bluuebunny/crossref_metadata_2025 huggingface dataset:
Freezing in nonacclimated oat: thermal response and histological observations of crowns during recovery
Authors: Livingston David P. , Tallury Shyamalrau P. , A. Owens Shirley , Livingston Jesse D. , Premkumar Ramaswamy
Published: June 2006

The complex nature of freezing in plants may be easier to understand if freezing is studied in nonacclimated plants at temperatures just below freezing. Thermal patterns of model systems frozen at –2.6 °C were compared with those of crown tissue from oat ( Avena sativa L.). Thermal patterns of live crowns more closely resembled those of fructan and sugar solutions with filter paper than of plain water or a BSA solution. When the percentage of water freezing in nonacclimated plants at –2.6 °C was manually limited to 10%, the survival was reduced from 100% in supercooled plants to 25%. During cold acclimation, the percentage of water freezing at –2.6 °C went from 79% to 54% after 3 weeks of cold acclimation and resulted in 100% survival. The nucleus of cells in the primary apical meristem of nonacclimated plants appeared to have disintegrated, an effect that was not observed in any cold-acclimated (unfrozen controls) plants. Nuclear pycnosis was observed in leaf sheaths surrounding the meristem and in cells directly below the meristem. Cells of secondary meristems and in the crown core appeared undamaged, but vessels in plants frozen for as little as 30 min were ruptured and appeared plugged. The distinctive nature of injury in the apical meristem and the rapid ability of the plant to acclimate during cold to the stress causing this injury indicate that specific tissue, namely the apical region of the crown, should be the focus of attention when attempting to determine cause and effect between genetics or metabolism and cold acclimation in winter cereals.
Three hundred years of human-induced change in an urban lake: paleolimnological analysis of Lac Saint-Augustin, Québec City, Canada
Authors: Pienitz Reinhard , Roberge Karine , Vincent Warwick F.
Published: June 2006

Lac Saint-Augustin provides a unique record of anthropogenic change during the settlement and evolution of Québec City, one of North America’s oldest cities. Lac Saint-Augustin is an urban lake that has been subject to three centuries of direct human impacts, with the most pronounced changes in trophic status and chemistry occurring within the last few decades. This accelerated eutrophication has greatly limited the present recreational opportunities for lake visitors and residents. A paleolimnological study of Lac Saint-Augustin was undertaken to identify the causes of this degradation and to place these changes within the context of historical development in the lake’s catchment. Biological and chemical indicators identified three major periods in the recent history of Lac Saint-Augustin. The first period (1670–1750) corresponds to the arrival of the first settlers at the lake and the construction of a diversion canal; at that time, the lake was characterized by oligo- to meso-trophic conditions (as indicated by diatom species of the genus Aulacoseira ) and low concentrations of chlorophyll a, total carotenoids, total phosphorus, and metals. The second period (1750–1904) corresponds to increased human colonization and was marked by slight increases in sedimentary metal and total phosphorus concentrations. The third period (1904–2002) coincides with an intensification of agriculture, the expansion of Québec City, and the urbanization of the catchment. At this time, there was a complete change in the diatom flora (predominance of Stephanodiscus hantzschii ) as well as major increases in fossil pigment concentrations, nutrients, and sedimentary chemical levels. Diatom species typical of saline waters also appeared coincident with the use of road salts on a highway that passes through the lake’s catchment. With the increasing demands for greater use of inland waters, multiproxy, long-term data of the kind provided here are essential to make informed management decisions.
The biotransformation of mercury in pH-stat cultures of microfungi
Authors: Kelly David J.A. , Budd Kenneth , Lefebvre Daniel D.
Published: June 2006

The biotransformation of mercury was monitored in Hymenoscyphus ericae (Read) Korf & Kernan, Neocosmospora vasinfecta E. F. Sm., and Verticillium terrestre (Link) Lindau following the exposure of these fungi to environmentally relevant doses of HgII(HgCl2) in aerated pH-controlled cultures. Mercury applied at 120 and 300 μg·L–1quickly associated with cells of N. vasinfecta. Within 3 h, approximately 80% of the remaining Hg in both treatments had been converted to β-HgS, and at 8 h, 15% and 53% of the original doses had been converted into volatile Hg0. Hymenoscyphus ericae was less efficient at converting HgIIto β-HgS, but it volatilized larger amounts of Hg0. A mercury-tolerant isolate of V. terrestre withstood levels of Hg in the parts per million. When exposed to 270, 1000, or 2000 μg·L–1HgCl2, 93% ± 3% of the amounts remaining in cultures of V. terrestre after 2 h was β-HgS. At 2 mg·L–1, 72% of the Hg was reduced to Hg0in 2 h. Volatilization accounts for the tolerance of V. terrestre to high doses of Hg, whereas the conversion of Hg to β-HgS was the major detoxifying mechanism at lower doses. The formation of β-HgS occurs preferentially with volatilization operating as the default pathway, when the former biotransformation mechanism is saturated.
Phylogenetic position ofArabis arenicolaand generic limits ofAphragmusandEutrema(Brassicaceae) based on sequences of nuclear ribosomal DNA
Authors: Warwick Suzanne I. , Al-Shehbaz Ihsan A. , Sauder Connie A.
Published: June 2006

