Cell-mediated immune response of postmetamorphic sea urchin juveniles against infectious stages of diatom Cylindrotheca closterium (Bacillariophyceae).

In this study, successive infectious stages by diatom Cylindrotheca closterium (Bacillariophyceae) are described for the first time during the early development of sea urchin at low temperature (8°C). Diatom cell-types enclosed or not by typical theca were capable of infection. As an immune response, red spherulocytes and amoebocytes migrated towards infested areas and restrained the infection spreading over shells in 2- and 3-month old urchins. Only amoebocyte cells appeared to be involved in the immune reaction of 1-month old specimens which turned out to be a less effective fence to stop infestation. The effectiveness of the inflammatory process caused by diatoms within sea urchin spines seemed to vary as a function of urchin age, cohort's type and individual cell pool.

Free-living stage of the unicellular algae Coccomyxa sp. parasite of the blue mussel (Mytilus edulis): Low-light adaptation, capacity for growth at a very wide salinity range and tolerance to low pH.

Coccomyxa parasitica and similar, unidentified Coccomyxa species infect the soft tissues of many bivalve species, giving them a conspicuous green coloration and leading to mantle and shell deformities. Very little information exists regarding the ecophysiology of parasitic Coccomyxa sp. and this limits our ability to understand how it can achieve its unusual life history. In the present study, the growth of Coccomyxa sp. Metis-sur-mer (KJ372210) in liquid culture was investigated. Coccomyxa sp. maximum growth rate was 0.75day-1 (equivalent to a doubling time of 22h), growth saturated at ∼100µmol quanta m-2s-1 and was still ∼20% of maximum at 13µmol quanta m-2s-1, the lowest photosynthetically available radiation (PAR) intensity tested. Coccomyxa sp. showed a very wide tolerance to salinity, with growth rate practically invariable over the salinity range 15-35. Even in natural spring water enriched with f/2 media, the growth rate was nearly half of maximum. Unlike the closely related acid-tolerant Coccomyxa sp. CPCC 508, Coccomyxa sp. Metis-sur-mer could not grow in acidic waters. Considering the ability of Coccomyxa sp. to achieve a high growth rate at low irradiance and its relative insensitivity to the prevailing salinity, it is somewhat surprising it has not yet infected bivalves at a larger scale worldwide.

First record of the green microalgae Coccomyxa sp. in blue mussel Mytilus edulis (L.) from the Lower St. Lawrence Estuary (Québec, Canada).

During autumn 2012 and spring 2013, blue mussels Mytilus edulis (L.) with strongly deformed (L-shaped) posterior shell margins and green spots in soft tissue (microalgae) were collected from intertidal zone along the south shore of the Lower St. Lawrence Estuary near Rimouski (Québec, Canada). Identification of algal cells infesting mussels as Coccomyxa sp. was confirmed by rRNA sequencing and HPLC pigment analysis. Flow cytometric analysis revealed the presence of algal cells in the hemolymph and extrapallial fluid in mussels with deformed and non-deformed shells; concentrations of algal cells were ranged from about 200mL(-1) in mussels with actually non-deformed shells to concentrations reaching up to 3.8×10(7)mL(-1) in mussels with heavily deformed ones. Chemical analyses of soft tissues led us to conclude that butyltin compounds and trace metals cannot be considered among factors responsible for the shell deformity observed. Using scanning electron microscopy, the biogenic nature of the erosion on the external shell surface and aragonitic lenses of prisms in the curvature zone of deformed shells (in sections) were recorded. The sequence of the green algae from M. edulis of the Lower St. Lawrence Estuary was closely related to Coccomyxa sp. infecting M. edulis from the Flensburg Fjord (North Sea) and Modiolus modiolus (L.) from the Vityaz Bay (Sea of Japan).

Genome size differences in Hyalella cryptic species.

The Hyalella azteca (Saussure) complex includes numerous amphipod cryptic species in freshwater habitats in America as revealed by DNA barcoding surveys. Two ecomorphs (small and large) have evolved numerous times in this complex. Few phenotypic criteria have been found to differentiate between the numerous species of this complex. The present study aims to explore genome size differences between some species of the H. azteca complex co-occurring in a Canadian boreal lake using flow cytometry. Nuclear DNA content was estimated for 50 individuals belonging to six COI haplotypes corresponding to four provisional species of the H. azteca complex. Species from the large ecomorph had C-values significantly larger than species from the small ecomorph, whereas slight differences were found among species of the small ecomorph. These differences in genome sizes might be linked to ecological and physiological differences among species of the H. azteca complex.

Age Dependent Dysfunction of Mitochondrial and ROS Metabolism Induced by Mitonuclear Mismatch.

Mitochondrial and nuclear genomes have to coevolve to ensure the proper functioning of the different mitochondrial complexes that are assembled from peptides encoded by both genomes. Mismatch between these genomes is believed to be strongly selected against due to the consequent impairments of mitochondrial functions and induction of oxidative stress. Here, we used a Drosophila model harboring an incompatibility between a mitochondrial tRNAtyr and its nuclear-encoded mitochondrial tyrosine synthetase to assess the cellular mechanisms affected by this incompatibility and to test the relative contribution of mitonuclear interactions and aging on the expression of impaired phenotypes. Our results show that the mitochondrial tRNA mutation caused a decrease in mitochondrial oxygen consumption in the incompatible nuclear background but no effect with the compatible nuclear background. Mitochondrial DNA copy number increased in the incompatible genotype but that increase failed to rescue mitochondrial functions. The flies harboring mismatch between nuclear and mitochondrial genomes had almost three times the relative mtDNA copy number and fifty percent higher rate of hydrogen peroxide production compared to other genome combinations at 25 days of age. We also found that aging exacerbated the mitochondrial dysfunctions. Our results reveal the tight interactions linking mitonuclear mismatch to mitochondrial dysfunction, mitochondrial DNA regulation, ROS production and aging.

