Czechia

Ammonia is a toxic nitrogenous waste causing ionoregulatory and neuronal dysfunction in aquatic animals. Ammonotelic animals excrete ammonia as is and must have therefore an efficient excretion process in place to keep blood/hemolymph ammonia levels in a tolerable range. While in fish and crustaceans, the excretory mechanism has been investigated in greater detail, the cellular regulation of these processes is rather unknown. To investigate which cellular pathways are involved in ammonia excretion, gills from osmoregulating green crabs were perfused with a hemolymph-like solution containing 500µM NH4Cl, mimicking hemolymph levels found after feeding. Activation of the PKA pathway by adding either Forskolin or 8-Bromo-cAMP, which is known to activate osmoregulatory NaCl uptake in crustaceans, to the perfusion solution caused a significant decrease in the ammonia excretion rate. By contrast, activating the PKG pathway by the addition of 8-Bromo-cGMP, caused an increase of excretion, which was blocked when PKG activity was inhibited via KT5823. When no ammonia was added to either side of the branchial epithelium, metabolic ammonia was released predominantly to the environment. Interestingly, the addition of 8-Bromo-cAMP caused not only an increase of ammoniagenesis, it also promoted that a higher proportion of metabolic ammonia is released towards the hemolymph side, while apical release remained unaltered.

SEB Conference Prague 2024

The cGMP/PKG pathway, but not the cAMP/PKA pathway promotes branchial ammonia excretion in the green shore crab

crustaceans

cellular regulation

ammonia

technical paper

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Mineralised CaCO3 exoskeletons exist in over half of marine invertebrate taxa and are vital for structural support and defence. Calcification of these structures involves seawater uptake of calcium and dissolved inorganic carbon (DIC) and net excretion of generated protons. In crustacea, such as the intensively farmed whiteleg shrimp (Penaeus vannamei), calcification is intermittent due to rhythmic moulting and rehardening of the mineralised exoskeleton. This results in periodically rapid ion and acid-base fluxes, suggesting that exoskeleton growth is tightly coupled to seawater salinity and carbonate chemistry. However, the relationship between seawater ion availability and calcification in crustacea remains poorly characterised. In this study we reveal that mass-specific calcium and DIC uptake in post-moult P. vannamei is among the highest ever recorded in an adult animal and can be maintained in remarkably dilute seawater. Experiments exposing P. vannamei to a range of seawater chemistries, reveal that maximum flux rates of calcium and acid-base equivalents over the 0-2-hr post-moult period are particularly susceptible to adverse seawater chemistry. Substrate-limiting uptake rates can be compensated for over the following 20 hours, although net uptake ceases by 22 hours post-moult, regardless of water chemistry. Importantly, we found that decreased seawater calcium/DIC uptake impacts exoskeletal macrostructure (ratios of mineral, protein, and chitin), as well as calcium carbonate mineralogy. These findings suggest that although P. vannamei exhibits a strong ability to obtain sufficient calcium and DIC for calcification even in extremely dilute seawater, this involves trade-offs to the speed of post-moult mineralisation and exoskeleton composition and structural integrity.

Effects of seawater salinity, [Ca2+] and [DIC] on post-moult calcium and acid-base fluxes in whiteleg shrimp (Penaeus vannamei)

Climate change is one of the greatest challenges of our era, and identifying the most vulnerable populations is urgently needed to guide conservation efforts. Although over 40% of amphibian species are currently listed as threatened, our understanding of their resilience to rising temperatures remains limited. This is primarily because knowledge of thermal tolerance is taxonomically and geographically biased. Data on amphibian heat tolerance limits only covers 7.5% of known species and is geographically biased towards temperate regions. This discrepancy is problematic, considering the high species richness in the tropics and the mounting evidence that tropical ectotherms are most susceptible to rising temperatures. In this study, we aimed to resolve existing biases in physiological data to assess the vulnerability of amphibians to global warming at truly global scales. We first employed a novel data imputation approach to predict the heat tolerance of 60% of amphibian species with high accuracy. We then assessed their vulnerability to daily temperature variation in different thermal refugia (terrestrial, aquatic, arboreal) using biophysical models. We found that 198 out of 5203 species are already exposed to overheating events in shaded terrestrial conditions. Despite accounting for heat tolerance plasticity, a 4°C global temperature increase would create a step-change in impact severity, pushing 9.4% of species beyond their physiological limits. In the Southern Hemisphere, tropical species encounter disproportionally more overheating events, while in the Northern Hemisphere, non-tropical species are more susceptible. Our findings challenge common evidence for latitudinal gradients in overheating risk and underscore the importance of considering climatic variability in vulnerability assessments. Importantly, our predictions lead to clear directives for research and management - pointing to specific populations and species with increased risk, predominantly in under-studied regions of the Global South. Our microclimate-explicit analyses also demonstrate the crucial role vegetation and water bodies play in mitigating the impacts of heat waves on amphibians. Immediate action is needed to preserve and manage these vital microhabitat features.