Sequence data from the nuclear ribosomal internal transcribed spacer (ITS) region of 45 taxa were used to determine the phylogenetic relationship of Arabis arenicola to Arabis , Arabidopsis , Braya , and Eutrema , and that of Eutrema to the purportedly related genera Aphragmus , Lignariella , Neomartinella , Platycraspedum , Taphrospermum , and Thellungiella . Arabis arenicola was originally described as Eutrema in 1830, transferred to Arabis in 1898, and has remained in Arabis to the present, even though it is morphologically more similar to Arabidopsis, Braya, and Eutrema. Sequence data were obtained from representative taxa of Arabis, Arabidopsis, and related Boechera and Catolobus, Braya and Neotorularia, and Eutrema, Aphragmus, Lignariella, Neomartinella, Platycraspedum, Taphrospermum, and Thellungiella. The five Arabis arenicola accessions examined had ITS sequences that were identical to each other and to four Arabidopsis lyrata accessions. In both maximum parsimony and maximum likelihood analyses, Arabis arenicola fell within the Arabidopsis clade and was closely aligned with Arabidopsis lyrata. Two of six purportedly related genera were not closely related to Eutrema. Both analyses placed Lignariella within a separate well-supported clade with Aphragmus, while the other four genera, Neomartinella, Platycraspedum, Taphrospermum, and Thellungiella, fell within a well-supported clade with Eutrema. Morphology and molecular data strongly suggest transferring Arabis arenicola to Arabidopsis, expanding Aphragmus to include Lignariella, and expanding Eutrema to include Neomartinella, Platycraspedum, Taphrospermum, and Thellungiella. New combinations in Arabidopsis and Aphragmus are proposed.
Two new Ophiostoma species lacking conidial states isolated from bark beetles and bark beetle-infested Abies species in Japan
Authors: Ohtaka Nobuaki , Masuya Hayato , Yamaoka Yuichi , Kaneko Shigeru
Published: June 2006

Two ophiostomatoid fungi without conidiophores and conidia were isolated from bark beetles and bark beetle-infested Abies spp. The teleomorph characters were similar to species of Ophiostoma, but the absence of the conidial stage hampered their exact generic assignment. Detailed morphological observations and molecular analysis clarified their generic affiliation. Consequently, they were placed in the genus Ophiostoma , but their morphology and DNA sequences did not coincide with any other species of Ophiostoma. Here, we propose these two species as Ophiostoma aoshimae sp. nov. and Ophiostoma rectangulosporium sp. nov. The former species is characterized by perithecial necks ornamented with projections and ellipsoid to oblong ascospores, and the latter species is characterized by perithecial necks ornamented with rectangular ascospores and white colonies.
Association of Gluconacetobacter diazotrophicus with roots of common bean (Phaseolus vulgaris) seedlings is promoted in vitro by UV light
Authors: Trujillo-López Alejandra , Camargo-Zendejas Oscar , Salgado-Garciglia Rafael , Cano-Camacho Horacio , Baizabal-Aguirre Víctor M. , Ochoa-Zarzosa Alejandra , López-Meza Joel E. , Valdez-Alarcón Juan J.
Published: June 2006

Gluconacetobacter diazotrophicus is a diazotrophic endophyte that is a potential biofertilizer. Little is known about the mechanisms of G. diazotrophicus interaction with its host plants. We tested the effect of UV light, as an inducer of secondary metabolite accumulation, on the association between common bean ( Phaseolus vulgaris L.) seedling roots and G. diazotrophicus. UV light irradiation of seedlings 4 h prior to bacterial inoculation increased the number of bacterial cells associated with the roots by 5.65-fold with respect to a nonirradiated control (p < 0.05). Gluconacetobacter diazotrophicus associates with root hairs and root border cells. Aggregation of bacterial cells was observed in root structures from UV-induced seedlings. Secondary metabolite accumulation was also observed in roots from UV-irradiated seedlings.
Inexpensive fine mapping and positional cloning in plants using visible, mapped transgenes
Authors: Dinka Stephen J. , Raizada Manish N.
Published: June 2006

Vast numbers of crop, fungal, and animal accessions as well as insect vectors and evolving eukaryotic pathogens await molecular analysis. Inexpensive methods are required to make map-based gene isolation accessible to more of the world’s researchers. Today, positional cloning relies on genotyping and phenotyping large numbers of progeny to detect chromosome recombination events that break linkage between the trait of interest and flanking molecular markers following meiosis. In the postgenome era, positional cloning will no longer be limited by the availability of high-density molecular markers but rather by the skilled labour and the expense of genotyping and phenotyping 103−104progeny to detect rare recombination events in a narrow chromosome block flanking the target gene of interest. Here, we review how linked, mapped transgenes that encode dominant, visible traits such as green fluorescent protein can be used to preselect meiotic recombinants inexpensively, thus reducing progeny genotyping and phenotyping requirements by >95% during positional cloning. Because transgene markers such as green fluorescent protein are genotype independent, transgenes created in one inbred line may be used to fine-map genetic variation in large numbers of genotypes.
Physiological influences in the development and function of the shoot apical meristem of microspore-derived embryos ofBrassica napus‘Topas’
Authors: Ramesar-Fortner Nicole S. , Yeung Edward C.
Published: June 2006

