Category: Publications

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

Arnar Pálsson, 22/09/2023

Submission of Guðbjörgs manuscript to PLoS One, second version of M.S. available on bioRxiv.

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

Guðbjörg Ósk Jónsdóttir, Laura-Marie von Elm, Finnur Ingimarsson, Samuel Tersigni, Sigurdur Sveinn Snorrason, Arnar Palsson, Sarah Elizabeth Steele

doi: https://doi.org/10.1101/2023.02.17.528955

The diversity of functional feeding anatomy is particularly impressive in fishes and correlates with various interspecific ecological specializations. Intraspecific polymorphism can manifest in divergent feeding morphology and ecology, often along a benthic pelagic axis. Arctic charr (Salvelinus alpinus) is a freshwater salmonid known for morphological variation and sympatric polymorphism and in Lake Þingvallavatn, Iceland, four morphs of charr coexist that differ in preferred prey, behaviour, habitat use, and external feeding morphology. We studied variation in six upper and lower jaw bones in adults of these four morphs using geometric morphometrics and univariate statistics. We tested for allometric differences in bone size and shape among morphs, morph effects on bone size and shape, and divergence along the benthic-pelagic axis. We also examined the degree of integration between bone pairs. We found differences in bone size between pelagic and benthic morphs for two bones (dentary and premaxilla). There was clear bone shape divergence along a benthic pelagic axis in four bones (dentary, articular angular, premaxilla and maxilla), as well as allometric shape differences between morphs in the dentary. Notably for the dentary, morph explained more shape variation than bone size. Comparatively, benthic morphs possess a compact and taller dentary, with shorter dentary palate, consistent with visible (but less prominent) differences in external morphology. As these morphs emerged in the last 10,000 years, these results indicate rapid functional evolution of specific feeding structures in arctic charr. This sets the stage for studies of the genetics and development of rapid and parallel craniofacial evolution.

categories Publications

Arnar Pálsson, 07/09/2023

Genetic structure and relatedness of brown trout (Salmo trutta) populations in the drainage basin of the Ölfusá river, South-Western Iceland

​1, 1, 2, 2, 1, 1
A total of 2,597 polymorphic loci from 317 individuals out of 555 originally analysed were retained after the stringent filtering steps outlined in Materials and Methods. These markers were used to address questions about the patterns of genetic differentiation between locations. We estimated population genetic parameters for each sampling site.

Plot of two principal components separates three clusters of landlocked brown trout, the Scottish reference group, and the anadromous populations. The percentage of the variance explained by these components is shown in parentheses. See ms for three letter code.

categories Publications

Genetic structure and relatedness of brown trout (Salmo trutta) populations in the drainage basin of the Ölfusá river, South-Western Iceland

Arnar Pálsson, 08/08/2023

Accepted in PeerJ. Good job by Marcos G. Lagunas.

Background. Lake Þingvallavatn in Iceland, a part of the river Ölfusá drainage basin, was presumably populated by brown trout soon after it formed at the end of the last Ice Age. The genetic relatedness of the brown trout in Þingvallavatn to other populations in the Ölfusá drainage basin is unknown. After the building of a dam at the outlet of the lake in 1959 brown trout catches declined, though numbers have now increased. The aim of this study was to assess effects of geographic isolation and potential downstream gene flow on the genetic structure and diversity in brown trout sampled in several locations in the western side of the watershed of River Ölfusá. We hypothesized that brown trout in Lake Þingvallavatn constituted several local spawning populations connected by occasional gene flow before the damming of the lake. We also estimated the effective population size (NE) of some of these populations and tested for signs of a recent population bottleneck in Lake Þingvallavatn.

Methods. We sampled brown trout inhabiting four lakes and 12 rivers within and near the watershed of River Ölfusá by means of electro- and net- fishing. After stringent data filtering, 2,597 polymorphic loci obtained from ddRADseq data from 317 individuals were ascertained as putative neutral markers.