How vulnerable are amphibians to global warming? 

The interaction of widespread stressors such as nitrate pollution and increasing temperatures associated with climate change are likely to affect aquatic ectotherms such as amphibians. The metamorphic and physiological traits of amphibian larvae during the critical onset of metamorphosis are particularly susceptible to these stressors. We conducted a common-garden experiment using Rana temporaria larvae subjected to four constant acclimation temperatures (18, 22, 26, 28 °C) crossed with three environmentally relevant nitrate concentrations (0, 50, 100 mg × L-1) to investigate the interactive and individual effects of these stressors on metamorphic (i.e., growth and development) and physiological traits (i.e., metabolism and heat tolerance) at the onset of metamorphosis. Larvae exposed to elevated nitrate concentrations and thermal stress displayed increased metabolic rates but decreased developmental rate, highlighting interactive effects of these stressors. However, nitrate pollution alone had no effect on either metamorphic or physiological traits, suggesting that detoxification processes were sufficient to maintain homeostasis but not in combination with increased acclimation temperatures. Furthermore, larvae exposed to nitrate displayed diminished abilities to exhibit temperature-induced plasticity in metamorphosis timing and heat tolerance, as well as reduced acclimation capacity in metabolic rate and heat tolerance to higher temperatures. These results highlight the importance of considering the exposure to multiple stressors when investigating how natural populations respond to global change.

Navigating ontogenetic pathways: amphibian developmental plasticity in a changing world

The skin microbiome is an integral part of its host, capable of aiding in wound healing and defending against pathogens. While the skin microbiome is susceptible to changes due to contact with the environment, it has also been shown to be host- or species-specific, implying that certain microbes play defined roles in the host-microbiome relationship. Bats present an interesting study system for exploring both the protective role and temporal changes in the skin microbiome, as bats alternate between active periods and hibernation throughout the year. During hibernation, a bat’s immune system becomes downregulated, making it more vulnerable to infection by surrounding pathogens. Despite constant exposure to the fungal pathogen responsible for white-nose syndrome in Nearctic bats, Palearctic bats remain uninfected. Symbionts residing on the skin of Palearctic bats may help mitigate infection by increasing the abundance of protective antifungal bacteria, thus defending the bats from fatal infection. To investigate whether the skin microbiome of bats could potentially become more protective during hibernation, we collected swab samples from five European bat species during both the active period and hibernation. A comparison of the sequenced samples will reveal whether the bacterial composition on the skin shifts to contain more bacteria with described antifungal properties during winter, when bats are torpid and exposed to the white-nose pathogen. This information will advance our understanding of how Palearctic bats survive exposure to the deadly fungus and could potentially be used in the development of probiotic treatments aimed at mitigating white-nose syndrome in Nearctic bats.

Seasonal shifts in the skin microbiome of bats and their relevance to bat immunity during hibernation