The effect of auxins and abscisic acid (ABA) on shoot apical meristem development and function was analyzed in microspore-derived embryos of Brassica napus L. ‘Topas’. Embryos were treated with an auxin transport inhibitor, tri-iodobenzoic acid (TIBA) or exogenous indole-3-acetic acid (IAA) at various stages during their development. If embryos were treated at the preglobular or globular stages of embryogenesis, they developed one fused cotyledon indicating a continuation of radial symmetry. However, if treated later in development, embryos were comparable to the control and formed two separate cotyledons. To demonstrate that this was not a pharmacological effect, an auxin antagonist, 2-(p-chlorophenoxy)-2-methylpropionic acid, included with the TIBA treatment produced normal embryos with two separate cotyledons. Histological observations revealed that the shoot apical meristem of the embryos treated with TIBA or IAA at the preglobular and globular stages was altered. Preglobular and globular stage embryos that were treated with TIBA exhibited a dramatic decline in conversion frequency compared with their controls. Embryos that were treated later in development had conversion frequencies comparable to their controls, and their shoot apical meristems also were similar to controls. Application of ABA at the preglobular and globular stages maintained meristem integrity and improved embryo conversion. However, ABA could not reverse the TIBA effect.
Pollinator visitation, pollen limitation, and selection on flower size through female function in contrasting habitats within a population of Campanula persicifolia
Authors: Hansen Vivi-Irèn , Totland Ørjan
Published: June 2006

We looked at whether flower visitation rates, pollen limitation on seed production, and phenotypic selection on flower size through female function varied across a sharp gradient in light intensity (open meadow vs. forest) within a population of the perennial plant Campanula persicifolia L. (Campanulaceae). Flower visitation rates of putative pollinators were similar in both habitats. Seed number per fruit was strongly pollen limited, with no difference in the magnitude of pollen limitation between the two habitats. This strong pollen limitation set the basis for significant phenotypic selection, through female function, on a trait that probably is important for pollinator attraction: flower size. This was revealed by path analysis and structural equation modelling. The lack of difference in pollen limitation on seed production in the two habitats may be explained by the similarity in flower visitation rates in the two habitats. Moreover, the similarity in pollen limitation in the two habitats probably resulted in a similar magnitude and direction of selection on flower size through female function. Our results suggest that pollen limitation and selection through female function may vary little across space within a popualtion despite large variation in the environmental conditions experienced by plants.
Differences between two green algae in biological availability of iron bound to strong chelators
Authors: Weger Harold G. , Matz Carlyn J. , Magnus Rachel S. , Walker Crystal N. , Fink Michael B. , Treble Ron G.
Published: June 2006

N,N′-di(2-hydroxybenzoyl)-ethylenediamine-N,N′-diacetic acid (HBED) is a very strong Fe3+ chelator. Strategy I vascular plants, which use a reductive system for iron acquisition, similar to many green algae, are able to access iron from HBED (R.L. Chaney. 1988. J. Plant Nutr. 11: 1033–1050). However, iron-limited cells of the Strategy I green alga Chlamydomonas reinhardtii Dangeard were unable to access iron present as Fe3+–HBED. In contrast, Fe3+ chelated with hydroxyethylethylenediaminetriacetic acid (HEDTA; a weaker chelator) was rapidly taken up by iron-limited Chlamydomonas cells. Chlamydomonas ferric reduction rates with Fe3+–HBED were approximately 15% of the rate observed with Fe3+–HEDTA, suggesting that low reduction rates with Fe3+–HBED might be one factor in the low rate of iron acquisition. By contrast, iron-limited cells of the Strategy I green alga Chlorella kessleri Fott et Nováková were able to rapidly assimilate Fe3+ chelated by HBED, although ferric reduction rates with Fe3+–HBED were approximately 38% the rate of activity with Fe3+–HEDTA. Similar differential iron uptake rates for the two algal species were obtained using the strong Fe3+ chelator (and siderophore analogue) desferrioxamine B mesylate and the cyanobacterial siderophore schizokinen. These results suggest that there are differences among Strategy I green algae in their abilities to acquire Fe3+ from various ferric chelates: not all Strategy I algae can equally access tightly complexed Fe3+. Chlamydomonas appears to be the first documented Strategy I organism that is unable to acquire iron from Fe3+–HBED. These results also suggest that green algal iron acquisition from siderophores is species dependent. Finally, we suggest that iron acquisition from Fe3+–HBED might serve as an assay for an organisms’ ability to access tightly complexed iron.
Increased image depth for epi-illumination microscopy
Authors: Wilson Trevor C. , Charlton W.A. , Posluszny Usher
Published: June 2006

Epi-illumination microscopy is a useful tool for studying morphology, but its use is limited by a small depth of field. Using digital editing, we have enhanced the depth of field for epi-illumination micrographs obtained for a number of shoot apices. For each specimen, an epi-illumination microscope fitted with Leitz Ultropak dipping cones was used to capture a series of digital images at successive levels of focus. Adobe® Photoshop® was used to produce one image by assembling only the focused areas of the image series. This stacking method offers a better way to present epi-illumination micrographs and increases the microscope’s usefulness as an alternative for conventional scanning electron microscopy. The method could be applied to images collected by other microscopical techniques.
Multi-species fruit and seed removal in a tropical deciduous forest in Mexico
Authors: Briones-Salas Miguel , Sánchez-Cordero Víctor , Sánchez-Rojas Gerardo
Published: June 2006

