Lasing in a ZnO waveguide: clear evidence of polaritonic gain obtained by monitoring the continuous exciton screening

The stimulated emission of exciton-polaritons was proposed as a means of lowering the lasing threshold because it does not require the dissociation of excitons to obtain an electron-hole plasma, as in a classical semiconductor laser based on population inversion. In this work we propose a method to prove unambiguously the polaritonic nature of lasing by combining experimental measurements with a model accounting for the permittivity change as a function of the carrier density. To do so we use angle resolved photoluminescence to observe the lasing at cryogenic temperature from a polariton mode in a zinc oxide waveguide structure, and to monitor the continuous shift of the polaritonic dispersion towards a photonic dispersion as the optical intensity of the pump is increased (up to 20 times the one at threshold). This shift is reproduced thanks to a model taking into account the reduction of the oscillator strength and the renormalization of the bandgap due to the screening of the electrostatic interaction between electrons and holes. Furthermore, the measurement of the carriers lifetime at optical intensities in the order of those at which the polariton lasing occurs enables us to estimate the carrier density, confirming it is lower than the corresponding Mott density for zinc oxide reported in the literature

A trade-off between mucocytes and bacteriocytes in Loripes orbiculatus gills (Bivalvia, Lucinidae): a mixotrophic adaptation to seasonality and reproductive status in a symbiotic species?

International audienceIn this study, we investigated the composition of the gill tissue relative to the reproductive status of the lucinid clam Loripes orbiculatus (sensus Poli, 1791) according to seasonal as well as biological parameters to provide insights into the physiological variability of this symbiotic bivalve. Temporal variation in population density was also studied. The species was investigated in Zostera noltii seagrass beds in the Thau lagoon (43°26'52.27'' N, 3°39'6.25'' E) in the south of France in a monthly sampling study from May 2013 to July 2015. A total of 257 individual adults of different sizes were analysed according to water temperature and salinity variations. The findings revealed a very stable Loripes density over time, with one single reproductive period during late spring/early summer. We also found that bacteriocytes and mucocytes in the gills were negatively correlated and highly variable in their respective proportions. Bacteriocytes remained dominant during cold periods, whereas mucocytes appeared mainly in the gills of large individuals when the water temperature increased in the spring. As mucocytes were also related with gonadal maturation, we hypothesize that these may allow the host to increase the proportion of heterotrophy in its nutrition during spring primary production to face the metabolic demands required for reproduction. It is possible that mucocytes may also be involved in host immunity

Diluted Seawater and Ammonia-N Tolerance of Two Mangrove Crab Species. New Insights to Understand the Vulnerability of Pristine Islands Ecosystems Organisms

Mangrove ecosystems are the primary receptors of anthropogenic pollution in tropical areas. Assessing the vulnerability of these ecosystems can be expressed, among other indicators, by studying the health of ‘ecosystem engineers’. In this study, mangrove forests facing opposing anthropogenic pressures were studied (i) in the uninhabited island of Europa (Mozambique Channel), considered as a pristine ecosystem, and, (ii) on the island of Mayotte, facing regular domestic wastewater discharges. Using an ecophysiological approach, the effects of diluted seawater (DSW) and increased ammonia-N were studied for two fiddler crab species: Gelasimus tetragonon (GT) on the island of Europa and Paraleptuca chlorophthalmus (PC) on the island of Mayotte. Osmoregulation curves and osmoregulatory capacity were determined along with O2 consumption rates after a 96 h exposure period. Histological analyses were also carried out on two important metabolic organs: the hepatopancreas and the posterior gills. Results indicate that both crab species are good hyper-hypo-osmoregulators but only PC can maintain its osmoregulatory capacity when exposed to ammonia-N. Oxygen consumption is increased in GT after 96 h of exposure to ammonia-N but this does not occur in PC. Finally, a thickening of the gill osmoregulatory epithelium was observed after 96 h in PC when exposed to ammonium but not in GT. Therefore, the two species do not have the same tolerance to DSW and increased ammonia-N. PC shows physiological acclimation capacities in order to better manage nitrogenous enrichments. GT did not show the same physiological plasticity when exposed to ammonia-N and could be more at risk by this kind of stress. These results along with those from other studies regarding the effects of domestic effluents on mangrove crabs are discussed. Therefore, the greater vulnerability of organisms occupying pristine ecosystems could induce major changes in mangrove functioning if crabs, that are engineer species of the ecosystem, are about to reduce their bioturbation activity or, even, disappear from the mangrove forests

