Heat shocks during egg incubation led to developmental, morphological, and behavioral differences in Arctic charr (Salvelinus alpinus).

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure, and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite the fact that the phenotype being essential for organism ecology and evolution. In this study, we tested the effects of heat shocks during the embryonic period on the phenotype of Arctic charr (Salvelinus alpinus). We repeatedly quantified multiple phenotypic traits, including morphology, development, and behavior, over a period of 4 months, from hatching to juvenile stage in individuals that had experienced heat shocks (+ 5°C on 24 h, seven times) during their embryonic stage and those that had not. We found that heat shocks led to smaller body size at hatching and a lower sociability. Interestingly, these effects weakened throughout the development of individuals and even reversed in the case of body size. We also found an accelerated growth rate and a higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long-lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and the unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity.

Molecular and physiological characterization of a crustacean cardioactive signaling system in a lophotrochozoan - the Pacific oyster (Crassostrea gigas): a role in reproduction and salinity acclimation.

The crustacean cardioactive peptide (CCAP) is an important neuropeptide involved in the regulation of a variety of physiological processes in arthropods. Although this family of peptides has an ancestral origin, its function remains poorly understood among protostome species - apart from arthropods. We functionally characterized three G protein-coupled receptors (GPCRs) in the oyster Crassostrea gigas, phylogenetically related to ecdysozoan CCAP receptors (CCAPRs) and to chordate neuropeptide S receptors (NPSRs). Cragi-CCAPR1 and Cragi-CCAPR2 were specifically activated by the Cragi-CCAP1 and Cragi-CCAP2 peptides, respectively, both derived from the same CCAP precursor. In contrast, Cragi-CCAPR3 was only partially activated by CCAP1 and CCAP2 at high concentrations. The Cragi-CCAPR1 and Cragi-CCAPR2 genes were expressed in various adult tissues. They are both most expressed in the gills, while Cragi-CCAPR3 is mainly expressed in the visceral ganglia (VG). Cragi-CCAP precursor transcripts are higher in the VG, the labial palps and the gills. Receptor and ligand-encoding transcripts are more abundantly expressed in the gonads in the first stages of gametogenesis, while the Cragi-CCAP precursor is upregulated in the VG in the last stages of gametogenesis. This suggests a role of the CCAP signaling system in the regulation of reproductive processes. A role in water and ionic regulation is also supported considering the differential expression of the CCAP signaling components in oysters exposed to brackish water.

Transcriptome Profiling of the Pacific Oyster Crassostrea gigas Visceral Ganglia over a Reproduction Cycle Identifies Novel Regulatory Peptides.

The neuropeptides involved in the regulation of reproduction in the Pacific oyster (Crassostrea gigas) are quite diverse. To investigate this diversity, a transcriptomic survey of the visceral ganglia (VG) was carried out over an annual reproductive cycle. RNA-seq data from 26 samples corresponding to VG at different stages of reproduction were de novo assembled to generate a specific reference transcriptome of the oyster nervous system and used to identify differentially expressed transcripts. Transcriptome mining led to the identification of novel neuropeptide precursors (NPPs) related to the bilaterian Eclosion Hormone (EH), crustacean female sex hormone/Interleukin 17, Nesfatin, neuroparsin/IGFBP, prokineticins, and urotensin I; to the protostome GNQQN, pleurin, prohormones 3 and 4, prothoracotropic hormones (PTTH), and QSamide/PXXXamide; to the lophotrochozoan CCWamide, CLCCY, HFAamide, and LXRX; and to the mollusk-specific NPPs CCCGS, clionin, FYFY, GNamide, GRWRN, GSWN, GWE, IWMPxxGYxx, LXRYamide, RTLFamide, SLRFamide, and WGAGamide. Among the complete repertoire of NPPs, no sex-biased expression was observed. However, 25 NPPs displayed reproduction stage-specific expression, supporting their involvement in the control of gametogenesis or associated metabolisms.

Characterization of an evolutionarily conserved calcitonin signalling system in a lophotrochozoan, the Pacific oyster (Crassostrea gigas).

In Protostoma, the diuretic hormone 31 (DH31) signalling system was long considered as the orthologue of the chordate calcitonin (CT) signalling system. Using the Pacific oyster (Crassostrea gigas) transcriptomic database GigaTON, we characterized seven G-protein-coupled receptors (GPCRs) named Cragi-CTR1-7 and phylogenetically related to chordate CT receptors (CTRs) and to protostome DH31 receptors. Two CT precursors (Cragi-CTP1 and Cragi-CTP2) containing two CT-type peptides and encoded by two distinct genes with a similar organization were also characterized. These oyster neuropeptides (Cragi-CT1/2) exhibit the two N-terminal paired cysteine residues and, except CTP2-derived peptide (Cragi-CTP2dp), show the C-terminal proline-amide motif typical of deuterostome CT-type peptides. All mature Cragi-CTs except Cragi-CTP2dp were detected in visceral ganglion extracts using mass spectrometry. Cell-based assays revealed that the previously characterized oyster receptors Cg-CT-R and Cragi-CTR2 were specifically activated by Cragi-CT1b and Cragi-CT2, respectively. This activation does not require the co-expression of receptor activity-modifying proteins (RAMPs). Thus, oyster CT signalling appears functionally more closely related to vertebrate CT/CTR signalling than to calcitonin gene-related peptide/calcitonin receptor-like receptor (CGRP/CLR) signalling. Gene expression profiles in different adult tissues and in oysters acclimated to brackish water suggest the potential implication of both Cg-CT-R/Cragi-CT1b and Cragi-CTR2/Cragi-CT2 in water and ionic regulations, although with apparently opposite effects. The present study represents the first comprehensive characterization of a functional CT-type signalling system in a protostome and provides evidence for its evolutionarily ancient origin and its early role in osmotic homeostasis.

