Eel urea transporter is localized to chloride cells and is salinity dependent

Urea transporters (UTs) in the ureotelic vertebrates have been well-characterized, but little is known about those of the ammonotelic teleost fishes. To clarify the physiological roles of UTs in the ammonotelic teleosts, we determined the structure, tissue and cellular localizations, and regulation of expression of eel UT (eUT) by cDNA cloning, Northern analysis, and immunohistochemistry. A full-length cDNA (approximately 1.9 kb) coding for a UT of 486 amino acid residues was isolated from a seawater eel gill cDNA library. Sequence comparison with those of other species indicated that the eUT is a short isoform with 10 transmembrane spans and has longer NH2- and COOH-terminal cytoplasmic tails compared with the mammalian counterparts. Northern blot analysis demonstrated high expression of eUT mRNA confined in the gill and a substantial increase of its levels when eels were transferred from freshwater to seawater. Immunohistochemistry showed that eUT is localized on the basolateral membranes of the chloride cells, establishing, at the cellular level, the site of urea excretion in the eel, an ammonotelic teleost.     

ilvU, a locus in Escherichia coli affecting the derepression of isoleucyl-tRNA synthetase and the RPC-5 chromatographic profiles of tRNAIle and tRNAVal.

A mutation in the ilvU locus of Escherichia coli has led to a complex phenotype that included resistance to thiaisoleucine, a loss of derepressibility of isoleucyl tRNA synthetase, and an alteration of the RPC-5 chromatographic profile of the branched-chain aminoacyl-tRNA's. The alterations were manifest in an increase in the amount of Species 2 of both tRNAIle and tRNAVal at the expense of Species 1. A similar alteration, but independent of (and additive to) that caused by the ilvU mutation, was observed upon limitation of either isoleucine or valine. The shift in profile caused by limitation was also independent of the reduced growth rate or the derepression of the isoleucine and valine biosynthetic enzymes that also result from limitation. During chloramphenicol treatment nearly all tRNAIle and tRNAVal formed appears as species 2. Upon recovery from chloramphenicol, Species 2 of both acceptors are converted to Species 1. It is proposed that the ilvU product not only allows derepression of isoleucyl-tRNA synthetase but also retards the conversion of tRNA2Ile to tRNA1Ile and that of tRNA2Val to tRNA1Val. The mutated ilvU loci abolish the derepression and are more efficient in retarding the conversion.     

Sequential up-regulation of thyroid hormone beta receptor, ornithine transcarbamylase, and carbamyl phosphate synthetase mRNAs in the liver of Rana catesbeiana tadpoles during spontaneous and thyroid hormone-induced metamorphosis.

During both spontaneous and thyroid hormone (TH)-induced metamorphosis, the Rana catesbeiana tadpole undergoes postembryonic developmental changes in its liver which are necessary for its transition from an ammonotelic larva to a ureotelic adult. Although this transition ultimately results from marked increases in the activities and/or de novo synthesis of the urea cycle enzymes, the precise molecular means by which TH exerts this tissue-specific response are presently unknown. Recent reports, using RNA from whole Xenopus laevis tadpole homogenates and indirect means of measuring TH receptor (TR) mRNAs, suggest a correlation between the up-regulation of TR beta-mRNAs and the general morphological changes occurring during amphibian metamorphosis. To assess whether or not this same relationship exists in a TH-responsive tissue, such as liver, we isolated and characterized a cDNA clone containing the complete nucleotide sequence for a R. catesbeiana urea cycle enzyme, ornithine transcarbamylase (OTC), as well as a genomic clone containing a portion of the hormone-binding domain of a R. catesbeiana TR beta gene. Through use of these homologous sequences and a heterologous cDNA fragment encoding rat carbamyl phosphate synthetase (CPS), we directly determined the relative levels of the TR beta, OTC, and CPS mRNAs in liver from spontaneous and TH-induced tadpoles. Our results establish that TH affects an up-regulation of mRNAs for its own receptor prior to up-regulating CPS and OTC mRNAs. Moreover, results with cultured tadpole liver demonstrate that TH, in the absence of any other hormonal influence, can affect an up-regulation of both the TR beta and OTC mRNAs.     