We determined patterns of post-dispersal fruit and seed removal for 11 common native plants, as well as sunflower seeds ( Helianthus annuus L.), within a tropical deciduous forest in Jalisco, Mexico. Removal values were high in Delonyx regia (Bojer) Raf. (90%), Crescentia alata Kunth. (87%), H. annus (81%), Pithecellobium dulces (Roxb.) Benth (81%), Albizia occidentalis Brandegee (80%), Coccoloba barbadensis Jacq. (80%), Recchia mexicana DC. (80%), Caesalpinia pulcherrima (L.) Sw. (79%), Enterolobium cyclocarpum (Jacq.) Griseb. (73%), moderate in Guazuma ulmifolia Lam. (42%) and Celtis iguanaeus Sarg. (44%), and low in Amphipterygium adstringens (Schlechtend.) Schiede ex Standl. (17%). Low removal rates (29%) in experimental patches open only to arthropods suggest that arthropods have a minor role in removing fruits and seeds of these species. Removal values were high in experimental patches open to all potential agents (77%) and semipermeable patches open to forest-dwelling rodents (76%), suggesting that the latter group, the most abundant terrestrial mammal in this forest, was an important agent for removing the fruits and seeds of study plants. Removal values were higher in experimental patches located in tropical deciduous forest than in tropical semideciduous forest, as well as higher in high density (patches of 30 fruits or seeds) than in low density (patches of five fruits or seeds) experimental patches for most study plants. Mice appear to selectively remove and hoard fruits and seeds according to their energy and nutritional content and the presence of secondary metabolites, and from from high-density food patches and preferred habitats. Nonindependent effects of species, habitat, and density suggest that a complex interplay of factors determines fruit and seed removal for the plants examined from the Chamela tropical forest.
Late Permian (Changhsingian) conodont biozonation and the basal boundary, Ganxi section, western Hubei Province, south China
Authors: Nafi Mutwakil , Wenchen Xia , Ning Zhang
Published: June 2006

Four neogondolellid conodont interval zones were recognized across the Changhsingian stage at Ganxi section, western Hubei Province, south China. They are in ascending order: the Clarkina wangi Zone, the Clarkina changxingensis changxingensis Zone, the Clarkina changxingensis yini Zone, and the Clarkina meishanensis meishanensis Zone. The present study suggests that the base of the Changhsingian can be defined by the first appearance datum (FAD) of Clarkina wangi within an evolutionary lineage from Clarkina longicuspidata to Clarkina wangi. The WuchiapingianChanghsingian boundary can be placed at the base of bed 104 at Ganxi section, south China because of the first occurrence of Clarkina wangi.
Mechanisms of slope failure on Pyramid Mountain, a subglacial volcano in Wells Gray Provincial Park, British Columbia
Authors: Neuffer Daniel P , Schultz Richard A , Watters Robert J
Published: June 2006

Pyramid Mountain is a subglacial volcano in Wells Gray Provincial Park in east-central British Columbia. Landslides deform the north and east flanks of the volcano. Field strength testing and rock mass classification designate the hyaloclastite breccia in which the landslides originated as a weak, massive rock mass: uniaxial compressive strengths (UCS) range from 24 to 35 MPa, and geologic strength index (GSI) and rock mass rating (RMR) values are 6070. The shear strength of fracture surfaces in the hyaloclastite breccia, as measured by laboratory direct shear tests, can be characterized by a friction angle ϕ of 18° and cohesion c of 0.110.66 MPa. Limit-equilibrium slope stability analyses show that the landslides were probably triggered by the rapid drawdown of a surrounding englacial lake with no seismic ground acceleration required. Slope measurements and slope stability modeling indicate that Pyramid Mountain was asymmetric prior to failure: the north and east flanks had slope angles of 35°40°, and the south and west flanks had slope angles of 21°33°. Slope asymmetry may result from closer ice confinement on up-gradient (north and east) flanks due to higher ice flux in this direction relative to down-gradient (south and west) flanks. At the time of failure, the volcanic edifice was at least partially lithified, with cohesive strengths of 0.190.52 MPa. Failures of lithified subglacial and subaqueous volcanic edifices may be triggered by rapid drawdown of surrounding water without seismic loading.
A preliminary radiolarian biozonation for the Lower Silurian of the Cape Phillips Formation, Nunavut, Canada
Authors: MacDonald Eugene W
Published: June 2006

Radiolaria from the Lower Silurian of the Cape Phillips Formation, Nunavut, Canada allow the definition of four biostratigraphic assemblages. The Haplotaeniatum assemblage extends from the basal Llandovery to topmost Coronograptus cyphus graptolite Biozone. The base is taken as the first occurrence of Haplotaeniatum nunavutensis; no samples were collected below the OrdovicianSilurian boundary. The top of the assemblage is defined by the first occurrence of Orbiculopylorum. The Orbiculopylorum assemblage is marked by the first occurrence of Orbiculopylorum. The boundary between this assemblage and the overlying Plussatispila assemblage is unclear because of a break in stratigraphy (upper Spirograptus turriculatus through Monograptus crispus graptolite biozones). The last occurrence of Orbiculopylorum defines the top of the assemblage. The base of the Plussatispila assemblage is defined by the last occurrence of Orbiculopylorum. A barren interval (Cyrtograptus insectus to lower Monograptus instrenuus  Cyrtograptus kolobus graptolite biozones) separates the Plussatispila assemblage and subsequent Ceratoikiscum assemblage. The first occurrence of Ceratoikiscum is taken as the boundary between these assemblages. The top of the Ceratoikiscum assemblage is not established, but is taken as the first occurrence of Inanihella tarangulica Group radiolarians. This zonation is comparable to, and a modification from, the global radiolarian biozonation of Noble and Aitchison (2000).
New eocrinoids from the Burgess Shale, southern British Columbia, Canada, and the Spence Shale, northern Utah, USA
Authors: Sprinkle James , Collins Desmond
Published: June 2006

