Host defense effectors expressed by hemocytes shape the bacterial microbiota from the Scallop Hemolymph

The interaction between host immune response and the associated microbiota has recently become a fundamental aspect of vertebrate and invertebrate animal health. This interaction allows the specific association of microbial communities, which participate in a variety of processes in the host including protection against pathogens. Marine aquatic invertebrates such as scallops are also colonized by diverse microbial communities. Scallops remain healthy most of the time, and in general, only a few species are fatally affected on adult stage by viral and bacterial pathogens. Still, high mortalities at larval stages are widely reported and they are associated with pathogenic Vibrio. Thus, to give new insights into the interaction between scallop immune response and its associated microbiota, we assessed the involvement of two host antimicrobial effectors in shaping the abundances of bacterial communities present in the scallop Argopecten purpuratus hemolymph. To do this, we first characterized the microbiota composition in the hemolymph from non-stimulated scallops, finding both common and distinct bacterial communities dominated by the Proteobacteria, Spirochaetes and Bacteroidetes phyla. Next, we identified dynamic shifts of certain bacterial communities in the scallop hemolymph along immune response progression, where host antimicrobial effectors were expressed at basal level and early induced after a bacterial challenge. Finally, the transcript silencing of the antimicrobial peptide big defensin ApBD1 and the bactericidal/permeability-increasing protein ApLBP/BPI1 by RNA interference led to an imbalance of target bacterial groups from scallop hemolymph. Specifically, a significant increase in the class Gammaproteobacteria and the proliferation of Vibrio spp. was observed in scallops silenced for each antimicrobial. Overall, our results strongly suggest that scallop antimicrobial peptides and proteins are implicated in the maintenance of microbial homeostasis and are key molecules in orchestrating host-microbiota interactions. This new evidence depicts the delicate balance that exists between the immune response of A. purpuratus and the hemolymph microbiota.info:eu-repo/semantics/publishedVersio

Temperature acclimatisation of swimming performance in the European Queen Scallop

The phenotypic plasticity of muscle performance and locomotory physiology allows the maintenance of essential activity capacity in the face of environmental change, and has been demonstrated in a wide phylogenetic range of eurythermal vertebrates. This study used the scallop, Aequipecten opercularis, as a model eurythermal invertebrate. Animals caught in different seasons demonstrated marked differences in their swimming performance and the relationship between, temperature and performance. When stimulated to swim at natural ranges of temperature, Winter (cold acclimatised), animals accelerated faster than autumn collected animals swimming at the same temperature (x 2 at 11degreesC) and attained higher velocities during jetting. The effects of acclimatisation were confined to the jetting phase and may be a mechanism for the maintenance of acceleration during predator-prey interactions. This is the first demonstration of the thermal acclimatisation of muscle performance in a mollusc and one of very few studies in invertebrates

Are we neglecting earth while conquering space? Effects of aluminized solid rocket fuel combustion on the physiology of a tropical freshwater invertebrate

Space launchers often use aluminized-solid fuel ("propergol") as propellant and its combustion releases tons of Al2O3 and HCl that sink in terrestrial and aquatic environments, polluting and decreasing water pH. We studied the impact of these events on the biochemical/physiological performance of the freshwater shrimp Macrobrachium jelskii, with wild specimens collected from a non-impacted site in French Guiana. In the laboratory, shrimps were exposed for one week to: i) undisturbed conditions; ii) Al2O3 exposure (0.5 mg L-1) at normal pH (6.6); iii) decreased pH (4.5) (mimicking HCl release in the environment) with no Al2O3; or iv) Al2O3 0.5 mg L-1 and pH 4.5, representing the average conditions found in the water bodies around the Ariane 5 launch pad. Results showed that shrimps bioaccumulated aluminium (Al) regardless of water pH. The combined effect of Al2O3 and low pH caused the most impact: acetylcholinesterase and carboxylesterase activities decreased, indicating neurotoxicity and reduced detoxification capacity, respectively. Animal respiration was enhanced with Al2O3 and pH variations alone, but the synergic interaction of both stressors caused respiration to decrease, suggesting metabolic depression. Oxidative damage followed a similar pattern to respiration rates across conditions, suggesting free radical-mediation in Al toxicity. Antioxidant activities varied among enzymes, with glutathione reductase being the most impacted by Al2O3 exposure. This study shows the importance of addressing space ports' impact on the environment, setting the bases for selecting the most appropriate biomarkers for future monitoring programs using a widespread and sensitive crustacean in the context of an increasing space-oriented activity across the world.publishe

