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At least 865 records · Page 48Linked to original sources
PubMed1998

Cryptic species in marine polychaete and their independent introduction from North America to Europe.

The vast body of ballast water carried across oceans by freight ships represents a major source for the introduction of foreign species into marine ecosystems. The worm Marenzelleria viridis, originally found only in North America, appeared in estuaries of the North Sea in 1979 and 6 years later also in the Baltic, where it has developed into a major faunal element. Two competing hypotheses are discussed here: either both populations owe their presence to a single introductory event in the North Sea, or each population originated from a separate introduction. Our phylogeographic analysis of Baltic, North Sea and American Marenzelleria, based on mitochondrial 16S rDNA sequences (326-bp segment) of 98 individuals from 17 localities on the North American, North Sea, and Baltic coasts not only favors the two-event hypothesis, but also separates the locations of origin for the introductions. Eighteen mitochondrial genotypes were identified altogether. In agreement with allozyme data, three lineages were identified: genotypes assigned to the same lineage differed from each other by up to 5 point mutations, and those assigned to different lineages differed by up to 17. The existence of three morphologically indistinguishable, and thus cryptic, species is therefore suggested. The individuals from the Baltic Sea probably originated from the Atlantic coast of the United States between Chesapeake Bay and Georgia, and the North Sea populations may stem from the U.S. coast region north of Chesapeake Bay to Nova Scotia. Despite their similar morphologies, the two European Marenzelleria species may differ ecologically with respect to their preference for habitat salinity. Assuming that transport via ballast water occurs quite frequently, we hypothesize that both European cryptic species of Marenzelleria may originally have been introduced to both the North Sea and the Baltic Sea but that neither of them was able to proliferate in both water bodies owing to their differential physiological performances at high and low salinities.

Animals↗
PubMed1994

Cloning, expression and purification of a sarcoplasmic calcium-binding protein from the sandworm Nereis diversicolor via a fusion product with chloramphenicol acetyltransferase.

A gene coding for the Nereis sarcoplasmic calcium-binding protein (NSCP) was synthesized and expressed in Escherichia coli. The sequence of the gene was derived from the protein sequence by reverse translation. It possesses a number of unique, regularly spaced, restriction endonuclease cleavage sites to facilitate future site-directed mutagenesis. For the cloning strategy the gene sequence was divided into four parts. Three parts were cloned by ligation of hybridized oligomers and one part by inverse PCR. The protein was expressed as a fusion protein with the bacterial chloramphenicol acetyl-transferase (CAT), which could be easily purified by affinity chromatography. At the junction of the CAT and NSCP moieties a recognition site for the proteolytic enzyme factor Xa was built in. However, the distance between the moieties appeared to be crucial to warrant cleavage. A kinetic analysis showed that NSCP prepared from the sandworm and the one expressed by E. coli behaved in the same way. This system provides a basis for site-specific mutagenesis studies, in order to elucidate the molecular mechanism of cation binding and concomitant conformational changes.

Amino Acid Sequence↗
PubMed1999

The spawning pheromone cysteine-glutathione disulfide ('nereithione') arouses a multicomponent nuptial behavior and electrophysiological activity in Nereis succinea males.

The pheromone nereithione (cysteine-glutathione disulfide), which is released by swimming females of the polychaete Nereis succinea to activate spawning behavior of N. succinea males, has recently been identified and synthesized. Nereithione activates sperm release at less than 10(-6) M, one to two orders of magnitude less than oxidized glutathione or any other glutathione derivative tested. The glutathione fragment gamma-glu-cys inhibited sperm release. Nereithione aroused three components of the male nuptial behavior: circling, sperm release, and accelerated swimming. Electrophysiological activity elicited by nereithione near the sperm release site consisted of initial large spikes, cyclic bursting activity, and small spikes lasting up to a minute and was dose dependent, rapid, reversible, and repeatable. This preparation is an excellent model system for characterizing the receptors and functions of a marine pheromone.

Animals↗
PubMed1993

Aspects of life development at deep sea hydrothermal vents.

Hydrothermal vent organisms are living in an unexpected deep-sea environment, several thousand meters below the surface, where the earth's crustal plates are spreading apart. The vent fluids are usually hot (350 degrees C), anoxic, and contain high concentrations of hydrogen sulfide. This environment may be considered as extreme given the pressure, the high temperature, the chemical toxicity of the fluids, and the total lack of photosynthetic production for animal nutrition. The recent discovery of the unique fauna of the hydrothermal vent communities has brought an unexpected mode of animal nutrition in which chemoautotrophic bacterial symbionts are maintained within specialized cells of the host animal. The bacterial symbionts obtain energy by oxidizing reduced sulfur compounds from the environment. A portion of this fixed carbon is used by the eukaryotic host. The present review will focus on four of the main topics studied on the paradigmatic vent organism Riftia pachyptila, a giant gutless tube worm: 1) the chemoautotrophic symbiosis, 2) the toxicity of hydrogen sulfide, 3) the characteristics of the extracellular matrices of the worms, especially data obtained on collagens, and 4) the influence of temperature and pressure on worm biology.

