Marvin Raoul Charles Roger Rene Choquet

• Schultz, Mads; Choquet, Marvin; Daase, Malin & Hoarau, Galice Guillaume (2025). Income and capital breeding Calanus reproduction in a subarctic fjord. Limnology and Oceanography. ISSN 0024-3590. 70(11), s. 3544–3551. doi: 10.1002/lno.70209. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Copepods of the genus Calanus are key species in the energy transfer from primary producers to higher trophic levels in Arctic and sub‐Arctic seas. The timing of reproduction can differ between species, depending on whether they rely on external energy sources to initiate reproduction (income breeders) or use internal energy sources (capital breeders), or both. The high morphological similarity among species, especially when co‐occurring in sympatry, has limited the reliability of species‐specific conclusions on life history traits in previous studies relying on morphological identification only. Here, we applied molecular species identification to reliably compare breeding strategies among co‐occurring Calanus hyperboreus , Calanus glacialis , and Calanus finmarchicus in a northern Norwegian fjord. Lipid content of adult females was measured with high temporal resolution over an entire annual cycle, and the presence of nauplii was determined for each species. Calanus hyperboreus and C. glacialis were found to be strict capital breeders, whereas C. finmarchicus acted as an income breeder.

• Coguiec, Estelle; Last, Kim S.; Cohen, Jonathan H.; Hobbs, Laura; Choquet, Marvin & Ershova, Elizaveta [Vis alle 8 forfattere av denne artikkelen] (2023). Photoperiodism and overwintering in boreal and sub-Arctic Calanus finmarchicus populations. Marine Ecology Progress Series. ISSN 0171-8630. 712, s. 49–65. doi: 10.3354/meps14307. Fulltekst i vitenarkiv Vis sammendrag

  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°N and boreal Loch Etive, 56°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.

• Schultz, Mads; Choquet, Marvin; Tverberg, Vigdis & Hoarau, Galice Guillaume (2023). Calanus helgolandicus-more than a guest in the north? Journal of Plankton Research. ISSN 0142-7873. 45(1), s. 33–36. doi: 10.1093/plankt/fbac070. Fulltekst i vitenarkiv
• Choo, Le Qin; Spagliardi, G; Malinsky, M; Choquet, Marvin; Goetze, Erica & Hoarau, Galice Guillaume [Vis alle 7 forfattere av denne artikkelen] (2023). Genome-wide phylogeography reveals cryptic speciation in the circumglobal planktonic calcifier Limacina bulimoides. Molecular Ecology. ISSN 0962-1083. 32(12). doi: 10.1111/mec.16931. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Little is known about when and how planktonic species arise and persist in the open ocean without apparent dispersal barriers. Pteropods are planktonic snails with thin shells susceptible to dissolution that are used as bio‐indicators of ocean acidification. However, distinct evolutionary units respond to acidification differently, and defining species boundaries is therefore crucial for predicting the impact of changing ocean conditions. In this global population genomic study of the shelled pteropod Limacina bulimoides , we combined genetic (759,000 single nucleotide polymorphisms) and morphometric data from 161 individuals, revealing three major genetic lineages ( F ST  = 0.29–0.41): an “Atlantic lineage” sampled across the Atlantic, an “Indo‐Pacific lineage” sampled in the North Pacific and Indian Ocean, and a “Pacific lineage” sampled in the North and South Pacific. A time‐calibrated phylogeny suggests that the lineages diverged about 1 million years ago, with estimated effective population size remaining high (~10 million) throughout Pleistocene glacial cycles. We do not observe any signatures of recent hybridization, even in areas of sympatry in the North Pacific. While the lineages are reproductively isolated, they are morphologically cryptic, with overlapping shell shape and shell colour distributions. Despite showing that the circumglobal L. bulimoides consists of multiple species with smaller ranges than initially thought, we found that these pteropods still possess high levels of genetic variability. Our study adds to the growing evidence that speciation is often overlooked in the open ocean, and suggests the presence of distinct biological species within many other currently defined circumglobal planktonic species.