Reproduction Immunity Trade-Off in a Mollusk: Hemocyte Energy Metabolism Underlies Cellular and Molecular Immune Responses

Immune responses, as well as reproduction, are energy-hungry processes, particularly in broadcast spawners such as scallops. Thus, we aimed to explore the potential reproduction-immunity trade-off in Argopecten purpuratus, a species with great economic importance for Chile and Peru. Hemocytes, key immunological cells in mollusks, were the center of this study, where we addressed for the first time the relation between reproductive stage, hemocyte metabolic energetics and their capacity to support immune responses at cellular and molecular levels. Hemocyte metabolic capacity was assessed by their respiration rates, mitochondrial membrane potential and citrate synthase (CS) activity. Cellular immune parameters such as the number of circulating and tissue-infiltrating hemocytes and their reactive oxygen species (ROS) production capacity were considered. Molecular immune responses were examined through the transcriptional levels of two pattern recognition receptors (ApCLec and ApTLR) and two anti-microbial effectors (ferritin and big defensin). Their expressions were measured in hemocytes from immature, matured and spawned scallops under basal, and one of the following challenges: (i) in vitro, where hemocytes were challenged with the β glucan zymosan, to determine the immune potentiality under standardized conditions; or (ii) in vivo challenge, using hemocytes from scallops injected with the pathogenic bacteria Vibrio splendidus. Results indicate a post-spawning decrease in the structural components of the immune system (hemocyte number/quality) and their potential capacity of performing immune functions (with reduced ATP-producing machinery and exhaustion of energy reserves). Both in vitro and in vivo challenges demonstrate that hemocytes from immature scallops have, in most cases, the best metabolic potential (increased CS activity) and immune performances, with for example, over threefold higher ROS production and tissue-infiltration capacity than those from mature and spawned scallops after the bacterial challenge. Agreeing with cellular responses, hemocytes from immature individuals induced the highest levels of immune receptors and antimicrobial effectors after the bacterial challenge, while spawned scallops presented the lowest values. Overall, results suggest a trade-off between resource allocation in reproduction and the immune responses in A. purpuratus, with hemocyte energy metabolic capacity potentially underlying cellular and molecular immune responses. Further research would be necessary to explore regulatory mechanisms such as signaling pleiotropy which may potentially be underlying this trade-off

Geographic and seasonal patterns and limits on the adaptive response to temperature of European Mytilus spp. and Macoma balthica populations

Seasonal variations in seawater temperature require extensive metabolic acclimatization in cold-blooded organisms inhabiting the coastal waters of Europe. Given the energetic costs of acclimatization, differences in adaptive capacity to climatic conditions are to be expected among distinct populations of species that are distributed over a wide geographic range. We studied seasonal variations in the metabolic adjustments of two very common bivalve taxa at European scale. To this end we sampled 16 populations of Mytilus spp. and 10 Macoma balthica populations distributed from 39° to 69°N. The results from this large-scale comprehensive comparison demonstrated seasonal cycles in metabolic rates which were maximized during winter and springtime, and often reduced in the summer and autumn. Studying the sensitivity of metabolic rates to thermal variations, we found that a broad range of Q10 values occurred under relatively cold conditions. As habitat temperatures increased the range of Q10 narrowed, reaching a bottleneck in southern marginal populations during summer. For Mytilus spp., genetic-group-specific clines and limits on Q10 values were observed at temperatures corresponding to the maximum climatic conditions these geographic populations presently experience. Such specific limitations indicate differential thermal adaptation among these divergent groups. They may explain currently observed migrations in mussel distributions and invasions. Our results provide a practical framework for the thermal ecophysiology of bivalves, the assessment of environmental changes due to climate change and its impact on (and consequences for) aquaculture