Results. Overall, the genetic relatedness of brown trout in the Ölfusá watershed reflected the connectivity and topography of the waterways. Ancestry proportion analyses and a phylogenetic tree revealed seven distinct clusters, some of which corresponded to small populations with reduced genetic diversity. There was no evidence of downstream gene flow from Lake Þingvallavatn, although gene flow was observed from much smaller mountain populations. Most locations showed low NE values (i.e., ~14.6 on average) while the putative anadromous trout from River Sog and the spawning population from River Öxará, that flows into Lake Þingvallavatn, showed notably higher NE values (i.e., 71.2 and 56.5, respectively). No signals of recent population bottlenecks were detected in the brown trout of Lake Þingvallavatn.

Discussion. This is the first time that the genetic structure and diversity of brown trout in the Ölfusá watershed have been assessed. Our results point towards the presence of a metapopulation in the watershed of Lake Þingvallavatn (and its tributaries), which has been influenced by restoration efforts and is now dominated by a genetic component originated in River Öxará. Many of the locations studied represent different populations. Those that are isolated in headwater streams and lakes are genetically distinct presenting low genetic diversity, yet they can be important in increasing the genetic variation in downstream populations. These populations should be considered for conservation and direct management.

categories Publications

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

Arnar Pálsson, 28/06/2023

This manuscript was rejected by Evolutionary Biology, on grounds of "The reviewers felt there was a need to demonstrate functional aspects of morphology moreso than the current version, while both felt that some novelty was lacking." One reviewer said the results were all predictable and wanted us to study species level diversity and the other reflects lack of understanding of geometric morphometrics. We are reformatting for another journal, more to follow.

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

Jónsdóttir, G.Ó., von Elm, L-M, Ingimarsson, F., Tersigni, S., Snorrason, S.S, Pálsson, A. and Steele, S.E.

https://www.biorxiv.org/content/10.1101/2023.02.17.528955v1

Abstract

The diversity of functional anatomy related to feeding is particularly impressive in fishes and correlates with various ecological specializations across species. Polymorphism within species can manifest in divergent feeding morphology and ecology, often along a benthic–pelagic axis. Arctic charr (Salvelinus alpinus) is a freshwater salmonid known for morphological variation and sympatric polymorphism. In Lake Þingvallavatn, Iceland, four morphs of arctic charr coexist that differ in preferred prey, behaviour, habitat use, and external feeding morphology. We studied variation in upper and lower jaw bones (six bones total) related to feeding, in adults of the four morphs using geometric morphometrics and univariate statistics. We tested for allometric differences in bone size and shape among morphs, morph effects on bone size and shape, and if benthic and pelagic ecologies associate with bone size and shape. We also examined the degree of integration between bone pairs. We found differences in bone size between pelagic and benthic morphs for two bones (dentary and premaxilla). There was clear bone shape divergence along a benthic–pelagic axis in four bones (dentary, articular-angular, premaxilla and maxilla), as well as allometric differences between morphs in the dentary. Most dramatic was the dentary, where morph explained more shape variation than bone size. Comparatively, benthic morphs possess a compact and taller dentary, with shorter dentary palate, consistent with visible (but less prominent) differences in external morphology. As these morphs emerged in the last 10,000 years, these results indicate rapid functional evolution of specific feeding structures in arctic charr. This sets the stage for studies of the genetics and development of rapid and parallel craniofacial evolution.

categories Publications

Adaptive cellular evolution or cellular system drift in hares

Arnar Pálsson, 20/05/2023

Adaptive cellular evolution or cellular system drift in hares

Arnar Palsson and Sarah Elizabeth Steele.

Perspective, in Molecular Ecology.