• Choquet, Marvin; Lizano, Apollo Marco Dalonos; Le Moan, Alan; Ravinet, Mark; Dhanasiri, Anusha & Hoarau, Galice Guillaume (2023). Unmasking microsatellite deceptiveness and debunking hybridization with SNPs in four marine copepod species of Calanus. Molecular Ecology. ISSN 0962-1083. 32(24), s. 6854–6873. doi: 10.1111/mec.17183. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Interspecific hybridization events are on the rise in natural systems due to climate change disrupting species barriers. Across taxa, microsatellites have long been the molecular markers of choice to identify admixed individuals. However, with the advent of high‐throughput sequencing easing the generation of genome‐wide datasets, incorrect reports of hybridization resulting from microsatellite technical artefacts have been uncovered in a growing number of taxa. In the marine zooplankton genus Calanus (Copepoda), whose species are used as climate change indicators, microsatellite markers have suggested hybridization between C. finmarchicus and C. glacialis, while other nuclear markers (InDels) never detected any admixed individuals, leaving the scientific community divided. Here, for the first time, we investigated the potential for hybridization among C. finmarchicus , C. glacialis , C. helgolandicus and C. hyperboreus using two large and independent SNP datasets. These were derived firstly from a protocol of target‐capture applied to 179 individuals collected from 17 sites across the North Atlantic and Arctic Oceans, including sympatric areas, and second from published RNA sequences. All SNP‐based analyses were congruent in showing that Calanus species are distinct and do not appear to hybridize. We then thoroughly re‐assessed the microsatellites showing hybrids, with the support of published transcriptomes, and identified technical issues plaguing eight out of 10 microsatellites, including size homoplasy, paralogy, potential for null alleles and even two primer pairs targeting the same locus. Our study illustrates how deceptive microsatellites can be when applied to the investigation of hybridization.

• Sen, Arunima; Andersen, Liselotte W.; Kjeldsen, Kasper U.; Michel, Loïc N.; Hong, Wei-Li & Choquet, Marvin [Vis alle 7 forfattere av denne artikkelen] (2023). The phylogeography and ecology of Oligobrachia frenulate species suggest a generalist chemosynthesis-based fauna in the arctic. Heliyon. 9(3). doi: 10.1016/j.heliyon.2023.e14232. Fulltekst i vitenarkiv Vis sammendrag

  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

• Choquet, Marvin; Lenner, Felix; Cocco, Arianna; Toullec, Gaelle; Corre, Erwan & Toullec, Jean-Yves [Vis alle 7 forfattere av denne artikkelen] (2023). Comparative population transcriptomics provide new insight into the evolutionary history and adaptive potential of World Ocean Krill. Molecular Biology and Evolution (MBE). ISSN 0737-4038. 40(11). doi: 10.1093/molbev/msad225. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Balazy, Kaja; Trudnowska, Emilia; Wojczulanis-Jakubas, Katarzyna; Jakubas, Dariusz; Præbel, Kim & Choquet, Marvin [Vis alle 14 forfattere av denne artikkelen] (2023). Molecular tools prove little auks from Svalbard are extremely selective for Calanus glacialis even when exposed to Atlantification. Scientific Reports. 13(1). doi: 10.1038/s41598-023-40131-7. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Lizano, Apollo Marco Dalonos; Smolina, Irina Vladimirovna; Choquet, Marvin; Kopp, Martina Elisabeth Luise & Hoarau, Galice Guillaume (2022). Insights into the species evolution of Calanus copepods in the northern seas revealed by de novo transcriptome sequencing. Ecology and Evolution. 12(2). doi: 10.1002/ece3.8606. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Hatlebakk, Maja K Viddal; Niehoff, Barbara; Choquet, Marvin; Hop, Haakon; Wold, Anette & Hoarau, Galice Guillaume [Vis alle 7 forfattere av denne artikkelen] (2022). Seasonal Enzyme Activities of Sympatric Calanus glacialis and C. finmarchicus in the High-Arctic. Frontiers in Marine Science. 9. doi: 10.3389/fmars.2022.877904. Fulltekst i vitenarkiv Vis sammendrag