UV effects on marine planktonic food webs: A synthesis of results from mesocosm studies.

UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical, chemical and light conditions mimicking those of the natural environment. In allowing the manipulation of UV intensities and light spectral composition, the experimental mesocosm approach has proven to be especially useful in assessing the impacts at the community level. This review of mesocosm studies shows that, although a UV increase even well above natural intensities often has subtle effects on bulk biomass (carbon and chlorophyll), it can significantly impact the food-web structure because of different sensitivity to UV among planktonic organisms. Given the complexity of UV impacts, as evidenced by results of mesocosm studies, interactions between UV and changing environmental conditions (e.g. eutrophication and climate change) are likely to have significant effects on the function of marine ecosystems.

INFLUENCE OF UV-B RADIATION ON NITROGEN UTILIZATION BY A NATURAL ASSEMBLAGE OF PHYTOPLANKTON.

A 7-day mesocosm experiment was conducted in July 1996 to investigate the effects of ambient UV-B radiation (UVBR) exclusion and two UVBR enhancements above ambient levels on NO3- , NH4+ and urea utilization in a natural plankton community (<240 µm) from the Lower St. Lawrence Estuary. The phytoplankton community was dominated by diatoms during the first 3 days and, afterward, by flagellates and dinoflagellates. The results of 4-h incubations just below the water surface show that, compared with ambient UVBR conditions, UVBR exclusion generally increased NO3- , NH4+ , and urea uptakes. During the last 4 days of the experiment, the percent increase in the specific uptake rate of urea under excluded UVBR conditions varied between 17% and 130% and was a linear function of the ambient UVBR dose removed. During the first 3 days, the phytoplankton community dominated by diatoms was able to withstand UVBR enhancements without any perceptible effect on nitrogen uptake. However, during the post-diatom bloom period, UVBR enhancements resulted in decreases in NO3- , NH4+ , and urea uptake compared with ambient UVBR conditions. The reduction of urea uptake under UVBR enhancements during the last 3 days varied between 23% and 64% and was linearly related to the enhanced UVBR dose. However, the different UVBR treatments did not affect the internal organic nitrogen composition (internal urea, free amino acids, and proteins) of the phytoplankton community experiencing vertical mixing in the mesocosms. The discrepancy between short-term uptake measurements at the surface and long-term effects in the mesocosms emphasizes the importance of vertical mixing on UVBR effects in natural ecosystems. This suggests that an increase in ambient UVBR would have a minimal effect on nitrogen utilization by natural phytoplankton assemblages if these are vertically mixed.

Alteration of shell nacre micromorphology in blue mussel Mytilus edulis after exposure to free-ionic silver and silver nanoparticles.

This study describes the morphology of inner shell surface (ISS) of the blue mussel Mytilus edulis Linnaeus after short-term exposures to radiolabeled silver in free-ionic ((110m)Ag(+)) and engineered nanoparticulate ((110m)AgNPs, <40 nm) phases. Radiolabeled silver in starting solutions was used in a similar low concentration (∼15 Bq mL(-1)) for both treatments. After exposure experiments radiolabeled silver was leached from the ISS using HCl. It concentration for shells from both treatments was ∼0.5 Bq mL(-1). Whole ISS of young individuals and prismatic layer of adults showed no evidence of any major alteration process after silver uptake. However, the nacre portion of adult mussels exposed to both treatments revealed distinct doughnut shape structures (DSS) formed by calcium carbonate micrograins that covered the surface of aragonite tablets. Scanning electron microscope (SEM) imaging revealed the existence of only minor differences in DSS morphology between mussels exposed to Ag(+) and AgNPs. From literature survey, DSS were also found in bivalves exposed to Cd(2+). The DSS occurring in a specimen of a field-collected bivalve is also shown. Formation of distinctive DSS can be explained by a disturbance of the shell calcification mechanism. Although the occurrence of DSS is not exclusively associated with metal bioavailability to the mussels, the morphology of DSS seems to be linked to the speciation of the metal used in the uptake experiments.

Large genomes among caridean shrimp.

Recent genome size estimates for Arctic amphipods have revealed the largest genomes known in the Crustacea. Here we provide additional data for 7 species of caridean shrimp collected from the Canadian Arctic and the Gulf of St. Lawrence. Genome sizes were estimated by flow cytometry and haploid C-values ranged from 8.53 +/- 0.30 pg in Pandalus montagui (Pandalidae) to 40.89 +/- 1.23 pg in Sclerocrangon ferox (Crangonidae). The value for S. ferox represents the largest decapod genome yet recorded and indicates a 38-fold variation in genome size within this order. These data suggest that large genomes may be relatively common in Arctic crustaceans, and underline the need for further comparative studies.

Amphipod genome sizes: first estimates for Arctic species reveal genomic giants.

The genome sizes of 8 species of amphipods collected from the Canadian Arctic were estimated by flow cytometry. Haploid genome sizes ranged from 2.94 +/- 0.04 pg DNA in Acanthostepheia malmgreni (Oedicerotidae) to 64.62 +/- 2.85 pg in Ampelisca macrocephala (Ampeliscidae). The value for Ampelisca macrocephala represents the largest crustacean genome size recorded to date (and also the largest within the Arthropoda) and indicates a 400-fold variation in genome size among crustaceans. The presence of such large genomes within a relatively small sample of Arctic amphipods is striking and highlights the need to further explore the relationships between genome size, development rates, and body size in both Arctic and temperate amphipods.