The family Lyracystidae n.fam. and genus Lyracystis n.gen. are proposed for the holotype and one paratype of the Middle Cambrian eocrinoid Gogia? radiata Sprinkle, the Burgess Shale "Arms" from the same unit, and many additional partial and more complete specimens of this eocrinoid collected from the Burgess Shale since 1975. A second species, Lyracystis reesei n.gen. and n.sp. is described from a single partly complete specimen from the similar-aged Spence Shale of northern Utah. Lyracystis has three wide V-shaped arms bearing numerous long straight brachioles in the notch, a partly organized theca having larger and smaller ridged plates with epispires, and a very long multiplated stalk made up of rounded or spiny small plates. Lyracystis is the longest-stalked, suspension-feeding echinoderm known from the Middle Cambrian. The three remaining paratypes of Gogia? radiata and four new specimens with possible branched brachioles from the Burgess Shale are renamed Gogia stephenensis n.sp.
Paleobathymetry of a Silurian shelf based on brachiopod assemblages: an oxygen isotope test
Authors: Azmy Karem , Veizer Jan , Jin Jisuo , Copper Paul , Brand Uwe
Published: June 2006

Primary δ18O signals of 97 brachiopod shells from the Lower Silurian (Llandovery) carbonate succession of Anticosti Island were used to test the hypothesis of water-depth and water-temperature gradient for the Silurian onshoreoffshore benthic assemblages (BA1BA5). The analyzed shells were from the Pentamerus palaformis, Pentamerus oblongus, Stricklandia planirostrata, Ehlersella davidsonii, and Triplesia anticostiensis communities, which have been interpreted to occupy different water depths. Screening of the shells, using petrographic and chemical criteria, confirmed good preservation of original material. Shells of P. palaformis, P. oblongus, E. davidsonii, and T. anticostiensis have very similar mean δ18O values (5 Vienna Peedee Belemnite (VPDB)), while shells of S. planirostrata have a somewhat lighter value (5.6). The δ18O values, in corroboration with taphonomic and paleoecologic data, suggest the following: (1) that the water mass of the Anticosti carbonate shelf was warm and well mixed vertically during the Early Silurian; (2) that the pentamerid brachiopod paleocommunities that lived at ~2090 m of water-depth show little δ18O differentiation in their shell composition; and (3) that the Pentamerus,Stricklandia, and Triplesia communities need to be investigated at the species level, as both taphonomic and oxygen isotopic data indicate that the Stricklandia planirostrata Community most likely lived in a notably warmer, shallower water than the Pentamerus palaformis Community and that Triplesia anticostiensis (BA5) lived at water temperature comparable to that of the Pentamerus habitat (BA3). This may suggest either that, at the generic level, the Pentamerus, Stricklandia, and Triplesia (Clorinda equivalent) communities may have had substantial overlap in their spatial distribution in the BA3BA4 paleobathymetric settings or that the isotope signals are too faint to record water depth differences on a tropical shelf.
Origin and orogenic role of the Chain Lakes massif, Maine and Quebec
Authors: Gerbi C C , Johnson S E , Aleinikoff J N
Published: June 2006

The Chain Lakes massif has long been an enigmatic component of the Appalachian orogen, but new structural, microstructural, and geochronological information provides the basis for the following new interpretation of the massif and its history. In the early Paleozoic, sediments and volcanic rocks from Laurentia or a Laurentian-derived microcontinent were deposited in a fore-arc basin on the western margin of the Iapetus ocean. Following intrusion of arc-related magmas, the sedimentaryvolcanic sequence was heated sufficiently to melt in place, resulting in stratigraphic disaggregation and diatexite formation. We dated monazite growth from this metamorphic event at 469 ± 4 Ma. Although some melt may have left the system, much remained, including water dissolved in the melt. Upon crystallization, this water drove thorough retrogression of the massif, causing pervasive pseudomorphism of porphyroblasts. With cooling and crystallization, the Chain Lakes massif became sufficiently rigid that it was not significantly deformed during the Middle Ordovician through Devonian stages of Appalachian orogenesis involving the arrival of several peri-Gondwanan microcontinents.
Systematic bias in estimates of reproductive potential of an Atlantic cod (Gadus morhua) stock: implications for stockrecruit theory and management
Authors: Marshall C Tara , Needle Coby L , Thorsen Anders , Kjesbu Olav Sigurd , Yaragina Nathalia A
Published: June 2006

Stockrecruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs·g1and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (19802001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.
Muscle enzymes reveal walleye (Sander vitreus) are less active when larger prey (cisco,Coregonus artedi) are present
Authors: Kaufman Scott D , Gunn John M , Morgan George E , Couture Patrice
Published: June 2006

