Environmental DNA-based biodiversity profiling along the Houdong River in north-eastern Taiwan

Background

This paper describes two datasets: species occurrences, which were determined by environmental DNA (eDNA) metabarcoding and their associated DNA sequences, originating from a research project which was carried out along the Houdong River (), Jiaoxi Township, Yilan, Taiwan. The Houdong River begins at an elevation of 860 m and flows for approximately 9 km before it empties into the Pacific Ocean. Meandering through mountains, hills, plains and alluvial valleys, this short river system is representative of the fluvial systems in Taiwan. The primary objective of this study was to determine eukaryotic species occurrences in the riverine ecosystem through the use of the eDNA analysis. The second goal was, based on the current dataset, to establish a metabarcoding eDNA data template that will be useful and replicable for all users, particularly the Taiwan community. The species occurrence data are accessible at the Global Biodiversity Information Facility (GBIF) portal and its associated DNA sequences have been deposited in the European Nucleotide Archive (ENA) at EMBL-EBI, respectively. A total of 12 water samples from the study yielded an average of 1.5 million reads. The subsequent species identification from the collected samples resulted in the classification of 432 Operational Taxonomic Units (OTUs) out of a total of 2,734. Furthermore, a total of 1,356 occurrences with taxon matches in GBIF were documented (excluding 4,941 incertae sedis, accessed 05-12-2023). These data will be of substantial importance for future species and habitat monitoring within the short river, such as assessment of biodiversity patterns across different elevations, zonations and time periods and its correlation to water quality, land uses and anthropogenic activities. Further, these datasets will be of importance for regional ecological studies, in particular the freshwater ecosystem and its status in the current global change scenarios.

New information

The datasets are the first species diversity description of the Houdong River system using either eDNA or traditional monitoring processes.

Gluconeogenesis in the extraembryonic yolk syncytial layer of the zebrafish embryo

Yolk-consuming (lecithotrophic) embryos of oviparous animals, such as those of fish, need to make do with the maternally derived yolk. However, in many cases, yolk possesses little carbohydrates and sugars, including glucose, the essential monosaccharide. Interestingly, increases in the glucose content were found in embryos of some teleost fishes; however, the origin of this glucose has been unknown. Unveiling new metabolic strategies in fish embryos has a potential for better aquaculture technologies. In the present study, using zebrafish, we assessed how these embryos obtain the glucose. We employed stable isotope (13C)-labeled substrates and injected them to the zebrafish embryos. Our liquid chromatography-mass spectrometry-based isotope tracking revealed that among all tested substrate, glutamate was most actively metabolized to produce glucose in the zebrafish embryos. Expression analysis for gluconeogenic genes found that many of these were expressed in the yolk syncytial layer (YSL), an extraembryonic tissue found in teleost fishes. Generation 0 (G0) knockout of pck2, a gene encoding the key enzyme for gluconeogenesis from Krebs cycle intermediates, reduced gluconeogenesis from glutamate, suggesting that this gene is responsible for gluconeogenesis from glutamate in the zebrafish embryos. These results showed that teleost YSL undergoes gluconeogenesis, likely contributing to the glucose supplementation to the embryos with limited glucose source. Since many other animal lineages lack YSL, further comparative analysis will be interesting.

Anthropogenic nitrogen pollution inferred by stable isotope records of crustose coralline algae

Since reef ecosystems can offer intricate habitats for various marine organisms, calcified reefs may contain valuable long-term environmental data. This study investigated stable isotopic composition of marine organisms from the Taoyuan and Linshanbi crustose coralline algae (CCA) reef ecosystems to understand sewage pollution. CCA samples from Taoyuan (Palaeo Xin A: ∼1000 years old and Palaeo G: ∼7000 years old) and Linshanbi (Palaeo L: ∼7000 years old and modern CCA) had significantly lower δ15N values (2.5-5.6 ‰) compared to modern CCA from Taoyuan (10.2 ± 1.2 ‰). Intertidal organisms from the Taoyuan CCA reef also showed higher δ15N values than those from Linshanbi CCA reef, indicating anthropogenic stress in both ecosystems. Long-term pollution monitoring and effective strategies to mitigate sewage pollution are recommended for these CCA reef ecosystems.

Single-worm long-read sequencing reveals genome diversity in free-living nematodes

Obtaining sufficient genetic material from a limited biological source is currently the primary operational bottleneck in studies investigating biodiversity and genome evolution. In this study, we employed multiple displacement amplification (MDA) and Smartseq2 to amplify nanograms of genomic DNA and mRNA, respectively, from individual Caenorhabditis elegans. Although reduced genome coverage was observed in repetitive regions, we produced assemblies covering 98% of the reference genome using long-read sequences generated with Oxford Nanopore Technologies (ONT). Annotation with the sequenced transcriptome coupled with the available assembly revealed that gene predictions were more accurate, complete and contained far fewer false positives than de novo transcriptome assembly approaches. We sampled and sequenced the genomes and transcriptomes of 13 nematodes from early-branching species in Chromadoria, Dorylaimia and Enoplia. The basal Chromadoria and Enoplia species had larger genome sizes, ranging from 136.6 to 738.8 Mb, compared with those in the other clades. Nine mitogenomes were fully assembled, and displayed a complete lack of synteny to other species. Phylogenomic analyses based on the new annotations revealed strong support for Enoplia as sister to the rest of Nematoda. Our result demonstrates the robustness of MDA in combination with ONT, paving the way for the study of genome diversity in the phylum Nematoda and beyond.

Duplicated paralog of sulfide: Quinone oxidoreductase contributes to the adaptation to hydrogen sulfide-rich environment in the hydrothermal vent crab, Xenograpsus testudinatus

The hydrothermal crab, Xenograpsus testudinatus (xtcrab) inhabits shallow-water, hydrogen sulfide (H₂S)-rich hydrothermal vent regions. Until now, the adaptative strategy of xtcrab to this toxic environment was unknown. Herein, we investigated the sulfide tolerance and detoxification mechanisms of xtcrabs collected in their high-sulfide hydrothermal vent habitat. Experimental immersion of xtcrab in various sulfide concentrations in the field or in aquaria assessed its high sulfide tolerance. HPLC measurement of hemolymph sulfur compounds highlighted xtcrab detoxification capacity via catabolism of sulfide into much less toxic thiosulfate. We focused on a key enzyme for H₂S detoxification, sulfide: quinone oxidoreductase (SQR). Cloning and phylogenetic analysis revealed two SQR paralogs in xtcrab, that we named xtSQR1 and xtSQR2. As shown by qPCR, xtSQR2 and xtSQR1 were expressed in the digestive gland, suggesting the involvement of both paralogs in the detoxification of food-related H₂S. In contrast, xtSQR1 transcript was highly expressed in the gill, while xtSQR2 was not detectable, suggesting a specific role of SQR1 in gill detoxification of H₂S of environmental origin. Comparison between xtcrabs in their hydrogen sulfide-rich hydrothermal habitat, and xtcrabs maintained for one month in sulfide-free seawater aquarium, showed higher transcript levels of gill xtSQR1 in sulfide-rich habitat, further supporting the specific role of xtSQR1 paralog in environmental H₂S detoxification in the gill. Gill SQR protein level as measured by Western blot, and gill SQR enzyme activity were also higher in sulfide-rich habitat. Immunohistochemical staining further showed that SQR expression was co-localized with Na⁺/K⁺-ATPase-positive epithelial and pillar cells of the gill filament. This is the first evidence of duplicate SQR genes in crustaceans. Overall, our study suggests that the subfunctionalization of duplicate xtSQR genes may play an important role in sulfide detoxification to maintain the sulfide homeostasis in X. testudinatus, providing an ecophysiological basis for its adaptation to the high-sulfide hydrothermal vent environment.

