The European sea bass (Dicentrarchus labrax L.) is a marine fish of key economic and cultural importance in Europe. It is now more an aquaculture than a fisheries species (>96% of the production in 2016), although modern rearing techniques date back only from the late 1980s. It also has high interest for evolutionary studies, as it is composed of two semispecies (Atlantic and Mediterranean lineages) that have come into secondary contact following the last glaciation. Based on quantitative genetics studies of most traits of interest over the past 10-15 years, selective breeding programs are now applied to this species, which is at the beginning of its domestication process. The availability of a good quality reference genome has accelerated the development of new genomic resources, including SNP arrays that will enable genomic selection to improve genetic gain. There is a need to improve feed efficiency, both for economic and environmental reasons, but this will require novel phenotyping approaches. Further developments will likely focus on the understanding of genotype-by-environment interactions, which will be important both for efficient breeding of farmed stocks and for improving knowledge of the evolution of natural populations. At the interface between both, the domestication process must be better understood to improve production and also to fully evaluate the possible impact of aquaculture escapees on wild populations. The latter is an important question for all large-scale aquaculture productions.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/age.12779

The European sea bass: a key marine fish model in the wild and in aquaculture.

Sunlight is the Earth's primary energy source and is exploited by an array of natural and man-made processes. Photosynthetic plants harness solar energy to convert carbon dioxide and water into biomass, and solar panels capture light and convert it to electricity. Sunlight is critical to life on Earth, and yet excessive exposure to sunlight can cause serious harm as it contains ultraviolet (UV) radiation, which damages the DNA of cells. In humans, this damage can lead to conditions such as cataracts and skin cancer. The marine organisms and animals that live in the upper ocean and on reefs are subject to intense and unrelenting sunlight. In their effort to protect against potentially deadly UV radiation, many small and particularly vulnerable marine organisms, such as bacteria and algae, produce UV-protective sunscreens. While UV-protective compounds have also been found in larger organisms, including fish and their eggs, the presence of these sunscreens has always been attributed to the animal sequestering the compounds from their environment or partnering with a sunscreen-producing microorganism. Now, Osborn, Almabruk, Holzwarth et al. have discovered a fish that is able to produce such a UV-protective compound completely on its own. After identifying the full set of genes—or pathway—responsible for generating the UV-protective compound, the same pathway was detected in a variety of diverse animals, including amphibians, reptiles, and birds. This opens up a new area of study, because besides providing UV protection, no one yet knows what other roles the molecule may have in these animals. Furthermore, introducing the complete pathway into yeast enabled these cells to produce the sunscreen. In the future, engineering a yeast population to produce large quantities of the natural sunscreen could lead to large-scale production of the UV-protective compound so it can be used in pharmaceuticals and cosmetics.

/pdf/de-novo-synthesis-of-a-sunscreen-compound-in-vertebrates-4nbl14znr2.pdf

De novo synthesis of a sunscreen compound in vertebrates

Shape, preservation, embedded components and groundmass characteristics allow distinction between herbivore excrements and the coprolites of omnivores or carnivores. Herbivore dung remains may occur in a wide range of onsite archaeological features but are also known from offsite situations. Fresh herbivore excrements are usually porous, loosely packed and consist mainly of poorly digested to undigested plant fragments, which are sometimes embedded in a brown to dark brown amorphous organic groundmass. Ruminant and horse excrements mainly consist of poorly digested plant fragments. Rodent excrements can be found in archaeological sediments. Because of the high organic content of herbivore excrements, dried ruminant dung is an excellent fuel, used since prehistoric times and still in use today, mainly in dry regions. Stabling or enclosure sediments have a lower porosity than equivalent unaffected excrements and show an impact of sediment agglomerates, mineral grains and other components due to trampling processes.

Excrements of Herbivores

A comparative analysis of bipolar and freehand experimental knapping products from Olduvai Gorge, Tanzania

A quantitative understanding of physiological thermal responses is vital for forecasting species distributional shifts in response to climate change. Many studies have focused on metabolic rate as a global metric for analyzing the sublethal effects of changing environments on physiology. Thermal performance curves (TPCs) have been suggested as a viable analytical framework, but standard TPCs may not fully capture physiological responses, due in part to failure to consider the process of metabolic depression. We derived a model based on the nonlinear regression of biological temperature-dependent rate processes and built a heart rate data set for 26 species of intertidal molluscs distributed from 33°S to ~40°N. We then calculated physiological thermal performance limits with continuous heating using T 1 / 2 H , the temperature at which heart rate is decreased to 50% of the maximal rate, as a more realistic measure of upper thermal limits. Results indicate that heat-induced metabolic depression of cardiac performance is a common adaptive response that allows tolerance of harsh environments. Furthermore, our model accounted for the high inter-individual variability in the shape of cardiac TPCs. We then used these TPCs to calculate physiological thermal safety margins (pTSM), the difference between the maximal operative temperature (95th percentile of field temperatures) and T 1 / 2 H of each individual. Using pTSMs, we developed a physiological species distribution model (pSDM) to forecast future geographic distributions. pSDM results indicate that climate-induced species range shifts are potentially less severe than predicted by a simple correlative SDM. Species with metabolic depression below the optimum temperature will be more thermal resistant at their warm trailing edges. High intraspecific variability further suggests that models based on species-level vulnerability to environmental change may be problematic. This multi-scale, mechanistic understanding that incorporates metabolic depression and inter-individual variability in thermal response enables better predictions about the relationship between thermal stress and species distributions.