Evolution of pace-of-life syndrome under conditions of maternal PCB contamination and global warming in early life stages of cold stenothermic fish (Arctic char).

The end of the 20th century was characterised by rapid modifications of ecosystem functioning under different pressures (such as eutrophication and toxic pollution). Increasing temperatures in the context of global warming could have indirect consequences, such as increased bioavailability of hydrophobic organic pollutants amongst aquatic species. According to the "pace-of-life syndrome" (POLS) theory, these stressors could lead to covariations in many life traits. Lake Bourget is the largest natural lake in France and has been highly polluted from the fifties to the eighties both with a high load of nutrients (wastewater discharge) and polychlorinated biphenyls (PCBs) (industrial effluent discharge). Despite improvements in water quality since the 21st century, PCB levels are still higher than the United States Environmental Protection Agency cut-off for wildlife protection. The population of Arctic char, a cold stenothermic salmonid, has remained low in Lake Bourget for the last ten years despite restocking efforts and complete re-oligotrophication. We hypothesised that PCB pollution can affect the Arctic char population and that the increase in water temperature could magnify the effects of PCB. Thus, this study aimed to investigate the effects of maternal PCB contamination on offspring using a multiparametric and multiscale approach. Female Arctic char were contaminated with PCB before spawning, and each fertilised spawn was incubated at two temperatures (4 and 8.5 °C). The results showed that co-exposure to increased temperature and maternal PCB contamination influenced biodemographic, physiological, and behavioural parameters. The effects were highly dependant on the developmental stage. Based on the POLS theory, a continuum of life traits that may reflect potential physiological and behavioural modifications in response to these concurrent stressors is highlighted.

A Novel Dop2/Invertebrate-Type Dopamine Signaling System Potentially Mediates Stress, Female Reproduction, and Early Development in the Pacific Oyster (Crassostrea gigas).

The dopaminergic signaling pathway is involved in many physiological functions in vertebrates, but poorly documented in protostome species except arthropods. We functionally characterized a novel dopamine receptor in the Pacific oyster (Crassostrea gigas), activated by dopamine and tyramine with different efficacy and potency orders. This receptor - Cragi-DOP2R - belongs to the D1-like family of receptors and corresponds to the first representative of the Dop2/invertebrate-type dopamine receptor (Dop2/INDR) group ever identified in Lophotrochozoa. Cragi-DOP2R transcripts were expressed in various adult tissues, with higher expression levels in the visceral ganglia and the gills. Following an experiment under acute osmotic conditions, Cragi-DOP2R transcripts significantly increased in the visceral ganglia and decreased in the gills, suggesting a role of dopamine signaling in the mediation of osmotic stress. Furthermore, a role of the Cragi-DOP2R signaling pathway in female gametogenesis and in early oyster development was strongly suggested by the significantly higher levels of receptor transcripts in mature female gonads and in the early embryonic stages.

Strong Effects of Temperature on the Early Life Stages of a Cold Stenothermal Fish Species, Brown Trout (Salmo trutta L.).

Temperature is the main abiotic factor that influences the life cycle of poikilotherms. The present study investigated the thermal tolerance and phenotypic plasticity of several parameters (development time, morphometric measures, bioenergetics) for both embryos and fry of a cold stenothermal fish species, brown trout (Salmo trutta L.) in order to allow for a holistic evaluation of the potential effects of temperature. Five temperatures (4°C, 6°C, 8°C, 10°C, and 12°C) were tested, and the effects of temperature were analyzed at three stages: hatching, emergence, and first food intake. A mean of 5,440 (S.E. ± 573) eggs, coming from seven females and seven males (seven families) captured close to Linkebeek (Belgium), were used for each temperature. Maximum survival of well-formed fry at first food intake and better use of energy budget were found at 6°C and 8°C, temperatures at which the possible contribution to the next generation should therefore be greatest. At 12°C, the experimental population fell dramatically (0.9% survival rate for well-formed fry at first food intake), and fry had almost no yolk sac at first food intake. The present results on survival at 12°C are in accordance with predictions of a sharp decrease in brown trout numbers in France over the coming decades according to climate change projections (1°C to 5°C temperature rise by 2100 for France). At 10°C, there was also a lower survival rate (55.4% at first food intake). At 4°C, the survival rate was high (76.4% at first food intake), but the deformity rate was much higher (22% at first food intake) than at 6°C, 8°C, and 10°C. The energetic budget showed that at the two extreme temperatures (4°C and 12°C) there was less energy left in the yolk sac at first food intake, suggesting a limited ability to survive starvation.