The gut microbiome is an important mediator of life-history traits in animals and performs essential functions that may allow hosts to exploit novel niches. However, sources of variation in microbiome abundance and composition within vertebrate species are poorly understood, particularly in wild birds. Here, we used 16S rRNA gene sequencing to describe the faecal microbiome of a trans-Saharan migratory passerine species breeding in Central Spain, the pied flycatcher (Ficedula hypoleuca), focusing on small-scale differences in bacterial composition and relative abundance between the natural habitat of the species (oakwood) and a newly created habitat (pinewood) located 1 km apart. We detected a difference in the composition of microbiomes of birds between the habitats, with birds from the oakwood showing a higher abundance of several bacterial taxa, such as Actinobacteriota and Proteobacteria. We observed no microbiome differences according to individual characteristics such as sex or age, although nestlings and females showed a higher abundance of certain bacteria, especially those in the oakwood habitat. We investigated metabolic pathways associated with the microbiome and detected a higher abundance of bacteria with fatty acid biosynthesis and degradation pathways and metabolite precursor and energy generation pathways in oakwood birds compared to pinewood birds. In the pinewood birds, we found a significant increase in bacteria with the L-alanine biosynthesis and pentose phosphate pathways. Our study improves our understanding of the gut microbiome composition of insectivore passerines and shows that local-scale environmental factors such as habitat are among the most important modulators of avian gut microbiome composition.

Small-scale habitat determines gut microbiota of a migratory passerine on its breeding ground

Healthy microbiota is very important for its host although defining it can be challenging because the composition of the microbiota is very diverse and highly variable depending on, for example, environment, genetics, and host health status. Drastic changes in environment or lifestyle can lead to the imbalance of microbiota. This can be problematic as healthy microbiota have myriad positive functions, including protection of a host from invasion of pathogenic bacteria and modulation of the immune system. We studied the effects of environmental conditions (water temperature and oxygen concentration) on zebrafish skin microbiota. We found that genotype did not have an effect on skin microbiota composition and extreme changes in water temperature only had a relatively minor effect. We further demonstrated that zebrafish skin microbiota composition changed when water temperature and oxygen concentration were altered but these perturbations did not permanently shift skin microbiota composition. Finally, we compared gut microbiota composition of healthy horses and horses suffering from inflammatory bowel disease (IBD). We show that IBD did not cause a dysbiosis in the entire gut microbiota but only approximately 200 OTUs (less than 1% of all analyzed OTUs) showed a significant increase or decrease in response to IBD. However, a metabolomic analysis revealed that the functioning of microbiota differed between healthy and IBD-horses. Overall, our results show that while zebrafish skin and horse gut microbiota appear robust and resilient to perturbations. However, a closer look revealed that the abundance of certain pathogenic bacteria was increased and microbiota metabolic were functions altered.

The robustness and resilience of skin and gut microbiota

Organisms require resources for growth, reproduction, and survival. However, due to limited resources, organisms must trade off limited resources among competing processes. They sense and monitor the availability of nutrients using nutrient-sensing pathways, which can initiate physiological changes or modify gene expression. Previous studies have proposed that the mechanistic target of rapamycin (mTOR), a signalling pathway, plays a fundamental role in facilitating adaptive plasticity when individuals face limitations in their energy resources. Despite the fundamental importance of this process in evolutionary biology, how nutritional limitation is regulated through the expression of genes governing this pathway and its consequential effects on fitness remain understudied, particularly in birds. We employed dietary restriction to mimic resource depletion and investigated its impact on body mass, reproduction, and gene expression in Japanese quails (Coturnix japonica). Quails were exposed to feeding at 20%, 30%, and 40%, restriction levels or ad libitum for 2 weeks. All restricted groups had reduced body mass, although decreases in the number and egg mass were only found in severe restrictions.Additionally, restriction reduced the expression of mTOR and insulin-like growth factor-1 (IGF1) genes, whereas the ribosomal protein S6 kinase-1 (RPS6K1) and autophagy-related genes (ATG9A and ATG5) were increased. Proportionally higher reproductive investment was associated with individual variation in mTOR expression. Furthermore, we observed sex-specific responses to body mass and gene expression, indicating that sexes can cope with nutritional deficits differently and emphasise the importance of considering sexual differences in studies of dietary restriction.