Mechanisms of acclimation to hypersalinity in two European sea bass lineages: a focus on the kidney function

European sea bass (Dicentrarchus labrax), a major aquaculture species, is distributed along the coasts of the North-Eastern Atlantic Ocean, Mediterranean and Black Sea. D. labrax enter lagoons and estuaries where salinity fluctuates and sometimes reaches levels over 60‰, notably in Mediterranean lagoons. Keeping in mind that European sea bass are genetically subdivided in an Atlantic and a Mediterranean lineage, we compared fish from Atlantic (A) and West Mediterranean (M) populations regarding their capacity to tolerate hypersalinity with a focus on the kidney, a key organ involved in water reabsorption at high salinity. Fish were analyzed following a two-week transfer from seawater (SW, 36‰) to either seawater (SW, 36‰) or hypersaline water (HW, 55‰). Plasma osmolality was significantly increased in the MHW group compared to the other groups. Plasma sodium levels were significantly increased in hypersaline water compared to seawater in both lineages whereas plasma chloride levels showed an opposite trend. In order to estimate water filtration at the kidney level, the size of renal glomeruli was investigated and showed a decreased glomerulus perimeter and area in hypersaline water compared to seawater. NKA was highly expressed in all kidney tubules notably collecting tubules and ducts. There was an effect of salinity on renal nka α1a mRNA expression with slightly lower transcript levels at 55‰ compared to 36‰. Relative protein amounts and activity of NKA however were significantly higher in fish exposed to hypersalinity regardless of their origin. AQP1a immunolabeling differed between proximal tubules subtypes and only faint AQP1a was detected in subapical parts of cells lining collecting ducts. The transcript levels of renal aqp 1a were lower in the HW group than the SW group whereas the expression of other aqp paralogs (aqp 1b, aqp 8b) did not change according to the analyzed conditions. This study showed an efficient acclimation of sea bass to high salinity by increasing active ion transport at the kidney and by decreasing the size of filtering glomeruli to minimize water loss through urine. Despite Mediterranean D. labrax are supposed to more often encounter high salinities in their habitat, their high blood osmolality in hypersaline water indicates that their overall response to hypersalinity seems not improved compared to the Atlantic lineage. However, at the kidney level, the traits analyzed differ slightly between genetic lineages, potentially as a response to high blood osmolalities in MHW

The gametogenic cycle of the non-native false limpet Siphonaria pectinata (Linnaeus, 1758) in the easternmost limit of its distribution range: implications for its future in the Eastern Mediterranean Basin

Place: Hellinikon Publisher: Natl Centre Marine Research WOS:000589690900010International audienceThe gametogenic cycle of the false-limpet Siphonaria pectinata from the Bizerte channel (Northern Tunisia) was studied through histological characterization of the hermaphroditic gonad during a 1-year study period (May 2015 - May 2016). Spawning intensity in the field as well as the gonadic index were calculated monthly. Both female and male gametes Were observed simultaneously within acini of adult individuals and continuously throughout the year. Oogenesis started in the mid-autumn (October), with gonads characterized mainly by proliferation of female cells. After that, oocytes progressively increased in number and volume until summer, when the evacuation stage frequency was the highest. From summer to autumn, some acini were empty from their oocyctes while some others had already begun the proliferation stage, suggesting the lack of a resting phase. Spermatogenesis was also a continuous process throughout the year, with spermatozoa being mainly observed in late spring (March). These findings suggested that environmental conditions are suitable for the establishment of S. pectinata, first mentioned in 1998 on the Tunisian coast and even suggest that it could continue spreading eastward in the Mediterranean Basin

