scholarly journals Why are mayflies (Ephemeroptera) lost following small increases in salinity? Three conceptual osmophysiological hypotheses

2018 ◽  
Vol 374 (1764) ◽  
pp. 20180021 ◽  
Author(s):  
Ben J. Kefford
Keyword(s):  
Turnover Rate ◽  
Ph Regulation ◽  
Research Effort ◽  
Ion Homeostasis ◽  
Single Species ◽  
Toxicity Tests ◽  
Future Prospects ◽  
Theme Issue ◽  
Vital Functions ◽  
Rate Of Increase

The salinity of many freshwaters is increasing globally as a result of human activities. Associated with this increase in salinity are losses of Ephemeroptera (mayfly) abundance and richness. The salinity concentrations at which Ephemeroptera decline in nature are lower than their internal salinity or haemolymph osmolality. Many species also suffer substantial mortality in single species laboratory toxicity tests at salinities lower than their internal salinity. These findings are problematic as conventional osmoregulation theory suggests that freshwater animals should not experience stress where external osmolality is greater than haemolymph osmolality. Here I explore three hypotheses to explain salt sensitivity in Ephemeroptera. These conceptual hypotheses are based on the observations that as the external sodium ion (Na + ) concentration increases so does the Na + turnover rate (both uptake and elimination rates increase). Sulphate ( ) uptake in mayflies also increases with increasing external although, unlike Na + , its rate of increase decreases with increasing external . The first hypothesis is premised on ion turnover being energetically costly. The first hypothesis proposes that individuals must devote a greater proportion of their energy to ion homeostasis at the expense of other uses including growth and development. Lethal levels of salinity presumably result from individuals not being able to devote enough energy to maintain ion homeostasis without critical loss of other vital functions. The second hypothesis is premised on the uptake of Na + exchanged for (an outgoing) H + , leading to (localized) loss of pH regulation. The third hypothesis is premised on localized Na + toxicity or poisoning with increased Na turnover as salinity increases. None of the proposed hypotheses is without potential problems, yet all are testable, and research effort should be focused at attempting to falsify them. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

Use of Biomonitoring to Control Toxics in the United States

1988 ◽  
Vol 20 (10) ◽  
pp. 101-108 ◽  
Author(s):  
Nelson A. Thomas
Keyword(s):  
Water Quality ◽  
Chronic Toxicity ◽  
National Policy ◽  
Single Species ◽  
Field Studies ◽  
The United States ◽  
Toxicity Tests ◽  
Toxic Pollutants ◽  
Receiving Waters ◽  
Biological Field

A biomonitoring program has been developed in support of the National Policy for the Development of Water Quality-Based Permit Limitations for Toxic Pollutants. The program focuses on the use of laboratory toxicity tests on aquatic plants and animals to predict ecosystem impact caused by toxic pollutants. Both acute and chronic toxicity tests were developed to test effluents and ambient waters. Laboratory and biological field studies were conducted at nine sites. Single species laboratory toxicity tests were found to be good predictors of impacts on the ecosystem when two or more species were used. Biomonitoring can be undertaken either on effluents and/or on the receiving waters. In that toxicity related to seeps, leachates and storm sewers has often been found upstream from dischargers, it is beneficial to conduct both effluent and ambient biomonitoring.

Slow ATP loss and the defense of ion homeostasis in the anoxic frog brain

2001 ◽  
Vol 204 (20) ◽  
pp. 3547-3551
Author(s):  
Debra L. Knickerbocker ◽  
Peter L. Lutz
Keyword(s):  
Initial Phase ◽  
Ion Homeostasis ◽  
Atp Depletion ◽  
Neuronal Membrane ◽  
Anoxia Tolerance ◽  
Frog Brain ◽  
Atp Levels ◽  
Anoxic Depolarization ◽  
Rate Of Increase ◽  
The Brain

