Czechia

The Atlantic bluefin tuna Thunnus thynnus (ABFT) is an extremely valuable marine fish, a pelagic predator with physiological adaptations to a lifestyle of ceaseless swimming, notably partial endothermy and obligatory ram ventilation. Very little is known about ABFT energetics but, by comparison to ‘normal’ teleosts, they are expected to have elevated standard and routine metabolic rates (SMR and RMR) and aerobic metabolic scope (AS), and high aerobic swimming performance. We used swim tunnel respirometry to investigate this in age 0+ juveniles (mass 550g, forklength 30cm) held at 19 °C. The tuna did not enjoy the tunnel, they lost equilibrium and became agitated below 1.4 bodylengths per second (BL s-1), refused to swim faster than 2.2 BL s-1, and had their highest metabolic rates when agitated. Their SMR was about 1.5 times those of other Mediterranean fishes at similar sizes and temperatures, whereas their AS was two to threefold higher. Video analysis of the juveniles in their rearing tank revealed they were actually cruising spontaneously at speeds between 2.5 and 3.5 BL s-1. Extrapolation of respirometry data to 3 BL s-1 indicated an RMR about fourfold higher than direct measures, by tank respirometry, in other Mediterranean species. These preliminary observations would confirm longstanding predictions about the comparative energetics of ABFT but more work is clearly needed and some is ongoing.

SEB Conference 2024

Insights into the in-vivo physiological energetics of juvenile Atlantic bluefin tuna

swimming speeds

respiratory metabolism

tuna

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technical paper


The branchiopod crustacean Artemia franciscana can produce diapause embryos (cysts) with a high trehalose and glycerol content capable of surviving complete dehydration (anhydrobiosis) and freezing. To investigate the molecular regulation of trehalose metabolism during diapause in A. franciscana we identified the genomic repertoire of trehalose metabolic enzymes and transporters in this species. Phylogenomic analyses of the transcripts and deduced proteins in relation to the sugar transporters of humans, Drosophila and other crustaceans revealed 20-28 potential trehalose transporters (Trets) in Artemia genomes, which could be phylogenetically subclassified into two clades (Tret1 and Tret2). These analyses revealed a major expansion of Tret2-type transporters in the Banchiopoda. We further identified two trehalose-6-phospate synthase (Tps1 and -2) and one trehalase (Treh) enzymes. However, normalization of the abundance of the Tret transcripts in the transcriptomes of adults, nauplii and cysts indicated that only Tret1B and -1A, as well as Tret2B3a and -2B3b, were accumulated >2-fold in desiccated cysts. Ectopic expression of different Trets (Tret1B, -1A, -2B3b, -2C2a and -2C2b) in Xenopus laevis oocytes showed that the identified channels can facilitate trehalose transport. Gene expression analysis by qRT-PCR confirmed the transcriptome data, but showed that the mRNAs encoding Tret1A, -1B and -2B3b, as well as Tps2 and Treh, were accumulated in hydrated and desiccated cysts following the same pattern than that of trehalose. These data uncover an unexpectedly high diversity of trehalose transporters in Branchiopoda and suggest that different Tret paralogs might play redundant roles for the accumulation of trehalose in Artemia diapause cysts.



Trehalose transporter gene diversity in the anhydrobiotic brine shrimp Artemia franciscana

While legally protected in Portugal since 1988, the Iberian wolf still faces conservation problems, mainly due to habitat fragmentation, caused by human activity, and poaching.
This study is part of a wolf monitoring project that aims to establish the reference situation of the wolf population to assess the impact of a mining exploration in northern Portugal. We measured faecal glucocorticoid metabolite concentrations in wolf scats as a non-invasive method to determine stress levels, using an enzyme immunoassay kit.
Wolf scats were collected in the area of two wolf packs, Barroso and Leiranco. Molecular methods were used to confirm the species, assign sex, wolf pack, and, whenever possible, individuals. During two years, we identified 15 individuals (11 males and 4 females) from Barroso’s pack area and 10 individuals (7 males and 3 females) from Leiranco’s pack area, of which we analysed 133 and 60 samples, respectively.
Results show that the Leiranco pack, inhabiting the area with higher human density, has higher levels of faecal cortisol. We also found, for both wolf packs, a significant seasonal effect; higher levels were found during the autumn, which corresponds to the main hunting season.
The present work is the first developed in Portugal aiming the characterization of cortisol levels in free-ranging wolves. Since this work is included in a long-term project, increasing the number of collected samples, and the analysis of other relevant variables influencing cortisol levels, will improve our understanding of the factors affecting wolf populations.

