Czechia

In fishes, the fish pseudobranch is the paired, small hemibranchs of mandibular arch-derived gill tissue. Each pseudobranch receives oxygenated arterial blood and the efferent blood travels to the eyes. In the Nile tilapia (Oreochromis niloticus), the pseudobranch is fully embedded without any freely exposed gill filaments to the water which precludes the typical gill function of gas exchange. The pseudobranch parenchyma cells are rich in mitochondria and have a tubular system similar to gill ionocytes indicating a high metabolic capacity. Despite being identified over 200 years ago, the pseudobranch has remained enigmatic. One hypothesis regarding its function is that it acidifies the blood to aid in oxygen unloading (Root shift) to aid eye oxygen delivery; however, supporting physiological data is lacking. In the present study we used RNAseq to characterize the gene repertoire of the pseudobranch by contrasting expression with gill tissue. We identified 2621 higher and 2502 lower expressed genes (|FC| &gt; 2 p&lt;0.05; PBr:Gill). This notably included higher pseudobranch expression of genes involved in the pentose phosphate shunt, and lactate metabolism as well as ion transport gene isoform differences (eg Na+/K+-ATPase α1a is higher in gill and α1b in pseudobranch). Transporters involved in Na+ uptake (nhe2, ncc2) were higher in gill too. However, the nhe5 was very highly expressed in pseudobranch and using immunohistochemistry Nhe5 was localized to the pillar cells (specialized endothelial cells) of the pseudobranch but not the gills. Together, these results suggest that in tilapia the pseudobranch may be involved in blood acidification.

SEB Conference Prague 2024

Elucidating the function of the enigmatic fish pseudobranch using transcriptomics. Novel expression of the Na+/H+-exchanger 5.

acid-base regulation

fish

rnaseq

In fishes, the fish pseudobranch is the paired, small hemibranchs of mandibular arch-derived gill tissue. Each pseudobranch receives oxygenated arterial blood and the efferent blood travels to the eyes. In the Nile tilapia (Oreochromis niloticus), the pseudobranch is fully embedded without any freely exposed gill filaments to the water which precludes the typical gill function of gas exchange. The pseudobranch parenchyma cells are rich in mitochondria and have a tubular system similar to gill ionocytes indicating a high metabolic capacity. Despite being identified over 200 years ago, the pseudobranch has remained enigmatic. One hypothesis regarding its function is that it acidifies the blood to aid in oxygen unloading (Root shift) to aid eye oxygen delivery; however, supporting physiological data is lacking. In the present study we used RNAseq to characterize the gene repertoire of the pseudobranch by contrasting expression with gill tissue. We identified 2621 higher and 2502 lower expressed genes (|FC| > 2 p<0.05; PBr:Gill). This notably included higher pseudobranch expression of genes involved in the pentose phosphate shunt, and lactate metabolism as well as ion transport gene isoform differences (eg Na+/K+-ATPase α1a is higher in gill and α1b in pseudobranch). Transporters involved in Na+ uptake (nhe2, ncc2) were higher in gill too. However, the nhe5 was very highly expressed in pseudobranch and using immunohistochemistry Nhe5 was localized to the pillar cells (specialized endothelial cells) of the pseudobranch but not the gills. Together, these results suggest that in tilapia the pseudobranch may be involved in blood acidification.

technical paper

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SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

Increasing drought frequency and duration pose a significant threat to fish species in dryland river systems. As ectotherms, thermal and hypoxia tolerances directly determine the capacity of fish species to persist in these environments during low flow periods when water temperatures are high and waterbodies become stratified. Managing the ecological function of dryland river refugia requires an understanding of how chronically elevated temperatures and hypoxia affect fish physiological performance, and their capacity to compensate performance in response. We studied the effects of chronic high temperature (30oC) or chronic hypoxia (50% air saturation) on two species of freshwater fish, golden perch Macquaria ambigua, and Murray cod, Maccullochella peelii. In both species, cross tolerance resulted in improved hypoxia and thermal tolerance limits following acclimation to either chronic hypoxia or high temperature. Physiological plasticity of the heart also resulted following acclimation to hypoxic waters in golden perch, increasing in size to support an elevated oxygen transport capacity. In Murray cod, body size significantly affected thermal and hypoxia responses. Small M. peelii were significantly less hypoxia tolerant than larger individuals, while larger fish were significantly less thermally tolerant than smaller fish. Our data suggests that acclimation to elevated temperature or elevated hypoxia can improve both hypoxia and thermal tolerance limits in some fish species, but that responses man differ across size classes. This information will be critical in developing habitat suitability models to inform policy decisions that serve to balance competing demands on freshwater resources in dryland rivers.

