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Modifications in the cytochrome c oxidase 2 gene of male-transmitted genome (Mcox2) have been found in some bivalve species that exhibit a unique mode of mitochondrial transmission named doubly uniparental inheritance (DUI). In DUI, paternal mitochondria (and their male mtDNA) as well as maternal mitochondria (and their corresponding female mtDNA) are transmitted to male offspring. Scrobicularia plana, a bivalve exhibiting this inheritance model possess an important in-frame insertion of ~ 4,8 kb in its Mcox2 gene that is translated into a polypeptide of 1892 amino acids (~ 220 kDa), the largest metazoan COX2 protein known to date. The insertion is conserved amongst individuals from different populations and, according to analysis of synonymous and non-synonymous substitution rates, evolves under purifying selection which would suggest maintenance of functionality in MCOX2. MCOX2 protein might act as a tag at the surface of male mitochondria to facilitate their sex-specific fate in bivalve embryos. The long-transcribed insertion could also explain low OXPHOS rates that were found in M mitochondria of DUI bivalves thus affecting male mitochondrial metabolism.

SEB Annual Conference 2022

Mcox2 in the DUI bivalve Scrobicularia plana encodes the longest known mitochondrial protein in metazoans

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2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years - Montpellier, France

technical paper

The Atlantic salmon (Salmo salar) is a unique species with regards to studies on life history, as it not only shows significant variation in age at maturity but also because a large proportion of the variation in this trait has been associated with a single genetic locus, vgll3. While this association is now well known, less is known about this gene’s mechanistic pathway and how it interacts with other environmental or genetic factors. To follow up on vgll3 as a large-effect locus for age at maturity in Atlantic salmon, we present a long-term common garden experiment aimed at studying the sources of variation for this trait, covering different vgll3 genotypes across two environmental temperature regimes, two feed treatments, and two populations-of-origin. We show that the effect of vgll3 genotype on maturation timing in male Atlantic salmon is consistent across the temperature treatments and populations. Additionally, we show a population-dependent effect of temperature, with the northern population having a smaller difference in maturation rates between the two temperature regimes. Finally, we discuss the relative contribution of these environmental and genetic factors to Atlantic salmon maturation timing.

Atlantic salmon maturation: contributions from large-effect locus and environmental factors in influencing maturation age in two populations in a common garden setting.

Acidified ocean system would affect marine livings was already proved. The inadequate potential difference and ions gradient may jam the neural transmitting in turn; moreover, the evoking pathological behavioral defects such as impaired visual capacity may impact the survival and fitness of several marine species. As such, the electrophysiological method, electro-retinography (ERG), is one of the most commonly used techniques to investigate the properties of the visual response to a light stimulus in aquatic animals. A simplified and low-cost ERG apparatus was assembled and used to determine the threshold of flicker electroretinogram (fERG) of bigfin reef squid under control (pH 8.1) or laboratory CO2-induced acidified conditions at the retinal level. An epoxy-insulated tungsten microelectrode was placed on the midline of the retina and enabled us to estimate the visual sensitivities practically in squid retina to a series of light-emitting diodes (LEDs) emitting different wavelengths. Under the control pH 8.1 conditions, the average critical flicker fusion (CFF) threshold toward a white light source in bigfin reef squid retina was found to be 47 Hz at the illumination level of 50 cd/m2, while the average CFF of CO2-acclimated squid is slightly increased by about 15%. In the future, pharmacological studies could further indicate whether this effect could be caused by the CO2-involved neuronal functional irregularity.

A visual sensory estimation system for detecting electroretinogram in bigfin reef squid under CO2 perturbation

Chronic temperature stress may leave freshwater fishes vulnerable to opportunistic pathogens, particularly during early life stages. Lake sturgeon, Acipenser fulvescens, populations within the northern expanse of their range in Manitoba, Canada, may be susceptible to high temperature thermal stress. We acclimated developing lake sturgeon for 21 days to two ecologically relevant temperatures (16 and 20oC) . Both acclimation treatments were exposed to 0, 30, and 60 µg.ml-1 bacterial lipopolysaccharides (endotoxins), as an immune stimulus, for 48 hr, with samples taken 4 and 48 hr during trial exposures and following a 7-day recovery period. We then measured whole body transcriptional (mRNA) and physiological (lysozyme activity, cortisol, glucose) responses involved in the innate immune, general stress, and fatty acid responses following acute exposure to bacterial endotoxins. Data detailing the responses involved in the above physiological processes revealed that while overall expression levels were higher at 20oC under control conditions, during bacterial stimulus 16oC reared lake sturgeon produced a more robust response with higher induced expression of the above responses than their 20oC acclimated counterparts. Additional whole-animal performance metrics (critical thermal maximum and metabolic rate) demonstrated acclimation-specific responses indicating compromised metabolic capacity following the initiation of immune related responses. Our study showed that acclimation to 20oC during early development impaired the activation of molecular pathways involved in the immune, stress, and fatty acid responses of lake sturgeon, highlighting the effects of chronic thermal stress on transcriptional activation and recruitment of downstream biological processes in this critically threatened and endangered species.

