bluuebunny/crossref_metadata_2025 huggingface dataset:
The Chemorepellent Slit3 Promotes Monocyte Migration
Authors: Geutskens Sacha B. , Hordijk Peter L. , van Hennik Paula B.
Published: November 2010

Directional migration is an essential step for monocytes to infiltrate sites of inflammation, a process primarily regulated by chemoattractants. Slits are large matrix proteins that are secreted by endothelial cells; they were reported to inhibit the chemoattractant-induced migration of different cell types, including leukocytes. The aim of this study was to determine the effect of Slit3 on primary monocyte migration and to address the underlying mechanisms. We show that Roundabout (Robo)1, one of the Robo receptors that recognize Slit3, is the only Robo homolog expressed by CD14+ monocytes. Interestingly, we found that stimulation with Slit3 increased the spontaneous and chemoattractant-induced migration of primary monocytes in vitro and increased the myeloid cell recruitment during peritoneal inflammation in vivo. In addition, Slit3 did not seem to act as a chemoattractant itself; it promoted directed migration triggered by chemoattractants, such as CXCL12, by inducing a chemokinetic effect. We further show that Slit3 prevented monocyte spreading and induced rounding of spread monocytes without affecting monocyte adhesion. Stimulation with Slit3 was not associated with changes in the levels of phosphorylated p38, p42/p44, or Src, known regulators of monocyte migration, but it directly acts on molecular pathways involved in basal leukocyte migration by activating RhoA. These findings show an unexpected response of monocytes to Slit3 and add insights into the possible role of Slit proteins during inflammatory cell recruitment.
On/Off TLR Signaling Decides Proinflammatory or Tolerogenic Dendritic Cell Maturation upon CD1d-Mediated Interaction with Invariant NKT Cells
Authors: Caielli Simone , Conforti-Andreoni Cristina , Di Pietro Caterina , Usuelli Vera , Badami Ester , Malosio Maria Luisa , Falcone Marika
Published: November 2010

Invariant NKT (iNKT) cells play an effector/adjuvant function during antimicrobial and antitumoral immunity and a regulatory role to induce immune tolerance and prevent autoimmunity. iNKT cells that differentially modulate adaptive immunity do not bear a unique phenotype and/or specific cytokine secretion profile, thus opening questions on how a single T cell subset can exert opposite immunological tasks. In this study, we show that iNKT cells perform their dual roles through a single mechanism of action relying on the cognate interaction with myeloid dendritic cells (DCs) and leading to opposite effects depending on the presence of other maturation stimuli simultaneously acting on DCs. The contact of murine purified iNKT cells with immature autologous DCs directly triggers the tolerogenic maturation of DCs, rendering them able to induce regulatory T cell differentiation and prevent autoimmune diabetes in vivo. Conversely, the interaction of the same purified iNKT cells with DCs, in the presence of simultaneous TLR4 stimulation, significantly enhances proinflammatory DC maturation and IL-12 secretion. The different iNKT cell effects are mediated through distinct mechanisms and activation of different molecular pathways within the DC: CD1d signaling and activation of the ERK1/2 pathway for the tolerogenic action, and CD40–CD40L interaction and NF-κB activation for the adjuvant effect. Our data suggest that the DC decision to undergo proinflammatory or tolerogenic maturation results from the integration of different signals received at the time of iNKT cell contact and could have important therapeutic implications for exploiting iNKT cell adjuvant/regulatory properties in autoimmune diseases, infections, and cancer.
Endoplasmic Reticulum Stress-Mediated Apoptosis of EBV-Transformed B Cells by Cross-Linking of CD70 Is Dependent upon Generation of Reactive Oxygen Species and Activation of p38 MAPK and JNK Pathway
Authors: Park Ga Bin , Kim Yeong Seok , Lee Hyun-Kyung , Song Hyunkeun , Cho Dae-Ho , Lee Wang Jae , Hur Dae Young
Published: November 2010

CD70 is expressed in normal activated immune cells as well as in several types of tumors. It has been established that anti-CD70 mAb induces complement-dependent death of CD70+ tumor cells, but how anti-CD70 mAb affects the intrinsic signaling is poorly defined. In this report, we show that ligation of CD70 expressed on EBV-transformed B cells using anti-CD70 mAb induced production of reactive oxygen species (ROS) and subsequent apoptosis. We observed an early expression of endoplasmic reticulum (ER) stress response genes that preceded the release of apoptotic molecules from the mitochondria and the cleavage of caspases. CD70-induced apoptosis was inhibited by pretreatment with the ER stress inhibitor salubrinal, ROS quencher N-acetylcysteine, and Ca2+ chelator BAPTA. We supposed that ROS generation might be the first event of CD70-induced apoptosis because N-acetylcysteine blocked increases of ROS and Ca2+, but BAPTA did not block ROS generation. We also found that CD70 stimulation activated JNK and p38 MAPK. JNK inhibitor SP600125 and p38 inhibitor SB203580 effectively blocked upregulation of ER stress-related genes and cleavage of caspases. Inhibition of ROS generation completely blocked phosphorylation of JNK and p38 MAPK and induction of ER stress-related genes. Taken together, we concluded that cross-linking of CD70 on EBV-transformed B cells triggered ER stress-mediated apoptosis via ROS generation and JNK and p38 MAPK pathway activation. Our report reveals alternate mechanisms of direct apoptosis through CD70 signaling and provides data supporting CD70 as a viable target for an Ab-based therapy against EBV-related tumors.
Leptin Modulates the Survival of Autoreactive CD4+ T Cells through the Nutrient/Energy-Sensing Mammalian Target of Rapamycin Signaling Pathway
Authors: Galgani Mario , Procaccini Claudio , De Rosa Veronica , Carbone Fortunata , Chieffi Paolo , La Cava Antonio , Matarese Giuseppe
Published: November 2010