Between a hot place and hypoxia: Physiological responses of fish to high temperature and hypoxia in dryland river systems

Florida Bay’s shallow seagrass beds experience daily diurnal fluctuations in environmental oxygen, leading to hypoxic episodes (PO2 < 2 mg∙L-1, 4.6 kPa) that have increased in recent decades. To survive, the native Gulf toadfish can employ a suite of adaptive cardiorespiratory and metabolic adjustments. Previous work has demonstrated that toadfish reduce heart rate (HF) and increase ventilatory amplitude during moderate hypoxia (PO2 ~2-4 kPa for 20 min). Toadfish also have a regulation index of 0.5, suggesting that they use strategies other than maintaining oxygen consumption to tolerate hypoxia. The objective of this study was to characterize the acute response of Gulf toadfish to severe hypoxia (< 2 kPa). We hypothesized that Gulf toadfish would respond to severe hypoxia by reducing energy expenditure while switching to anaerobic metabolism. Cannulated adult toadfish (0.062 kg ± 0.003; n=29) were exposed to either control conditions (normoxia for 4 h) or hypoxia (PO2 ~ 0.44 kPa for 3 h followed by 1 h recovery). Cardiovascular and ventilatory parameters were monitored and blood samples were taken from both groups at t = 0, 1.5, and 4 h, and analyzed for pH, glucose, lactate, and other endpoints. Hypoxia-exposed fish experienced a ~72% decrease in HF and a ~25% decrease in VF during hypoxia exposure. Moreover, plasma glucose concentrations increased 5-fold, and plasma lactate concentrations increased 10-fold while pH decreased by 2.7% during hypoxia exposure. Our findings support our hypothesis that toadfish survive hypoxia by reducing energy expenditure and switching to anaerobic metabolism.

The key mechanisms associated with the survival of Gulf toadfish, Opsanus beta, when in severe hypoxia

Migratory flight is an intensive exercise that requires birds to maintain high aerobic capacities for many hours or days. Maintaining oxygen supply to flight muscles is therefore important during migration, especially since tracking studies have shown that songbirds will ascend to altitudes of 6,000 m during migratory flight where oxygen is less readily available (hypoxia). Whether there are adaptations or seasonal plasticity along the oxygen cascade and hypoxic chemoreflex that allow songbirds to fly at such high altitudes during the migratory season is unknown. Research during my postdoc has shown that migratory songbirds exhibit seasonal plasticity along the oxygen cascade which enhance oxygen uptake and movement to the flight muscle during migration. This includes changes in breathing pattern, haemoglobin-oxygen binding affinity, and muscle fiber size and phenotype. We have also shown that the magnitude of seasonal plasticity may be dictated by migratory distance and/or whether the songbird species is migratory or resident. Additionally, in yellow-rumped warblers there appears to be a blunted hypoxic chemoreflex in response to flight at high altitude (~3,000 m above sea level). Measurements of adrenaline concentration increased with flight, but were not significantly higher when flight was conducted at high altitude. Together, these findings show that songbirds exhibit seasonal plasticity along the oxygen cascade which would be important for maintain oxygen movement to the flight muscle during high altitude flight.