Cellular mechanisms underlying extraordinary sulfide tolerance in a crustacean holobiont from hydrothermal vents

The shallow-water hydrothermal vent system of Kueishan Island has been described as one of the world's most acidic and sulfide-rich marine habitats. The only recorded metazoan species living in the direct vicinity of the vents is Xenograpsus testudinatus, a brachyuran crab endemic to marine sulfide-rich vent systems. Despite the toxicity of hydrogen sulfide, X. testudinatus occupies an ecological niche in a sulfide-rich habitat, with the underlying detoxification mechanism remaining unknown. Using laboratory and field-based experiments, we characterized the gills of X. testudinatus that are the major site of sulfide detoxification. Here sulfide is oxidized to thiosulfate or bound to hypotaurine to generate the less toxic thiotaurine. Biochemical and molecular analyses demonstrated that the accumulation of thiosulfate and hypotaurine is mediated by the sodium-independent sulfate anion transporter (SLC26A11) and taurine transporter (Taut), which are expressed in gill epithelia. Histological and metagenomic analyses of gill tissues demonstrated a distinct bacterial signature dominated by Epsilonproteobacteria. Our results suggest that thiotaurine synthesized in gills is used by sulfide-oxidizing endo-symbiotic bacteria, creating an effective sulfide-buffering system. This work identified physiological mechanisms involving host-microbe interactions that support life of a metazoan in one of the most extreme environments on our planet.

Temperature increases induce metabolic adjustments in the early developmental stages of bigfin reef squid (Sepioteuthis lessoniana)

Climate changes, such as extreme temperature shifts, can have a direct and significant impact on animals living in the ocean system. Ectothermic animals may undergo concerted metabolic shifts in response to ambient temperature changes. The physiological and molecular adaptations in cephalopods during their early life stages are largely unknown due to the challenge of rearing them outside of a natural marine environment. To overcome this obstacle, we established a pelagic bigfin reef squid (Sepioteuthis lessoniana) culture facility, which allowed us to monitor the effects of ambient thermal elevation and fluctuation on cephalopod embryos/larvae. By carefully observing embryonic development in the breeding facility, we defined 23 stages of bigfin reef squid embryonic development, beginning at stage 12 (blastocyst; 72 h post-egg laying) and continuing through hatching (~1 month post-egg laying). Since temperature recordings from the bigfin reef squid natural habitats have shown a steady rise over the past decade, we examined energy substrate utilization and cellular/metabolic responses in developing animals under different temperature conditions. As the ambient temperature increased by 7 °C, hatching larvae favored aerobic metabolism by about 2.3-fold. Short-term environmental warming stress inhibited oxygen consumption but did not affect ammonium excretion in stage (St.) 25 larvae. Meanwhile, an aerobic metabolism-related marker (CoxI) and a cellular stress-responsive marker (HSP70) were rapidly up-regulated upon acute warming treatments. In addition, our simulations of temperature oscillations mimicking natural daily rhythms did not result in significant changes in metabolic processes in St. 25 animals. As the ambient temperature increased by 7 °C, referred to as heatwave conditions, CoxI, HSP70, and antioxidant molecule (SOD) were stimulated, indicating the importance of cellular and metabolic adjustments. As with other aquatic species with high metabolic rates, squid larvae in the tropical/sub-tropical climate zone undergo adaptive metabolic shifts to maintain physiological functions and prevent excessive oxidative stress under environmental warming.

Teleostean fishes may have developed an efficient Na+ uptake for adaptation to the freshwater system

Understanding Na⁺ uptake mechanisms in vertebrates has been a research priority since vertebrate ancestors were thought to originate from hyperosmotic marine habitats to the hypoosmotic freshwater system. Given the evolutionary success of osmoregulator teleosts, these freshwater conquerors from the marine habitats are reasonably considered to develop the traits of absorbing Na⁺ from the Na⁺-poor circumstances for ionic homeostasis. However, in teleosts, the loss of epithelial Na⁺ channel (ENaC) has long been a mystery and an issue under debate in the evolution of vertebrates. In this study, we evaluate the idea that energetic efficiency in teleosts may have been improved by selection for ENaC loss and an evolved energy-saving alternative, the Na⁺/H⁺ exchangers (NHE3)-mediated Na⁺ uptake/NH₄⁺ excretion machinery. The present study approaches this question from the lamprey, a pioneer invader of freshwater habitats, initially developed ENaC-mediated Na⁺ uptake driven by energy-consuming apical H⁺-ATPase (VHA) in the gills, similar to amphibian skin and external gills. Later, teleosts may have intensified ammonotelism to generate larger NH₄⁺ outward gradients that facilitate NHE3-mediated Na⁺ uptake against an unfavorable Na⁺ gradient in freshwater without consuming additional ATP. Therefore, this study provides a fresh starting point for expanding our understanding of vertebrate ion regulation and environmental adaptation within the framework of the energy constraint concept.

Multigenerational inspections of environmental thermal perturbations promote metabolic trade-offs in developmental stages of tropical fish

Global warming both reduces global temperature variance and increases the frequency of extreme weather events. In response to these ambient perturbations, animals may be subject to trans- or intra-generational phenotype modifications that help to maintain homeostasis and fitness. Here, we show how temperature-associated transgenerational plasticity in tilapia affects metabolic trade-offs during developmental stages under a global warming scenario. Tropical tilapia reared at a stable temperature of 27 °C for a decade were divided into two temperature-experience groups for four generations of breeding. Each generation of one group was exposed to a single 15 °C cold-shock experience during its lifetime (cold-experienced CE group), and the other group was kept stably at 27 °C throughout their lifetimes (cold-naïve CN group). The offspring at early life stages from the CE and CN tilapia were then assessed by metabolomics-based profiling, and the results implied that parental cold-experience might affect energy provision during reproduction. Furthermore, at early life stages, progeny may be endowed with metabolic traits that help the animals cope with ambient temperature perturbations. This study also applied the feature rescaling and Uniform Manifold Approximation and Projection (UMAP) to visualize metabolic dynamics, and the result could effectively decompose the complex omic-based datasets to represent the energy trade-off variability. For example, the carbohydrate to free amino acid conversion and enhanced compensatory features appeared to be hypothermic-responsive traits. These multigenerational metabolic effects suggest that the tropical ectothermic tilapia may exhibit transgenerational phenotype plasticity, which could optimize energy allocation under ambient temperature challenges. Knowledge about such metabolism-related transgenerational plasticity effects in ectothermic aquatic species may allow us to better predict how adaptive mechanisms will affect fish populations in a climate with narrow temperature variation and frequent extreme weather events.

The Ovarian Transcriptome at the Early Stage of Testis Removal-Induced Male-To-Female Sex Change in the Protandrous Black Porgy Acanthopagrus schlegelii

Unlike gonochoristic fishes, sex is fixed after gonadal differentiation (primary sex determination), and sex can be altered in adults (secondary sex determination) of hermaphroditic fish species. The secondary sex determination of hermaphroditic fish has focused on the differences between testicular tissue and ovarian tissue during the sex change process. However, comprehensive studies analyzing ovarian tissue or testicular tissue independently have not been performed. Hermaphroditic black porgy shows a digonic gonad (ovarian tissue with testicular tissue separated by connective tissue). Protandrous black porgy has stable maleness during the first two reproductive cycles (<2 years old), and approximately 50% enter femaleness (natural sex change) during the third reproductive cycle. Precocious femaleness is rarely observed in the estradiol-17β (E2)-induced female phase (oocytes maintained at the primary oocyte stage), and a reversible female-to-male sex change is found after E2 is withdrawn in <2-year-old fish. However, precocious femaleness (oocytes entering the vitellogenic oocyte stage) is observed in testis-removed fish in <2-year-old fish. We used this characteristic to study secondary sex determination (femaleness) in ovarian tissue via transcriptomic analysis. Cell proliferation analysis showed that BrdU (5-bromo-2′-deoxyuridine)-incorporated germline cells were significantly increased in the testis-removed fish (female) compared to the control (sham) fish (male) during the nonspawning season (2 months after surgery). qPCR analysis showed that there were no differences in pituitary-releasing hormones (lhb and gtha) in pituitary and ovarian steroidogenesis-related factors (star, cyp11a1, hsd3b1, and cyp19a1a) or female-related genes (wnt4a, bmp15, gdf9, figla, and foxl2) in ovarian tissues between intact and testis-removed fish (2 months after surgery). Low expression of pituitary fshb and ovarian cyp17a1 was found after 2 months of surgery. However, we did find small numbers of genes (289 genes) showing sexual fate dimorphic expression in both groups by transcriptomic analysis (1 month after surgery). The expression profiles of these differentially expressed genes were further examined by qPCR. Our present work identified several candidate genes in ovarian tissue that may be involved in the early period of secondary sex determination (femaleness) in black porgy. The data confirmed our previous suggestion that testicular tissue plays an important role in secondary sex determination in protandrous black porgy.

