions, and to changes in the amount and type of hidden genetic variance that can evolve. We performed a common garden experiment whereby two ecomorphs from each of two Icelandic lakes were reared under conditions ...

Research paper thumbnail of Segregation in spawning and early life history among polymorphic Arctic charr, Salvelinus alpinus, in Thingvallavatn, Iceland

Journal of Fish Biology, 2006

Research paper thumbnail of Does Breeding Site Fidelity Drive Phenotypic and Genetic Sub-Structuring of a Population of Arctic Charr?

Evolutionary Ecology, 2006

There is now increasing acceptance that divergence of phenotypic traits, and the genetic structur... more There is now increasing acceptance that divergence of phenotypic traits, and the genetic structuring that underlie such divergence, can occur in sympatry. Here we report the serendipitous discovery of a sympatric polymorphism in the upper Forth catchment, Scotland, in a species for which high levels of phenotypic variation have been reported previously, the Arctic charr, Salvelinus alpinus. Attempting to determine the proximate mechanisms through which this pattern of phenotypic variation is maintained, we examine the use of the available feeding resource and the genotypic and phenotypic structure of charr in this system. We show clear differences in head morphology between charr from three very closely connected lakes with no barrier to movement (Lochs Doine, Voil and Lubnaig) and also differences in muscle stable isotope signatures and in stomach contents. There were significant differences at 6 microsatelite loci (between Lubnaig and the other two lochs) and very low estimates of effective migration between populations. We conclude that, despite living in effective sympatry, strong genetic and phenotypic sub-structuring is likely maintained by very high levels of site fidelity, especially during spawning, resulting in functional allopatric divergence of phenotype.

Research paper thumbnail of Characterisation and expression of the paired box protein 7 (Pax7) gene in polymorphic Arctic charr (Salvelinus alpinus)

Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2006

Research paper thumbnail of Habitat use of arctic charrSalvelinus alpinus in Thingvallavatn, Iceland

Environmental Biology of Fishes, 1987

... However, the dietary segregation of sympatric morphs may to some extent be interactive (sensu... more ... However, the dietary segregation of sympatric morphs may to some extent be interactive (sensuBrian 1956) as the niche overlap is high in ... 6°C and no classically defined thermocline is de-veloped (Lindegaard 1980), although a thermal stratification does exist (Lastein 1983 ...

Research paper thumbnail of Adaptive Speciation in Northern Freshwater Fishes