  In the Arctic shelf seas, the mesozooplankton biomass is dominated by the arctic copepod Calanus glacialis, but its boreal congeneric C. finmarchicus is expanding northwards. Even though it is already there, C. finmarchicus may not be able to truly establish itself in the Arctic seas and potentially replace C. glacialis. We compared metabolic and digestive enzyme activities of sympatric C. glacialis and C. finmarchicus from Isfjorden, Svalbard and off-shelf north of Svalbard. The seasonal regulation of anabolic and catabolic enzyme activities was generally similar for the two species, but with some interspecific differences corresponding to their ontogeny. Wake-up from overwintering started earlier in adults of C. glacialis than in C. finmarchicus, while the onset of dormancy started early in the overwintering stages of both species. Furthermore, C. glacialis showed an earlier and higher mobilization of lipase enzyme activities, indicating higher efficiency in assimilating dietary lipids compared to C. finmarchicus. Similar population sizes and population structures for C. finmarchicus off-shelf north of Svalbard and in Isfjorden support a similar origin. Still, C. finmarchicus was able to match regulation of enzyme activities to the bloom even though the bloom peaked approximately a month later off-shelf north of Svalbard, indicating that food availability is an important signal for the final step of termination of diapause. Even though the two species largely follow the same patterns of metabolic enzyme activities, the more efficient lipid anabolism of C. glacialis may give it an advantage over C. finmarchicus in high-Arctic unpredictable environments with short-pulsed primary production regimes.

• Choo, Le Qin; Bal, Thijs M.P.; Choquet, Marvin; Smolina, Irina V.; Ramos-Silva, Paula & Marletaz, Ferdinand [Vis alle 9 forfattere av denne artikkelen] (2020). Novel genomic resources for shelled pteropods: a draft genome and target capture probes for Limacina bulimoides, tested for cross-species relevance. BMC Genomics. 21(11). doi: 10.1186/s12864-019-6372-z. Fulltekst i vitenarkiv Vis sammendrag

  Pteropods are planktonic gastropods that are considered as bio-indicators to monitor impacts of ocean acidification on marine ecosystems. In order to gain insight into their adaptive potential to future environmental changes, it is critical to use adequate molecular tools to delimit species and population boundaries and to assess their genetic connectivity. We developed a set of target capture probes to investigate genetic variation across their large-sized genome using a population genomics approach. Target capture is less limited by DNA amount and quality than other genome-reduced representation protocols, and has the potential for application on closely related species based on probes designed from one species.

• Skottene, Elise; Tarrant, Ann M.; Altin, Dag; Olsen, Rolf Erik; Choquet, Marvin & Kvile, Kristina Ø (2020). Lipid metabolism in Calanus finmarchicus is sensitive to variations in predation risk and food availability. Scientific Reports. 10. doi: 10.1038/s41598-020-79165-6. Fulltekst i vitenarkiv Vis sammendrag

  Late developmental stages of the marine copepods in the genus Calanus can spend extended periods in a dormant stage (diapause) that is preceded by the accumulation of large lipid stores. We assessed how lipid metabolism during development from the C4 stage to adult is altered in response to predation risk and varying food availability, to ultimately understand more of the metabolic processes during development in Calanus copepods. We used RNA sequencing to assess if perceived predation risk in combination with varied food availability affects expression of genes associated with lipid metabolism and diapause preparation in C. finmarchicus. The lipid metabolism response to predation risk differed depending on food availability, time and life stage. Predation risk caused upregulation of lipid catabolism with high food, and downregulation with low food. Under low food conditions, predation risk disrupted lipid accumulation. The copepods showed no clear signs of diapause preparation, supporting earlier observations of the importance of multiple environmental cues in inducing diapause in C. finmarchicus. This study demonstrates that lipid metabolism is a sensitive endpoint for the interacting environmental effects of predation pressure and food availability. As diapause may be controlled by lipid accumulation, our findings may contribute towards understanding processes that can ultimately influence diapause timing.

