Abstract
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.
Highlights
Diatoms are key phytoplankton organisms in the world’s oceans and are considered essential in the transfer of energy through marine food chains
In recent studies [20,21], we showed that expression levels of selected genes of interest (GOI) were significantly reduced when females of the copepod Calanus helgolandicus (C. helgolandicus) were fed for two days (d) on the diatom Skeletonema marinoi (S. marinoi) which is known to produce high quantities of polyunsaturated aldehydes (PUAs) and several other oxylipins including fatty acid hydroperoxides, hydroxyl- and keto-fatty acids, and epoxyalcohols [3]
Cytochrome Oxidase subunit I region (COI) sequence in animals collected from the Adriatic Sea corresponded to the haplotype H8 (GenBank accession number AY942593) associated with specimens living in the NE Atlantic and/or Adriatic Sea
Summary
Diatoms are key phytoplankton organisms in the world’s oceans and are considered essential in the transfer of energy through marine food chains. Teratogenesis and reduction in egg production and hatching success have been observed for wild copepods feeding on the natural winter/ spring diatom-dominated bloom in the Mediterranean Sea (i.e. Adriatic Sea [1,2]), in North and South Pacific (i.e. Dabob Bay, Washington, USA [17] and the coastal zone off Dichato, Chile [18]) and in the Baltic Sea [19] Such antiproliferative compounds may impact on herbivory by sabotaging future generations of grazers, thereby allowing diatom blooms to persist when grazing pressure would otherwise have caused them to crash
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