SUMMARY For most vertebrates, cutting off the oxygen supply to the brain results in a rapid (within minutes) loss of ATP, the failure of ATP-dependent ion-transport process, subsequent anoxic depolarization of neuronal membrane potential and consequential neuronal death. The few species that survive brain anoxia for days or months, such as the freshwater turtle Trachemys scripta, avoid anoxic depolarization and maintain brain ATP levels through a coordinated downregulation of brain energy demand processes. The frog Rana pipiens represents an intermediate in anoxia-tolerance, being able to survive brain anoxia for hours. However, the anoxic frog brain does not defend its energy stores. Instead, anoxia-tolerance appears to be related to a retarded rate of ATP depletion. To investigate the relationship between this slow ATP depletion and the loss of ionic homeostasis, cerebral extracellular K+ concentrations were monitored and ATP levels measured during anoxia, during the initial phase of anoxic depolarization and during complete anoxic depolarization. Extracellular K+ levels were maintained at normoxic levels for at least 3 h of anoxia, while ATP content decreased by 35 %. When ATP levels reached 0.33±0.06 mmol l–1 (mean ± s.e.m., N=5), extracellular K+ levels slowly started to increase. This value is thought to represent a critical ATP concentration for the maintenance of ion homeostasis. When extracellular [K+] reached an inflection value of 4.77±0.84 mmol l–1 (mean ± s.e.m., N=5), approximately 1 h later, the brain quickly depolarized. Part of the reduction in ATP demand was attributable to an approximately 50 % decrease in the rate of K+ efflux from the anoxic frog brain, which would also contribute to the retarded rate of increase in extracellular [K+] during the initial phase of anoxic depolarization. However, unlike the anoxia-tolerant turtle brain, adenosine did not appear to be involved in the downregulation of K+ leakage in the frog brain. The increased anoxia-tolerance of the frog brain is thought to be a matter more of slow death than of enhanced protective mechanisms.

Effects of sediment-spiked lufenuron on benthic macroinvertebrates in outdoor microcosms and single-species toxicity tests

2016 ◽  
Vol 177 ◽  
pp. 464-475 ◽  
Author(s):  
T.C.M. Brock ◽  
D.A. Bas ◽  
J.D.M. Belgers ◽  
L. Bibbe ◽  
M-C. Boerwinkel ◽  
...  
Keyword(s):  
Benthic Macroinvertebrates ◽  
Single Species ◽  
Toxicity Tests

The Army Operator Workload (OWL) Program: Review and Prospects

1989 ◽  
Vol 33 (20) ◽  
pp. 1471-1475
Author(s):  
Richar E. Christ ◽  
Allen L. Zaklad ◽  
Alvah C. Bittner ◽  
Susan G. Hill ◽  
Paul M. Linton
Keyword(s):  
Applied Research ◽  
Research Effort ◽  
Lessons Learned ◽  
Assessment Methods ◽  
Program Review ◽  
Future Prospects ◽  
Army Research Institute ◽  
The Future ◽  
Basic And Applied Research ◽  
Operator Workload

The Operator Workload (OWL) Program is a just-completed, three-year, basic and applied research effort sponsored by the Army Research Institute (ARI). As part of the Army's research thrust into workload, the OWL Program was directed to establish guidance for the assessment of OWL associated with the operation of Army systems. Its intent was to identify and integrate the most relevant of workload research into a set of practicable workload assessment methods for Army developers, and then apply and validate these methods on selected Army systems. Lessons learned from OWL studies of these systems formed the basis for guidance for Army system developers. This paper overviews the objectives, the accomplishments, and the future prospects of the OWL Program.

The novel class of seven transmembrane segment inverted repeat carriers

2017 ◽  
Vol 398 (2) ◽  
pp. 165-174 ◽  
Author(s):  
Yung-Ning Chang ◽  
Eric R. Geertsma
Keyword(s):  
Ph Regulation ◽  
Ion Homeostasis ◽  
Domain Architecture ◽  
Inverted Repeats ◽  
The Novel ◽  
Transmembrane Segment ◽  
Structural Class ◽  
Transmembrane Segments ◽  
Structural Framework ◽  
Sequence Relationship

Abstract Solute carriers from the SLC4, SLC23, and SLC26 families are involved in pH regulation, vitamin C transport and ion homeostasis. While these families do not share any obvious sequence relationship, they are united by their unique and novel architecture. Each member of this structural class is organized into two structurally related halves of seven transmembrane segments each. These halves span the membrane with opposite orientations and form an intricately intertwined structure of two inverted repeats. This review highlights the general design principles of this fold and reveals the diversity between the different families. We discuss their domain architecture, structural framework and transport mode and detail an initial transport mechanism for this fold inferred from the recently solved structures of different members.

scholarly journals Comparative Aquatic Toxicity of Gold Nanoparticles and Ionic Gold Using a Species Sensitivity Distribution Approach

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
Tarryn L. Botha ◽  
Tanyn E. James ◽  
Victor Wepener
Keyword(s):  
Gold Nanoparticles ◽  
Aquatic Toxicity ◽  
Single Species ◽  
Species Sensitivity Distribution ◽  
Toxicity Tests ◽  
Species Sensitivity ◽  
Sensitivity Distribution ◽  
Hazardous Concentration ◽  
Toxic Potential ◽  
Ionic Gold