Nutrient-sensing genes expression mediate resource allocation in Japanese quails

Regulating the Organelle Band Organization in Male Meiosis of Arabidopsis
Yingrui Ma
Meiosis is a unique cell division process for sexual reproduction in plants and animals. In the meiotic cell cycle, a single round of DNA replication is followed by two rounds of chromosome division, called meiosis I and meiosis II. After Meiosis I, the divided homologous chromosomes are separated by the newly synthesized cell wall or a cell wall like structure. In dicotyledons, instead of a real cell wall, a band structure consisting of vesicles derived from different organelles, called an organelle band, is formed after the first chromosome division. The disruption of this structure in meiosis II can result in nuclear restitution and production of unreduced gametes. The mutation that leads to the disorder of the organelle band is named jason (jas). In this study, a suppressor of jas, called pel, was obtained through forward genetic screening. PEL is a vesicle membrane located protein, and located in the cytoplasm during meiotic cell cycle. The recovered organelle band in jas pel is sensitive to exocytotic vesicle trafficking inhibitors, suggesting that exocytotic vesicle trafficking pathway is important for organelle band maintenance in jas pel. Furthermore, destabilized actin filaments are found to partially recover the jas phenotype. vesicles can be transferred through actin filament, PEL and PEL interaction proteins transfer of exocytotic vesicles through actin filaments within male meiocytes. Taken together, this research suggests a process which involved exocytotic vesicle trafficking and actin dynamic to maintain the organelle band, acting as a physical barrier to prevent nuclear restitution during male meiosis.

Regulating the Organelle Band Organization in Male Meiosis of Arabidopsis

Mentoring programmes can improve the attainment and retention of minoritized students in higher education, but schemes vary widely in their design and delivery. Universities have been urged to measure the effect of such programmes and to identify their most effective features at a local level. PEMENTOS (PEer MEntoring TO Succeed) was designed as such. Mentors and mentees were asked to arrange a number of in-person, one-hour “core meetings”. Mentors attended a mid-point review meeting, and both mentors and mentees were invited to attend an end-of-programme meeting. Pre- and post-intervention surveys showed that the sampled mentees were statistically significantly more confident and less worried about university life at the end of the programme than they were to start with. The biggest increases in confidence were seen in response to the statements “I feel confident about managing my time” and “I feel confident about planning my revision”, and the biggest reductions in worry were seen in response to the statement “I feel worried about adapting to university life” and “I feel worried about how to meet people and make friends”. Non-white mentees reported a greater increase in confidence about socializing with their peers and about managing their finances than white mentees did. We found that mentees logged in to our VLE at almost twice the rate of non-participants, and the fraction of assessment submissions was higher for mentees than for mentors and non-participants. Class attendance was also higher for mentees than non-participants, painting an encouraging picture of enhanced engagement among PEMENTOS participants.

PEMENTOS: An EDI-Focused Peer-Mentoring Scheme

For most organisms, the correct functioning of the immune system is essential to deal with pathogens and parasites. However, immune activation does not come without a cost. Indeed, immune activation is expected to trade off different reproductive components, potentially leading to accelerated reproductive senescence and even affecting the life history trajectories of offspring. We have recently investigated these questions in male field crickets (G. bimaculatus) using a combination of experimental approaches. Results from these long-term studies indicate that immune system activation reduces male investment in some but not all reproductive components. Immune-challenged males reduced their investment in mate attraction (i.e. calling effort) and courtship behaviour over time but did not alter their sperm production. Curiously, although sperm production was unaffected, immune-challenged males prioritised their resources for sperm protection, resulting in reduced accumulation of sperm damage, including DNA, and increased fertility. In addition, we found strong evidence that such immune-induced changes in the male germ line integrity have both short- and long-term intergenerational effects. The young offspring of immune-challenged males developed higher levels of activity and exploratory behaviour (i.e. bolder personalities), behavioural changes that even persisted into adulthood and led to different ageing trajectories. Overall, our findings highlight how immune activation can accelerate the decline of some reproductive traits, but suggest that males may respond to such reproductive costs by prioritising germline protection, with long-term consequences for offspring life-history trajectories. Furthermore, our results highlight the complex interplay between immune function, reproductive senescence and offspring phenotypes, providing valuable insights into evolutionary dynamics.

The cGMP/PKG pathway, but not the cAMP/PKA pathway promotes branchial ammonia excretion in the green shore crab

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Effects of seawater salinity, [Ca2+] and [DIC] on post-moult calcium and acid-base fluxes in whiteleg shrimp (Penaeus vannamei)

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The cGMP/PKG pathway, but not the cAMP/PKA pathway promotes branchial ammonia excretion in the green shore crab

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Next from SEB Conference Prague 2024

Effects of seawater salinity, [Ca2+] and [DIC] on post-moult calcium and acid-base fluxes in whiteleg shrimp (Penaeus vannamei)

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

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RESOURCES

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