| 1. |
- Balazy, Kaja, et al.
(författare)
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Molecular tools prove little auks from Svalbard are extremely selective for Calanus glacialis even when exposed to Atlantification
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Two Calanus species, C. glacialis and C. finmarchicus, due to different life strategies and environmental preferences act as an ecological indicators of Arctic Atlantification. Their high lipid content makes them important food source for higher trophic levels of Arctic ecosystems including the most abundant Northern Hemisphere's seabird, the little auk (Alle alle). Recent studies indicate a critical need for the use of molecular methods to reliably identify these two sympatric Calanus species. We performed genetic and morphology-based identification of 2600 Calanus individuals collected in little auks foraging grounds and diet in summer seasons 2019-2021 in regions of Svalbard with varying levels of Atlantification. Genetic identification proved that 40% of Calanus individuals were wrongly classified as C. finmarchicus according to morphology-based identification in both types of samples. The diet of little auks consisted almost entirely of C. glacialis even in more Atlantified regions. Due to the substantial bias in morphology-based identification, we expect that the scale of the northern expansion of boreal C. finmarchicus may have been largely overestimated and that higher costs for birds exposed to Atlantification could be mostly driven by a decrease in the size of C. glacialis rather than by shift from C. glacialis to C. finmarchicus.
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| 2. |
- Choquet, Marvin, et al.
(författare)
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Comparative Population Transcriptomics Provide New Insight into the Evolutionary History and Adaptive Potential of World Ocean Krill
- 2023
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Ingår i: Molecular biology and evolution. - : Oxford University Press. - 0737-4038 .- 1537-1719. ; 40:11
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Tidskriftsartikel (refereegranskat)abstract
- Genetic variation is instrumental for adaptation to changing environments but it is unclear how it is structured and contributes to adaptation in pelagic species lacking clear barriers to gene flow. Here, we applied comparative genomics to extensive transcriptome datasets from 20 krill species collected across the Atlantic, Indian, Pacific, and Southern Oceans. We compared genetic variation both within and between species to elucidate their evolutionary history and genomic bases of adaptation. We resolved phylogenetic interrelationships and uncovered genomic evidence to elevate the cryptic Euphausia similis var. armata into species. Levels of genetic variation and rates of adaptive protein evolution vary widely. Species endemic to the cold Southern Ocean, such as the Antarctic krill Euphausia superba, showed less genetic variation and lower evolutionary rates than other species. This could suggest a low adaptive potential to rapid climate change. We uncovered hundreds of candidate genes with signatures of adaptive evolution among Antarctic Euphausia but did not observe strong evidence of adaptive convergence with the predominantly Arctic Thysanoessa. We instead identified candidates for cold-adaptation that have also been detected in Antarctic fish, including genes that govern thermal reception such as TrpA1. Our results suggest parallel genetic responses to similar selection pressures across Antarctic taxa and provide new insights into the adaptive potential of important zooplankton already affected by climate change.
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| 3. |
- Choquet, Marvin, et al.
(författare)
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The complete mitochondrial genome of the copepod Calanus glacialis
- 2017
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Ingår i: Mitochondrial DNA Part B. - : Informa UK Limited. - 2380-2359. ; 2:2, s. 506-507
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Tidskriftsartikel (refereegranskat)abstract
- Calanus glacialis, a marine planktonic copepod, is a keystone species in the Arctic Ocean. In this study, we shotgun sequenced the total DNA of one C. glacialis individual, using the NextSeq® Illumina platform, in order to determine its mitochondrial genome sequence. We successfully assembled and annotated this 20,674bp long sequence, which included 13 protein-coding genes, 2 rRNA genes and 22 tRNA genes. Common gene-coding regions of 19 other species were used to reconstruct a phylogenetic tree, using mitogenomes of the phylogenetically closest copepods available. The new resource described here constitutes a tool of interest for better understanding the structure and dynamics of C. glacialis populations.
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| 4. |
- Coguiec, Estelle, et al.
(författare)
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Photoperiodism and overwintering in boreal and sub-Arctic Calanus finmarchicus populations
- 2023
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Ingår i: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 712, s. 49-65
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Tidskriftsartikel (refereegranskat)abstract
- The copepod Calanus finmarchicus, a key species in the North Atlantic, generally spends the non-productive season by descending into deep waters and entering diapause, a physiological state characterized by reduced metabolism and arrested development. In the open ocean, overwintering depths are below 600 m, where temperature and light conditions are favourable to initiate diapause. However, C. finmarchicus has also been reported diapausing in areas with shallow water depth such as fjords, coastal waters and shelf seas. In these environments, the temperature and light conditions are different, and it has been hypothesized that under such conditions C. finmarchicus may remain active throughout winter. Here, we investigated changes in the swimming activity of C. finmarchicus from shallow fjords in the eastern North Atlantic during overwintering in response to ambient photoperiod. We conducted monthly experiments with populations from 2 fjords from different latitudes (sub-Arctic Ramfjord, 69 degrees N and boreal Loch Etive, 56 degrees N), measuring the locomotor activity of individual C. finmarchicus stage CVs exposed to a natural light:dark cycle. At both locations, peaks in activity in response to the light cycle were observed to shift from nocturnal during the early overwintering phase to diurnal during mid and late overwintering phase, with a minimal intensity observed during the mid-overwintering phase. In Ramfjord, activity and rhythmicity were generally lower than in Loch Etive. We conclude that C. finmarchicus remains active throughout its overwintering period when in shallow (<200 m) locations but down-regulates its locomotor activity during the main overwintering phase, which we describe as a winter resting state as distinct from classical diapause.