Non-invasive assessment of stress hormone cortisol in two wild packs of Iberian Wolf (Canis lupus signatus) in northern Portugal

Chemical cues play a crucial role in aquatic environments, with most research focusing on cues related to injury and stress. However, there have been limited studies on identifying specific chemical components within these cues, unveiling a knowledge gap in chemosensory biology. Our previous studies have demonstrated that heat stress can likewise prompt the release of olfactory cues, that propagate within a group and induce stress in naïve developing zebrafish (Danio rerio). Using metabolomics, we identified glucose, phosphocholine, and 3-mercaptolactate as potential components of heat-induced stress metabolites. Hatching was impaired by stress metabolites. In this study, we verified whether 3-mercaptolactate and phosphocholine are indeed potential stress metabolites by assessing their impacts on hatching rate and gene expression in control metabolite (CM) and thermal stress metabolite (SM) groups. Indeed, both compounds significantly impaired hatching and as a result were found to cause bent tails in zebrafish larvae. Genes associated with the metabolism of these compounds (prg4a -phosphocholine; ldha and mpst – 3-mercaptolactate) were differentially expressed, with the expression of mpst, associated with the metabolism of 3-mercaptolactate, trending downwards in metabolite receivers. While further research into the mechanism of action is ongoing, these results indicate how lipid and sulfur-containing compounds can be used for heat-induced stress communication in developing embryos.

Phosphocholine and 3-mercaptolactate as potential stress metabolites in zebrafish (Danio rerio)

Fjords are physically isolated areas characterised by distinct oceanic conditions,
making them perfect case-
studies to investigate the consequences of local adaptation and in situ long-term
acclimatisation in marine
organisms. In these environments, global change drivers such as ocean acidification
(OA) pose a significant
threat to marine ecosystems, including keystone zooplankton species such as the
copepod Calanus glacialis.
Both local adaptation and long-term acclimatisation may lead to differential responses
of C. glacialis to OA
along its range of geographical distribution. Consequently, our study aimed to explore
how these phenomena
can influence the ability of various populations of C. glacialis to cope with future OA
conditions. To do so,
copepods were collected from four fjords spanning from southern Norway to Svalbard,
and exposed in the
laboratory under controlled conditions to seven different increasing concentrations of
pCO 2 (300 to 30,000
ppm) over time to explore the threshold at which each population shows signs of
sensitivity to OA. Targeted
metabolomes for each treatment were profiled using high-performance LC-MS/MS, to
quantify 49 metabolites
involved in metabolism. Our analyses will help identifying signs of local
acclimatisation, which would be visible
if copepods show population-specific metabolome profiles in response to altered ocean
chemistry. Moreover,
breakpoint analyses will be used to characterise potential abrupt changes in the
relationships between the
pCO 2 stress gradient and copepods’ metabolomics response. Our work will provide
crucial insights to help
predicting the long-term impacts of OA on C. glacialis populations.