Elevated temperatures dampen innate immune responses of developing lake sturgeon (Acipenser fulvescens) when challenged with bacterial lipopolysaccharides

Sea stars move with crawling and bouncing gaits that are generated by the action of hundreds of tube feet. Bouncing at high speed is characterized by the feet moving in synchrony, which is unlike the asynchronous and slow crawling motion. It is unclear what forces are generated by individual tube feet and how those forces coordinate to generate distinct gaits. We have therefore investigated the mechanics of locomotion in sea stars at the levels of individual feet and the whole body through a combination of experimentation and mathematical modeling. These efforts have included a definition for the mechanical advantage and gearing of helically wound hydrostatic skeletons, as well as the development of an optical under-water force plate. Our results suggest that tube feet primarily serve to push against the substratum and that the gait transition is generated by the collective dynamics of tube feet that are mechanically coupled to a common body. Therefore, the transition to synchronous bouncing may be generated purely through mechanics, without a need for a change in nervous control.






The collective mechanics and control of locomotion in sea stars

Bone trabeculae are known to remodel during the life of vertebrates, aligning themselves in accordance with the forces going through the bones. Heavy animals p resent very high forces passing through their limb bones during locomotion, through body weight and the necessarily important muscle pull associated. It is expected that their cortical and trabecular structures will adapt to those constraints, but a quantified description of how trabecular architecture varies in the limb bones of heavy animals is not available. Here we use a new approach to quantitatively and precisely describe the distribution of anisotropy and compactness of cancellous bone in the six limb long bones of all living species of rhinoceroses, the heaviest animals capable of galloping. We show that trabecular compactness and anisotropy are correlated in our sample. Highly anisotropic and compact trabeculae are concentrated along articulations and muscle insertion areas, and dissipate the forces into the more resistant cortical bone. The radius, ulna and tibia present a simple, vertical anisotropy pattern associated with body weight support (or triceps pull for the ulna), whereas the humerus and femur present a more complex trabecular pattern, linked with attachment areas for powerful muscles that generate anisotropic trabeculae in various directions. Few variations were observed between species, highlighting that rhinos share a common strategy for bone resistance allowing galloping while weighing up to three tons. Further studies on their more cursorial relatives and on fossil rhinos, some of which reached 20 tons, could yield interesting complementary results for untangling the adaptations to heavy weight and cursoriality in perissodactyls.

Whole bone distribution of trabecular compactness and anisotropy reveals how long bones sustain important forces in rhinoceroses

A typical feature of many biological materials is the ability to react to experienced mechanical stress, as described in the “mechanostat” model by H.M. Frost. In this study we investigated so far unknown possible reactions to stress of one of the evolutionary most successful forms of skeletons: the insect exoskeleton. Locusts (Locusta migratoria) were raised under controlled conditions at increased mechanical load using a custom build centrifuge. Although the increase of mechanical stress notably decreased the survival rate, locusts surprisingly survived for several weeks at up to 8g. Biomechanical properties such as strength and stiffness of locust hindleg tibia were characterised using standardized mechanical tests. Further analysis using X-ray microtomography and a novel, simple staining method examine possible responses of the exoskeletons two main layers, exocuticle (outer layer) and endocuticle (inner layer). For the first time, our results show that insect exoskeleton cuticle material (e.g. Youngs modulus, bending strength) and structural properties (thickness of exo-, and endocuticle) were significantly influenced by the experienced mechanical stress. These findings not only allow us to better understand the biomechanical role of exo- and endocuticle within an insect exoskeleton however also help us to discuss the evolutionary context and validity of the “mechanostat” model for the largest and most successful group of animal species.

Effect of mechanical stress on insect exo- and endocuticle

Evolutionary studies often search for population divergence, increasingly at microgeographic spatial scales and across contemporary time scales, reflecting the extent and pace of natural selection. The expectation tends to be that local populations should adapt to environmental variation, including variation associated with human-modified environments. A long history of theoretical and empirical studies supports this expectation, and indeed natural selection should diverge populations as it drives them toward local adaptive optima. Yet, perhaps more often than we are eager to admit, we fail to find evidence for local adaptation, and when this happens, we struggle to describe the mechanisms that can generate these patterns. For instance, what do we make of data that fail to clearly demonstrate local adaptation, such as when presumptively divergent populations are found to be equivalently adapted to contrasting environments? Or, how do we interpret the persistence of locally maladaptive trait variation? Or, how do we reconcile adaptive population demographic trajectories with maladaptive trait variation? Here, we discuss a framework of (mal)adaptation that emphasizes the importance of considering both absolute and relative fitness when interpreting local population divergence. We then use this framework to interpret outcomes from amphibian populations that show evidence of both adaptive and maladaptive divergence in response to road adjacency and runoff pollution.

