The biotic ligand model and a cellular approach to class B metal aquatic toxicity

The biotic ligand model (BLM) and a cellular molecular mechanism approach represent two approaches to the correlation of metal speciation with observed toxicity to aquatic organisms. The two approaches are examined in some detail with particular reference to class B, or soft metals. Kinetic arguments are presented to suggest situations that can arise where the BLM criterion of equilibrium between all metal species in the bulk solution and the biotic ligand may not be satisfied and what might the consequences be to BLM predictive capability. Molecular mechanisms of toxicity are discussed in terms of how a class B metal might enter a cell, how it is distributed in a cell, and how the cell might respond to the unwanted metal. Specific examples are given for copper as an organism trace essential metal, which is toxic in excess, and for silver, a non-essential metal. As class B metals all bind strongly to sulfur, regulation of these metals requires that all S(II-) species be accounted for in aquatic systems, even under oxic conditions.     

Experimental atherosclerosis: a historical overview

Almost one-hundred years ago the first evidence of experimental atherosclerosis was reported. Over the past century, significant advances have been made in the development of animal models of human coronary artery disease. In this minireview, induction of atherosclerotic lesions in several animal models including rodents (mice, rabbits, rats, hamsters, guinea pigs), avian (pigeons, chickens, quail), swine, carnivora (dogs, cats), and non-human primates is discussed. The limitations and advantages of the animal models of atherosclerosis have been summarized. The transgenic/knockout animal models have greatly enhanced our understanding of atherosclerosis. Compared to wild-type counterparts, the knockout/transgenic animals develop atherogenesis faster without a need for a highly atherogenic diet. Although almost all investigations support a causal role for increased plasma cholesterol levels in the development of atherosclerotic vascular disease, an increasing body of evidence indicates serious invqlvement of other factors including oxidative stress, inflammation, infection and other emerging risk factors.     

Metal bioavailability to phytoplankton--applicability of the biotic ligand model

To elicit a biological response from a target organism and/or to accumulate within this organism, a metal must first interact with a cell membrane. For hydrophilic metal species, this interaction with the cell surface can be represented in terms of the formation of M-X-cell surface complexes, e.g. M(z+)+(-)X-cell<-->M-X-cell, where -X-cell is a cellular ligand present at the cell surface. According to the free-ion model, or its derivative the biotic ligand model (BLM), the biological response elicited by the metal will be proportional to [M-X-cell]. In this paper, using freshwater algae as our test species, we examine some of the key assumptions that underlie the BLM, namely that metal internalization is slow relative to the other steps involved in metal uptake (i.e. the M-X-cell complex is in equilibrium with metal species in solution), that internalization occurs via cation transport, and that internalization must occur for toxicity to appear. Recent experiments with freshwater algae are described, demonstrating anomalously high metal accumulation and/or toxicity in the presence of a common low molecular weight metabolite (alanine), or in the presence of an assimilable inorganic anion (thiosulfate). The possible implications of these findings for the application of the BLM to higher organisms are discussed.     

Metal sulfides in oxygenated aquatic systems: implications for the biotic ligand model

The Biotic Ligand Model (BLM) attempts to predict metal toxicity to aquatic organisms on the basis of metal speciation and effects at the cell surface. Current versions of the BLM for silver and copper consider metal binding by inorganic ligands, dissolved organic matter (DOM) and also competition at the cell surface from calcium and protons (pH). Recent studies reported in the geochemical and ecotoxicological literature have indicated the importance of sulfide as a ligand, even in fully oxygenated aquatic systems. Speciation calculations for oxygenated waters do not currently include reduced sulfur as a ligand and as a consequence, no version of the BLM model has been published including reduced sulfur. This reflects the limitations on our knowledge regarding reduced sulfur in aquatic systems. In this paper we highlight the need to include reduced sulfur in the Biotic Ligand Model, with the interaction between silver and inorganic metal sulfides as a specific example. The geochemical importance of metal sulfides as ligands for silver and the effect of 'dissolved' metal sulfide and other ligands on metal toxicity and accumulation are described and reviewed. Recommendations are made for future work needed to incorporate sulfide ligands into the BLM's modeling framework.     

Animal lectins: a historical introduction and overview

Some proteins we now regard as animal lectins were discovered before plant lectins, though many were not recognised as carbohydrate-binding proteins for many years after first being reported. As recently as 1988, most animal lectins were thought to belong to one of two primary structural families, the C-type and S-type (presently known as galectins) lectins. However, it is now clear that animal lectin activity is found in association with an astonishing diversity of primary structures. At least 12 structural families are known to exist, while many other lectins have structures apparently unique amongst carbohydrate-binding proteins, although some of those "orphans" belong to recognised protein families that are otherwise not associated with sugar recognition. Furthermore, many animal lectins also bind structures other than carbohydrates via protein-protein, protein-lipid or protein-nucleic acid interactions. While animal lectins undoubtedly fulfil a variety of functions, many could be considered in general terms to be recognition molecules within the immune system. More specifically, lectins have been implicated in direct first-line defence against pathogens, cell trafficking, immune regulation and prevention of autoimmunity.     

Plant metabolomics in biotic and abiotic stress: a critical overview

Abiotic and biotic stresses affect plant physiology and growth. The development of metabolomics, along with other -omics technologies, allowed in depth analysis of the reactive processes characterizing plant stress as the result of the alteration of metabolites and gene expressions. Here, we organize and interpret data from 151 studies to provide an overview about metabolomic shift after exposure to either abiotic or biotic stresses including drought, salinity, heat, heavy metal, cold, pathogens and insects. Data showed that amino acids, organic acids, sugars, and sugar alcohols quantities are influenced by stresses. Proline for example, increased in almost every stress condition, while other molecules increased or decreased depending specifically on plant tissue, plant species and type of applied stress. We concluded that although it is difficult to predict precisely what a stress will cause, some general metabolic trends can be described and improve our understanding of plant response to biotic and abiotic stresses.

