Impact of the diatom-derived polyunsaturated aldehyde 2-trans,4-trans decadienal on the feeding, survivorship and reproductive success of the calanoid copepod Temora stylifera

Abstract Many diatoms, a major class of unicellular algae contributing to over 45% of oceanic primary production, are known to induce deleterious effects on reproductive processes in crustacean copepods. This is mainly due to the production of teratogenic oxylipins, including polyunsaturated aldehydes (PUAs). Here we tested the direct effect of the PUA 2E,4E-decadienal (DD) on feeding activity, survivorship and reproductive success of the calanoid copepod Temora stylifera. DD-inoculated cultures induced high mortality at concentrations above 3 μg mL−1 compared to controls in both males and females, with males having a higher mortality. Low DD concentrations triggered an increase in female filtration and ingestion rates. Egg production rates and hatching times were also higher in the presence of DD, whereas egg hatching success decreased with increasing DD concentration. Our study shows, for the first time, that the presence of diatom PUAs may increase feeding rates in copepods

Using chemical language to shape future marine health

“Infochemicals” (information‐conveying chemicals) dominate much of the underwater communication in biological systems. They influence the movement and behavior of organisms, the ecological interactions between and across populations, and the trophic structure of marine food webs. However, relative to their terrestrial equivalents, the wider ecological and economic importance of marine infochemicals remains understudied and a concerted, cross‐disciplinary effort is needed to reveal the full potential of marine chemical ecology. We highlight current challenges with specific examples and suggest how research on the chemical ecology of marine organisms could provide opportunities for implementing new management solutions for future “blue growth” (the sustainable use of ocean resources) and maintaining healthy marine ecosystems

Molecular Evidence of the Toxic Effects of Diatom Diets on Gene Expression Patterns in Copepods

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy through marine food chains. However, these unicellular plants at times produce secondary metabolites such as polyunsaturated aldehydes and other products deriving from the oxidation of fatty acids that are collectively termed oxylipins. These cytotoxic compounds are responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment in marine organisms such as crustacean copepods.Here we show that two days of feeding on a strong oxylipin-producing diatom (Skeletonema marinoi) is sufficient to inhibit a series of genes involved in aldehyde detoxification, apoptosis, cytoskeleton structure and stress response in the copepod Calanus helgolandicus. Of the 18 transcripts analyzed by RT-qPCR at least 50% were strongly down-regulated (aldehyde dehydrogenase 9, 8 and 6, cellular apoptosis susceptibility and inhibitor of apoptosis IAP proteins, heat shock protein 40, alpha- and beta-tubulins) compared to animals fed on a weak oxylipin-producing diet (Chaetoceros socialis) which showed no changes in gene expression profiles.Our results provide molecular evidence of the toxic effects of strong oxylipin-producing diatoms on grazers, showing that primary defense systems that should be activated to protect copepods against toxic algae can be inhibited. On the other hand other classical detoxification genes (glutathione S-transferase, superoxide dismutase, catalase, cytochrome P450) were not affected possibly due to short exposure times. Given the importance of diatom blooms in nutrient-rich aquatic environments these results offer a plausible explanation for the inefficient use of a potentially valuable food resource, the spring diatom bloom, by some copepod species

Ingestion and incorporation of freshwater diatoms by Daphnia pulicaria: do morphology and oxylipin production matter?

In order to explain differences in the growth and reproduction of Daphnia pulicaria fed various freshwater diatoms, we measured ingestion rates and carbon incorporation for six cultured diatom species: the single-celled Stephanodiscus hantzschii, Stephanodiscus minutulus and Cyclotella meneghiniana, and the colony-forming Asterionella formosa, Fragilaria capucina and Fragilaria sp. Two of the colony-forming species, when damaged, produced polyunsaturated aldehydes (oxylipins) that have been found to impair the reproduction of marine copepods. We tested two hypotheses: (i) feeding and incorporation rates are affected by diatom morphology; and (ii) polyunsaturated aldehydes act as feeding deterrents. Daphnia body length versus ingestion rate regressions differed for single-celled and colony-forming diatoms. Ingestion rates for single-celled diatoms showed clear size dependencies and high correlation coefficients, while the dependency was weak for colony-forming diatoms and individual variability was high. This difference was not observed for carbon incorporation rates, which showed low variability for all diatoms. Asterionella formosa yielded the lowest incorporation rates due to low incorporation efficiency, while all other diatoms were incorporated at similar rates. Thus, morphological differences of the diatoms had no effect on carbon uptake by Daphnia. The presence or absence of polyunsaturated aldehydes did not cause different ingestion rates; hence the aldehydes are not feeding deterrents