Consequences of local adaptation/in situ acclimatisation of an Arctic copepod on its metabolomics response to an ocean acidification gradient

General biotic and abiotic contamination of water bodies is widely recognised. Zebra mussel (ZM) is commonly used in biomonitoring of water quality for its capacity to filter a great volume of water, and accumulate contaminants present in aquatic environments. The ZM’s digestive gland is a key organ in assessing the health status of the organism and concentrates high amounts of naturally occurring mixtures and pollutants. ZMs’ organs can adequately present the aquatic environment's health status and “early warning” for biomonitoring. The gut microbiota may significantly influence health and responses to environmental stressors of the organisms. The interaction between sentinel species and their microbiota has prompted questions, especially regarding their potential as indicators in environmental monitoring. Nevertheless, environmental factors can impact the composition and metabolism of gut microbiota responsible for breaking down and detoxifying xenobiotics.
To advance our understanding of microbiota's role, we conducted both field and controlled studies. The first aim assesses the gut microbiota composition (16s rDNA sequencing) and physiological state in ZMs in-situ. The organisms were caged for 21 days in oligotrophic to eutrophic sites varying in food sources, bacterial load and water chemistry. In parallel, controlled experiments aimed to determine the optimal conditions (food quantity) for maximizing the filtration rate and effective removal of microorganisms. It occurred with the initial algae concentration of 10^5cells/mL and microbial populations at 10^5UFC/mL. Higher filtration rates cause higher contact with contaminants and feeding. This first step will enable us to investigate the impact of stressors under laboratory conditions on gut microbiota.


How Does the Gut Microbiota of Zebra Mussels (Dreissena polymorpha) Serve as a Key Indicator of Organism and Aquatic Health?

Mussels from the Mytilus edulis species complex are euryhaline osmoconformers that adjust their internal osmolarity to match that of their surroundings. This adaptive strategy poses a significant challenge to the metabolic machinery of the mussels, including mitochondria. An earlier study showed that mussels from different populations achieve optimal mitochondrial respiration at salinities near their prevailing habitat salinity. Given the euryhaline biology of mussels, we hypothesised that osmotic optima for the mitochondrial function will show plasticity to salinity acclimation. To test this hypothesis, mussels from the southern Baltic Sea (Mytilus edulis x trossulus transition zone) were acclimated to either 6 (hypoosmotic) or 15 (control) salinity and the mitochondrial performance curve was generated by measuring respiration of isolated hepatopancreas mitochondria at a range of osmotic concentrations (230–915 mOsm/kg). We found that the optima of the oxidative phosphorylation (OXPHOS, indicative of ATP synthesis capacity) and mitochondrial coupling were shifted towards a lower osmolality under hypoosmotic conditions. Additionally, the OXPHOS respiration was consistently higher, while efflux of reactive oxygen species (ROS) and fractional electron leak were lower in mussels acclimated to salinity 6 compared to those at salinity 15. This response of mitochondria from hypoosmotically exposed mussels resembles that of mitochondria from north Baltic Sea mussels (M. trossulus) that were collected and acclimated at their natural salinity (6) in a previous study. Thus, it appears as though a salinity of 6 offers optimal conditions for mussel populations from the north and south Baltic Sea.

Salinity dependent mitochondrial respiration in mussels of the Mytilus edulis species complex

The Antarctic Ocean is one of the only places on earth where all biological processes happen between -2 and 2°C. At these temperatures, our models for life fall apart. Diffusion, protein folding, energy and metabolism are all processes that are poorly understood in the cold, where processes are slow and energy is scarce. The gap in our understanding of cold-adapted life comes partly from the lack of suitable equipment to properly observe these systems. Our team has recently developed a method to perform high resolution imaging of cold live samples, therefore shedding a new light to observe these systems in physiological conditions. The development of this new method offers perspectives for studying the rate of molecular, cellular and sub-cellular processes. Observing cells from Antarctic animals in vivo reveals some surprising dynamics, in particular when comparing the speed of organelle movement in the cold compared to temperate organelle speed. This opens avenues to investigate how the energy budget of cold-adapted cells is spent, and what survival strategies have evolved from such a constrained environment.
This new microscopy method could also be used to study the dynamics of similar systems when their environment is warming up, or for other applications in biotechnology, including but not limited to questions about phase separation, diffusion models and protein aggregation.


Microscopes and Antarctic fish: How developing high-resolution microscopy for 0°C imaging sheds a new light on cold-adapted systems.