Involvement of IGF-1R-PI3K-AKT-mTOR pathway in increased number of GnRH3 neurons during androgen-induced sex reversal of the brain in female tilapia

The neuroplastic mechanism of sex reversal in the fish brain remains unclear due to the difficulty in identifying the key neurons involved. Mozambique tilapia show different reproductive behaviours between sexes; males build circular breeding nests while females hold and brood fertilized eggs in their mouth. In tilapia, gonadotropin-releasing hormone 3 (GnRH3) neurons, located in the terminal nerve, regulate male reproductive behaviour. Mature males have more GnRH3 neurons than mature females, and these neurons have been indicated to play a key role in the androgen-induced female-to-male sex reversal of the brain. We aimed to elucidate the signalling pathway involved in the androgen-induced increase in GnRH3 neurons in mature female tilapia. Applying inhibitors to organotypic cultures of brain slices, we showed that the insulin-like growth factor (IGF)-1 receptor (IGF-1R)/PI3K/AKT/mTOR pathway contributed to the androgen-induced increase in GnRH3 neurons. The involvement of IGF-1 and IGF-1R in 11-ketotestosterone (11-KT)-induced development of GnRH3 neurons was supported by an increase in Igf-1 mRNA shortly after 11-KT treatment, the increase of GnRH3 neurons after IGF-1 treatment and the expression of IGF-1R in GnRH3 neurons. Our findings highlight the involvement of IGF-1 and its downstream signalling pathway in the sex reversal of the tilapia brain.

Adaptive metabolic responses in a thermostabilized environment: Transgenerational trade-off implications from tropical tilapia

Relatively warm environments caused by global warming enhance the productivity of aquaculture activities in tropical/subtropical regions; however, the intermittent cold stress (ICS) caused by negative Arctic Oscillation can still result in major economic losses. In contrast to endotherms, ectothermic fishes experience ambient temperature as an abiotic factor that is central to performance and survival. Therefore, the occurrence of extreme temperatures caused by climate change has ignited a surge of scientific interest from ecologists, economists and physiologists. In this study, we test the transgenerational effects of rearing cold-experienced (CE) and cold-naïve (CN) strains of tropical tilapia. Our results show that compared to CN tilapia, the CE strain preferentially converts carbohydrates into lipids in liver at a regular temperature of 27 °C. Besides, at a low temperature of 22 °C, the CE strain exhibits a broader aerobic scope than CN fish, and their metabolite profile suggests a metabolic shift towards the utilization of glutamate derivatives. Therefore, in response to thermal perturbations, this transgenerational metabolic adjustment provides evidence into the adaptive trade-off mechanisms in tropical fish. Nevertheless, global warming may result in less thermal variation each year, and the stabilized ambient temperature may cause tropical tilapia to gradually exhibit lower energy deposits in liver. In addition to those habitants in cold and temperate regions, a lack of cold exposure to multiple generations of fish may decrease the native cold-tolerance traits of subtropical/tropical organisms; this notion has not been previously explored in terms of the biological effects under anthropogenic climate change.

To cope with a changing aquatic soundscape: Neuroendocrine and antioxidant responses to chronic noise stress in fish

Anthropogenic underwater noises that change aquatic soundscapes represent an important issue in marine conservation. While it is evident that strong underwater acoustic pollutants may cause significant damage to fish at short ranges, the physiological effects of long-term exposure to relatively quiet but continuous noise are less well understood. Here, we present a summary of the known impacts of long-term underwater noise on hypothalamic-pituitary-interrenal (HPI) axis-mediated physiological responses, oxidant/antioxidant balance, and neurotransmitter regulation in fish. Cortisol is known to play a central role in physiological stress response, most often as a mediator of acute response. However, recent research indicates that noise exposure may also induce chronic corticosteroid responses, which involve increased rates of cortisol turnover. Moreover, continuous noise affects oxidative stress and antioxidant systems in vertebrates and fish, suggesting that oxidative species may mediate some noise-induced physiological responses and make these systems valuable noise stress markers. Lastly, noise stress is also known to affect neurotransmitters in the brain that may cause neurophysiological and behavioral changes. The neurochemical mechanisms underlying observed behavioral disorders in fish after exposure to changing acoustic environments are a topic of active research. Overall, a growing body of evidence suggests that chronic noise pollution could be a threat to fish populations. In future work, systematic and comparative investigations into long-term and transgenerational adaptive neuronal and metabolic responses to noise will be important to understand the physiological patterns and dynamics of noise response relevant to fish conservation.

Estrogen-related receptor γ2 controls NaCl uptake to maintain ionic homeostasis

Estrogen-related receptors (ERRs) are known to function in mammalian kidney as key regulators of ion transport-related genes; however, a comprehensive understanding of the physiological functions of ERRs in vertebrate body fluid ionic homeostasis is still elusive. Here, we used medaka (Oryzias melastigma), a euryhaline teleost, to investigate how ERRs are involved in ion regulation. After transferring medaka from hypertonic seawater to hypotonic freshwater (FW), the mRNA expression levels of errγ2 were highly upregulated, suggesting that Errγ2 may play a crucial role in ion uptake. In situ hybridization showed that errγ2 was specifically expressed in ionocytes, the cells responsible for Na+/Cl- transport. In normal FW, ERRγ2 morpholino knockdown caused reductions in the mRNA expression of Na+/Cl- cotransporter (Ncc), the number of Ncc ionocytes, Na+/Cl- influxes of ionocytes, and whole-body Na+/Cl- contents. In FW with low Na+ and low Cl-, the expression levels of mRNA for Na+/H+ exchanger 3 (Nhe3) and Ncc were both decreased in Errγ2 morphants. Treating embryos with DY131, an agonist of Errγ, increased the whole-body Na+/Cl- contents and ncc mRNA expression in Errγ2 morphants. As such, medaka Errγ2 may control Na+/Cl- uptake by regulating ncc and/or nhe3 mRNA expression and ionocyte number, and these regulatory actions may be subtly adjusted depending on internal and external ion concentrations. These findings not only provide new insights into the underpinning mechanism of actions of ERRs, but also enhance our understanding of their roles in body fluid ionic homeostasis for adaptation to changing environments during vertebrate evolution.

Effects of emersion on acid-base regulation, osmoregulation, and nitrogen physiology in the semi-terrestrial mangrove crab, Helice formosensis

Emersion limits water availability and impairs the gill function of water-breathing animals resulting in a reduced capacity to regulate respiratory gas exchange, acid-base balance, and nitrogenous waste excretion. Semi-terrestrial crustaceans such as Helice formosensis mitigate these physiological consequences by modifying and recycling urine and branchial water shifting some branchial workload to the antennal glands. To investigate how this process occurs, Helice formosensis were emersed for up to 160 h and their hemolymph and urinary acid-base, nitrogenous waste, free amino acids, and osmoregulatory parameters were investigated. Upon emersion, crabs experienced a respiratory acidosis that is restored by bicarbonate accumulation and ammonia reduction within the hemolymph and urine after 24 h. Prolonged emersion caused an overcompensatory metabolic alkalosis potentially limiting the crab's ability to remain emersed. During the alkalosis, hemolymph ammonia was maintained at control levels while urinary ammonia remained reduced by 60% of control values. During emersion, ammonia may be temporarily converted to alanine as part of the Cahill cycle until re-immersion where crabs can revert alanine to ammonia for excretion coinciding with the crabs' observed delayed ammonia excretion response. The presence of high hemolymph alanine concentrations even when immersed may indicate this cycle's use outside of emersion or in preparation for emersion. Furthermore, H. formosensis appears to be uniquely capable of actively suppressing its rate of desiccation in absence of behavioral changes, in part by creating hyperosmotic urine that mitigates evaporative water loss.

Threshold and spectral sensitivity of vision in medaka Oryzias latipes determined by a novel template wave matching method

We propose a new analytical method for determining the response threshold in electroretinogram (ERG) in which the wave shows a biphasic slow dc-potential shift. This method uses the recorded wave to the highest intensity stimuli in each wavelength tested as a template wave f(t), and it was compared with other recorded waves obtained under lower intensities g(t). Our test recordings in medaka Oryzias latipes were analogous between the template and the compared waveforms, although there were differences in amplitude and time lag (τ, peak time difference) which occurred as a result of the difference in stimulus intensity. Cross-correlation analysis was applied. Based on the obtained cross-correlation function C_fg(τ) in each comparison, τ was determined as the time lag at which the cross-correlation coefficient R_fg(τ) showed the maximum value. Determined thresholds that were based on both the experimenter's visual inspection and this new method agreed well when the adoption condition was set to satisfy R(τ) ≥ 0.7 and τ ≤ 150 ms in scotopic or τ ≤ 120 ms in photopic conditions. We concluded that this "template wave matching method" is a quick and reliable objective assessment that can be used to determine the threshold. This study analyzed ERG recordings in response to 6 kinds of wavelength light stimuli (380 nm to 620 nm) at different photon flux densities. We report the threshold levels and relative spectral sensitivities in scotopic and photopic vision of medaka.

