Symposium of Molecular Evolution: In Honor of Marty Kreitman’s Scientific Career

Arnar Pálsson, 06/03/2024

It was at the Drosophila meeting in San Diego 10-14th of April 2002. I had arrived with my uncle Einar Arnason and his late wife Betty, after driving down from Passadena. In the ginormous reception ball room we snacked and drank, until Einar was bundled by a springly fellow with wired hair and manners. Marty Kreitman had arrived at the scene.

Drosophila Research Conference (drosophila-conf.org)

I had greatly admired his population genetic work, though it was the work Marty did with Misha Ludwig that particularly impressed me. The first did population genetics on the best characterized regulatory element at the time, the stripe 2 enhancer of the eve (even-skipped) gene of D. melanogaster, and then moved to functional studies, comparing the element between species. See for instance a very impressive paper on chimeras of D. melanogaster and D. pseudoobscura s2e enhancers.

Evidence for stabilizing selection in a eukaryotic enhancer element.

Ludwig MZ, Bergman C, Patel NH, Kreitman M.Nature. 2000 Feb 3;403(6769):564-7. doi: 10.1038/35000615.PMID: 10676967 

To make a long story short, serendipity helped me make Marty´s acquaintance and a year later I started a postdoc with him and Misha at the University of Chicago. There we had three fun years doing population genetics on enhancers and analyzing gene expression in embryos.

Functional evolution of a cis-regulatory module. 2005. Ludwig MZ, Palsson A, Alekseeva E, Bergman CM, Nathan J, Kreitman M. PLoS Biology. 3(4):e93. (doi:10.1371/journal.pbio.0030093 PDF)

Canalization of segmentation and its evolution in Drosophila. 2007. Lott SE, Kreitman M, Palsson A, Alekseeva E, Ludwig MZ. Proc Natl Acad Sci U S A. 104(26):10926-31. (doi: 10.1073/pnas.0701359104 PDF)

Naturally Occurring Deletions of Hunchback Binding Sites in the Even-Skipped Stripe 3+7 Enhancer. 2014. Palsson A, Wesolowska N, Reynisdóttir S, Ludwig MZ, Kreitman M. PLoS ONE 9(5): e91924. doi:10.1371/journal.pone.0091924.

In the summer of 2022 former trainees and friends of Marty arranged a nice farewell symposium for him in Chicago. Thankfully I got to participate via zoom, and see some of the great people again.

categories Articles about science, Publications

(Icelandic) Diversity of bones - resubmission in progress

Arnar Pálsson, 07/02/2024

The manuscript got quite favorable replies.

https://www.biorxiv.org/content/10.1101/2023.02.17.528955v2 

We are continuing uploading the figures to Figshare+ and code to Github.

And adjusting the figures with new colour-blind friendlier palette.

See for instance.

categories Publications

(Icelandic) 13 pistlar fyrir vísindavefinn 2023

Arnar Pálsson, 19/01/2024

Sorry, this entry is only available in Icelandic.

categories Vísindavefur - svör

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

Arnar Pálsson, 04/01/2024

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

Published:13 December 2023 https://doi.org/10.1098/rspb.2023.2302
Originally submitted May 4th 2023.
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 the development of personality traits. 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 and ecological divergence gradient. We tested the plastic potential of boldness in juveniles of five Icelandic Arctic charr morphs (Salvelinus alpinus), including two pairs of sympatric morphs, displaying various degrees of genetic and ecological divergence from the ancestral anadromous charr, split between treatments mimicking benthic versus pelagic feeding modalities. We show that differences in mean boldness are mostly affected by genetics. While the benthic treatment led to bolder individuals overall, the environmental effect was rather weak, suggesting that boldness lies under strong genetic influence with reduced plastic potential. Finally, we found hints of differences by morphs in boldness canalization through reduced variance and plasticity, and higher consistency in boldness within morphs. These findings provide new insights on how behavioural development may impact adaptive diversification.

First output from our large plasticity project that started with sampling in the summer of 2018.

Sampling in the stream connecting Vatnshlíðarvatn and Arnarvatn. One morph spawns in this stream the other in the outlet of Vatnshlíðarvatn.

Bjarni and Siggi making crosses of the Vatnshlíðarvatn morphs

Last sampling effort in November 2019. Leanne, Sarah and Dagný in the back, Kalina and Fia in front row. Heroic effort by all.

categories Publications

Variation in personality shaped by evolutionary history, genotype, and developmental plasticity

Arnar Pálsson, 14/11/2023

"Dear Dr DellingerI am pleased to inform you that your manuscript RSPB-2023-2302 entitled "Variation in personality shaped by evolutionary history, genotype, and developmental plasticity in response to feeding modalities in the Arctic charr" has been accepted for publication in Proceedings B."

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

Very welcome outcome. Congrats to Sarah Steele and Marion Dellinger who led the study.

Boldness in behavior varied substantially by morphs, and also by families in some of the morphs, though noticably least in Anadromous (left) and planktivorous charr from Þingvallavatn (right).

Boldness variation by families of 5 Arctic charr ecomorphs

 

categories 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

Lúsmý, maurar og fleiri dýr

Arnar Pálsson, 30/06/2023

Nýsköpunarsjóður námsmanna gerir fjórum líffræðinemar og BS líffræðingar kleift að verkefnum um skordýr á Íslandi við Líffræðistofu Háskóla Íslands nú í sumar.

Við höfum áður fjallað um maurarannsóknir en auk þess er kastljósinu nú beint að lúsmýi og ávaxtaflugum. Það eru nýlegir landnemar hérlendis. Lúsmýið er alræmt fyrir bit og almenn leiðindi, en ávaxtaflugur eru dýrkaðar og dáðar vegna fegurðar sinnar og fengileiks. Sumir eru reyndar smeykir við ávaxtaflugur, en þær bíta ekki fólk, bera ekki sjúkdóma og verða bara til ama ef þær verpa í bananann sem við gleymdum undir ískáp.

Í lúsmý verkefninu er ætlunin að kanna hvenær sumarsins þær koma fram, hvort um sé að ræða einn eða tvo toppa klaksins, hvaða búsvæðum flugurnar klekjast helst úr og hver dreifing þeirra á landsvísu er. Beitt verður aðferðum skordýrafræði og stofnerfðafræði. Hér að neðan eru myndir af klakgildrum og vettvangi rannsókna í Kjósinni.

categories General biology, Uncategorized

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