Adaptation, Physiological↗
PubMed1986

Potassium channels in Myxicola giant axons.

This article describes an initial step in the study of potassium ion (K+) channel properties and their role in the control of patterns of action potential frequency. The purpose of the study was to determine the effect of the K+ channel blocker 4-aminopyridine on the conductance of the K+ channels in Myxicola. If this pharmacologic agent modifies one or more of the multiple kinetic components of the K+ channel conductance, it may be expected to alter the physiological properties of normal and pathological nerve fibers. Experiments were performed on 19 internally perfused voltage-clamped Myxicola infundibulum giant axons. After accounting for the time-dependent accumulation of K+ in the surrounding periaxonal spaces, the K+ conductance activates biphasically. The external application of 4-aminopyridine (20 mmol/L) specifically blocks the fast component of activation of the K+ conductance.

4-Aminopyridine↗
PubMed1999

Phylogenetic approaches to nomenclature: a comparison based on a nemertean case study.

Phylogenetic approaches to biological nomenclature are becoming increasingly common. Here I compare the behaviour of two such approaches, the phylogenetic system of definition and the phylogenetic system of reference, when there is a shift in the preference of phylogenetic hypotheses. The comparison is based on a case study from nemertean systematics and is the first to compare two different phylogenetic approaches throughout three stages of change, including two stages of phylogenetic nomenclature. It is concluded that a phylogenetic system of reference in combination with uninomials is superior in conveying phylogenetic information.

Animals↗
PubMed2001

A three-dimensionally preserved fossil polychaete worm from the Silurian of Herefordshire, England.

Polychaete body fossils are rare, and are almost invariably compressed and too poorly preserved for meaningful comparison with extant forms. We here describe Kenostrychus clementsi gen. et sp. nov. from the Silurian Herefordshire Konservat-Lagerstätte of England, in which three-dimensional external morphology is preserved with a fidelity unprecedented among fossil polychaetes. The fossils, which are preserved in calcite, were serially ground and photographed at 30 microm intervals to produce computer-generated reconstructions of the original external surface. The new genus has a generalized polychaete morphology with large biramous parapodia, unspecialized anterior segments and a small prostomium with median and lateral antennae and ventral prostomial palps. Cirriform branchiae arise from the ventral surface of each notopodium, and may be homologous with the inter-ramal branchiae of the extant nephtyids. Through cladistic analysis, Kenostrychus is interpreted as a member of a stem group of either the Phyllodocida or the Aciculata (Phyllodocida + Eunicida). Direct comparison with other fossil forms is difficult, but hints that inter-ramal respiratory structures may be primitive within the Phyllodocida and/or the Aciculata.

Animals↗
PubMed2004

Thermal selection of PGM allozymes in newly founded populations of the thermotolerant vent polychaete Alvinella pompejana.

Alvinella pompejana lives on the top of chimneys at deep-sea hydrothermal vents of the East Pacific Rise. It is thought to be one of the most thermotolerant and eurythermal metazoans. Our experimental approach combines methods of population genetics and biochemistry, considering temperature as a potential selective factor. Phosphoglucomutase (Pgm-1 locus) is one of the most polymorphic loci of A. pompejana and exhibits four alleles, from which alleles 90 and 100 dominate with frequencies of approximately 0.5 in populations. Results from previous studies suggested that allele 90 might be more thermostable than allele 100. Significant genetic differentiation was found by comparing contrasted microhabitats, especially the young, still hot, versus older and colder chimneys, with allele 90 being at highest frequency on young chimneys. Moreover the frequency of allele 90 was positively correlated with mean temperature at the opening of Alvinella tubes. In parallel, thermostability and thermal optimum experiments demonstrated that allele 90 is more thermostable and more active at higher temperatures than allele 100. This dataset supports an additive model of diversifying selection in which allele 90 is favoured on young hot chimneys but counterbalanced over the whole metapopulation by the dynamics of the vent ecosystem.

Animals↗
PubMed2005

Shallow marine benthic invertebrates of the Seychelles Plateau: high diversity in a tropical oligotrophic environment.