• Choquet, Marvin; Burckard, Gauthier; Skreslet, Stig; Hoarau, Galice Guillaume & Søreide, Janne E. (2020). No evidence for hybridization between Calanus finmarchicus and Calanus glacialis in a subarctic area of sympatry. Limnology and Oceanography. ISSN 0024-3590. doi: 10.1002/lno.11583. Fulltekst i vitenarkiv Vis sammendrag

  In the North Atlantic and the Arctic Ocean, four species of the copepod genus Calanus dominate the zooplankton biomass. Because of their morphological resemblance, knowledge of their respective distribution range has long been biased by misidentification, until the recent use of molecular tools uncovered numerous areas of sympatry. As hybridization between Calanus finmarchicus and Calanus glacialis has been claimed in the East‐Canadian Arctic based on microsatellites, we investigated further the potential for interbreeding in newly uncovered areas of sympatry. Calanus species and stage composition were analyzed during winter in two Norwegian subarctic fjords, using molecular markers developed specifically for species identification and hybrid detection between C. finmarchicus and C. glacialis. Overall, C. glacialis were the most abundant throughout the winter, followed by C. finmarchicus and Calanus hyperboreus with only a few records of Calanus helgolandicus. The presence of C. glacialis, C. hyperboreus, and C. finmarchicus' nauplii was recorded, indicating that these species reproduce locally. In January and February, the simultaneous occurrence of males and females of both C. finmarchicus and C. glacialis suggested a potential for interspecies mating. However, genetic admixture tests performed on all 1126 individuals revealed no signal of hybridization, implying a strong reproductive isolation mechanism. We conclude that no evidence supports a potential for hybridization between C. finmarchicus and C. glacialis.

• Skottene, Elise; Tarrant, Ann; Olsen, Anders Johny; Altin, Dag; Hansen, Bjørn Henrik & Choquet, Marvin [Vis alle 8 forfattere av denne artikkelen] (2019). A Crude Awakening: Effects of Crude Oil on Lipid Metabolism in Calanoid Copepods Terminating Diapause. The Biological Bulletin. ISSN 0006-3185. 237(2), s. 90–110. doi: 10.1086/705234. Fulltekst i vitenarkiv Vis sammendrag

  Calanus finmarchicus and Calanus glacialis are keystone zooplankton species in North Atlantic and Arctic marine ecosystems because they form a link in the trophic transfer of nutritious lipids from phytoplankton to predators on higher trophic levels. These calanoid copepods spend several months of the year in deep waters in a dormant state called diapause, after which they emerge in surface waters to feed and reproduce during the spring phytoplankton bloom. Disruption of diapause timing could have dramatic consequences for marine ecosystems. In the present study, Calanus C5 copepodites were collected in a Norwegian fjord during diapause and were subsequently experimentally exposed to the water-soluble fraction of a naphthenic North Sea crude oil during diapause termination. The copepods were sampled repeatedly while progressing toward adulthood and were analyzed for utilization of lipid stores and for differential expression of genes involved in lipid metabolism. Our results indicate that water-soluble fraction exposure led to a temporary pause in lipid catabolism, suggested by (i) slower utilization of lipid stores in water-soluble fraction-exposed C5 copepodites and (ii) more genes in the b-oxidation pathway being downregulated in water-soluble fraction-exposed C5 copepodites than in the control C5 copepodites. Because lipid content and/or composition may be an important trigger for termination of diapause, our results imply that the timing of diapause termination and subsequent migration to the surface may be delayed if copepods are exposed to oil pollution during diapause or diapause termination. This delay could have detrimental effects on ecosystem dynamics.