Latitudinal thermal gradient effect on the cost of living of the intertidal porcelain crab Petrolisthes granulosus

Species with wide latitudinal distributions are exposed to significant abiotic gradients throughout their geographic range. Thermal gradients are especially important for ectothermic species inhabiting the intertidal zone because they affect their life history traits and fitness. In order to identify the role of latitudinal thermal gradients (specifically the exposition to different thermal maximums) in the cost of living of intertidal crustaceans, we compared specific fitness-related traits, such as body size and reproductive capacity (reproductive output, size at onset of sexual maturity and egg volume) in Petrolisthes granulosus individuals from 3 sites across an extensive latitudinal gradient (covering similar to 50% of its total distributional range): Iquique (20 degrees 16' 12 '' S), Coquimbo (30 degrees 04' 12 '' S) and Concepcion (36 degrees 40' 45 '' S). Furthermore, metabolic rate experiments were conducted to assess the energetic cost associated with high temperatures encountered in P. granulosus habitats. We observed that the southernmost population (Concepcion) had a larger body size and presented larger size classes that did not exist in northerly populations. The latitudinal trend shown by growth and reproductive capacity traits was negatively linked to the associated thermal gradient. However, no differences were found in the relationship between energetic cost (in terms of metabolic rate) and temperatures experienced by P. granulosus. Thus, the patterns of body size and reproductive capacity observed for P. granulosus could not be explained by differences in energetic costs generated by the different thermal regimes of the study sites. Further studies should consider other environmental (e.g. quantity and quality of available food) and/or genetic factors that may be influencing the latitudinal patterns observed for body size and reproductive output in P. granulosus

Effect of predation risk and ectoparasitic louse flies on physiological stress condition of the red-tailed tropicbird (Phaethon rubricauda) from Rapa Nui and Salas & Gómez islands

Background Introduced predators at seabird colonies and parasites may have lethal and/or sub-lethal consequences for bird populations. We assessed the potential sub-lethal negative effects of these stressors in a native seabird listed as vulnerable in its south-eastern pacific distribution. This study was conducted in two red-tailed tropicbird (Phaethon rubricauda) colonies, one located in Rapa Nui Island, which is threatened by the presence of introduced predators, and the other located in Salas & Gómez Island, which has no introduced predators, but birds are infested by ectoparasitic louse flies. Methods The effects on physiological stress traits of both, predation risk on different nest types (protected and exposed) on Rapa Nui, and different levels of louse flies’ parasitic loads on Salas & Gómez were studied. Three variables were analyzed: the heterophil/lymphocyte (H/L) ratio, the transcriptional levels of mRNA HSP70 in blood, and the body condition. These stress indicators and leukocyte counts were compared between colonies. Results No significant differences were found in any stress indicator between different nest types within Rapa Nui, showing that the effect of predator’s presence was the same for adults nesting in both, protected and exposed nests. No significant correlation was found between louse flies’ parasitic loads and any stress indicators in the birds of Salas & Gómez. Also, there was no difference in any stress indicator between islands. However, a significant opposite trend between islands was found in the eosinophil, lymphocyte, and monocyte counts when related to body condition. Conclusions We found a lack of significant differentiation in all the stress level indicators assessed within and between islands. The presence of louse flies in Salas & Gómez vs. the absence of this parasite at Rapa Nui may be the cause for the significant difference in the trend of eosinophil, lymphocyte and monocyte counts between the islands. However, further studies are necessary to elucidate the reason for this difference and to better investigate the lethal effects of introduced predators on the Rapa Nui colony to evaluate appropriate conservation measures for this native seabird