Electrophysiological abnormalities produced by ammonium in isolated perfused brook trout, Salvelinus fontinalis, hearts

Electrocardiographic (ECG) abnormalities and arrhythmias have been observed in hyperammonemic patients and in animals injected with ammonium salts. Ammonium is excreted directly into the environment by fish, and it is a potent fish toxin, but the effects of ammonium on the cardiovascular system of fish are unknown. This study investigated the cardiotoxic effects of ammonium on isolated perfused fish hearts. These were compared with ammonium-induced cardiac electrophysiological abnormalities observed in humans and other experimental animals. Isolated perfused fish hearts exhibit ammonium-induced cardiac abnormalities similar to the ammonium-induced abnormalities seen in the hearts of higher vertebrates. Therefore, we conclude that the myocardium of ammonotelic species does not possess a specialized ammonium detoxification mechanism, and that ammonium is cardiotoxic to salmonid fish.     

Comparison of xanthine: NAD+ oxidoreductase from liver of toad Bufo viridis and other vertebrates

1. Xanthine oxidoreductase was isolated from toad Bufo viridis (a mainly ureotelic amphibian species) and partially purified. The enzyme occurred as a stable xanthine: NAD+ oxidoreductase (EC 1.1.1.204), unconvertible to the oxidase form. 2. Some properties of the enzyme resembled those of xanthine oxidoreductase from an ammonotelic fish, Cyprinus carpio, and the ureotelic rat, but in other aspects it was similar to this enzyme from an uricotelic snake, Natrix natrix. 3. Inhibition of the toad enzyme by NADH at high non-physiological concentrations rules out a modulation of its oxypurine-hydroxylating activity by in vivo changes in the NADH/NAD+ ratio. Therefore, toad xanthine oxidoreductase plays no regulatory role in the purine nucleotide metabolism.     

Litter quality effects of beech and hornbeam on undergrowth species diversity in Luxembourg forests on limestone and decalcified marl

Question: Do beech and hornbeam differ in undergrowth species diversity, and could these differences be explained by mass of the organic layer, pH or soil moisture? Could species richness under beech and hornbeam be explained by differences in N dynamics? Location: Ancient forests dominated by beech and hornbeam in Luxembourg, on decalcified and lime‐rich parent material. Methods: Species composition and soil characteristics, i.e. mass of the organic layer, pH, moisture content, bulk density and air‐filled pore space, were determined under beech and hornbeam on decalcified marl and limestone, and analysed with cluster analysis, correspondence analysis and ANOVA, with tree species and parent material as independent factors. Net N mineralization, nitrification and N in soil and microbial biomass were determined in a laboratory incubation experiment over a pH gradient, and correlated with species richness. Results: Species richness was lower under beech than under hornbeam on both decalcified marl and on limestone. Mass of the organic layer was higher under beech in all cases, but pH and soil moisture only differed between tree species on decalcified marl. Species richness increased with soil N, microbial N and nitrification in the mineral topsoil, but was not correlated with net N mineralization, and was negatively correlated with nitrification in the organic layer and with efficiency of N mineralization per unit microbe. Conclusion: Litter quality affected species richness on both limestone and decalcified marl via the organic layer, but only on decalcified marl in terms of pH or soil moisture. Species richness did not seem to be stimulated by high overall net N mineralization or high nitrate availability in the organic layer, but only by high nitrate in the mineral topsoil.     

Adenosine triphosphate-activated adenylate deaminase from marine invertebrate animals. Properties of the enzyme from lugworm (Arenicola cristata) body-wall muscle.

Adenylate deaminase (AMP aminohydrolase, EC 3.5.4.6) from lugworm (Arenicola cristata) body-wall muscle was partially purified by extraction in KCl solutions and chromatography on phosphocellulose. Enzyme activity was eluted from the column at two salt concentrations. Both forms show co-operative binding of AMP (Hill coefficient, h, 2.85) with s0.5 values of 20 mM and 15.6 mM. ATP and ADP act as positive effectors lowering h to 1.07 and s0.5 to 2mM. The apparent Ka (activation) for ATP was 1.5mM. GTP is an inhibitor with an apparent Ki of 0.12 mM. In vivo the ATP-activated adenylate deaminase is in the active form and may be regulated by changes in GTP concentrations. Adenylate deaminase may act as a primary ammonia-forming enzyme in ammonotelic marine invertebrates with the purine nucleotide cycle.     