• Choquet, Marvin; Smolina, Irina Vladimirovna; Dhanasiri, Anusha Krishanthi Shyama; Blanco-Bercial, Leocadio; Kopp, Martina Elisabeth Luise & Jüterbock, Alexander Oliver [Vis alle 8 forfattere av denne artikkelen] (2019). Towards population genomics in non-model species with large genomes: a case study of the marine zooplankton Calanus finmarchicus. Royal Society Open Science. 6(2). doi: 10.1098/rsos.180608. Fulltekst i vitenarkiv
• Boavida, Joana R.; Becheler, Ronan; Choquet, Marvin; Franck, N.; Taviani, Marco & Bourillet, Jean-Francois [Vis alle 10 forfattere av denne artikkelen] (2019). Out of the Mediterranean? Post-glacial colonization pathways varied among cold-water coral species. Journal of Biogeography. ISSN 0305-0270. 46(5), s. 915–931. doi: 10.1111/jbi.13570. Fulltekst i vitenarkiv
• Basedow, Sünnje Linnéa; Mckee, David; Lefering, Ina; Gislason, Astthor; Daase, Malin & Trudnowska, Emilia [Vis alle 9 forfattere av denne artikkelen] (2019). Remote sensing of zooplankton swarms. Scientific Reports. 9(1). doi: 10.1038/s41598-018-37129-x. Fulltekst i vitenarkiv Vis sammendrag

  Zooplankton provide the key link between primary production and higher levels of the marine food web and they play an important role in mediating carbon sequestration in the ocean. All commercially harvested fish species depend on zooplankton populations. However, spatio-temporal distributions of zooplankton are notoriously difficult to quantify from ships. We know that zooplankton can form large aggregations that visibly change the color of the sea, but the scale and mechanisms producing these features are poorly known. Here we show that large surface patches (>1000 km 2 ) of the red colored copepod Calanus finmarchicus can be identified from satellite observations of ocean color. Such observations provide the most comprehensive view of the distribution of a zooplankton species to date, and alter our understanding of the behavior of this key zooplankton species. Moreover, our findings suggest that high concentrations of astaxanthin-rich zooplankton can degrade the performance of standard blue-green reflectance ratio algorithms in operational use for retrieving chlorophyll concentrations from ocean color remote sensing.

• Skottene, Elise; Tarrant, Ann M.; Olsen, Anders Johny; Altin, Dag; Østensen, Mari-Ann & Hansen, Bjørn Henrik [Vis alle 9 forfattere av denne artikkelen] (2019). The β-oxidation pathway is downregulated during diapause termination in Calanus copepods. Scientific Reports. 9(1). doi: 10.1038/s41598-019-53032-5. Fulltekst i vitenarkiv Vis sammendrag

  Calanus copepods are keystone species in marine ecosystems, mainly due to their high lipid content, which is a nutritious food source for e.g. juvenile fish. Accumulated lipids are catabolized to meet energy requirements during dormancy (diapause), which occurs during the last copepodite stage (C5). The current knowledge of lipid degradation pathways during diapause termination is limited. We characterized changes in lipid fullness and generated transcriptional profiles in C5s during termination of diapause and progression towards adulthood. Lipid fullness of C5s declined linearly during developmental progression, but more β-oxidation genes were upregulated in early C5s compared to late C5s and adults. We identified four possible master regulators of energy metabolism, which all were generally upregulated in early C5s, compared to late C5s and adults. We discovered that one of two enzymes in the carnitine shuttle is absent from the calanoid copepod lineage. Based on the geographical location of the sampling site, the field-samples were initially presumed to consist of C. finmarchicus. However, the identification of C. glacialis in some samples underlines the need for performing molecular analyses to reliably identify Calanus species. Our findings contributes to a better understanding of molecular events occurring during diapause and diapause termination in calanoid copepods.