     

Refinement and field validation of a biotic ligand model predicting acute copper toxicity to Daphnia magna

A previously developed biotic ligand model (BLM) was validated for its capacity to predict acute 48-h EC(50) values of copper to Daphnia magna in 25 reconstituted media with different pH values and concentrations of artificial dissolved organic carbon, Ca, Mg and Na. Before the BLM validation, fitting of measured (with a copper ion-selective electrode) and calculated (with the BLM) Cu(2+)-activity was performed by adjusting the WHAM model V (i.e. the metal-organic speciation part of the BLM) copper-proton exchange constant to pK(MHA)=1.9. Using this value, the 48-h EC(50) values observed agreed very well with BLM-predicted EC(50) values for tests performed at pH<8, but not at all for tests performed at pH>8. Additional experiments demonstrated that this was due to toxicity of the CuCO(3) complex, which is the most abundant inorganic copper species at pH>8. This was incorporated into the initial BLM by allowing the binding of CuCO(3) (next to Cu(2+) and CuOH(+)) to the biotic ligand of D. magna. The affinity of CuOH(+) and CuCO(3) for the biotic ligand was approximately five- and 10-fold lower than that of Cu(2+), respectively. With the refined BLM, 48-h EC(50) values could be accurately predicted within a factor of two not only in all 25 reconstituted media, but also in 19 natural waters. This validated and refined BLM could support efforts to improve the ecological relevance of risk assessment procedures applied at present.     

The exploitation of living resources in the Dutch Wadden Sea: a historical overview

An overview, based on written sources and personal observations, is presented of exploitation of living resources in and around the Dutch Wadden Sea during the past few centuries. It is concluded that before about 1900 exploitation was almost unrestricted. Exploitation of plants has been documented for saltmarshes and eelgrass beds. Fisheries have occurred for two species of hydroids, two species of polychaetes, one echinoderm species, at least seven species of molluscs, three species of crustaceans, and tens of species of fish. Hunting and egg collecting targeted almost all species of birds. Finally, two species of seals were exploited: information on exploitation of cetaceans is not available. Hence, it is likely that overexploitation may have been involved in the extirpation of several species. This supports an earlier suggestion that overexploitation played a part in the disappearance of at least 17 species from the Dutch Wadden Sea. This conclusion is confirmed by the observation that several extirpated species have returned after protective measures were introduced for the Dutch Wadden Sea area.     

The chemical nature of the factor responsible for embryonic induction: An historical overview

The discovery by Hans Spemann of the “organizer” tissue and its ability to induce the formation of the amphibian embryo’s neural tube inspired leading embryologists to attempt to elucidate embryonic induction’s underlying mechanisms. Since then several studies have described several developmental model system to better understand the role of specific signaling molecules, the interplay of different signals and tissue interactions in regulating tissue induction and patterning events. Different groups of workers set out to subject embryonic amphibian tissues and inductive adult organs to various extraction methods in the hope that the active agents could be isolated and chemically identified. In addition, a large number of well characterized chemical compounds were tested.     

The Leporid Datum: a late Miocene biotic marker

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A historical biogeographical protocol for studying biotic diversification by taxon pulses

Aim To present a historical biogeographical protocol for distinguishing biotic diversification by taxon pulse radiations from biotic diversification by vicariance. Location Mexico and northern Central America. Methods Brooks Parsimony Analysis (BPA), phylogenetic inference, linear correlation analysis. Results The taxon pulse radiation of 33 clades in nine areas of endemism in Mesoamerica is based on nine episodes of biotic expansion from three areas, and six episodes of vicariance, involving four geographical splits. Nineteen per cent of speciation events are due to vicariance, 25% to peripheral isolates speciation and 56% are within‐area events. The species–area curve has a correlation coefficient (r²) of 0.47. Extinction events and species richness are highly correlated (r² = 0.75), but colonization events and species richness are poorly correlated (r² = 0.36), suggesting that colonization is not the main determinant of the species–area relationship. Colonization events are more poorly correlated with size of area (r² = 0.05) than are in situ speciation events (r² = 0.60). Colonization events and in situ events are poorly correlated (r² = 0.02). All areas of endemism have reticulated histories, and have acted as both sources and islands at various times. Main conclusions Taxon pulses can be distinguished from maximum vicariance using this protocol; refining it requires a method for generating area cladograms from complex data and incorporation of direct dating of evolutionary events.     

Distribution of the freshwater fishes of Japan: an historical overview

Japanese freshwater fishes, including lampreys, comprise 15 orders, 35 families, and 96 genera, with 211 species and subspecies. Most belong to the families Cyprinidae (29% of species and subspecies), Gobiidae (21%), Salmonidae (10%), and Cobitidae (8%). Cyprinids and cobitids presumably originated from east Asia, gobiids from southeast Asia, and cottids and salmonids from the north Pacific. Japanese freshwater fishes include 88 endemic species and subspecies, of which three have been extirpated. Fishes introduced into natural rivers and lakes for inland commercial fisheries and sport fishing, and by accident, include many exotic species, of which 23 now inhabit natural freshwaters. These often have destroyed the local fish fauna by predation, and caused genetic pollution by hybridization with local strains. Destruction of freshwater environments by land development also poses a threat to Japanese freshwater fish communities. In addition Japanese freshwater systems have been markedly altered by development of rice paddy fields which have caused some species to decline but others to flourish, and changed the distribution patterns of fishes between upstream and downstream areas. To conserve endangered species and declining communities of Japanese freshwater fishes, we need to clarify the characteristics of their original habitats and the effects of developing paddy fields, from both the ecological and historical points of view.