Biodiversity, productivity and the temporal stability of productivity: patterns and processes

Theory predicts that the temporal stability of productivity, measured as the ratio of the mean to the standard deviation of community biomass, increases with species richness and evenness. We used experimental species mixtures of grassland plants to test this hypothesis and identified the mechanisms involved. Additionally, we tested whether biodiversity, productivity and temporal stability were similarly influenced by particular types of species interactions. We found that productivity was less variable among years in plots planted with more species. Temporal stability did not depend on whether the species were planted equally abundant (high evenness) or not (realistically low evenness). Greater richness increased temporal stability by increasing overyielding, asynchrony of species fluctuations and statistical averaging. Species interactions that favoured unproductive species increased both biodiversity and temporal stability. Species interactions that resulted in niche partitioning or facilitation increased both productivity and temporal stability. Thus, species interactions can promote biodiversity and ecosystem services.     

Histochemical studies on the mucopolysaccharides of the developing chick kidney. II. Mucopolysaccharides of the collecting tubules and excretory ducts.

Mucopolysaccharides of the collecting tubules and excretory ducts of developing chick kidney were studied histochemically to elucidate the relations, between the changing chemical properties of these compounds and excretory processes during pronephric, mesonephric and metanephric developmental stages. At the pronephric ammonotelic stage the collecting tubules contain only neutral mucopolysaccharides, whereas at the mesonephric ureotelic stage neutral mucopoly saccharides are found till the 9th day. Sialic acids make their appearance in luminal border regions of the mesonephric collecting tubules from the 9th day on, their concentration being highest on the 15th day. Hyaluronic acid is observed from the 16th day on. Its concentration is predominant in hatched young birds and increases with age. The physiological significance of alterations in the mucopolysaccharides contents is discussed.     

Assessing protection for imperiled species of nevada, U.S.A.: are species slipping through the cracks of existing protections?

To assess whether imperiled species are covered by existing protections in the biologically-rich state of Nevada, U.S.A., we compared the distribution of reserves with known imperiled species occurrences. For species poorly represented in reserves, we determined whether they were receiving alternate protection under the U.S. Endangered Species Act or voluntary conservation plans. A majority (212, 55%) of Nevada’s 384 imperiled species had fewer than 25% of occurrences in reserves and most (282, 68%) had fewer than 50% of occurrences in reserves. Of imperiled species with less than 25% or fewer than two occurrences in reserves, only 9% are currently receiving alternate protection from the Endangered Species Act or voluntary plans. These results suggest that providing protection for imperiled species in Nevada will require both an expansion of the existing reserve system, which currently covers 14% of the state, and protection of more species under the Endangered Species Act or other programs. By dividing Nevada into equal-sized hexagons and scoring each of these hexagons based on a rarity-weighted richness index of imperiled species occurrences, we identified 19 imperiled species hot spots in Nevada. No imperiled species occurrences were protected in seven (37%) and less than half were protected in 11 (58%) of these hot spots. Protecting these areas could provide important additional protection for imperiled species in Nevada. Evaluations of protective measures for biological diversity should include the full suite of protections, including both reserves and laws and regulations.     

Haemolymph osmolality,acid-base balance and shift of ammonotelic to ureotelic excretory pattern of Penaeus japonicus exposed to ambient ammonia

1. Urea-N and nitrite-N excretions of Penaeus japonicus (11.70 ± 2.30 g) increased, but ammonia-N excretion decreased with increased ambient ammonia-N, as they were exposed individually to 0.055 (control), 1.011, 5.121, 10.032 and 20.335 mg/l ammonia-N after 24 hr.2. Haemolymph pH, PCO₂ and osmolality of shrimp displayed an inverse linear relationship with concentration of ambient ammonia-N.3. Shrimp exposed to 10.032 mg/l ammonia-N after 24 hr significantly affected (P < 0.05) haemolymph PCO₂ and osmoregulatory capacity.4. Accumulated ammonia-N in the haemolymph of shrimp following exposure to ambient ammonia-N at 5.121 mg/l or greater caused a shift from an ammonotelic to a ureotelic pattern, and may cause catabolism of hemocyanin and protein to free amino acids to balance osmoregulation.     