Soft sedimentary biotopes are extensive in the shallow Western Indian Ocean, especially on the Seychelles Plateau and Mascarene Ridge, yet pro rata compared with coral reefs the research effort devoted to them has been minimal. In this study we examine the benthic mollusc and polychaete worm assemblages of the shallow waters (11-62 m) around Mahe, in the Seychelles, and make direct comparisons with the temperate Irish Sea area and subtropical waters of Hong Kong, China (using identical methodology). Two assemblages were recognized, characterized by depth and sediment type. Of these, assemblage A (in shallow carbonate sands) was the most diverse, with diversity and richness measures exceeding those from the Irish Sea or Hong Kong. Hong Kong generally had the poorest fauna. Considering the Bivalvia alone, estimates of taxonomic distinctness showed this to be least for Seychelles assemblage A. The degree of conformity of the results to the concept of the latitudinal gradient in species richness and the possible underlying causes are discussed. Comparisons with other data suggest that the Seychelles support a benthic fauna at least as diverse as any other described from the tropics. A tentative examination of total bivalve species richness suggests a total of 400-500 for the Seychelles. This is in keeping with other Indian Ocean localities, but higher than known figures for continental east Africa. The findings of this paper support the case for widespread ecological and taxonomic studies of the Western Indian Ocean benthic invertebrates.

Animals↗
PubMed1979

Pollution-induced changes in populations.

The effects of pollution by organic matter, oil or industrial waste on marine communities are remarkably similar. Diversity values fall, biomass and numbers of organisms initially rise and then fall as the pollution load is increased. Diversity indices are, however, insensitive to pollution-induced changes and have to be assessed subjectively. Departure from a log-normal distribution of individuals among species offers a sensitive and objective method of assessing perturbation effects on communities. Under severe pollution stress, the dominant species are those which have a flexible life-history ranging from direct development to a planktonic larva and the ability to undergo short-term genetic selection. Species have a somewhat less flexible life-history strategy show increased abundance under conditions of slight pollution. The increase in abundance of seven or eight neither rare nor common species, which gives the departure from a log-normal distribution, is suggested as being the most significant and the earliest detectable change caused by pollution in a community. Thus the presence of a species in a polluted area may be more a question of life-history strategy than the tolerance of adverse environmental conditions. If this hypothesis is correct, considerable doubt must beplaced on the ecological relevance of data from toxicity tests.

Animals↗
PubMed2002

Population growth rate as a basis for ecological risk assessment of toxic chemicals.

Assessing the ecological risks of toxic chemicals is most often based on individual-level responses such as survival, reproduction or growth. Such an approach raises the following questions with regard to translating these measured effects into likely impacts on natural populations. (i) To what extent do individual-level variables underestimate or overestimate population-level responses? (ii) How do toxicant-caused changes in individual-level variables translate into changes in population dynamics for species with different life cycles? (iii) To what extent are these relationships complicated by population-density effects? These issues go to the heart of the ecological relevance of ecotoxicology and we have addressed them using the population growth rate as an integrating concept. Our analysis indicates that although the most sensitive individual-level variables are likely to be equally or more sensitive to increasing concentrations of toxic chemicals than population growth rate, they are difficult to identify a priori and, even if they could be identified, integrating impacts on key life-cycle variables via population growth rate analysis is nevertheless a more robust approach for assessing the ecological risks of chemicals. Populations living under density-dependent control may respond differently to toxic chemicals than exponentially growing populations, and greater care needs to be given to incorporating realistic density conditions (either experimentally or by simulation) into ecotoxicological test designs. It is impractical to expect full life-table studies, which record changes in survival, fecundity and development at defined intervals through the life cycle of organisms under specified conditions, for all relevant species, so we argue that population growth rate analysis should be used to provide guidance for a more pragmatic and ecologically sound approach to ecological risk assessment.

Animals↗
PubMed1997

Vibrio diabolicus sp. nov., a new polysaccharide-secreting organism isolated from a deep-sea hydrothermal vent polychaete annelid, Alvinella pompejana.

A deep-sea, facultatively anaerobic, heterotrophic, mesophilic new organism was isolated from the polychaete annelid Alvinella pompejana collected from a deep-sea hydrothermal field in the East Pacific Rise. On the basis of phenotypic characteristics, phylogenetic analyses, and DNA-DNA relatedness, this organism was identified as a new species of the genus Vibrio, for which the name Vibrio diabolicus is proposed. In batch cultures in the presence of glucose, this organism produced an innovative exopolysaccharide. This polymer had high contents of both uronic acids and hexosamines and was similar to other polysaccharides with interesting biological activities.

Animals↗