Seasonal flexibility along the oxygen cascade allows for high-altitude flights in migratory songbirds

In nearshore environments, exposure of marine invertebrates to low pH/low dissolved oxygen (DO) conditions fluctuate over diel timescales. It is unclear how contrasting diel variability along coastal upwelling regions can determine distinct spatial patterns in the exposure of marine populations to such extreme conditions on a daily basis, e.g. ‘upwelling center’ vs. ‘upwelling shadows’. Here, we investigate the interactive effect of diel pH and DO fluctuations on the metabolic performance of different populations of the kelp crab Taliepus dentatus during upwelling and downwelling events. We deployed DO and pH sensors in two different environmentally-contrasting coastal sites in Chile; and then the diurnal cycles of DO and pH were replicated at our laboratory under common-garden conditions. Estimates of metabolic rate and respiratory quotient (RQ) were determined along other biochemical analyses (Hemolymph pH, glucose and lactate). Oceanographic data showed clear diel fluctuations in DO/pH during downwelling, while during upwelling, DO daily cycle was maintained although with extreme hypoxia at night, and the pH diel cycle was decoupled, exposing organisms to quasi-permanent low pH conditions. When mimicking such fluctuations at the Lab, we observed that metabolism was depressed upon low pH/low DO at night. Moreover, upwelling cycle had significant impact on metabolic rates, which was depressed during upwelling. Individuals collected from the active upwelling site showed an increase in hemolymph pH and lactate content in comparison to those from the upwelling shadow, especially during low pH/low DO conditions, suggesting this boosted acid-base balance is one of the compensatory mechanisms for local adaptation.

Decoupling in oxygen and pH fluctuations drive contrasting physiological responses in kelp crabs across an environmental mosaic in a coastal upwelling system

Heatwaves and hypoxic events are major stressors for marine fishes in an era of global change. We investigated impacts of these extreme events on growth and indicators of metabolism in the three genetically distinct populations of European seabass, Atlantic (AT), West and East-Mediterranean (WM, EM). Fish were reared in common garden in three seasonal thermal regimes that reflect their natural environments (eAT 10.2-18.4°C; eWM 12.5-23.0°C; eEM 16.7-28.0°C) and, at peak summer temperature, subsamples were weighed, measured and exposed in triplicate for 10 days to a heatwave (+4°C), hypoxia (50% saturation), heatwave+hypoxia, or control. At the end of the events, weight and length were measured, and blood samples were collected to measure plasma indicators of energy and hydromineral homeostasis (glucose, lactate, triglycerides, protein, calcium, chloride, sodium, osmotic pressure). By comparison to the control, in eAT warming from 18.4 to 22.4°C stimulated feeding and growth, an effect abolished by hypoxia and hypoxia+heatwave. In eWM, there was little effect of heatwave or hypoxia on growth, but heatwave+hypoxia caused some inhibition. In eEM, all the extreme events caused loss of appetite and weight loss. Despite evolving in different thermal environments, the three populations did not differ in the effects of the extreme events on growth, plasma indicators are being analysed. The results demonstrate that heatwaves can be beneficial for growth in cold environments, that seabass are resilient to moderate hypoxia even when in combination to a heatwave, but extreme events clearly have negative effects in warmer environments.

Impacts of heatwaves and hypoxia on three European seabass Dicentrarchus labrax populations reared in three seasonal thermal regimes

This talk will cover my development as a “scholar of teaching and learning”, specifically focusing on my interest in the nexus between teaching and research in Higher Education. 
 
There is plenty of rhetoric about the links between discipline research and teaching/learning, but despite the apparent trend towards research-oriented curricula, there are a number of documented challenges to ensuring meaningful links between these twin missions of higher education.  This talk will explore the mutual benefits of linking teaching and research, introducing an adapted framework that articulates how research can be incorporated into the teaching curriculum, and then exploring how a research-mindset can be employed to improve educational offerings. I’ll describe the barriers and opportunities I have encountered, focusing on the practical steps that all educators can take to enhance their teaching practice and contribute to the Scholarship of Teaching and Learning.