Sequential up-regulation of thyroid hormone β receptor,ornithine transcarbamylase,and carbamyl phosphate synthetase mRNAs in the liver of Rana catesbeiana tadpoles during spontaneous and thyroid hormone-induced metamorphosis

During both spontaneous and thyroid hormone (TH)-induced metamorphosis, the Rana catesbeiana tadpole undergoes postembryonic developmental changes in its liver which are necessary for its transition from an ammonotelic larva to a ureotelic adult. Although this transition ultimately results from marked increases in the activities and/or de novo synthesis of the urea cycle enzymes, the precise molecular means by which TH exerts this tissue-specific response are presently unknown. Recent reports, using RNA from whole Xenopus laevis tadpole homogenates and indirect means of measuring TH receptor (TR) mRNAs, suggest a correlation between the up-regulation of TRβ-mRNAs and the general morphological changes occurring during amphibian metamorphosis. To assess whether or not this same relationship exists in a TH-responsive tissue, such as liver, we isolated and characterized a cDNA clone containing the complete nucleotide sequence for a R. catesbeiana urea cycle enzyme, ornithine transcarbamylase (OTC), as well as a genomic clone containing a portion of the hormone-binding domain of a R. catesbeiana TRβ gene. Through use of these homologous sequences and a heterologous cDNA fragment encoding rat carbamyl phosphate synthetase (CPS), we directly determined the relative levels of the TRβ, OTC, and CPS mRNAs in liver from spontaneous and TH-induced tadpoles. Our results establish that TH affects an up-regulation of mRNAs for its own receptor prior to up-regulating CPS and OTC mRNAs. Moreover, results with cultured tadpole liver demonstrate that TH, in the absence of any other hormonal influence, can affect an up-regulation of both the TRβ and OTC mRNAs. © 1992 Wiley-Liss, Inc.     

Species dynamics alter community diversity–biomass stability relationships

The relationship between community diversity and biomass variability remains a crucial ecological topic, with positive, negative and neutral diversity–stability relationships reported from empirical studies. Theory highlights the relative importance of Species–Species or Species–Environment interactions in driving diversity–stability patterns. Much previous work is based on an assumption of identical (stable) species‐level dynamics. We studied ecosystem models incorporating stable, cyclic and more complex species‐level dynamics, with either linear or non‐linear density dependence, within a locally stable community framework. Species composition varies with increasing diversity, interacting with the correlation of species' environmental responses to drive either positive or negative diversity–stability patterns, which theory based on communities with only stable species‐level dynamics fails to predict. Including different dynamics points to new mechanisms that drive the full range of diversity–biomass stability relationships in empirical systems where a wider range of dynamical behaviours are important.     

Plant biodiversity inventory and conservation of two tropical dry evergreen forests on the Coromandel coast, south India

Species diversity, population structure, abundance and dispersion patterns of all woody plants 10cm gbh were inventoried in two 1-ha plots of tropical dry evergreen (sacred grove or temple) forests at Kuzhanthaikuppam (KK) and Thirumanikkuzhi (TM) on the Coromandel coast of south India. Site KK is a stunted forest (average tree height ca 6 m) and TM a tall forest (average tree height ca 10 m). A total of 54 species (in 47 genera and 31 families) were recorded. Species richness and stand density were 42 and 38 species and 1367 and 974 individuals ha–1 respectively for the sites KK and TM. About 50% of the total species were common to both the sites. Site TM is twofold more voluminous (basal area 29.48 m2 ha–1) than KK (basal area 15.44 m2 ha–1). Nearly one third of the individuals are multi-stemmed in the low-statured site KK whereas one fourth of the tree density is multi-stemmed in TM. Species abundance pattern varied between the two sites. The abundance of three species in KK and two species in TM is pronounced. Memecylon umbellatum, the most abundant species contributing to one third of total stand density in KK, is least represented in TM. Species richness, density and diversity indices decreased with increasing girth threshold. Most species exhibited clumped dispersion of individuals both at 0.25 and 1-ha scales. Population structure for girth frequency is an expanding one for both the sites, except for basal area distribution in KK. Variations in plant diversity and abundance are related to site attributes and human impacts. In the light of habitat uniqueness, species richness and sacred grove status, the need for conservation is emphasized.     

Species traits and recolonization processes after flood disturbances in riverine macrophytes

Macrophyte recolonization after two major flood disturbances (winter 1990 and autumn 1991) was studied for 3 years in 11 contiguous permanent quadrats located along a transect from one bank to the other across a former channel of the Rhône River. Floods induced changes in substrate grain-size from fine to coarser sediment and swept away all the plants present before disturbance. Re-establishment of species started on or near the banks in fine sediment areas that can act as refuges for propagules during disturbance or as regeneration niches for propagules brought in by floods. From the banks, the species expanded towards the center of the channel in coarse sediment. The transect was fully colonized by macrophytes the second year after a major flood. All these species, as well as those observed before the 1990 flood, can be considered as pioneer species adapted to frequent disturbances. Information identified from personal previous observations and collected in literature concerning selected species traits was analysed statistically using a fuzzy-coding technique and confronted with date of re-establishment of each species after disturbance. Species composition before disturbance and selected species traits allow us to predict species composition in disturbed areas. The first species to re-establish were able to produce turions or other non-subterranean vegetative organs. Species that disseminate both by lateral spread and regeneration by stem fragments re-establish later, before helophytes that also disseminate by lateral spread but flower each year.Abbreviations CA Correspondence Analysis Species abbreviations used in figures and tables are listed in Appendix 1     