Gold nanoparticles (nAu) are used in drug delivery systems allowing for targeted cellular distribution. The effects of increased use and release of nanoparticles into the environment are not well known. A species sensitivity distribution (SSD) allows for the ecotoxicological hazard assessment of a chemical based on single species toxicity tests. Aquatic toxicity needs to be related to particle characterization in order to understand the effects. The behaviour of nAu in the medium changed as the concentration increased. The toxic potential of ionic gold and nAu was expressed as a hazardous concentration where 5% of species will be harmed (HC5). The HC5 for nAu was much higher (42.78 mg/L) compared to the ionic gold (2.44 mg/L). The differences between the hazard potentials of nAu and ionic gold were attributed to the nAu not releasing any Au ions into solution during the exposures and following an aggregation theory response. Exposures to ionic gold on the other hand followed a clear dose dependent response based on the concentration of the ionic metal. Although SSDs present an indication of the relative hazard potential of nanoparticles, the true worth can only be achieved once other nanoparticle characteristics and their behavior in the environment are also considered.

scholarly journals On competition between different species of graminivorous insects

1945 ◽  
Vol 132 (869) ◽  
pp. 362-395 ◽  
Keyword(s):  
Census Data ◽  
Single Species ◽  
The Other ◽  
Ecological Niches ◽  
Initial Population ◽  
General Validity ◽  
Rhizopertha Dominica ◽  
Rate Of Increase ◽  
Limited Food ◽  
Determining Factor

The growth of pure populations of the beetles Rhizopertha dominica and Oryzaephilus surinamensis , and of the moth Sitotroga cerealella , was observed in a standard medium of wheat. This was maintained at a constant level by the periodic removal of ‘conditioned’ frass and the addition of fresh grains. The population of each species rose to a maximum and remained fluctuating about this value indefinitely. A comparison of the rates of oviposition, with the rates at which adults emerged, showed that in the maximum population there was an enormous mortality (always over 90%) in the immature stages. When pairs of species competed Rhizopertha eliminated Sitotroga because their larvae, between which most of the competition occurred, have the same needs and habits. But each of these species was able to survive with Oryzaephilus because this species occupies a different ‘ecological niche’. The Verhulst-Pearl ‘logistic’ equation (1), for the growth of population of a single species in a limited environment, and the Lotka-Volterra simultaneous equations (2), for the growth of population of two species competing for the same limited environment, were fitted to the census data from all the experiments. The biological assumptions on which they are based proved to be true for practical purposes for Rhizopertha and Sitotroga populations. These assumptions are that the value of the potential rate of increase remains statistically constant and that all the factors inhibiting increase are linearly related to population density. Further­ more, a single factor, larval competition, was represented by the single indices standing for interspecific inhibition. It follows that the maximum population (or equilibrium position) should be independent of the initial population, and this proved to be so for all species. Equations (2) did not always fit the observed points very well, but they were always success­ful in predicting the outcome of competition. It does not follow from this that these equa­tions have any general validity. Their basic assumptions are by no means universally true and, unless they are shown to be so for a particular species under known, environmental conditions, no biological deductions can be drawn from them. Where they do apply they describe the course of change of population of two competing organisms with an accuracy which depends on the constancy of the coefficients involved. Two kinds of organism will be able to survive together only if they differ in needs and habits, i. e. occupy different ecological niches. Populations living in a medium of unrenewed wheat rose to a maximum and then declined as the food became exhausted and ‘conditioning’ increased. The eventual extinction of the population was due, not to the cessation of oviposition, but to the failure of the larvae to survive. The longevity of Rhizopertha adults was lower in unrenewed than in renewed medium, and lower still when this species was competing with Sitotroga in unrenewed medium. The longevity of the other species, and the sex ratio of Sitotroga , were apparently unaffected by these conditions. The fecundity of Rhizopertha females decreased with time, and the length of Sitotroga adults of both sexes decreased in succeeding generations. The competitive relation­ship between both Sitotroga and Rhizopertha , and Oryzaephilus shifted slightly in favour of the former species in unrenewed as compared with renewed media. In a renewed medium this relationship probably depends chiefly on the destruction of eggs and pupae by adults and larvae, for which the more predaceous Oryzaephilus is better placed. In an unrenewed medium the ability of the larvae to make the best use of the limited food supply is the determining factor, and here the other two species have the advantage. The competitive relationship between Rhizopertha and Sitotroga remained the same in both media.