Adaptations occur at many levels, from e.g. DNA sequence of regulatory elements and cellular homeostatic systems, to organismal physiology and behaviour (Mayr, 1997). Established adaptations are maintained by purifying and stabilizing selection. Students of animal diversity tend to focus on higher order traits, anatomy, physiology, organismal function and interactions. The core cellular and metabolic systems of metazoans evolved early in their history, and are assumed to be rather similar between groups. The housekeeping functions and core metabolic functions of cells are generally considered relatively static, especially among closely related species. The extent to which evolution shapes core cellular metabolism and physiology in animals is largely unexplored. Ecological opportunities or strong positive selection can alter basal metabolic rate, activity levels and life-history traits (e.g. lifespan, age of maturity, offspring number) and potentially lead to divergence in core cellular and metabolic trait systems (Norin & Metcalfe, 2019; Speakman, 2005). Furthermore, systems under stabilizing selection can also change. Developmental systems of related species may produce the same phenotype or structure, but experience drift that can alter connections and even lead to turnover of cogs in the system (True & Haag, 2001). Are the cellular functions of animals highly constrained, subject to cellular system drift or affected by positive selection? This was tackled by a new study by Kateryna Gaertner and colleagues in a From the Cover manuscript in this issue of Molecular Ecology (Gaertner et al., 2022), using fibroblasts from the closely related but ecologically distinct brown and mountain hares.

categories Publications

Variation in personality shaped by evolutionary history, genotype, and developmental plasticity in response to feeding modalities in the Arctic charr

Arnar Pálsson, 04/05/2023

Variation in personality shaped by evolutionary history, genotype, and developmental plasticity in response to feeding modalities in the Arctic charr

AUTHORS

Marion Dellinger, Sarah E. Steele, Evert Sprockel, Joris Philip, Arnar Pálsson, David Benhaïm

Submitted manuscript, sorry not on BioRxiv.

ABSTRACT

Animal personality has been shown to be influenced by both genetic and environmental factors and shaped by natural selection. Currently, little is known about mechanisms influencing personality traits development. This study examines the extent to which personality development is genetically influenced and/or environmentally responsive (plastic). We also investigated the role of evolutionary history, assessing whether personality traits could be canalized along a genetic divergence gradient. We tested the plastic potential of boldness in juveniles of five Icelandic Arctic charr morphs (Salvelinus alpinus) displaying various degrees of genetic divergence from the ancestral charr, split between treatments mimicking benthic vs. pelagic feeding modalities. We show that differences in mean boldness are mostly affected by genetics. While the benthic treatment led to bolder individuals, the environmental effect was rather weak, suggesting that boldness lies under strong genetic influence with reduced plastic potential. Nevertheless, the repeatability of boldness response to treatment varied among morphs, suggesting the early environment may drive personality emergence within populations. Finally, we found hints of differences by morphs in boldness canalization through reduced variance and higher consistency in boldness within morphs. These findings provide new insights on how behavioural development may impact adaptive diversification.

categories Publications

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

Arnar Pálsson, 24/02/2023

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus)

Jónsdóttir, G.Ó., von Elm, L-M, Ingimarsson, F., Tersigni, S., Snorrason, S.S, Pálsson, A. and Steele, S.E.

Submitted to Evolutionary Biology. https://www.biorxiv.org/content/10.1101/2023.02.17.528955v1

Abstract

The diversity of functional anatomy related to feeding is particularly impressive in fishes and correlates with various ecological specializations across species. Polymorphism within species can manifest in divergent feeding morphology and ecology, often along a benthic–pelagic axis. Arctic charr (Salvelinus alpinus) is a freshwater salmonid known for morphological variation and sympatric polymorphism. In Lake Þingvallavatn, Iceland, four morphs of arctic charr coexist that differ in preferred prey, behaviour, habitat use, and external feeding morphology. We studied variation in upper and lower jaw bones (six bones total) related to feeding, in adults of the four morphs using geometric morphometrics and univariate statistics. We tested for allometric differences in bone size and shape among morphs, morph effects on bone size and shape, and if benthic and pelagic ecologies associate with bone size and shape. We also examined the degree of integration between bone pairs. We found differences in bone size between pelagic and benthic morphs for two bones (dentary and premaxilla). There was clear bone shape divergence along a benthic–pelagic axis in four bones (dentary, articular-angular, premaxilla and maxilla), as well as allometric differences between morphs in the dentary. Most dramatic was the dentary, where morph explained more shape variation than bone size. Comparatively, benthic morphs possess a compact and taller dentary, with shorter dentary palate, consistent with visible (but less prominent) differences in external morphology. As these morphs emerged in the last 10,000 years, these results indicate rapid functional evolution of specific feeding structures in arctic charr. This sets the stage for studies of the genetics and development of rapid and parallel craniofacial evolution.