Are European sea bass as euryhaline as expected? Intraspecific variation in freshwater tolerance

WOS:000475657500006International audienceIn teleosts, the regulation of hydromineral balance has a direct impact on several physiological functions, biochemical processes, and can influence behaviour, distribution and survival. As European sea bass Dicentrarchus labrax undertake seasonal migrations from seawater (SW) to brackish, estuarine and fresh water (FW) in their habitat, this study investigates their capacity to tolerate fresh water and explores intraspecific variations in physiological responses. Juvenile D. labrax were transferred from SW to FW at various ages. Freshwater-tolerant and non-tolerant phenotypes were discriminated according to behavioural and morphological characteristics. About 30% of the fish exposed to FW were identified as freshwater intolerant following FW challenges performed at different ages. Interestingly, intolerant fish exhibited the same phenotypic traits: erratic swimming, lower speed, isolation from the shoal and darker colour. Freshwater-intolerant fish were also characterised by a significant lower blood osmolality compared to tolerant fish, and significantly lower Na+/K+-ATPase α1a expression in the posterior kidney. An imbalance in ion regulatory mechanisms was further confirmed by a blood Na+/Cl− ratio imbalance observed in some freshwater-intolerant fish. The analysis of glucocorticoid and mineralocorticoid receptor expression levels in gills and kidney revealed significant differences between freshwater-intolerant and -tolerant fish in both organs, suggesting differential stress-related responses. This study clearly shows an intraspecific difference in the responses following FW transfer with a decreased renal ion uptake capacity as a major cause for freshwater intolerance

Circulating MicroRNAs Indicative of Sex and Stress in the European Seabass (Dicentrarchus labrax): Toward the Identification of New Biomarkers

MicroRNAs (miRNAs) constitute a new category of biomarkers. Studies on miRNAs in non-mammalian species have drastically increased in the last few years. Here, we explored the use of miRNAs as potential, poorly invasive markers, to identify sex and characterize acute stress in fish. The European seabass (Dicentrarchus labrax) was chosen as a model because of its rapid response to stress and its specific sex determination system, devoid of sexual chromosomes. We performed a small RNA-sequencing analysis in the blood plasma of male and female European seabass (mature and immature) as well as in the blood plasma of juveniles submitted to an acute stress and sampled throughout the recovery period (at 0 h, 0.5 h, 1.5 h and 6 h). In immature individuals, both miR-1388-3p and miR-7132a-5p were up-regulated in females, while miR-499a-5p was more abundant in males. However, no miRNAs were found to be differentially expressed between sexes in the blood plasma of mature individuals. For the acute stress analysis, five miRNAs (miR-155-5p, miR-200a-3p, miR-205-1-5p, miR-143-3p, and miR-223-3p) followed cortisol production over time. All miRNAs identified were tested and validated by RT-qPCR on sequenced samples. A complementary analysis on the 3′UTR sequences of the European seabass allowed to predict potential mRNA targets, some of them being particularly relevant regarding stress regulation, e.g., the glucocorticoid receptor 1 and the mineralocorticoid receptor. The present study provides new avenues and recommendations on the use of miRNAs as biomarkers of sex or stress of the European seabass, with potential application on other fish species

Natural cortisol production is not linked to the sexual fate of European sea bass

International audienceIn this study, we aimed to investigate the relationship between cortisol and the determination of sexual fate in the commercially important European sea bass (Dicentrarchus labrax). To test our hypothesis, we designed two temperature-based experiments (19 ℃, 21 ℃ and 23 ℃, experiment 1; 16 ℃ and 21 ℃, experiment 2) to assess the effects of these thermal treatments on European sea bass sex determination and differentiation. In the fish from the first experiment, we evaluated whether blood cortisol levels and expression of stress key regulatory genes were different between differentiating (149 to 183 dph) males and females. In the second experiment, we assessed whether cortisol accumulated in scales over time during the labile period for sex determination as well as the neuroanatomical localisation of brain cells expressing brain aromatase (cyp19a1b) and corticotropin-releasing factor (crf) differed between males and females undergoing molecular sex differentiation (117 to 124 dph). None of the gathered results allowed to detect differences between males and females regarding cortisol production and regulatory mechanisms. Altogether, our data provide strong physiological, molecular and histochemical evidence, indicating that in vivo cortisol regulation has no major effects on the sex of European sea bass