The Distribution of Ferritins in Marine Copepods

Iron is an essential element for the functioning of cellular processes. Ferritins, the major intracellular iron storage proteins, convert the free Fe2+ into the nontoxic Fe3+ which can be stored and transported where needed. To date, little is known about the iron metabolism in copepods; however, in these crustaceans, ferritins have been used as biomarkers of stress and diapause. A limiting factor of these studies has been the use of a single ferritin transcript as a biomarker. In this paper, we in silico mined the publicly available copepod transcriptomes to characterize the multiplicity of the ferritin transcripts in different orders and families. We also examined the expression of ferritin in three ecologically important copepods—Calanus finmarchicus, C. helgolandicus and Temora stylifera—during development and under stress conditions. A full-length transcript encoding ferritin heavy chain has been identified in all 27 mined transcriptomes, with 50% of the species possessing multiple transcripts. Ferritin expression increased in C. finmarchicus during the early–late development transition, and in T. stylifera females exposed to oxylipins at sea. Overall, our results suggest that copepod ferritins can be involved in iron storage, larval development and stress response, thus representing potential biomarker genes for ocean health status monitoring

Copepod population-specific response to a toxic diatom diet.

Diatoms are key phytoplankton organisms and one of the main primary producers in aquatic ecosystems. However, many diatom species produce a series of secondary metabolites, collectively termed oxylipins, that disrupt development in the offspring of grazers, such as copepods, that feed on these unicellular algae. We hypothesized that different populations of copepods may deal differently with the same oxylipin-producing diatom diet. Here we provide comparative studies of expression level analyses of selected genes of interest for three Calanus helgolandicus populations (North Sea, Atlantic Ocean and Mediterranean Sea) exposed to the same strain of the oxylipin-producing diatom Skeletonema marinoi using as control algae the flagellate Rhodomonas baltica. Expression levels of detoxification enzymes and stress proteins (e.g. glutathione S-transferase, glutathione synthase, superoxide dismutase, catalase, aldehyde dehydrogenases and heat shock proteins) and proteins involved in apoptosis regulation and cell cycle progression were analyzed in copepods after both 24 and 48 hours of feeding on the diatom or on a control diet. Strong differences occurred among copepod populations, with the Mediterranean population of C. helgolandicus being more susceptible to the toxic diet compared to the others. This study opens new perspectives for understanding copepod population-specific responses to diatom toxins and may help in underpinning the cellular mechanisms underlying copepod toxicity during diatom blooms

Is postembryonic development in the copepod Temora stylifera negatively affected by diatom diets?

Diatoms are major components of the marine microalgae and are generally considered to be the principal food source for small pelagic crustaceans such as copepods. Recently, some species of this algal class have been shown to produce abortifacient compounds (aldehydes) that block copepod embryogenesis, thereby acting as a form of birth control for predatory copepods. To test if diatoms also have deleterious effects on postembryonic development, several diatom species were used to rear larval stages of the calanoid copepod Temora stylifera to adulthood. Our results show that T stylifera was only able to complete development from hatching to adulthood when reared with the flagellates Isochrysis galbana and the dinoflagellates Prorocentrum minimum and Oxyrrhis marina. The daily development and mortality rates observed were in the range of those reported from previous studies on T stylifera (0.68-0.82 stage/day and 9.9-12.4%/day, respectively). In contrast, larvae reared on the diatoms Thalassiosira rotula, Skeletonema costatum and Phaeodactylum tricornutum were unable to complete development to adulthood and died without passing the naupliar phase or during the early copepodite stages. Daily mortality rates were higher than for nondiatom species (20.3-35.5%/day). Inhibitory effects on growth were not correlated to cell size of the algae. Final survivorship of larvae fed P. minimum and L galbana significantly improved (70-80%) when larvae were generated from females preconditioned with P. minimum for 24 h. The same treatment had no beneficial effect on larvae fed with T rotula or S. costatum, which died again before the adult stage. Although larvae completed development in one replicate with T rotula and final survivorship improved to 34% (compared to 7% in nauplii from nonconditioned females), this value was, in any case, lower than with nondiatom diets. No morphological aberrations were found in larvae fed on diatoms, even though they were unable to complete their life cycle and died for unknown reasons. By contrast, nauplii produced by females fed the diatom T rotula for 7 days showed strong congenital defects such as asymmetrical bodies and reduced number of feeding appendages. Our results suggest that diatoms, which have already been shown to have deleterious effects on copepod embryonic development, may also have insidious effects on larval growth of this copepod species. (C) 2002 Elsevier Science B.V. All rights reserved