 

categories Publications

Manuscript on craniofacial variation in sympatric ecomorphs of Arctic charr

Arnar Pálsson, 09/11/2022

This darling is nearly ready for submission. Very cool results from a study led by Guðbjörg Ósk Jónsdóttir and Sarah Steele, based on pioneering work by Finnur Ingimarsson and Sigurður S. Snorrason.

Diversity in the internal functional feeding elements of sympatric morphs of Arctic charr (Salvelinus alpinus) 

Jónsdóttir, G.Ó., von Elm, L-M, Ingimarsson, F., Tersigni, S., Snorrason, S.S, Pálsson, A. and Steele, S.E. 

One cool figure from the manuscript, showing shape variation in bones in the four sympatric morphs of Arctic charr in Lake Þingvallavatn.

Shape variation in the articular angular, part of the lower jaw, PCA of individuals and the first two axes of shape variation (after size correction).

Colour coding follows previous publications, large benthic (Green), small benthic (blue), planktivorous (red) and piscivorous charr (purple).

The morphs are genetically separable, with a twist...

Jóhannes Guðbrandsson, Kalina H. Kapralova, Sigríður R. Franzdóttir, Þóra Margrét Bergsveinsdóttir, Völundur Hafstað, Zophonías O. Jónsson, Sigurður S. Snorrason, Arnar Pálsson. 2019. Extensive genetic differentiation between recently evolved sympatric Arctic charr morphs Ecology and Evolution.  9:10964–10983. doi: 10.1002/ece3.5516.

categories Publications

A novel region within a conserved domain in ATG7 emerged in vertebrates.

Arnar Pálsson, 24/08/2022

A nice paper by Valgerður Hjaltalín and colleagues was accepted to Autophagy Reports. She worked on this during covid, with some help from us and others. Then added a nice experimental data to the manuscript during revisions. More on this as it emerges on the journal website.

A novel region within a conserved domain in ATG7 emerged in vertebrates.

Valgerdur J. Hjaltalin, Vivian Pogenberg, Kévin J. A. Ostacolo, Arnar Pálsson, Margrét Helga Ogmundsdottir

categories Publications

DNA methylation differences during development distinguish sympatric morphs of Arctic charr (Salvelinus alpinus)

Arnar Pálsson, 25/07/2022
DNA methylation differences during development distinguish sympatric morphs of Arctic charr (Salvelinus alpinus)
Accepted in Molecular Ecology, first published: 18 July 2022
https://doi.org/10.1111/mec.16620

Changes in DNA methylation in specific coding or non-coding regions can influence development and potentially divergence in traits within species and groups. While the impact of epigenetic variation on developmental pathways associated with evolutionary divergence is the focus of intense investigation, few studies have looked at recently diverged systems. Phenotypic diversity between closely related populations of Arctic charr (Salvelinus alpinus), which diverged within the last 10 000 years, offers an interesting ecological model to address such effects. Using bisulfite sequencing, we studied general DNA methylation patterns during development in the four sympatric morphs of Arctic charr from Lake Thingvallavatn. The data revealed strong differences between developmental timepoints and between morphs (mainly along the benthic – limnetic axis), both at single CpG sites and in 1,000bp-regions. Genes located close to differentially methylated CpG sites were involved in nucleosome assembly, regulation of osteoclast differentiation, and cell-matrix adhesion. Differentially methylated regions were enriched in tRNA and rRNA sequences, and half of them were located close to transcription start sites. The expression of 14 genes showing methylation differences over time or between morphs was further investigated by qPCR and nine of these were found to be differentially expressed between morphs. Four genes (ARHGEF37-like, H3-like, MPP3 and MEGF9) showed a correlation between methylation and expression. Lastly, histone gene clusters displayed interesting methylation differences between timepoints and morphs, as well as intragenic methylation variation. The results presented here provide a motivation for further studies on the contribution of epigenetic traits, such as DNA methylation, to phenotypic diversity and developmental mechanisms.

categories Publications