Drinking rate and rectal fluid production of juvenile Atlantic salmon (1–2 g) in freshwater were investigated in unfed fish and recently fed fish. Drinking was also investigated following activation ...of the renin–angiotensin system (RAS) by two hypotensive agents, a nitric oxide (NO) donor sodium nitroprusside (SNP) and bacterial lipopolysaccharide (LPS). In unfed fish the basal drinking rate was 0.13 μL g
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h
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and rectal fluid production was 0.076 μL g
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. In recently fed fish both drinking rate and rectal fluid production increased significantly by about fivefold compared to unfed fish, and similar values were obtained for fish exposed to PS for 24 h. Exposure to SNP resulted in about a tenfold elevation of drinking rate and rectal fluid production, compared to unfed fish. Absorption of water by the gut was in the range 35–60% for all treatments. Drinking may have a role in processing food in the gut and the fluid in the gut may subjected to absorptive and secretory processes. The most likely route for removal of water absorbed by the gut is excretion via the kidney and this would result in an increased osmoregulatory burden on the fish. In polluted waters drinking could be increased through stimulation of the endogenous RAS by vasodilators, e.g., LPS and the gut could be a significant target for toxin exposure.
Over two thirds of the earth's surface is covered by water, and adaptation to the aquatic habitats dominated the first 150 to 200 million years of vertebrate development. More than half the living ...vertebrates are aquatic. Fish have evolved to colonise almost every type of aquatic habitat, and today they are a hugely diverse group of about 25,000 species. Evolution of this great diversity has resulted in fascinatingly different designs for special modes of life as well as solutions to the problems common to them all. Comparisons help to reveal the biological and physiological compromises fish have to make to satisfy the often conflicting demands on their lives. Today fish are found in almost every imaginable watery habitat, which include the shallows and depths of the oceans, coastal waters and estuaries, rivers, streams, lakes, ponds, and ephemeral water bodies. Many species inhabit freezing waters in polar regions whilst others thrive in ponds fed by thermal springs. Some have abandoned the water and become air breathers. Tunas in the open oceans swim rapidly and outperform their prey. How do they generate the forces required for high-speed swimming? Study of these fish shows that they have large masses of warmed red muscle, and that the required amounts of oxygen are delivered by unusually efficient respiratory and circulatory systems. Some freshwater carp are able to survive the long periods of very low oxygen levels that periodically occur in some ponds and lakes. How is their metabolism switched from aerobic to anaerobic pathways? The challenges of living in a particular environment are in part met by adaptations of body form and physiological function. Yet there are wider and equally important questions, such as why are these species successful in their particular environments? Answers to such questions may be found in the study of behaviour, in the dynamics of populations, in the ecology of the species and in evolutionary theory.
Fishes have evolved to colonise almost every type of aquatic habitat and today they are a hugely diverse group of over 25,000 species. This book presents a current and comprehensive overview of fish ...physiology to demonstrate how living fishes function in their environment.
The carbon cycle of a lake is a balance between supply from the atmosphere and catchment, and the net demand exerted by primary producers, minus losses back to the atmosphere and to sediment storage. ...Evaluating the sum of these processes and reconstructing them from sediment records of lake history requires a range of methods and a multi-proxy approach. One promising technique is to explore the carbon-isotope composition (δ13Cdiatom) of organic matter incorporated within the silica frustules of diatom algae. Here we present a 25,000-year record of δ13Cdiatom from the sediments of crater Lake Challa on the eastern flank of Mt. Kilimanjaro, and along with other proxy data we make inferences about the three major phases in the history of the lake's carbon cycle. From 25 ka to 15.8 ka years BP, δ13Cdiatom is positively correlated with the δ13C of bulk sediment organic matter (δ13Cbulk), indicating that high diatom productivity, as recorded by high % biogenic silica at this time, was preferentially removing 12C and enriching the δ13C of lake-water dissolved inorganic carbon. From 15.8 to 5.5 ka the correlation between δ13Cdiatom and δ13Cbulk breaks down, suggesting carbon supply to the lake satisfied or exceeded the demand from productivity. From 5.5 ka BP the positive correlation resumes, indicating an increase in the internal demand for carbon relative to external supply. Diatom frustule-bound carbon isotopes offer an original tool in examining long-term fluctuations in a lake's carbon budget and how the balance between supply and demand has changed through time.
The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of ...nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply uranium-lead (U-Pb) zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ∼250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ∼750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.