Optimal foraging behaviour in walleye (Sander vitreus) was tested in eight lakes: four containing large prey (cisco, Coregonus artedi) and four without cisco. All eight lakes contained small prey (yellow perch, Perca flavescens). Activity costs and growth potential of walleye were estimated using white muscle enzymes. Anaerobic capacity, measured by lactate dehydrogenase (LDH), increased with walleye size and was lower in lakes with cisco. Aerobic capacity, measured by citrate synthase (CS), decreased with walleye size only in lakes without cisco. Growth potential of walleye, estimated by nucleoside diphosphokinase (NDPK), increased with size only in lakes with cisco. Overall, when cisco were available walleye were less active, able to maintain aerobic capacities, and increased their growth potential as they grew larger. Yellow perch LDH, CS, and NDPK were lower in lakes with cisco. This suggests that yellow perch were less active in lakes where walleye had an alternative large prey species, but yellow perch had higher growth potential when they were the only prey, reflecting the advantage of growth beyond edible sizes. This study reveals that there are physiological benefits for both predators and prey in communities with a wider range of prey sizes.
Fish predation on Eurasian watermilfoil (Myriophyllum spicatum) herbivores and indirect effects on macrophytes
Authors: Ward Darren M , Newman Raymond M
Published: June 2006

We assessed the effect of fish predation on native and naturalized insect herbivores of the invasive aquatic plant Eurasian watermilfoil (Myriophyllum spicatum) using manipulative field experiments within lakes and a field survey across lakes. For the field experiments, we manipulated sunfish (Lepomis spp.) density in cages in the littoral plant beds of two contrasting lakes: one with many sunfish, few watermilfoil herbivores, and abundant Eurasian watermilfoil; and one with few sunfish, many herbivores, and little Eurasian watermilfoil. Watermilfoil herbivores, including the milfoil weevil (Euhrychiopsis lecontei) and aquatic caterpillars, were suppressed by fish in both experiments. Herbivore density was also negatively related to sunfish abundance in the multiple-lake survey. We conclude that abundant sunfish can strongly suppress watermilfoil herbivores. Furthermore, in one of our experiments there was a marginally significant effect of fish exclosure on watermilfoil, suggesting that fish suppression of watermilfoil herbivores can have a positive, indirect effect on plant growth. Fish predation on macrophyte herbivores may be an important trophic interaction in freshwater lakes.
Ontogenetic dynamics of mercury accumulation in Northwest Atlantic sea lamprey (Petromyzon marinus)
Authors: Drevnick Paul E , Horgan Martin J , Oris James T , Kynard Boyd E
Published: June 2006

We examined the ontogenetic dynamics of mercury accumulation in sea lamprey (Petromyzon marinus) from the Connecticut River, USA. Mercury concentrations in eggs (mean 84 ng·g1wet weight) were lowest of all life stages and correlated to concentrations in females. There was a higher rate of maternal transfer of mercury to eggs compared with teleosts. Ammocoetes had high mercury concentrations for their trophic level (e.g., mean of age-4 ammocoetes 492 ng·g1wet weight). A further investigation of four streams showed that ammocoetes reflected the level of contamination in their nursery streams. Concentrations of mercury decreased during metamorphosis from ammocoete to adult. Mercury concentrations in adults ranged from 83 to 942 ng·g1wet weight and, unlike teleosts, showed no relation to sex, length, or weight. We provide evidence from stable isotope analyses that this high variability is due to feeding ecology. There are fundamental differences in mercury accumulation between sea lamprey and teleosts.
Nearshoreoffshore comparison of chlorophyll a and phytoplankton production in the dreissenid-colonized eastern basin of Lake Erie
Authors: Depew David C , Guildford Stephanie J , Smith Ralph E.H
Published: June 2006

Planktonic primary production, chlorophyll a (chl a), underwater light climate, and total phosphorus were measured at 18 stations during 2001 and 2002 in eastern Lake Erie to characterize spatial and seasonal patterns in this system colonized by dreissenid mussels (Dreissena spp.). Areal production rates and chl a displayed a seasonal pattern typical of the Laurentian Great Lakes, with highest production in the early and late summer. Daily and seasonal (MayOctober) primary production was significantly lower nearshore than offshore. Although light attenuation was similar between nearshore and offshore, the nearshore light climate was generally more favorable for phytoplankton because of shallower mixing depths. However, chl a was significantly lower nearshore, which accounted for most of the depression in production rates. Nearshore chl a was lower than predicted from relationships with total phosphorus in comparable dreissenid-free systems. Offshore, subepilimnetic communities contributed up to 67% of daily production but only up to 19% of seasonal production. The depression of chl a and primary production in the nearshore was a reversal from historic patterns in eastern Lake Erie and from the pattern traditionally expected in large lakes. Decreased external nutrient loading and dreissenid colonization may both have contributed to this new spatial pattern, but dreissenids appear to be key agents.
Influence of the vertical structure of macrophyte stands on epiphyte community metabolism
Authors: Vis Chantal , Hudon Christiane , Carignan Richard
Published: June 2006