Characterising insect diversity on Australia’s remnant native grasslands: ants (Hymenoptera: Formicidae) and beetles (Coleoptera) at Craigieburn Grasslands Reserve,Victoria

Ants and beetles sampled by pitfall trapping on a large grassland remnant near Melbourne, Victoria, are enumerated and discussed. Species richness of both groups differed little between grassy flat areas and more rocky knolls, or between early and late summer. Seasonal differences in abundance were found in both taxa: beetles were more abundant in early summer, and ants more abundant in late summer. Implications of such differences for rapid sampling of grassland insects in the region are discussed.     

Saturating effects of species diversity on life-history evolution in bacteria

Species interactions can play a major role in shaping evolution in new environments. In theory, species interactions can either stimulate evolution by promoting coevolution or inhibit evolution by constraining ecological opportunity. The relative strength of these effects should vary as species richness increases, and yet there has been little evidence for evolution of component species in communities. We evolved bacterial microcosms containing between 1 and 12 species in three different environments. Growth rates and yields of isolates that evolved in communities were lower than those that evolved in monocultures, consistent with recent theory that competition constrains species to specialize on narrower sets of resources. This effect saturated or reversed at higher levels of richness, consistent with theory that directional effects of species interactions should weaken in more diverse communities. Species varied considerably, however, in their responses to both environment and richness levels. Mechanistic models and experiments are now needed to understand and predict joint evolutionary dynamics of species in diverse communities.     

Why the Phylogenetic Species Concept?—Elementary

Although species play a number of unique and necessary roles in biology, none are more important than as the elements of phylogeny, nomenclature, and biodiversity study. Species are not divisible into any smaller units among which shared derived characters can be recognized with fidelity. Biodiversity inventory, assessment, and conservation are dependent upon a uniformly applicable species concept. Species are the fundamental units in formal Linnaean classification and zoological nomenclature. The Biological Species Concept, long given nominal support by most zoologists, forced an essentialy taxonomic problem (what are species?) into a population genetics framework (why are there species?). Early efforts at a phylogenetic species concept focused on correcting problems in the Biological Species Concept associated with ancestral populations, then applying phylogenetic logic to species themselves. Subsequently, Eldredge and Cracraft, and Nelson and Platnick, each proposed essentially identical and truly phylogenetic species concepts that permitted the rigorous recognition of species prior to and for the purposes of phylogenetic analysis, yet maintained the integrity of the Phylogenetic Species Concept outside of cladistic analysis. Such phylogenetic elements have many benefits, including giving to biology a unit species concept applicable across all kinds of living things including sexual and asexual forms. This is possible because the Phylogenetic Species Concept is based on patterns of character distributions and is therefore consistent with the full range of possible evolutionary processes that contribute to species formation, including both biotic and abiotic (even random) factors.     

The Association of Dispersal and Persistence Traits of Plants with Different Stages of Succession in Central European Man-Made Habitats

Traits related to seed dispersal, clonality and bud bank affect the success or failure of plant species. Using data from 13 successional seres in various human-made habitats the spectra of traits associated with dispersal and persistence were compared to determine the traits that can be used to predict the occurrence of particular plant species at each stage in a succession and how the importance of these traits changes over time. Differences in the traits of species associated with primary and secondary successions were also studied. Species with seeds that are dispersed by water (hydrochory) decreased in abundance during the course of succession. Species with a splitting main root, monocyclic and dicyclic shoots also decreased in abundance. Species capable of forming a potential below-ground bud bank, hypogeogenous rhizome and retaining a long-term connection with clonal offspring increased in abundance. The results indicate that seed dispersal is more important in determining the species composition in the early stages of succession whereas bud banks and clonal traits are more important in the later stages and for colonizing a locality. Primary and secondary seres did not remarkably differ in the trait spectra of the species present indicating that these trends occur in both types of succession.