Insulin-like growth factor 1 triggers salt secretion machinery in fish under acute salinity stress

Timely adjustment of osmoregulation upon acute salinity stress is essential for the survival of euryhaline fish. This rapid response is thought to be tightly controlled by hormones; however, there are still questions unanswered. In this work, we tested the hypothesis that the endocrine hormone, insulin-like growth factor 1 (Igf1), a slow-acting hormone, is involved in the activation of salt secretion mechanisms in euryhaline medaka (Oryzias melastigma) during acclimation to acute salinity stress. In response to a 30-ppt seawater (SW) challenge, Na+/Cl- secretion was enhanced within 0.5 h, with concomitant organization of ionocyte multicellular complexes and without changes in expression of major transporters. Igf1 receptor inhibitors significantly impair the Na+/Cl- secretion and ionocyte multicellular complex responses without affecting transporter expression. Thus, Igf1 may activate salt secretion as part of the teleost response to acute salinity stress by exerting effects on transporter function and enhancing the formation of ionocyte multicellular complexes. These findings provide new insights into hormonal control of body fluid ionic/osmotic homeostasis during vertebrate evolution.

High-power structured laser modes: manifestation of quantum Green's function

The distributions of resonant frequencies in an astigmatic cavity are theoretically confirmed to be analogously equivalent to the quantum energy structures of two-dimensional commensurate harmonic oscillators. In the first part [Opt. Lett.45, 4096 (2020)OPLEDP0146-959210.1364/OL.399251] of this two-part series study, the lasing modes were verified to reveal a variety of vortex array structures. Here, in the second part of this two-part series study, the lasing modes are confirmed to agree very well with the quantum Green's functions that correspond to a bundle of Lissajous figures in the high-order regime.

Specialized adaptations allow vent-endemic crabs (Xenograpsus testudinatus) to thrive under extreme environmental hypercapnia

Shallow hydrothermal vent environments are typically very warm and acidic due to the mixing of ambient seawater with volcanic gasses (> 92% CO₂) released through the seafloor making them potential ‘natural laboratories’ to study long-term adaptations to extreme hypercapnic conditions. Xenograpsus testudinatus, the shallow hydrothermal vent crab, is the sole metazoan inhabitant endemic to vents surrounding Kueishantao Island, Taiwan, where it inhabits waters that are generally pH 6.50 with maximum acidities reported as pH 5.50. This study assessed the acid–base regulatory capacity and the compensatory response of X. testudinatus to investigate its remarkable physiological adaptations. Hemolymph parameters (pH, [HCO₃⁻], \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2, [NH₄⁺], and major ion compositions) and the whole animal’s rates of oxygen consumption and ammonia excretion were measured throughout a 14-day acclimation to pH 6.5 and 5.5. Data revealed that vent crabs are exceptionally strong acid–base regulators capable of maintaining homeostatic pH against extreme hypercapnia (pH 5.50, 24.6 kPa \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2) via HCO₃⁻/Cl⁻ exchange, retention and utilization of extracellular ammonia. Intact crabs as well as their isolated perfused gills maintained \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2tensions below environmental levels suggesting the gills can excrete CO₂ against a hemolymph-directed \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{P}}_{{{\text{CO}}_{2} }}$$\end{document}PCO2 gradient. These specialized physiological mechanisms may be amongst the adaptations required by vent-endemic animals surviving in extreme conditions.

High-power structured laser modes: direct generation of a vortex array

The frequency degeneracy induced by the astigmatism in a nearly hemispherical cavity is originally exploited to generate vortex array laser modes with the output power up to 300 mW. The inhomogeneous Helmholtz equation is employed to derive the wave function for manifesting the characteristics of the lasing modes. The theoretical wave function explicitly reveals the role of the Gouy phase in the formation of vortex arrays. Numerical analyses are further performed to confirm that the thermal lensing effect in the laser crystal assists the lasing transverse order to increase with increasing pump power. It is believed that the high efficiency enables the present laser modes to be useful in the applications of structured vortex beams.

Energy and nitrogenous waste from glutamate/glutamine catabolism facilitates acute osmotic adjustment in non-neuroectodermal branchial cells

Maintenance of homeostasis is one of the most important physiological responses for animals upon osmotic perturbations. Ionocytes of branchial epithelia are the major cell types responsible for active ion transport, which is mediated by energy-consuming ion pumps (e.g., Na⁺-K⁺-ATPase, NKA) and secondary active transporters. Consequently, in addition to osmolyte adjustments, sufficient and immediate energy replenishment is essenttableial for acclimation to osmotic changes. In this study, we propose that glutamate/glutamine catabolism and trans-epithelial transport of nitrogenous waste may aid euryhaline teleosts Japanese medaka (Oryzias latipes) during acclimation to osmotic changes. Glutamate family amino acid contents in gills were increased by hyperosmotic challenge along an acclimation period of 72 hours. This change in amino acids was accompanied by a stimulation of putative glutamate/glutamine transporters (Eaats, Sat) and synthesis enzymes (Gls, Glul) that participate in regulating glutamate/glutamine cycling in branchial epithelia during acclimation to hyperosmotic conditions. In situ hybridization of glutaminase and glutamine synthetase in combination with immunocytochemistry demonstrate a partial colocalization of olgls1a and olgls2 but not olglul with Na⁺/K⁺-ATPase-rich ionocytes. Also for the glutamate and glutamine transporters colocalization with ionocytes was found for oleaat1, oleaat3, and olslc38a4, but not oleaat2. Morpholino knock-down of Sat decreased Na⁺ flux from the larval epithelium, demonstrating the importance of glutamate/glutamine transport in osmotic regulation. In addition to its role as an energy substrate, glutamate deamination produces NH₄⁺, which may contribute to osmolyte production; genes encoding components of the urea production cycle, including carbamoyl phosphate synthetase (CPS) and ornithine transcarbamylase (OTC), were upregulated under hyperosmotic challenges. Based on these findings the present work demonstrates that the glutamate/glutamine cycle and subsequent transepithelial transport of nitrogenous waste in branchial epithelia represents an essential component for the maintenance of ionic homeostasis under a hyperosmotic challenge.

Did Acidic Stress Resistance in Vertebrates Evolve as Na+ /H+ Exchanger-Mediated Ammonia Excretion in Fish?

How vertebrates evolved different traits for acid excretion to maintain body fluid pH homeostasis is largely unknown. The evolution of Na⁺ /H⁺  exchanger (NHE)-mediated NH₄ ⁺ excretion in fishes is reported, and the coevolution with increased ammoniagenesis and accompanying gluconeogenesis is speculated to benefit vertebrates in terms of both internal homeostasis and energy metabolism response to acidic stress. The findings provide new insights into our understanding of the possible adaptation of fishes to progressing global environmental acidification. In human kidney, titratable H⁺ and NH₄ ⁺ comprise the two main components of net acid excretion. V-type H⁺ -ATPase-mediated H⁺ excretion may have developed in stenohaline lampreys when they initially invaded freshwater from marine habitats, but this trait is lost in most fishes. Instead, increased reliance on NHE-mediated NH₄ ⁺ excretion is gradually developed and intensified during fish evolution. Further investigations on more species will be needed to support the hypothesis. Also see the video abstract here https://youtu.be/vZuObtfm-34.

Personality and physiological traits predict contest interactions in Kryptolebias marmoratus

Personality and physiological traits often have close relationships with dominance status, but the significance and/or direction of the relationships vary between studies. This study examines whether two personality traits (aggressiveness and boldness) and three physiological traits (testosterone and cortisol levels and oxygen consumption rates) are associated with contest decisions/performance using a mangrove killifish Kryptolebias marmoratus. The results show that individuals that attacked their own mirror images (an aggressiveness index) at higher rates or had higher levels of testosterone were more likely to attack their opponent and win non-escalated contests, while individuals that had higher levels of cortisol were more likely to lose. After the contests, (1) individuals that had attacked their opponents or won had higher post-contest oxygen consumption rates, and (2) individuals that had attacked their opponents also had higher post-contest levels of cortisol. Although no significant correlations were detected among pre-contest physiological traits, post-contest levels of cortisol were positively correlated with oxygen consumption rates. Overall, personality and physiological traits provide useful predictors for the fish's contest decisions/performance. Contest interactions subsequently modified post-contest physiological traits and potentially also promoted associations between them. Nevertheless, the fish's physiological traits remained rather consistent over the entire study period.