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| 5. |
- Lizano, Apollo Marco, et al.
(författare)
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Insights into the species evolution of Calanus copepods in the northern seas revealed by de novo transcriptome sequencing
- 2022
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Copepods of the zooplankton genus Calanus play a key role in marine ecosystems in the northern seas. Although being among the most studied organisms on Earth, due to their ecological importance, genomic resources for Calanus spp. remain scarce, mostly due to their large genome size (from 6 to 12 Gbps). As an alternative to whole-genome sequencing in Calanus spp., we sequenced and de novo assembled transcriptomes of five Calanus species: Calanus glacialis, C. hyperboreus, C. marshallae, C. pacificus, and C. helgolandicus. Functional assignment of protein families based on clusters of orthologous genes (COG) and gene ontology (GO) annotations showed analogous patterns of protein functions across species. Phylogenetic analyses using maximum likelihood (ML) of 191 protein-coding genes mined from RNA-seq data fully resolved evolutionary relationships among seven Calanus species investigated (five species sequenced for this study and two species with published datasets), with gene and site concordance factors showing that 109 out of 191 protein-coding genes support a separation between three groups: the C. finmarchicus group (including C. finmarchicus, C. glacialis, and C. marshallae), the C. helgolandicus group (including C. helgolandicus, C. sinicus, and C. pacificus) and the monophyletic C. hyperboreus group. The tree topology obtained in ML analyses was similar to a previously proposed phylogeny based on morphological criteria and cleared certain ambiguities from past studies on evolutionary relationships among Calanus species.
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| 6. |
- Schultz, Mads, et al.
(författare)
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Calanus helgolandicus : more than a guest in the north?
- 2023
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Ingår i: Journal of Plankton Research. - : Oxford University Press. - 0142-7873 .- 1464-3774. ; 45:1, s. 33-36
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Tidskriftsartikel (refereegranskat)abstract
- Molecular identification of Calanus helgolandicus has revealed a more northern distribution for this boreal species than previously reported. We investigated an Arctic fjord to determine if local reproduction is taking place. Combining time series data from depth stratified sampling with molecular tools for species identification, we found C. helgolandicus from all stages throughout the year including males and females as well as a nauplius. These findings constitute strong evidence that C. helgolandicus is reproducing north of the Arctic Circle and their role in the ecosystem should be investigated further.
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| 7. |
- Sen, Arunima, et al.
(författare)
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The phylogeography and ecology of Oligobrachia frenulate species suggest a generalist chemosynthesis-based fauna in the arctic
- 2023
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Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- We used ancient DNA (aDNA) extraction methods to sequence museum voucher samples of Oligobrachia webbi, a frenulate siboglinid polychaete described from a northern Norwegian fjord over fifty years ago. Our sequencing results indicate a genetic match with the cryptic seep species, Oligobrachia haakonmosbiensis (99% pairwise identity for 574 bp mtCOI fragments). Due to its similarity with O. webbi, the identity of O. haakonmosbiensis has been a matter of debate since its description, which we have now resolved. Furthermore, our results demonstrate that chemosynthesis-based siboglinids, that constitute the bulk of the biomass at Arctic seeps are not seep specialists. Our data on sediment geochemistry and carbon and nitrogen content reveal reduced conditions in fjords/sounds, similar to those at seep systems. Accumulation and decomposition of both terrestrial and marine organic matter results in the buildup of methane and sulfide that apparently can sustain chemosymbiotic fauna. The occurrence of fjords and by extension, highly reducing habitats, could have led to Arctic chemosymbiotic species being relatively generalist with their habitat, as opposed to being seep or vent specialists. Our stable isotope analyses indicate the incorporation of photosynthetically derived carbon in some individuals, which aligns with experiments conducted on frenulates before the discovery of chemosynthesis that demonstrated their ability to take up organic molecules from the surrounding sediment. Since reduced gases in non-seep environments are ultimately sourced from photosynthetic processes, we suggest that the extreme seasonality of the Arctic has resulted in Arctic chemosymbiotic animals seasonally changing their degree of reliance on chemosynthetic partners. Overall, the role of chemosynthesis in Arctic benthos and marine ecosystems and links to photosynthesis may be complex, and more extensive than currently known.
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