Toward a unified approach to understanding (mal)adaptation

Blue-mussels from the M. edulis species-complex (M. edulis x M. trossulus x M. galloprovincialis) are an abundant element of the benthos community, found in the high latitude habitats of both hemispheres of the globe. Aside their ecological value, these foundation species are relevant to the aquaculture industry, with over 182 thousand tonnes produced globally each year. These taxa withstand a wide range of environmental conditions and the 3 species easily hybridise in regions where their distribution overlaps. Significant effort has been made to investigate the consequences of environmental stress on the physiology of these species. However, our understanding on the genomic mechanisms underlying hybridisation and local adaptation remains limited. To refine our understanding of such processes in this species complex, we sequenced 24 blue mussel populations distributed globally using a whole-genome low coverage approach. A total of 50k SNPs were used to develop a medium-density SNP-array, a tool that will allow the rapid and consistent genotyping of individuals. To guarantee that putative SNPs associated with environmental stress were included in the array, we selected mussel populations thriving across a gradient of environmental conditions in terms of temperature, salinity and CO2. The rapid high-throughput screening of SNPs facilitates the investigation of genomic structure among populations and can contribute to our understanding on ongoing local adaptation and hybridisation in these taxa. Besides, genome wide association studies, combining omics with physiology, will allow the characterisation of genotypes resilient to environmental stress, relevant in light of climate change.  

Exploring genomic diversity within the blue mussel species-complex

Social context influences all aspects of life, including how organisms interact with their surroundings, perceive stressors, and respond to toxicants in their environment. With the condition of aquatic environments declining worldwide, furthering our understanding of the factors that affect the success of species will be essential for their survivability. As such, we examined how copper (Cu) contamination affects behaviour and physiology of three-spined stickleback (Gasterosteus aculeatus) as a function of their social environment. We hypothesized that exposing sticklebacks to Cu, while experiencing the stress of isolation, will lead to greater uptake of Cu and subsequent behavioural responses, as opposed to exposing sticklebacks to Cu in a group setting. Wild-caught fish were exposed to environmentally relevant Cu concentrations of 50µg/L and 150µg/L for 96 hours then assessed for activity level, social cohesion, and foraging. Furthermore, tissues (gill, liver, and intestine) were collected to measure organ-specific bioaccumulation of ions and enzyme activity (Na+/K+/ATPase, H+-ATPase). The interplay between toxicology and social behaviour is not well understood, and as such is not considered in risk assessment standard practice. This potentially leaves a significant gap in our understanding of organismal response to toxicants. Observing response to copper after isolation and group exposures may highlight the need to account for the social environment to truly represent the vulnerability of populations.

Influences of Anthropogenic Stress on the Sociality of Three-Spined Stickleback (Gasterosteus Aculeatus)

Sources of metals in the Antarctic marine environment can vary due to glacial melt. The limpet Nacella conccina, a well-distributed specie at Antarctic coastal zone, is able to deal with some different copper concentrations. During the experiments limpets were exposed to 0.12 µgL-1 and 0.25 µgL-1 of copper at 12, 24, 48 h (N=6/metal/concentration/time, temperature 0°C and salinity 34 ppt). Gills were analysed using proteomics techniques. We detected 78 significantly altered proteins (two-way ANOVA, p&lt;0.02) on 2D electrophoresis gels. Among these 47 were identified using tandem mass spectrometry. Antioxidant proteins including Mn-superoxide dismutase and ferritin were identified. This is an indication of the increased production of ROS. The chaperones involved in the maturation of proteins present in the endoplasmic reticulum showed variations in function of a possible change in the cellular redox state. Modifications in the acid-base balance of gill cells can be linked to changes in carbonic anhydrase after exposure to copper. The dynamics of proteins such as arginine kinase, glycolytic triose phosphate isomerase, as well as pyruvate dehydrogenase, can be linked to a higher rate of ATP renewal. We hypothesised that substituting protein-binding metals by copper causes an increase in ROS and acid-base effects in the gills, leading to protein maturation inhibition in the endoplasmic reticulum, an increment in ATP buffering by arginine kinase and glycolytic proteins, and changes in Cdc42 abundance impacting the cytoskeletal filaments. These observations help to shed light on the interrelationships between metabolism, energy balance and short time copper stress tolerance in Antarctic limpets.

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Mcox2 in the DUI bivalve Scrobicularia plana encodes the longest known mitochondrial protein in metazoans

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Atlantic salmon maturation: contributions from large-effect locus and environmental factors in influencing maturation age in two populations in a common garden setting.

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