Physiological determinants of biogeography: The importance of metabolic depression to heat tolerance.

Androgenesis is a form of uniparental reproduction leading to progenies inheriting only the paternal set of chromosomes. It has been achieved with variable success in a number of freshwater species and can be attained by artificial fertilization of genetically inactivated eggs following exposure to gamma (γ), X-ray or UV irradiation (haploid androgenesis) and by restoration of diploidy by suppression of mitosis using a pressure or thermal shock. The conditions for the genetic inactivation of the maternal genome in the European sea bass (Dicentrarchus labrax L.) were explored using different combinations of UV irradiation levels and durations. UV treatments significantly affected embryo survival and generated a wide range of developmental abnormalities. Despite the wide range of UV doses tested (from 7.2 to 720 mJ x cm(-2)), only one dose (60 mJ x cm(-2) x min(-1) with 1 min irradiation) resulted in a small percentage (14%) of haploid larvae at hatching in the initial trials as verified by flow cytometry. Microsatellite marker analyses of three further batches of larvae produced by using this UV treatment showed a majority of larvae with variable levels of paternal and maternal contributions and only one larva displaying pure paternal inheritance. The results are discussed also in the context of an assessment of the UV-absorbance characteristics of egg extracts in this species that revealed the presence of gadusol, a compound structurally related to mycosporine-like amino acids (MAAs) with known UV-screening properties.

/pdf/genetic-inactivation-of-european-sea-bass-dicentrarchus-2vm0pq0c8l.pdf

Genetic inactivation of European sea bass (Dicentrarchus labrax L.) eggs using UV-irradiation: observations and perspectives.

Multiple working hypotheses for hyperallometric reproduction in fishes under metabolic theory

http://manuscript.elsevier.com/S0044848622000515/pdf/S0044848622000515.pdf

A novel method to individually track spawning females in aquaculture tanks using the European sea bass (Dicentrarchus labrax) as a model

Rapid environmental changes will be the major challenge that most biota will have to deal with in the near future. Extreme events, such as marine heatwaves, are becoming more frequent and could be spatially uniform at a regional scale for a relatively long period of time. To date, most research on heatwaves have focused on sessile organisms, but these extreme events can also impact mobile species. Here we simulated a three-week marine heatwave to investigate its effects on the male reproductive performance of a Mediterranean Sea emblematic species, the European sea bass Dicentrarchus labrax. Males from the control condition (≈ 13 °C) produced significantly more sperm than those exposed to a relatively warm thermal treatment (≈ 16 °C). However, neither the percentage of motile spermatozoa nor most of the other sperm motility parameters were significantly affected by the rearing temperature, over the whole period. Overall, our results suggest only moderated effects of a potential winter heatwave on the reproductive performance of male European sea bass. This article is protected by copyright. All rights reserved.

/pdf/a-simulated-marine-heatwave-impacts-european-sea-bass-sperm-29sdmywn.pdf

A simulated marine heatwave impacts European sea bass sperm quantity, but not quality.

Introduction Natural and synthetic estrogens are pollutants found in aquatic ecosystems at low concentrations reaching ng.L-1 to μg.L-1. At these concentrations, they are able to interfere with the fish endocrine system. When waterborne exposure occurs at early life stages, when blood estrogens concentrations are low, this may have significant consequences for estrogen-sensitive functions such as skeletal development. Methods To better understand how (xeno)estrogens may affect early head mineralization, 12 days post-hatch larvae of the European seabass Dicentrarchus labrax were experimentally exposed for 4 days to the natural estrogen estradiol E2 and to the xenoestrogen bisphenol A (BPA), both used at either regulatory concentration of water quality or a 100 times higher concentration. Head mineralization level was assessed using Alizarin red staining, together with the relative quantification of mRNA expression levels of several genes playing key roles in skeletogenesis and estrogen signaling pathways. Results We showed that (xeno)estrogen exposure at early larval stage increases the expression of skeleton-associated genes: matrix proteins encoding genes (col1a2, col2a1a, col2a1b, bgp1a, bgp1b, sparc), proteolytic enzyme encoding genes (ctsk) and transcription and signaling factors (sox9a, sox9b, ihha, runx2, rankl). Although transcriptional overexpression of these genes was significant in larvae exposed to 40 ng.L-1 E2 and to 1.6 and 160 μg.L-1 BPA, increased mineralization was detected only in E2-exposed larvae, suggesting a difference in head skeleton development and remodeling in BPA-treated larvae. Discussion Our results suggest that these phenotypic differences could be due to the implication of other estrogenic signaling pathways involving both nuclear and membrane-bound estrogen receptors (ERs and GPERs), but also estrogen-related receptors (ERRs). This study brings new insights into the regulatory mechanisms of skeletogenesis by E2 and BPA and into the effects of waterborne exposure to (xeno)estrogens on the early skeletal development of teleost fishes.

/pdf/short-term-effects-of-estradiol-and-bisphenol-a-on-gene-8swia4be.pdf

Stephane Lallement

Papers

Genetic inactivation of European sea bass (Dicentrarchus labrax L.) eggs using UV-irradiation: observations and perspectives.

Multiple working hypotheses for hyperallometric reproduction in fishes under metabolic theory

A novel method to individually track spawning females in aquaculture tanks using the European sea bass (Dicentrarchus labrax) as a model

A simulated marine heatwave impacts European sea bass sperm quantity, but not quality.

Short-term effects of estradiol and bisphenol A on gene expression associated with early head mineralization in the seabass Dicentrarchus labrax