A comparison between toxicity tests using single species and a microbial process

Chemosphere ◽  
1999 ◽  
Vol 38 (14) ◽  
pp. 3277-3290 ◽  
Author(s):  
Patrick van Beelen ◽  
Arja K. Fleuren-Kemilä
Keyword(s):  
Single Species ◽  
Toxicity Tests ◽  
Microbial Process

scholarly journals Review article: A systematic review and future prospects of flood vulnerability indices

2021 ◽  
Author(s):  
Luana Lavagnoli Moreira ◽  
Mariana Madruga de Brito ◽  
Masato Kobiyama
Keyword(s):  
Temporal Dynamics ◽  
Research Effort ◽  
Future Research ◽  
Future Prospects ◽  
Flood Vulnerability ◽  
Research Directions ◽  
Linear Aggregation ◽  
Future Research Directions ◽  
The City ◽  
Equal Weighting

Abstract. This paper provides a state-of-art account on flood vulnerability indices, highlighting worldwide trends and future research directions. A total of 95 peer-reviewed articles published between 2002–2019 were systematically analyzed. An exponential rise in research effort is demonstrated, with 80 % of the articles being published since 2015. The majority of these studies (62.1 %) focused on the neighborhood followed by the city scale (14.7 %). Min-max normalization (30.5 %), equal weighting (24.2 %), and linear aggregation (80.0 %) were the most common methods. With regard to the indicators used, a focus was given to socio-economic aspects (e.g. population density, illiteracy rate, gender), whilst components associated with the citizen's coping and adaptive capacity were slightly covered. Gaps in current research include a lack of sensitivity and uncertainty analyzes (present in only 9.5 % and 3.2 % of papers, respectively); inadequate or inexistent validation of the results (present in 13.7 % of the studies); lack of transparency regarding the rationale for weighting and indicator selection; and use of static approaches, disregarding temporal dynamics. We discuss the challenges associated with these findings for the assessment of flood vulnerability and provide a research agenda for attending to these gaps.

Ecotoxicological Effect Indices: A Rapidly Evolving System

1987 ◽  
Vol 19 (11) ◽  
pp. 1-12 ◽  
Author(s):  
John Cairns ◽  
James R. Pratt
Keyword(s):  
Standard Dose ◽  
Biological Effects ◽  
Single Species ◽  
Test System ◽  
Integrated System ◽  
Toxicity Tests ◽  
Hazard Evaluation ◽  
Strong Interactions ◽  
Sensitive Species ◽  
Effective Manner

Ecotoxicology has evolved from a modest number of single species, acute toxicity tests to an integrated system of hazard evaluation for predicting adverse effects of chemicals and complex mixtures on environmental health. The process of screening and regulating chemicals and industrial discharges has improved water quality but has generally not been validated in receiving ecosystems. This deficiency results from the regulation of individual chemicals that rarely occur alone in the environment and from the size of the problem. Many receiving ecosystems have literally hundreds of discharges of complex effluents. Typical single species laboratory tests fail to account for the complexity of ecosystems and the strong interactions that may occur among the component species. Evidence is accumulating that complex test systems such as microcosms and mesocosms can fill this void. Microcosms and mesocosms can be constructed and experiments conducted in a cost-effective manner, and several end points can be measured in complex systems using the standard dose-response paradigm. For example, the current regulation of chlorine discharges is based on three chronic exposures to chlorinated sewage effluent. In a microcosm test, we determined adverse biological effects at nearly an order of magnitude less chlorine (1 μg/1) for the loss of microbial species. To be effective hazard evaluation tools, microcosms and mesocosms must include ecologically meaningful processes and must be useful in making decisions regarding environmental safety and harm. This can only be done with adequate statistical design and intensive sampling. Nevertheless, laboratory ecosystems can be useful in making direct measurements of effects on a large number of interacting species and can be tied to a site-specific problem in a particular ecosystem or can be standardized by using regional type ecosystems as references. By using complex natural communities, the ability to validate test system predictions increases since the test system complexity mimics that found in the real world. Despite hopes that a few sensitive species might be used to make decisions quickly on environmental effects, ecological health will only be maintained when scientists and regulators come to grips with the problem of protecting ecologically important processes as well as sensitive species. This will mean developing tests with increasing environmental realism in which environmentally realistic concentrations of chemicals can be tested without resorting to the use of safety factors or extrapolation from limited data bases. Developing such tests does not mean skyrocketing costs for screening chemicals and effluents, but suggests that regulators and toxicologists will need to deal with new information and learn new skills rather than relying on historically pleasing but ecologically deficient testing programs.

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