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.

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.

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.

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

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.

European fire ants found in Iceland. / Evrópskir eldmaurar (Myrmica rubra) á Íslandi. Marco Mancini, Andreas Guðmundsson og Arnar Pálsson. Accepted by the Icelandic naturalist (Náttúrufræðingurinn).

Phylogenetic analyses revealed emergence in vertebrates of a novel region within a conserved domain in ATG7. Valgerdur J. Hjaltalin, Vivian Pogenberg, Arnar Pálsson, Margrét Helga Ogmundsdottir. (being revised).

DNA methylation differences during development distinguish sympatric morphs of Arctic charr (Salvelinus alpinus). Sebastien Matlosz, Benjamin Sigurgeirsson, Sigrídur Rut Franzdóttir, Arnar Pálsson, Zophonías O. Jónsson. (not on bioRxiv, second revision sent in).

Sebastien sent the revised manuscript again. Must say I am very excited about this study and its implications.

From the abstract.

• The data revealed strong differences between developmental timepoints and between morphs (mainly along the benthic – limnetic axis), both at single CpG sites and in 1000bp-regions. Genes located close to differentially methylated CpG sites were involved in nucleosome assembly, TGF-β regulation, and cell matrix adhesion.