• Daase, Malin; Kosobokova, Ksenia; Last, Kim S; Cohen, Jonathan H.; Choquet, Marvin & Hatlebakk, Maja Karoline Viddal [Vis alle 7 forfattere av denne artikkelen] (2018). New insights into the biology of Calanus spp. (Copepoda) males in the Arctic. Marine Ecology Progress Series. ISSN 0171-8630. 607, s. 53–69. doi: 10.3354/meps12788. Fulltekst i vitenarkiv Vis sammendrag

  Adult males of <i>Calanus</i> copepods in the Arctic are mainly observed between late autumn and late spring, and are seldom recorded during summer. Due to logistical constraints, there are still relatively few studies on zooplankton in high-latitude regions during the winter, and subsequently, little is known about <i>Calanus</i> males. Here, we present data on abundance, spatial distribution, prosome length, lipid content, respiration and swimming activity of i>Calanus</i> adults, along with adult sex ratios in i>Calanus</i> populations from 5 Arctic fjords in Svalbard, Norway (78-80° N) during the polar night in January 2015, 2016 and 2017. Adult males and females of i>Calanus</i> were observed at all locations and occurred throughout the entire water column. Morphological examination and molecular identification of i>Calanus</i> males proved that all males encountered belong to <i>Calanus glacialis</i>, even in the fjords where overwintering copepodite stage CV of <i>C. finmarchicus</i> dominated at the time. Adult sex ratios in <i>C. glacialis</i> populations varied from 1 male per 4 females to 2 males per female. From 3 to 18% of females carried spermatophores attached to the genital segment. Lipid content in males was slightly higher than in females. Shipboard experiments showed that males had higher swimming activity and respiration rates than females. Our observations indicate that adult males of <i>C. glacialis</i> stay active and demonstrate active mating behavior in mid-winter, and that the mating phenology of <i>C. glacialis</i> is decoupled from that of <i>C. finmarchicus</i> in the study area in January.

• Choquet, Marvin; Kosobokova, Ksenia; Kwaśniewski, Sławomir; Hatlebakk, Maja Karoline Viddal; Dhanasiri, Anusha Krishanthi Shyama & Melle, Webjørn Raunsgård [Vis alle 10 forfattere av denne artikkelen] (2018). Can morphology reliably distinguish between the copepods Calanus finmarchicus and C. glacialis, or is DNA the only way? Limnology and Oceanography : Methods. 16(4), s. 237–252. doi: 10.1002/lom3.10240. Fulltekst i vitenarkiv Vis sammendrag

  Copepods of the genus Calanus play a key role in marine food webs as consumers of primary producers and as prey for many commercially important marine species. Within the genus, Calanus glacialis and Calanus finmarchi- cus are considered indicator species for Arctic and Atlantic waters, respectively, and changes in their distributions are frequently used as a tool to track climate change effects in the marine ecosystems of the northern hemisphere. Despite the extensive literature available, discrimination between these two species remains challenging. Using genetically identified individuals, we simultaneously checked the morphological characters in use for C. glacialis and C. finmarchicus identification to compare the results of molecular and morphological identification. We stud- ied the prosome length (1); the antennules and the genital somite pigmentation (2); the morphology of the fifth pair of swimming legs and of the mandible (3). Our results show that none of these morphological criteria can reli- ably distinguish between C. glacialis and C. finmarchicus . This has severe implications for our current understand- ing of plankton ecology as a large part of our knowledge of Calanus may be biased due to species misidentification and may subsequently require reinvestigation with the systematic use of molecular tools.

• Choquet, Marvin Raoul Charles Roger Ren; Bengtsson-Palme, Johan; Hoarau, Galice Guillaume & Monteiro, Homére Alves (2017). The complete mitochondrial genome of the copepod Calanus glacialis. Mitochondrial DNA Part B: Resources. 2(2). doi: 10.1080/23802359.2017.1361357. Fulltekst i vitenarkiv
• Choquet, Marvin Raoul Charles Roger Ren; Hatlebakk, Maja Karoline Viddal; Dhanasiri, Anusha Krishanthi Shyama; Kosobokova, Ksenia N.; Smolina, Irina Vladimirovna & Søreide, Janne [Vis alle 15 forfattere av denne artikkelen] (2017). Genetics redraws pelagic biogeography of Calanus. Biology Letters. ISSN 1744-9561. 13(12). doi: 10.1098/rsbl.2017.0588. Fulltekst i vitenarkiv Vis sammendrag

  Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis, dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus. We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.