The physical structure of submerged aquatic plant communities differentially influences the availability of light and substratum in the water column and, thus, the functional role of epiphytes growing on macrophytes. We examined the depth distribution of photosynthesis and respiration of epiphyte communities within macrophyte stands of contrasting growth forms over a 2-year period in Lake Saint-Pierre (St. Lawrence River). To do so, we used a modelling approach, combining laboratory measurements of photosynthesis and respiration with field data of macrophyte and epiphyte biomass and vertical light attenuation. In stands dominated by canopy-forming macrophytes, shading resulted in strong vertical gradients in epiphyte metabolism, with a positive net oxygen balance in the canopy and a negative net oxygen balance in the bottom portion of the stand. In low-growing macrophyte stands, the net oxygen balance of epiphytes was either positive or negative, depending on water transparency and depth. Epiphyte communities had a daily negative net oxygen balance under light conditions below ~10% of surface light intensity. Areal production simulations demonstrated that neglecting variations in the vertical distribution of epiphytes, macrophytes, and light within macrophyte stands can result in errors in areal production estimates of >100%.
Integrating design- and model-based inference to estimate length and age composition in North Pacific longline catches
Authors: Miller T J , Skalski J R
Published: June 2006

Age and size structure are attributes of fishery stocks important for predicting future productivity. As such, estimating age and length composition of catches has long been an important fisheries management activity. Many observer programs sample catches to obtain length measurements and otoliths (or other structures for ageing) from targeted species. In North Pacific groundfish fisheries, observers collect these data through a stratified multiphase sampling design. Sampling variance and covariance estimates for catch- or proportions-at-length or -age that reflect the randomization inherent in the sampling design provide important measures of uncertainty that correspond to measurement error components in length- or age-structured stock assessment models. We compare sampling variances and covariances of Pacific cod (Gadus macrocephalus) proportions-at-length and sablefish (Anoplopoma fimbria) proportions-at-age with those provided by the overdispersed multinomial model sometimes used in these assessment models. For example, the sampling variance estimates for 2002 Pacific cod proportion-at-length estimates in the Bering Sea  Aleutian Islands are at most 13% of the variances provided by multinomial and square-root sample size assumptions. Furthermore, some proportion estimates are positively correlated, whereas only negative correlation occurs with the multinomial distribution.
Response of nutrients, biofilm, and benthic insects to salmon carcass addition
Authors: Claeson Shannon M , Li Judith L , Compton Jana E , Bisson Peter A
Published: June 2006

Salmon carcass addition to streams is expected to increase stream productivity at multiple trophic levels. This study examined stream nutrient (nitrogen, phosphorus, and carbon), epilithic biofilm (ash-free dry mass and chlorophyll a), leaf-litter decomposition, and macroinvertebrate (density and biomass) responses to carcass addition in three headwater streams of southwestern Washington State, USA. We used stable isotopes (δ13C and δ15N) to trace incorporation of salmon-derived (SD) nutrients into stream food webs. SD nutrients were assimilated by biofilm, benthic insects (Perlidae and Limnephilidae spp.), and age-1 steelhead (Oncorhynchus mykiss gairdneri). SD nutrients peaked ~2 weeks after carcass addition for insects and fish feeding on carcasses, but indirect uptake of SD nutrients by biofilm and insects was delayed by ~2 months. A strong stable isotope signal did not always correspond with measurable biological change. At reaches 1050 m downstream from carcasses, ammonium concentration, leaf-litter decomposition, and benthic insect density all increased relative to upstream control sites. The strongest responses and greatest SD-nutrient uptake were observed 10 m from decomposing carcasses, with effects generally decreasing to undetectable levels 250 m downstream. Carcass addition to headwater streams can have a transient effect on primary and secondary trophic levels, but responses may be limited to specific taxa near carcass locations.
Using impact assessment methods to determine the effects of a marine reserve on abundances and sizes of valuable tropical invertebrates
Authors: Lincoln-Smith M P , Pitt K A , Bell J D , Mapstone B D
Published: June 2006

Procedures for impact assessment, including "beyond-BACI" (beforeafter controlimpact) and proportional differences (ratios between impact and control treatments) were used to test population replenishment of marine invertebrates at a marine conservation area (MCA) and three fished (control) areas in the Solomon Islands of the southwestern tropical Pacific. Within shallow reef terrace habitat, the MCA caused abundance and size of the topshell Trochus niloticus to increase but did not affect holothurians (sea cucumbers) or the giant clam Tridacna maxima. Abundance of the nonexploited topshell Tectus pyramis was unchanged at the MCA but increased at the controls, possibly because of changes in abundance of T. niloticus. Within deep slope habitat, the MCA caused increased abundance of the sea cucumber Holothuria fuscogilva and prevented possible declines in abundances of Thelanota anax and all holothurians combined but had no effect on abundances of Holothuria atra or Holothuria fuscopunctata. Power analysis comparing the MCA with controls indicated that further, relatively modest increases in abundance or size of some species would have a good chance of being detected statistically. The beyond-BACI procedure holds promise for enabling rigorous evaluation of marine reserves as management tools at different spatial scales; the use of proportional differences is simpler but has limited management value.
Whole-lake effects of invasive crayfish (Orconectes spp.) and the potential for restoration
Authors: Rosenthal Sadie K , Stevens Samantha S , Lodge David M
Published: June 2006