Unraveling the genotype by environment interaction in a thermosensitive fish with a polygenic sex determination system

In most animals, sex determination occurs at conception, when sex chromosomes are segregated following Mendelian laws. However, in multiple reptiles and fishes, this genetic sex can be overridden by external factors after fertilization or birth. In some species, the genetic sex may also be governed by multiple genes, further limiting our understanding of sex determination in such species. We used the European sea bass (Dicentrarchus labrax) as a model and combined genomic (using a single nucleotide polymorphism chip) and transcriptomic (RNA-Sequencing) approaches to thoroughly depict this polygenic sex determination system and its interaction with temperature. We estimated genetic sex tendency (eGST), defined as the estimated genetic liability to become a given sex under a liability threshold model for sex determination, which accurately predicts the future phenotypic sex. We found evidence that energetic pathways, concerning the regulation of lipids and glucose, are involved in sex determination and could explain why females tend to exhibit higher energy levels and improved growth compared to males. Besides, early exposure to high-temperature up-regulated sox3, followed by sox9a in individuals with intermediate eGST, but not in individuals showing highly female-biased eGST, providing the most parsimonious explanation for temperature-induced masculinization. This gonadal state was maintained likely by DNA methylation and the up-regulation of several genes involved in histone modifications, including jmjd1c. Overall, we describe a sex determination system resulting from continuous genetic and environmental influences in an animal. Our results provide significant progress in our understanding of the mechanisms underlying temperature-induced masculinization in fish

Combined genomic approached to unravel sex determination in the European Sea Bass

6th International Symposium on Genomics in Aquaculture (GIA 2022), 4-6 May 2022, GranadaFish sex determination is often considered as governed by either genetic or environmental factors, but the European sea bass (Dicentrarchus labrax) defies this theory. In this species, a polygenic threshold sex determination system was demonstrated (Vandeputte et al. 2007), where the genetic sex tendency is influenced by larval rearing temperature to determine the phenotypic sex (Piferrer et al, 2005). In this study, we applied two thermal treatments during early larval stage, a low temperature protocol (16°C, LT), known to favour balanced sex-ratios and a high temperature masculinizing protocol (21°C, HT). We combined various “-omics” approaches to characterize this temperature-dependent polygenic sex determination of European sea bass. We produced 8 families by mating 8 males with the same female. The progenies were reared in common garden under two thermal treatments (LT, HT) in triplicate. Fish at four different key developmental stages encompassing the temperature sensitive period were sampled. We predicted the genetic sex tendency (eGST) of the animals using a genomic relationship matrix derived from 57K SNPs from the DLabCHIP array (Griot et al., 2021) with a threshold animal model. This was completed by a transcriptomic approach, whole-body energy measurements. The proportion of females was 53.4% at LT and 25.3% at HT, showing a marked masculinization at high temperature. We found that the eGST accurately predicted the future phenotypic sex. We provided evidence that energetic pathways, concerning the regulation of lipids and glucose, are involved in sex determination and could explain why females tend to exhibit higher energy levels and improved growth compared to males. Overall, we describe for the first time a sex determination system resulting from continuous genetic and environmental influences in an animal, which provides significant progress in our understanding of the mechanisms underlying temperature-induced masculinization in fishThe study was supported by the European Maritime and Fisheries Fund (3S, Seabass Sex and Stress, grant number 4320175237) and from the European Union's Horizon 2020 Grant Agreement 652831 (AQUAEXCEL2020, Transnational Access project ”Transsexbass”)Peer reviewe