Climatic changes involved an important increase in the global mean surface temperature and frequency of heat waves, being a significant health risk reported in diverse big and medium-sized mammals. The analysis of energy expenditure components is key for understanding the processes of heat loss and thermoregulation. One of the highest heat expenditure activities is feeding; mammal metabolism can increase around 25-50% of the resting metabolic rate (RMR). It has been suggested that smaller animals could exhibit elevated fitness under warmer temperatures; however, this has not been tested on small wild mammals during the postprandial state. We addressed this issue in two non-endangered wild mouse species, the wood mouse (Apodemus sylvaticus) and the Algerian mouse (Mus spretus) kept in laboratory conditions. RMR and postprandial heat increment (HI) were measured by open flow respirometry at cool conditions (20°C) and within the thermoneutral zone (28°C). RMR was measured after overnight fasting of 16 -21 hours. Food was provided at 10% of the animal's body mass to evaluate the HI. We expected that mice would prioritize thermoregulation efficiency to food consumption. At warmer temperatures mice decrease their food intake to reduce HI, allowing efficient thermoregulation without compromising RMR. These adjustments could evidence possible changes in diet selection at higher temperatures related to the nutritional composition to reducing thermogenesis.

Does the Temperature Increment Affect the Post-Prandial Energy Metabolic Rate in Small Wild Animals?

The effect of temperature on biological functions can vary among individuals of the same species according to the environment they inhabit. In this sense, intraspecific variations in the energetic balance can provide insights on microevolutionary processes occurring at the population scale.
The aim of our work was to investigate intraspecific differences in fundamental energetic functions, namely energy acquisition via feeding, energy expenditure via standard metabolic rate, and energy allocation via growth in response to temperature, in a species living along a large latitudinal gradient. We exposed the common periwinkle, Littorina littorea, from 10 different locations in North America, to 12 temperatures (5 to 27 C) in a common garden experiment, and measured survival, feeding rate, growth, metabolic rate, and CTmax. Populations’ thermal performance curves were obtained and suggested that the thermal energy budget differs among different locations. Energy acquisition through feeding and energy allocation to growth differed only for locations at the species limits, which may be subjected to stronger selective pressure. Survival and CTmax were found to be lower at higher temperatures for snails from lower latitudes, this likely reflecting increased energetic needs for maintenance. However, the remarkable differences in the shape of metabolic rate may reflect local variations in energy expenditure strategies. Specifically, snails from different climates may use different strategies to adjust their energy budget to changing temperatures. Our study provides evidence of potential local and clinal adaptation of the investigated species to varying environmental conditions, helping to define its current (and likely future) range limits.


Variations in the energetic balance among populations of a marine gastropod living along a large latitudinal gradient.

Aquatic animals including fish species are being exposed to climate-related stressors such as temperature and hypoxia with increasing severity and frequency. Group living is an adaptive behaviour found in many species, including the majority of fish species, and associated with improved foraging success and protection from predators. As conditions change, however, individual motivations for group living may also change. Individual behaviours such as sociability, exploratory behaviour (boldness), and activity level, may be affected by climate-related stressors. This may lead to changes in group dynamics and shoal disruption. This study used rummy-nose tetra Hemigrammus rhodostomus as a model species, and tested boldness, sociability, and activity level in individuals under three conditions of temperature, and three conditions of oxygen level. Fish were then placed in groups of six under the same set of treatments, and group behaviour monitored for each individual. In this way, we hope to elucidate how individual changes in behaviour will impact group dynamics. We predict that individual sociability will be reduced, and boldness and activity increased, under increased temperature and low oxygen levels and that this will translate to reduced group cohesion under climate stressor conditions. We also predict significant interindividual variation in sociability, boldness, and activity level, and that this will impact the tendency of different individuals to associate together. Our study is the first, to our knowledge, to incorporate climate-related stressors into the study of effects of individual behaviour on group dynamics, and will provide much-needed information on a key adaptive behaviour in a changing world.

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Trehalose transporter gene diversity in the anhydrobiotic brine shrimp Artemia franciscana

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