Effects of invasive species are often extrapolated to whole systems based on small-scale, short-term, and (or) single-system studies. For example, previous laboratory studies and in-lake cage experiments suggest that invasive crayfish Orconectes rusticus and O. propinquus reduce macrophyte and snail abundance in north temperate lakes, and snapshot lake surveys provide supporting evidence. Still, these impacts have not been demonstrated in multiple whole lakes over time. Thus, in summer of 2003, we resurveyed benthic invertebrates and macrophytes in lakes originally surveyed by the Michigan Department of Natural Resources in the late 1930s. Our multilake survey supports the macrophyte results from small-scale and comparative studies: macrophyte species richness and abundance declined significantly in invaded lakes relative to uninvaded lakes. We next conducted a laboratory seed-bank study to examine the potential for macrophyte restoration in a lake occupied by rusty crayfish for at least 15 years. Only two macrophyte species (Najas flexilis and Chara spp.) germinated from sediments from the invaded lake compared with eight species from reference sediments. This suggests that invaded lakes may have depauperate seed banks and that restoration of invaded macrophyte communities may require manual planting, even if crayfish could be removed.
Aggregated yield and fishing effort in multispecies fisheries: an empirical analysis
Authors: Lorenzen Kai , Almeida Oriana , Arthur Robert , Garaway Caroline , Khoa Sophie Nguyen
Published: June 2006

Many tropical fisheries are inherently of a multispecies nature, with any given type of fishing gear harvesting a wide range of species. Species-aggregated relationships between fishing effort and yield or catch per unit of effort (CPUE) provide important information for the management of such fisheries, as well as insights into ecosystem-level responses to fisheries exploitation. We used a model selection approach to study species-aggregated, yieldeffort relationships in spatially replicated, multispecies inland fisheries. Of three alternative models considered, the data strongly supported a sigmoid functional form (Akaike weight 0.95) over the alternative, asymptotic exponential or quadratic (Schaefer) models (Akaike weights 0.03 and 0.02, respectively). The sigmoid form implies the occurrence of an inflexion point in the rising part of the yieldeffort curve and no decline in aggregated yield even at the highest effort levels observed. Aggregated CPUE declines steeply near the origin of the effort scale before stabilizing or rising to a local maximum and then declining inversely with further increases in effort. This highly nonlinear response suggests that extreme caution is required when interpreting aggregated CPUE as an indicator of fishing impacts on exploited communities. Further research is required to identify the mechanisms generating the observed relationship.
Transgenerational marking of embryonic otoliths in marine fishes using barium stable isotopes
Authors: Thorrold Simon R , Jones Geoffrey P , Planes Serge , Hare Jonathan A
Published: June 2006

We describe a new technique for transgenerational marking of embryonic otoliths that promises significant advancements in the study of larval dispersal and population connectivity in marine fishes. The approach is based on maternal transmission of 137Ba from spawning females to egg material that is ultimately incorporated into the otoliths of embryos produced by an individual after exposure to the isotope. We injected females of a benthic-spawning clownfish (Amphiprion melanopus) and a pelagic-spawning serranid (Centropristis striata) with enriched 137BaCl2 and then reared the resulting progeny through to settlement. Barium isotope ratios in the cores of larval otoliths were quantified using laser ablation inductively coupled plasma mass spectrometry. Larval otoliths from both species contained unequivocal Ba isotope signatures over a wide range of doses (0.823 µg 137Ba·g female1). Female A. melanopus continued to produce marked larvae over multiple clutches and for at least 90 days after a single injection. The ability to administer different combinations of stable Ba isotopes provides a new means of mass-marking larvae of benthic- and pelagic-spawning fishes from multiple populations over extended spawning periods.
Optical modal gain in multiple quantum-well semiconductor lasers based on InP
Authors: Wartak M S , Weetman P , Alajoki T , Aikio J , Heikkinen V , Pikhtin N A , Rusek P
Published: June 2006

An approach to determine the optical modal gain spectra in multiple quantum-well semiconductor lasers based on InP in terms of the current at electrodes is presented. The link between the current at the electrodes and the density of carriers inside each quantum well was provided by rate equations with the inclusion of carrier transport effects. Description of hole dispersion is based on a 4 × 4 Luttinger–Kohn Hamiltonian and was done with the electrostatic effects of the carrier charges. Electrostatic effects were included via a self-consistent solution of electron and hole wave equations and the Poisson equation. The optical gain for the TE (transverse electric) mode has been determined with the inclusion of non-Markovian effects, Coulombic enhancement, and band-gap renormalization. The theoretical approach was compared with experimental measurements of the optical gain on a laser structure consisting of four quantum wells using the Hakki–Paoli method. The important role played by the leakage current was revealed when the results were compared. PACS No.: 73.63.Hs, 78.20.Bh, 78.20.Ci
Energy levels for the stable isotopes of atomic helium(4He I and 3He I)
Authors: Morton Donald C , Wu Qixue , Drake G WF
Published: June 2006

We calculate very accurate ab initio ionization energies for both 4He I and 3He I as well as the isotope shifts for n = 1 to 10, L = 0 to 7 and combined these with precise laboratory data to produce a new table of levels for 4He I and the first table for 3He I. We adopted an experimental ionization potential of 5945 204 290 ± 33 MHz for 4He I and derived 5944 890 770 ± 33 MHz for 3He I. Additional calculations of the magnetic perturbations of 3He I provide the hyperfine levels, which compare favourably with the available measurements.PACS Nos.: 31.30.Gs, 31.30.Jv