Chemosensory-Related Genes in Marine Copepods

Living organisms deeply rely on the acquisition of chemical signals in any aspect of their life, from searching for food, mating and defending themselves from stressors. Copepods, the most abundant and ubiquitous metazoans on Earth, possess diversified and highly specified chemoreceptive structures along their body. The detection of chemical stimuli activates specific pathways, although this process has so far been analyzed only on a relatively limited number of species. Here, in silico mining of 18 publicly available transcriptomes is performed to delve into the copepod chemosensory genes, improving current knowledge on the diversity of this multigene family and on possible physiological mechanisms involved in the detection and analysis of chemical cues. Our study identifies the presence of ionotropic receptors, chemosensory proteins and gustatory receptors in copepods belonging to the Calanoida, Cyclopoida and Harpacticoida orders. We also confirm the absence in these copepods of odorant receptors and odorant-binding proteins agreeing with their insect specificity. Copepods have evolved several mechanisms to survive in the harsh marine environment such as producing proteins to respond to external stimulii. Overall, the results of our study open new possibilities for the use of the chemosensory genes as biomarkers in chemical ecology studies on copepods and possibly also in other marine holozooplankters

Relative gene expression levels of aldehyde dehydrogenases (ALDH) in the copepod <i>Calanus helgolandicu</i>s.

<p>Changes in ALDH2, ALDH3, ALDH6, ALDH7, ALDH8 and ALDH9 gene expression levels in Swedish (a), English Channel (b) and Adriatic (c) <i>C. helgolandicus</i> females fed <i>Skeletonema marinoi</i> (<i>S. marinoi</i>) for 24 or 48 h compared to expression levels in females fed on the control <i>Rhodomonas baltica</i> (represented in the figure by x-axis). The ribosomal protein S20 was used as reference gene to normalize the data.</p

Unraveling diagnostic uncertainty in transition phase from relapsing-remitting to secondary progressive multiple sclerosis

Background: Clinicians struggle to timely diagnose secondary-progressive multiple sclerosis (SP-MS), with a ‘transition phase’ period of diagnostic uncertainty. We aimed at defining clinical markers predicting evolution to SP-MS. Methods:: We reviewed 210 newly diagnosed MS patients experiencing at least one confirmed disability worsening (CDW). CDWs were classified as disability worsening either due to incomplete recovery following relapse (r-CDW), or independent of relapse activity (nr-CDW). Logistic regression and Cox regression models were used to evaluate variables at CDW associated with SP-MS diagnosis. Results: On CDW, higher EDSS (OR: 2.73, p=0.002) and nr-CDW (OR: 2.63, p=0.03) were associated with conversion to SP-MS over the follow-up. In addition, the risk of SP-MS was higher in patients with EDSS>3.0 at CDW (HR: 2.26, p<0.001), and with time to second CDW <24 months (HR: 0.98, p<0.001), compared with patients that experienced a CDW but did not receive SP-MS diagnosis (AUC: 0.95, Sensitivity: 0.83, Specificity: 0.96). Conclusion: At their first CDW, patients with higher EDSS, experiencing CDW without relapse and developing a further CDW within 2 years are at higher risk of SP-MS conversion. This provides proxies for conversion to SP-MS since first episode of CDW