Largescale mullet (Planiliza macrolepis) can recover from thermal pollution-induced malformations

It is well known in aquaculture that hyperthermic perturbations may cause skeleton malformations in fish, but this phenomenon has rarely been documented in wild species. One rare location where thermal pollution has increased the proportion of malformed fish in wild population is in the waters near the Kuosheng Nuclear Power Plant in Taiwan. At this site, the threshold temperature and critical exposure time for inducing deformations have not been previously determined. In addition, it was unclear whether juvenile fish with thermal-induced malformations are able to recover when the temperature returns below the threshold. In the present study, juvenile largescale mullet (Planiliza macrolepis) were kept at temperatures ranging from 26°C and 36°C for 1–4 weeks, after which malformed fish were maintained at a preferred temperature of 26°C for another 8 weeks. The vertebrae bending index (VBI) of fish was increased after 2 weeks at 36°C, and deformed vertebral columns were detected by radiography after 4 weeks. However, malformations were not observed in groups kept at or below 34°C. Moreover, at the end of the recovery period, both the VBI and the vertebrae malformations had returned to normal. The results of this study may help to more precisely determine potential environmental impacts of thermal pollution and raise the possibility that the capacity for fish vertebrae to recover from the impacts of chronic thermal exposures may be an important consideration in marine fish conservation.

Androgen induced cellular proliferation, neurogenesis, and generation of GnRH3 neurons in the brain of mature female Mozambique tilapia

The neuroplastic mechanisms in the fish brain that underlie sex reversal remain unknown. Gonadotropin-releasing hormone 3 (GnRH3) neurons control male reproductive behaviours in Mozambique tilapia and show sexual dimorphism, with males having a greater number of GnRH3 neurons. Treatment with androgens such as 11-ketotestosterone (KT), but not 17β-estradiol, increases the number of GnRH3 neurons in mature females to a level similar to that observed in mature males. Compared with oestrogen, the effect of androgen on neurogenesis remains less clear. The present study examined the effects of 11-KT, a non-aromatizable androgen, on cellular proliferation, neurogenesis, generation of GnRH3 neurons and expression of cell cycle-related genes in mature females. The number of proliferating cell nuclear antigen-positive cells was increased by 11-KT. Simultaneous injection of bromodeoxyuridine and 11-KT significantly increased the number of newly-generated (newly-proliferated) neurons, but did not affect radial glial cells, and also resulted in newly-generated GnRH3 neurons. Transcriptome analysis showed that 11-KT modulates the expression of genes related to the cell cycle process. These findings suggest that tilapia could serve as a good animal model to elucidate the effects of androgen on adult neurogenesis and the mechanisms for sex reversal in the fish brain.

Assimilation of nitrogen and carbon isotopes from fish diets to otoliths as measured by nanoscale secondary ion mass spectrometry

RATIONALE

Nitrogen and carbon stable isotope ratios (δ¹⁵ N and δ¹³ C values) of carbonate-bound organic materials in otoliths can provide information to address the biological and ecological functions of fish. Correct interpretation of otolith δ¹⁵ N and δ¹³ C profiles requires knowledge of the metabolic routes of nitrogen and carbon isotopes. However, the isotopic assimilation of δ¹⁵ N and δ¹³ C compositions from diets to otoliths has rarely been investigated.

METHODS

This study traced the daily nitrogen and carbon isotopic assimilation between diets and otoliths using nanoscale secondary ion mass spectrometry (NanoSIMS). Isotopically labeled algae (Tetraselmis chui) were fed to tilapia (Oreochromis niloticus) for 14-17 days. NanoSIMS and conventional isotope ratio mass spectrometry were used to measure δ¹⁵ N and δ¹³ C variations in the otoliths and fish muscle, respectively.

RESULTS

Otolith δ¹⁵ N values abruptly surged from natural abundance levels by 1000-2300‰ after the fish ate ¹⁵ N-spiked algae with δ¹⁵ N values of approximately 2200‰. However, the δ¹⁵ N values of fish muscle increased to only approximately 500‰ at the end of the feeding experiment. Much higher δ¹⁵ N values (3700-14 000‰) and moderate δ¹³ C values (60-200‰) were detected in the otoliths after the tilapia ate ¹⁵ N- and ¹³ C-spiked algae with a δ¹⁵ N value of 36667‰ and a δ¹³ C value of 272‰. Mapping analysis showed sub-micrometer-scale distribution of ¹⁵ N embedded in the otolith growth increments with a low-to-high δ¹⁵ N signal after the tilapia shifted diets from non-spiked to ¹⁵ N-labeled algae.

CONCLUSIONS

These results suggest that otolith nitrogen and carbon isotopes from food were directly assimilated on the same day. Food is the major and in some cases only source of otolith nitrogen isotopes but makes only a partial contribution to otolith carbon isotopes. Therefore, the δ¹⁵ N values recorded in the sclerochronological layers of the otoliths can be used to determine the trophic levels, food sources and diet changes of fish.

Variability in larval gut pH regulation defines sensitivity to ocean acidification in six species of the Ambulacraria superphylum

The unusual rate and extent of environmental changes due to human activities may exceed the capacity of marine organisms to deal with this phenomenon. The identification of physiological systems that set the tolerance limits and their potential for phenotypic buffering in the most vulnerable ontogenetic stages become increasingly important to make large-scale projections. Here, we demonstrate that the differential sensitivity of non-calcifying Ambulacraria (echinoderms and hemichordates) larvae towards simulated ocean acidification is dictated by the physiology of their digestive systems. Gastric pH regulation upon experimental ocean acidification was compared in six species of the superphylum Ambulacraria. We observed a strong correlation between sensitivity to ocean acidification and the ability to regulate gut pH. Surprisingly, species with tightly regulated gastric pH were more sensitive to ocean acidification. This study provides evidence that strict maintenance of highly alkaline conditions in the larval gut of Ambulacraria early life stages may dictate their sensitivity to decreases in seawater pH. These findings highlight the importance of identifying and understanding pH regulatory systems in marine larval stages that may contribute to substantial energetic challenges under near-future ocean acidification scenarios.

The effects of continuously acoustical stress on cortisol in milkfish (Chanos chanos)

Strong underwater acoustic noise has been known that may cause hearing loss and actual stress in teleost. However, the long-term physiological effects of relatively quiet but continuously noise on fish were less understood. In present study, milkfish, Chanos chanos, were exposed to the simulated-wind farm noise either quiet (109dB re 1μPa/125.4Hz; approx. 10-100m distant from the wind farm) or noisy (138dB re 1μPa/125.4Hz; nearby the wind farm) conditions for 24h, 3days and 1week. Comparing to the control group (80dB re 1μPa/125.4Hz), the fish exposed to noisy conditions had higher plasma cortisol levels in the first 24h. However, the cortisol levels of 24h spot returned to the resting levels quickly. The fish exposed under noisy condition had significantly higher head kidney star (steroidogenic acute regulatory) and hsd11b2 (11-β-hydroxysteroid dehydrogenase 2) mRNA levels at the following treatment time points. In addition, noise exposure did not change hypothalamus crh (Corticotropin-releasing hormone) mRNA levels in this experiment. The results implied that the weak but continuously noise was a potential stressor to fish, but the impacts may be various depending on the sound levels and exposure time. Furthermore, this study showed that the continuous noise may up-regulate the genes that are related to cortisol synthesis and possibly make the fish more sensitive to ambient stressors, which may influence the energy allocation appearance in long-term exposures.