Grain size is a key agronomic trait that contributes to grain yield in hexaploid wheat. Grain length and width were evaluated in an international collection of 157 wheat accessions. These accessions ...were genetically characterized using a genotyping-by-sequencing (GBS) protocol that produced 73,784 single nucleotide polymorphism (SNP) markers. GBS-derived genotype calls obtained on Chinese Spring proved extremely accurate when compared to the reference (> 99.9%) and showed > 95% agreement with calls made at SNP loci shared with the 90 K SNP array on a subset of 71 Canadian wheat accessions for which both types of data were available. This indicates that GBS can yield a large amount of highly accurate SNP data in hexaploid wheat. The genetic diversity analysis performed using this set of SNP markers revealed the presence of six distinct groups within this collection. A GWAS was conducted to uncover genomic regions controlling variation for grain length and width. In total, seven SNPs were found to be associated with one or both traits, identifying three quantitative trait loci (QTLs) located on chromosomes 1D, 2D and 4A. In the vicinity of the peak SNP on chromosome 2D, we found a promising candidate gene (TraesCS2D01G331100), whose rice ortholog (D11) had previously been reported to be involved in the regulation of grain size. These markers will be useful in breeding for enhanced wheat productivity.
Drinking in freshwater-adapted rainbow trout fry was investigated in response to the administration of angiotensin I, angiotensin II, the angiotensin II antagonist saralasin, and the ...angiotensin-converting enzyme inhibitor enalapril. Rainbow trout fry (0. 8-1.5 g), as previously shown, drank at a rate of about 0.7-0.9 mL kg⁻¹ h⁻¹ in freshwater, and the intramuscular administration of angiotensin I or angiotensin II increased drinking rates maximally to about 4-5 mL kg⁻¹ h-1', while intraperitoneal injections at a similar dose were less potent. Intramuscular administration of increasing levels of angiotensin II (0.2-2 nmol g⁻¹ of Asn¹, Val⁵-angiotensin II) resulted in a dose-dependent increase of drinking rate, and this response was partially but significantly inhibited by the administration of the angiotensin II receptor blocker saralasin (Sar¹, Val⁵, Ala⁸-angiotensin II). Drinking rates were also increased (maximally to about 5 mL kg⁻¹ h⁻¹) in response to intramuscular injection of increasing levels of angiotensin I, with maximum responses between 0.26 and 0.35 nmol⁻¹ g, and this response was significantly lowered by the administration of enalapril and by saralasin. The administration of losartan (DuP 753), a selective inhibitor of the receptor subtype AT, in mammals, had an inconsistent effect on drinking in freshwater and seawater-adapted fish. Although the role of drinking in juvenile freshwater fish is not understood, the present results constitute further evidence for the involvement of the renin-angiotensin system in control of drinking in fish.
Virus particles are highly abundant in seawater and, on average, outnumber microbial cells approximately 10-fold at the surface and 16-fold in deeper waters; yet, this relationship varies across ...environments. Here, we examine the influence of a suite of environmental variables, including nutrient concentrations, salinity and temperature, on the relationship between the abundances of viruses and prokaryotes over a broad range of spatial and temporal scales, including along a track from the Northwest Atlantic to the Northeast Pacific via the Arctic Ocean, and in the coastal waters of British Columbia, Canada. Models of varying complexity were tested and compared for best fit with the Akaike Information Criterion, and revealed that nitrogen and phosphorus concentrations, as well as prokaryote abundances, either individually or combined, had significant effects on viral abundances in all but hypoxic environments, which were only explained by a combination of physical and chemical factors. Nonetheless, multivariate models of environmental variables showed high explanatory power, matching or surpassing that of prokaryote abundance alone. Incorporating both environmental variables and prokaryote abundances into multivariate models significantly improved the explanatory power of the models, except in hypoxic environments. These findings demonstrate that environmental factors could be as important as, or even more important than, prokaryote abundance in describing viral abundance across wide-ranging marine environments.
Small molecules offer powerful ways to alter protein function. However, most proteins in the human proteome lack small-molecule probes, including the large class of non-catalytic transmembrane ...receptors, such as death receptors. We hypothesized that small molecules targeting the interfaces between transmembrane domains (TMDs) in receptor complexes may induce conformational changes that alter receptor function. Applying this concept in a screening assay, we identified a compound targeting the TMD of death receptor p75NTR that induced profound conformational changes and receptor activity. The compound triggered apoptotic cell death dependent on p75NTR and JNK activity in neurons and melanoma cells, and inhibited tumor growth in a melanoma mouse model. Due to their small size and crucial role in receptor activation, TMDs represent attractive targets for small-molecule manipulation of receptor function.
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•We identified a compound targeting the transmembrane domain of death receptor p75NTR•NSC49652 induced profound conformational changes and receptor activity•NSC49652 induced melanoma cell death, and inhibited melanoma tumor growth in vivo•TMDs represent attractive targets for small-molecule manipulation of receptor function
Small molecules offer powerful ways to alter protein function. However, most proteins in the human proteome lack small-molecule probes. Goh et al. Identified a small molecule that interacts with the transmembrane domain of death receptor p75NTR, which induces melanoma cell death, and inhibits melanoma tumor growth in vivo.
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