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• Choquet, Marvin & Struck, Torsten H (2025). Group of the month, May: The Krill. doi: https:/blog.annelida.de/2025/05/19/group-of-the-month-may-the-krill/. Fulltekst i vitenarkiv
• Choquet, Marvin (2025). Océans, changement climatique et plancton. Fulltekst i vitenarkiv
• Choquet, Marvin (2025). Towards understanding adaptation to predict resilience and the future of oceanic zooplankton in a changing climate. Fulltekst i vitenarkiv
• Choquet, Marvin & Hestvik, Ingebjørg (2024). De er mat for fisken i havet: Raudåte kan ha vært feilidentifisert i flere tiår. [Internet]. Forskning.no. Fulltekst i vitenarkiv
• Choquet, Marvin & Hestvik, Ingebjørg (2024). Avanserte genetiske metoder ga svar på om to tilsynelatende like hoppekreps kunne pare seg med hverandre. [Internet]. Forskning.no. Fulltekst i vitenarkiv
• Søreide, Janne; Hatlebakk, Maja Karoline Viddal; Pitusi, Vanessa; Daase, Malin Hildegard Elisabeth; Præbel, Kim & Gradinger, Rolf Rudolf [Vis alle 14 forfattere av denne artikkelen] (2022). Meltdown of the Arctic Ocean: Dead end or new opportunities? Fram Forum. ISSN 1893-5532. Fulltekst i vitenarkiv
• Choquet, Marvin; Smolina, Irina Vladimirovna & Hoarau, Galice Guillaume (2021). No evidence for hybridization in Calanus: Reply to the comment by Parent et al. Limnology and Oceanography. ISSN 0024-3590. 66(10), s. 3603–3606. doi: 10.1002/lno.11931. Fulltekst i vitenarkiv
• Hansen, Bjørn Henrik; Altin, Dag; Choquet, Marvin; Grøsvik, Bjørn Einar; Sørensen, Lisbet & Nepstad, Raymond (2021). Zooplankton-based monitoring of offshore produced water discharges. Fulltekst i vitenarkiv
• Choquet, Marvin (2020). Customize and get the most out of your reduced representation sequencing experiment with the new simulation software RADinitio. Molecular Ecology Resources. ISSN 1755-098X. s. 1–4. doi: 10.1111/1755-0998.13218. Fulltekst i vitenarkiv
• Skottene, Elise; Tarrant, Ann M.; Olsen, Anders Johny; Altin, Dag; Hansen, Bjørn Henrik & Choquet, Marvin [Vis alle 8 forfattere av denne artikkelen] (2020). Oil exposure disrupts lipid metabolism during diapause in calanoid copepods. Fulltekst i vitenarkiv
• Smolina, Irina; Choquet, Marvin; Kopp, Martina; Bucklin, Ann & Hoarau, Galice (2015). Genome-wide gene,c varia,on in popula,ons of Calanus finmarchicus and C. glacialis across their distribu,onal ranges. Fulltekst i vitenarkiv
• Hansen, Bjørn Henrik; Altin, Dag; Choquet, Marvin; Sørensen, Lisbet; Egeness, Mari Jystad & Rønsberg, Marianne Unaas [Vis alle 7 forfattere av denne artikkelen] (2022). Body burdens of PAHs and alkylated phenols in copepods in the Ekofisk region - Water column monitoring 2021. SINTEF Ocean AS. ISSN 9788271744472. Fulltekst i vitenarkiv Vis sammendrag

  This report summarizes the findings from the Water Column Monitoring in April 2021 where zooplankton (Calanus finmarchicus) were collected and sampled around the Ekofisk region in the North Sea. Extraction and analyses of polycyclic aromatic hydrocarbons and alkylated phenols in copepod were determined to provide data for comparison to DREAM-MER simulations.

• Choquet, Marvin; Hoarau, Galice & Søreide, Janne Elin (2017). Combining ecological and molecular approaches to redefine the baseline knowledge of the genus Calanus in the North Atlantic and the Arctic Oceans. Nord universitet. ISSN 9788293165187. Fulltekst i vitenarkiv

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