Perfused Gills Reveal Fundamental Principles of pH Regulation and Ammonia Homeostasis in the Cephalopod Octopus vulgaris

In contrast to terrestrial animals most aquatic species can be characterized by relatively higher blood [Formula: see text] concentrations despite its potential toxicity to the central nervous system. Although many aquatic species excrete [Formula: see text] via specialized epithelia little information is available regarding the mechanistic basis for NH₃/[Formula: see text] homeostasis in molluscs. Using perfused gills of Octopus vulgaris we studied acid-base regulation and ammonia excretion pathways in this cephalopod species. The octopus gill is capable of regulating ammonia (NH₃/[Formula: see text]) homeostasis by the accumulation of ammonia at low blood levels (<260 μM) and secretion at blood ammonia concentrations exceeding in vivo levels of 300 μM. [Formula: see text] transport is sensitive to the adenylyl cyclase inhibitor KH7 indicating that this process is mediated through cAMP-dependent pathways. The perfused octopus gill has substantial pH regulatory abilities during an acidosis, accompanied by an increased secretion of [Formula: see text]. Immunohistochemical and qPCR analyses revealed tissue specific expression and localization of Na⁺/K⁺-ATPase, V-type H⁺-ATPase, Na⁺/H⁺-exchanger 3, and Rhesus protein in the gill. Using the octopus gill as a molluscan model, our results highlight the coupling of acid-base regulation and nitrogen excretion, which may represent a conserved pH regulatory mechanism across many marine taxa.

Temperature Modulates the Effects of Ocean Acidification on Intestinal Ion Transport in Atlantic Cod, Gadus morhua

CO₂-driven seawater acidification has been demonstrated to enhance intestinal bicarbonate secretion rates in teleosts, leading to an increased release of CaCO₃ under simulated ocean acidification scenarios. In this study, we investigated if increasing CO₂ levels stimulate the intestinal acid–base regulatory machinery of Atlantic cod (Gadus morhua) and whether temperatures at the upper limit of thermal tolerance stimulate or counteract ion regulatory capacities. Juvenile G. morhua were acclimated for 4 weeks to three CO₂ levels (550, 1200, and 2200 μatm) covering present and near-future natural variability, at optimum (10°C) and summer maximum temperature (18°C), respectively. Immunohistochemical analyses revealed the subcellular localization of ion transporters, including Na⁺/K⁺-ATPase (NKA), Na⁺/H⁺-exchanger 3 (NHE3), Na⁺/HCO3− cotransporter (NBC1), pendrin-like Cl⁻/HCO3− exchanger (SLC26a6), V-type H⁺-ATPase subunit a (VHA), and Cl⁻ channel 3 (CLC3) in epithelial cells of the anterior intestine. At 10°C, proteins and mRNA were generally up-regulated for most transporters in the intestinal epithelium after acclimation to higher CO₂ levels. This supports recent findings demonstrating increased intestinal HCO3− secretion rates in response to CO₂ induced seawater acidification. At 18°C, mRNA expression and protein concentrations of most ion transporters remained unchanged or were even decreased, suggesting thermal compensation. This response may be energetically favorable to retain blood HCO3− levels to stabilize pH_e, but may negatively affect intestinal salt and water resorption of marine teleosts in future oceans.

Strong Ion Regulatory Abilities Enable the Crab Xenograpsus testudinatus to Inhabit Highly Acidified Marine Vent Systems

Hydrothermal vent organisms have evolved physiological adaptations to cope with extreme abiotic conditions including temperature and pH. To date, acid-base regulatory abilities of vent organisms are poorly investigated, although this physiological feature is essential for survival in low pH environments. We report the acid-base regulatory mechanisms of a hydrothermal vent crab, Xenograpsus testudinatus, endemic to highly acidic shallow-water vent habitats with average environment pH-values ranging between 5.4 and 6.6. Within a few hours, X. testudinatus restores extracellular pH (pHe) in response to environmental acidification of pH 6.5 (1.78 kPa pCO₂) accompanied by an increase in blood HCO3- levels from 8.8 ± 0.3 to 31 ± 6 mM. Branchial Na⁺/K⁺-ATPase (NKA) and V-type H⁺-ATPase (VHA), the major ion pumps involved in branchial acid-base regulation, showed dynamic increases in response to acidified conditions on the mRNA, protein and activity level. Immunohistochemical analyses demonstrate the presence of NKA in basolateral membranes, whereas the VHA is predominantly localized in cytoplasmic vesicles of branchial epithelial- and pillar-cells. X. testudinatus is closely related to other strong osmo-regulating brachyurans, which is also reflected in the phylogeny of the NKA. Accordingly, our results suggest that the evolution of strong ion regulatory abilities in brachyuran crabs that allowed the occupation of ecological niches in euryhaline, freshwater, and terrestrial habitats are probably also linked to substantial acid-base regulatory abilities. This physiological trait allowed X. testudinatus to successfully inhabit one of the world's most acidic marine environments.

Recent advances in understanding trans-epithelial acid-base regulation and excretion mechanisms in cephalopods

Cephalopods have evolved complex sensory systems and an active lifestyle to compete with fish for similar resources in the marine environment. Their highly active lifestyle and their extensive protein metabolism has led to substantial acid-base regulatory abilities enabling these organisms to cope with CO2 induced acid-base disturbances. In convergence to teleost, cephalopods possess an ontogeny-dependent shift in ion-regulatory epithelia with epidermal ionocytes being the major site of embryonic acid-base regulation and ammonia excretion, while gill epithelia take these functions in adults. Although the basic morphology and excretory function of gill epithelia in cephalopods were outlined almost half a century ago, modern immunohistological and molecular techniques are bringing new insights to the mechanistic basis of acid-base regulation and excretion of nitrogenous waste products (e.g. NH3/NH4 (+)) across ion regulatory epithelia of cephalopods. Using cephalopods as an invertebrate model, recent findings reveal partly conserved mechanisms but also novel aspects of acid-base regulation and nitrogen excretion in these exclusively marine animals. Comparative studies using a range of marine invertebrates will create a novel and exciting research direction addressing the evolution of pH regulatory and excretory systems.

Molecular Physiology of an Extra-renal Cl(-) Uptake Mechanism for Body Fluid Cl(-) Homeostasis

The development of an ion regulatory mechanism for body fluid homeostasis was an important trait for vertebrates during the evolution from aquatic to terrestrial life. The homeostatic mechanism of Cl^- in aquatic fish appears to be similar to that of terrestrial vertebrates; however, the mechanism in non-mammalian vertebrates is poorly understood. Unlike in mammals, in which the kidney plays a central role, in most fish species, the gill is responsible for the maintenance of Cl^- homeostasis via Cl^- transport uptake mechanisms. Previous studies in zebrafish identified Na⁺-Cl^- cotransporter (NCC) 2b-expressing cells in the gills and skin as the major ionocytes responsible for Cl^- uptake, similar to distal convoluted tubular cells in mammalian kidney. However, the mechanism by which basolateral ions exit from NCC cells is still unclear.

Of the in situ hybridization signals of twelve members of the clc Cl^- channel family, only that of clc-2c exhibited an ionocyte pattern in the gill and embryonic skin. Double in situ hybridization/immunocytochemistry confirmed colocalization of apical NCC2b with basolateral CLC-2c. Acclimation to a low Cl^- environment increased mRNA expression of both clc-2c and ncc2b, and also the protein expression of CLC-2c in embryos and adult gills. Loss-of-function of clc-2c resulted in a significant decrease in whole body Cl^- content in zebrafish embryos, a phenotype similar to that of ncc2b mutants; this finding suggests a role for CLC-2c in Cl^- uptake. Translational knockdown of clc-2c stimulated ncc2b mRNA expression and vice versa, revealing cooperation between these two transporters in the context of zebrafish Cl^- homeostasis. Further comparative genomic and phylogenetic analyses revealed that zebrafish CLC-2c is a fish-specific isoform that diverged from a kidney-predominant homologue, in the same manner as NCC2b and its counterparts (NCCs).

Several lines of molecular and cellular physiological evidences demonstrated the cofunctional role of apical NCC2b and basolateral CLC-2c in the gill/skin Cl^- uptake pathway. Taking the phylogenetic evidence into consideration, fish-specific NCC2b and CLC-2c may have coevolved to perform extra-renal Cl^- uptake during the evolution of vertebrates in an aquatic environment.