My SoTL journey- a personal perspective

The process of joining compatible plants that then continue to grow together, also known as plant grafting, offers a platform for manipulating agronomically relevant traits spanning both favourable and undesirable traits. In this study, we investigated the changes in crop productivity between eggplant and tomato heterografts using a comprehensive approach that integrates phenotypic, physiologic, and genomic data. We observed that a rootstock can affect the physiology and horticultural trait of the scion. Through genomic analysis and an innovative mapping approach, we identified potential mobile RNA molecules associated to the alteration observed. Our study highlights how grafting could be a valuable tool as an alternative perspective to investigating the molecular basis of phenotypic traits, thereby laying the groundwork for further investigations aimed at optimizing crop yield.

Mobile RNAs and their potential role in grafting-induced traits in Solanaceous heterografts

A limitation of genomic prediction models is that they do not readily incorporate or take into account genotype by environment effects, which decrease the prediction accuracy of genomic selection (GS) across different growing conditions. In a large collaborative project with commercial breeding companies, we tested whether GS prediction accuracy could be improved by taking into account the environmental influence on phenotype by incorporating a large number of phenomic markers using high-throughput field phenotyping methods. To assess the effectiveness of the approach on a scale approximating that of a practical breeding programme, 44 winter wheat elite populations comprising 2,994 lines were grown on two sites contrasting in soil type over two years. Remote sensing data were collected from multi- and hyperspectral cameras mounted on drones and piloted aircraft, and were combined with ground-based visual crop assessment scores and ultra-local spatial variations in soil physical properties. The predictive power for grain yield was tested with or without incorporating genome-wide marker data sets. Models using phenomic traits alone had a greater predictive value (R2 = 0.39–0.47) than genomic data (approximately R2 = 0.1). The average improvement in predictive power by combining trait and marker data was 6%–12% over the best phenomic-only model, and performed best when data from one full location was used to predict the yield on an entire second location. The results suggest that genetic gain can be increased by utilising phenomic data, perhaps most efficiently at early stages of the breeding cycle.

Phenomic and genomic prediction of yield in winter wheat

Understanding crop yield requires navigating the intricate interaction between genotype and environments (GxE), which presents challenges for accurate predictions due to the plant's plastic responses. To study the environmental impacts on grain yield, we addressed two questions: Q1) Do environmental factors affect the consistency (R2trait) of trait performance? Q2) Can physiological relationships between traits across field environments be represented by simulation (APSIM-wheat)? To explore the GxE effect on trait performance of yield (R2yield), we utilise a multi-environment trials (MET) dataset featuring 220 genotypes and 45 environments over three years, five locations and three managements. The management includes combinations of two treatments: total nitrogen fertiliser application (high-HN: 220 kg N ha-1, low-LN: 110 kg N ha-1) and fungicide application (with-WF, without-NF). Resulting three managements are HN_WF, HN_NF and LN_NF. R2trait is calculated using standardised major axis (SMA) regression between two environments grouped by three environmental factors: management, location and year. Trait-trait Pearson correlation (r) was calculated between nine traits in both field and simulation dataset. Our results reveal: 1) significance differences in R2yield between all environmental factors, notably with HN_WF reducing R2yield comparing to HN_NF, indicating varying genotypic responses to fungicide. 2) simulation results confirm a trade-off between grain number and grain protein, but highlight discrepancies in dry matter allocation to grain yield and straw dry matter at maturity between fields and simulation. These insights underscore the indispensable role of understanding environmental influences on trait performance for precise phenotype prediction and crop modelling.

Unravelling yield consistency in winter wheat (Triticum aestivum L.): insights from multi-environment trials and crop simulation

Metabolic rate represents an organism’s cost of living, as it sets its demands for food and oxygen from the environment. Yet, within species, an approximately 2-fold variation in metabolic rate exists among comparable individuals, so that one individual can have twice the metabolic rate of another of the same age, size, and sex. In addition to this variation in metabolic rate at a given size, variation also exists among individuals in how steeply metabolic rate changes (scales) with body size, but the causes and consequences of individual variation in metabolic rate and its scaling relationship with body size are poorly understood. Using examples from my work on fish, I will here discuss how and why there is variation in metabolic rate and its scaling, and what it means for our understanding of the physiology, ecology, and life-history of animals.

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Between a hot place and hypoxia: Physiological responses of fish to high temperature and hypoxia in dryland river systems

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