Evolution of extreme stomach pH in bilateria inferred from gastric alkalization mechanisms in basal deuterostomes

The stomachs of most vertebrates operate at an acidic pH of 2 generated by the gastric H⁺/K⁺-ATPase located in parietal cells. The acidic pH in stomachs of vertebrates is believed to aid digestion and to protect against environmental pathogens. Little attention has been placed on whether acidic gastric pH regulation is a vertebrate character or a deuterostome ancestral trait. Here, we report alkaline conditions up to pH 10.5 in the larval digestive systems of ambulacraria (echinoderm + hemichordate), the closest relative of the chordate. Microelectrode measurements in combination with specific inhibitors for acid-base transporters and ion pumps demonstrated that the gastric alkalization machinery in sea urchin larvae is mainly based on direct H⁺ secretion from the stomach lumen and involves a conserved set of ion pumps and transporters. Hemichordate larvae additionally utilized HCO₃⁻ transport pathways to generate even more alkaline digestive conditions. Molecular analyses in combination with acidification experiments supported these findings and identified genes coding for ion pumps energizing gastric alkalization. Given that insect larval guts were also reported to be alkaline, our discovery raises the hypothesis that the bilaterian ancestor utilized alkaline digestive system while the vertebrate lineage has evolved a strategy to strongly acidify their stomachs.

Induction of Phosphoenolpyruvate Carboxykinase (PEPCK) during Acute Acidosis and Its Role in Acid Secretion by V-ATPase-Expressing Ionocytes

Vacuolar-Type H⁺-ATPase (V-ATPase) takes the central role in pumping H⁺ through cell membranes of diverse organisms, which is essential for surviving acid-base fluctuating lifestyles or environments. In mammals, although glucose is believed to be an important energy source to drive V-ATPase, and phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme for gluconeogenesis, is known to be activated in response to acidosis, the link between acid secretion and PEPCK activation remains unclear. In the present study, we used zebrafish larva as an in vivo model to show the role of acid-inducible PEPCK activity in glucose production to support higher rate of H⁺ secretion via V-ATPase, by utilizing gene knockdown, glucose supplementation, and non-invasive scanning ion-selective electrode technique (SIET). Zebrafish larvae increased V-ATPase-mediated acid secretion and transiently expression of Pck1, a zebrafish homolog of PEPCK, in response to acid stress. When pck1 gene was knocked down by specific morpholino, the H⁺ secretion via V-ATPase decreased, but this effect was rescued by supplementation of glucose into the yolk. By assessing changes in amino acid content and gene expression of respective enzymes, glutamine and glutamate appeared to be the major source for replenishment of Krebs cycle intermediates, which are subtracted by Pck1 activity. Unexpectedly, pck1 knockdown did not affect glutamine/glutamate catalysis, which implies that Pck1 does not necessarily drive this process. The present study provides the first in vivo evidence that acid-induced PEPCK provides glucose for acid-base homeostasis at an individual level, which is supported by rapid pumping of H⁺ via V-ATPase at the cellular level.

Control of metamorphic buffer structure and device performance of In(x)Ga(1-x)As epitaxial layers fabricated by metal organic chemical vapor deposition

Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique's precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (∼10(6) cm(-2)), while keeping each individual SG layer slightly exceeding the critical thickness (∼80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 10(12) eV(-1) cm(-2) in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

Prevalence and genotype of Giardia duodenalis from faecal samples of stray dogs in Hualien city of eastern Taiwan

Giardia duodenalis is a zoonotic protozoan parasite that causes diarrhea through waterborne transmission or fecal-oral infection. The cysts are chlorine-resistant and, therefore, can pollute drinking water and induce a pandemic disease. In this study, we aimed to detect G. duodenalis infection in stray dogs in Hualien, Taiwan. We collected faecal samples from 118 dogs and amplified DNA sequences of the β-giardin gene by nested polymerase chain reactions (nested PCR). Eleven of the 118 faecal samples tested positive for the parasite. The genotype analysis of the 11 samples indicated that 7 samples belonged to assemblage C and four samples belonged to assemblage D. Our study provided a better understanding of the infection rate and genotypes of G. duodenalis in dogs from Hualien City, and human infection could not be induced by this zoonotic infection pathway in Hualien City.

Endothelin-1 regulates H⁺-ATPase-dependent transepithelial H⁺ secretion in zebrafish

Endothelin-1 (EDN1) is an important regulator of H⁺ secretion in the mammalian kidney. EDN1 enhances renal tubule H⁺-ATPase activity, but the underlying mechanism remains unclear. To further elucidate the role of EDN1 in vertebrates' acid-base regulation, the present study used zebrafish as the model to examine the effects of EDN1 and its receptors on transepithelial H⁺ secretion. Expression of EDN1 and one of its receptors, EDNRAa, was stimulated in zebrafish acclimated to acidic water. A noninvasive scanning ion-selective electrode technique was used to show that edn1 overexpression enhances H⁺ secretion in embryonic skin at 3 days post fertilization. EDNRAa loss of function significantly decreased EDN1- and acid-induced H⁺ secretion. Abrogation of EDN1-enhanced H⁺ secretion by a vacuolar H⁺-ATPase inhibitor (bafilomycin A1) suggests that EDN1 exerts its action by regulating the H⁺-ATPase-mediated H⁺ secretion. EDN1 does not appear to affect H⁺ secretion through either altering the abundance of H⁺-ATPase or affecting the cell differentiation of H⁺-ATPase-rich ionocytes, because the reduction in secretion upon ednraa knockdown was not accompanied by decreased expression of H⁺-ATPase or reduced H⁺-ATPase-rich cell density. These findings provide evidence that EDN1 signaling is involved in acid-base regulation in zebrafish and enhance our understanding of EDN1 regulation of transepithelial H⁺ secretion in vertebrates.

Downregulation of proteins involved in the endoplasmic reticulum stress response and Nrf2-ARE signaling in lymphoblastoid cells of spinocerebellar ataxia type 17

Spinocerebellar ataxia type 17 (SCA17) is caused by CAG repeat expansion in the TATA-box binding protein gene. Studies of several polyglutamine (polyQ) expansion diseases have suggested that the expanded polyQ proteins misfold and induce oxidative stress to contribute to cell death. Substantial deficits in peripheral tissues including lymphocytes have been shown and these peripheral abnormalities could also be found in neurons possessing polyQ disease proteins. In this study, we used a lymphoblastoid cell model to investigate the functional implication of SCA17 expanded alleles and assess the potential therapeutic strategies that may ameliorate the effects of expanded polyQ. Proteomics studies of patient/control pairs including two-dimensional (2-D) gel electrophoresis, mass spectrometry and immunoblotting were conducted. A total of 8 proteins with reduced expression changes greater than 1.3-fold were identified, including previously reported HSPA5 and HSPA8. Among 6 proteins further semi-quantified by immunoblotting and real-time PCR, the reduced expression of HYOU1, PDIA3, P4HB, NQO1 and HMOX1 was confirmed. Treatment with resveratrol and genipin up-regulated NQO1 and HMOX1 expression and reduced oxidative stress in patients' lymphoblastoid cells. The results illustrate downregulation of proteins involved in the endoplasmic reticulum stress response (HYOU1, HSPA5, PDIA3, and P4HB) and Nrf2-ARE signaling (NQO1 and HMOX1) in SCA17 lymphoblastoid cells. Compounds increasing anti-oxidative activity such as resveratrol and genipin may serve as a potential therapeutic strategy for SCA17.

Development in a naturally acidified environment: Na+/H+-exchanger 3-based proton secretion leads to CO2 tolerance in cephalopod embryos

BACKGROUND

Regulation of pH homeostasis is a central feature of all animals to cope with acid-base disturbances caused by respiratory CO2. Although a large body of knowledge is available for vertebrate and mammalian pH regulatory systems, the mechanisms of pH regulation in marine invertebrates remain largely unexplored.

RESULTS

We used squid (Sepioteuthis lessoniana), which are known as powerful acid-base regulators to investigate the pH regulatory machinery with a special focus on proton secretion pathways during environmental hypercapnia. We cloned a Rhesus protein (slRhP), V-type H+-ATPase (slVHA) and the Na+/H+ exchanger 3 (slNHE3) from S. lessoniana, which are hypothesized to represent key players in proton secretion pathways among different animal taxa. Specifically designed antibodies for S. lessoniana demonstrated the sub-cellular localization of NKA, VHA (basolateral) and NHE3 (apical) in epidermal ionocytes of early life stages. Gene expression analyses demonstrated that slNHE3, slVHA and slRhP are up regulated in response to environmental hypercapnia (pH 7.31; 0.46 kPa pCO2) in body and yolk tissues compared to control conditions (pH 8.1; 0.045 kPa pCO2). This observation is supported by H+ selective electrode measurements, which detected increased proton gradients in CO2 treated embryos. This compensatory proton secretion is EIPA sensitive and thus confirms the central role of NHE based proton secretion in cephalopods.

CONCLUSION

The present work shows that in convergence to teleosts and mammalian pH regulatory systems, cephalopod early life stages have evolved a unique acid-base regulatory machinery located in epidermal ionocytes. Using cephalopod molluscs as an invertebrate model this work provides important insights regarding the unifying evolutionary principles of pH regulation in different animal taxa that enables them to cope with CO2 induced acid-base disturbances.

Spatial expression and functional flexibility of monocarboxylate transporter isoforms in the zebrafish brain

The present study provides in vivo evidence to prove the functional plasticity of monocarboxylate transporters (MCTs) in brains of vertebrates using zebrafish (Danio rerio) as a model. In the mammalian central nervous system (CNS), energy demands are largely met by oxidation of glucose. In recent studies, in addition to glucose, lactate is also considered an energy substrate for the CNS. Astrocytes were demonstrated to play an important role in transporting lactate as metabolic substrate from capillaries to neurons through monocarboxylate transporters (MCTs). The present study was to use zebrafish as an in vivo model to test the hypothesis of whether the various MCT homologs play differential roles in the development and functioning of the CNS. Using RT-PCR and double in situ hybridization coupling with immunocytochemical staining experiments, zebrafish MCTs1-4 were all found to be expressed in brains of embryos, and were further elucidated to be localized in both neurons and astrocytes. Loss-of-functions by morpholino knockdown further provided in vivo evidences to infer that zMCTs1, -2, and -4 may be involved in metabolite transport and functioning in the developing brain. Subsequent rescue experiments with capped mRNAs of specific isoforms further indicated that zMCT2 is an indispensable monocarboxylate-transporting route for CNS development and function in zebrafish. This information is essential for identifying proper candidates of MCT isoforms that are involved in the development and functioning of the CNS.

WITHDRAWN: Spatial expression and functional flexibility of monocarboxylate transporter isoforms in the zebrafish brain

Available online (Note: this date will be generated and inserted by the publishing platform and is not part of the typesetter's XML and will not appear in the PDF version) This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

New insights into ion regulation of cephalopod molluscs: a role of epidermal ionocytes in acid-base regulation during embryogenesis

The constraints of an active life in a pelagic habitat led to numerous convergent morphological and physiological adaptations that enable cephalopod molluscs and teleost fishes to compete for similar resources. Here, we show for the first time that such convergent developments are also found in the ontogenetic progression of ion regulatory tissues; as in teleost fish, epidermal ionocytes scattered on skin and yolk sac of cephalopod embryos appear to be responsible for ionic and acid-base regulation before gill epithelia become functional. Ion and acid-base regulation is crucial in cephalopod embryos, as they are surrounded by a hypercapnic egg fluid with a Pco(2) between 0.2 and 0.4 kPa. Epidermal ionocytes were characterized via immunohistochemistry, in situ hybridization, and vital dye-staining techniques. We found one group of cells that is recognized by concavalin A and MitoTracker, which also expresses Na(+)/H(+) exchangers (NHE3) and Na(+)-K(+)-ATPase. Similar to findings obtained in teleosts, these NHE3-rich cells take up sodium in exchange for protons, illustrating the energetic superiority of NHE-based proton excretion in marine systems. In vivo electrophysiological techniques demonstrated that acid equivalents are secreted by the yolk and skin integument. Intriguingly, epidermal ionocytes of cephalopod embryos are ciliated as demonstrated by scanning electron microscopy, suggesting a dual function of epithelial cells in water convection and ion regulation. These findings add significant knowledge to our mechanistic understanding of hypercapnia tolerance in marine organisms, as it demonstrates that marine taxa, which were identified as powerful acid-base regulators during hypercapnic challenges, already exhibit strong acid-base regulatory abilities during embryogenesis.

Involvement of calcitonin and its receptor in the control of calcium-regulating genes and calcium homeostasis in zebrafish (Danio rerio)

Calcitonin (CT) is one of the hormones involved in vertebrate calcium regulation. It has been proposed to act as a hypocalcemic factor, but the regulatory pathways remain to be clarified. We investigated the CT/calcitonin gene-related peptide (CGRP) family in zebrafish and its potential involvement in calcium homeostasis. We identified the presence of four receptors: CTR, CRLR1, CRLR2, and CRLR3. From the phylogenetic analysis, together with the effect observed after CT and CGRP overexpression, we concluded that CTR appears to be a CT receptor and CRLR1 a CGRP receptor. The distribution of these two receptors shows a major presence in the central nervous system and in tissues involved in ionoregulation. Zebrafish embryos kept in high-Ca(2+)-concentration medium showed upregulation of CT and CTR expression and downregulation of the epithelial calcium channel (ECaC). Embryos injected with CT morpholino (CALC MO) incubated in high-Ca(2+) medium, showed downregulation of CTR together with upregulation on ECaC mRNA expression. In contrast, overexpression of CT cRNA induced the downregulation of ECaC mRNA synthesis, concomitant with the downregulation in the calcium content after 30 hours postfertilization. At 4 days postfertilization, CT cRNA injection induced upregulation of hypercalcemic factors, with subsequent increase in the calcium content. These results suggest that CT acts as a hypocalcemic factor in calcium regulation, probably through inhibition of ECaC synthesis.

Elevated seawater Pco2 differentially affects branchial acid-base transporters over the course of development in the cephalopod Sepia officinalis

The specific transporters involved in maintenance of blood pH homeostasis in cephalopod molluscs have not been identified to date. Using in situ hybridization and immunohistochemical methods, we demonstrate that Na+/K+-ATPase ( soNKA), a V-type H+-ATPase ( soV-HA), and Na+/HCO3− cotransporter ( soNBC) are colocalized in NKA-rich cells in the gills of Sepia officinalis. mRNA expression patterns of these transporters and selected metabolic genes were examined in response to moderately elevated seawater Pco2 (0.16 and 0.35 kPa) over a time course of 6 wk in different ontogenetic stages. The applied CO2 concentrations are relevant for ocean acidification scenarios projected for the coming decades. We determined strong expression changes in late-stage embryos and hatchlings, with one to three log2-fold reductions in soNKA, soNBCe, socCAII, and COX. In contrast, no hypercapnia-induced changes in mRNA expression were observed in juveniles during both short- and long-term exposure. However, a transiently increased ion regulatory demand was evident during the initial acclimation reaction to elevated seawater Pco2. Gill Na+/K+-ATPase activity and protein concentration were increased by ∼15% during short (2–11 days) but not long-term (42-days) exposure. Our findings support the hypothesis that the energy budget of adult cephalopods is not significantly compromised during long-term exposure to moderate environmental hypercapnia. However, the downregulation of ion regulatory and metabolic genes in late-stage embryos, taken together with a significant reduction in somatic growth, indicates that cephalopod early life stages are challenged by elevated seawater Pco2.

Exploring uncoupling proteins and antioxidant mechanisms under acute cold exposure in brains of fish

Exposure to fluctuating temperatures accelerates the mitochondrial respiration and increases the formation of mitochondrial reactive oxygen species (ROS) in ectothermic vertebrates including fish. To date, little is known on potential oxidative damage and on protective antioxidative defense mechanisms in the brain of fish under cold shock. In this study, the concentration of cellular protein carbonyls in brain was significantly increased by 38% within 1 h after cold exposure (from 28°C to 18°C) of zebrafish (Danio rerio). In addition, the specific activity of superoxide dismutase (SOD) and the mRNA level of catalase (CAT) were increased after cold exposure by about 60% (6 h) and by 60%–90% (1 and 24 h), respectively, while the specific glutathione content as well as the ratio of glutathione disulfide to glutathione remained constant and at a very low level. In addition, cold exposure increased the protein level of hypoxia-inducible factor (HIF) by about 50% and the mRNA level of the glucose transporter zglut3 in brain by 50%–100%. To test for an involvement of uncoupling proteins (UCPs) in the cold adaptation of zebrafish, five UCP members were annotated and identified (zucp1-5). With the exception of zucp1, the mRNA levels of the other four zucps were significantly increased after cold exposure. In addition, the mRNA levels of four of the fish homologs (zppar) of the peroxisome proliferator-activated receptor (PPAR) were increased after cold exposure. These data suggest that PPARs and UCPs are involved in the alterations observed in zebrafish brain after exposure to 18°C. The observed stimulation of the PPAR-UCP axis may help to prevent oxidative damage and to maintain metabolic balance and cellular homeostasis in the brains of ectothermic zebrafish upon cold exposure.