Chronic inflammation can associate with autoreactive immune responses, including CD4+ T cell responses to self-Ags. In this paper, we show that the adipocyte-derived proinflammatory hormone leptin can affect the survival and proliferation of autoreactive CD4+ T cells in experimental autoimmune encephalomyelitis, an animal model of human multiple sclerosis. We found that myelin olygodendrocyte glycoprotein peptide 35–55 (MOG35–55)-specific CD4+ T cells from C57BL/6J wild-type mice could not transfer experimental autoimmune encephalomyelitis into leptin-deficient ob/ob mice. Such a finding was associated with a reduced proliferation of the transferred MOG35–55-reactive CD4+ T cells, which had a reduced degradation of the cyclin-dependent kinase inhibitor p27kip1 and ERK1/2 phosphorylation. The transferred cells displayed reduced Th1/Th17 responses and reduced delayed-type hypersensitivity. Moreover, MOG35–55-reactive CD4+ T cells in ob/ob mice underwent apoptosis that associated with a downmodulation of Bcl-2. Similar results were observed in transgenic AND-TCR- mice carrying a TCR specific for the pigeon cytochrome c 88–104 peptide. These molecular events reveal a reduced activity of the nutrient/energy-sensing AKT/mammalian target of rapamycin pathway, which can be restored in vivo by exogenous leptin replacement. These results may help to explain a link between chronic inflammation and autoimmune T cell reactivity.
Cutting Edge: Hierarchy of Maturity of Murine Memory B Cell Subsets
Authors: Tomayko Mary M. , Steinel Natalie C. , Anderson Shannon M. , Shlomchik Mark J.
Published: November 2010

The paucity of murine memory B cell markers has been a significant impediment to the study of memory. The most commonly used marker is IgG, which is neither sensitive nor specific, because activated nonmemory cells can be IgG+, and memory cells can be IgM+. In this article, we show that, together, PD-L2 (CD273), CD80, and CD73 define at least five phenotypic subsets of murine memory B cells. These subsets are generated from naive cells bearing a single BCR in response to a single T-dependent Ag. This diversity is independent of class switch, because IgG1- and IgM-bearing memory cells are found within each compartment. Memory subsets defined by PD-L2, CD80, and CD73 are biologically distinct from one another, because they differ in ontogeny and selection. Together, these distinctions suggest that there is a spectrum of memory B cells and progressive acquisition from more naive-like to more memory-like properties.
Occupancy of Lymphocyte LFA-1 by Surface-Immobilized ICAM-1 Is Critical for TCR- but Not for Chemokine-Triggered LFA-1 Conversion to an Open Headpiece High-Affinity State
Authors: Feigelson Sara W. , Pasvolsky Ronit , Cemerski Saso , Shulman Ziv , Grabovsky Valentin , Ilani Tal , Sagiv Adi , Lemaitre Fabrice , Laudanna Carlo , Shaw Andrey S. , Alon Ronen
Published: November 2010

Lymphocyte arrest and spreading on ICAM-1–expressing APCs require activation of lymphocyte LFA-1 by TCR signals, but the conformational switches of this integrin during these critical processes are still elusive. Using Ab probes that distinguish between different LFA-1 conformations, we found that, unlike strong chemokine signals, potent TCR stimuli were insufficient to trigger LFA-1 extension or headpiece opening in primary human lymphocytes. Nevertheless, LFA-1 in these TCR-stimulated T cells became highly adhesive to both anchored and mobile surface-bound ICAM-1, although it failed to bind soluble ICAM-1 with measurable affinity. Rapid rearrangement of LFA-1 by immobilized ICAM-1 switched the integrin to an open headpiece conformation within numerous scattered submicron focal dots that did not readily collapse into a peripheral LFA-1 ring. Headpiece-activated LFA-1 microclusters were enriched with talin but were devoid of TCR and CD45. Notably, LFA-1 activation by TCR signals as well as subsequent T cell spreading on ICAM-1 took place independently of cytosolic Ca2+. In contrast to LFA-1–activating chemokine signals, TCR activation of LFA-1 readily took place in the absence of external shear forces. LFA-1 activation by TCR signals also did not require internal myosin II forces but depended on intact actin cytoskeleton. Our results suggest that potent TCR signals fail to trigger LFA-1 headpiece activation unless the integrin first gets stabilized by surface-bound ICAM-1 within evenly scattered actin-dependent LFA-1 focal dots, the quantal units of TCR-stimulated T cell arrest and spreading on ICAM-1.
TLR Ligation Triggers Somatic Hypermutation in Transitional B Cells Inducing the Generation of IgM Memory B Cells
Authors: Aranburu Alaitz , Ceccarelli Sara , Giorda Ezio , Lasorella Rosa , Ballatore Giovanna , Carsetti Rita
Published: November 2010

TLR9 activation by unmethylated CpG provides a homeostatic mechanism to maintain B cell memory in the absence of Ag. In this study, we demonstrate that CpG also triggers the generation of somatically mutated memory B cells from immature transitional B cells. In response to CpG, a fraction of transitional B cells proliferates and introduces somatic hypermutations in the H chain V regions. The nonproliferating pool of transitional B cells mostly maintains germline configurations. Mutations are VH specific: VH5 is the least mutated family, whereas VH1 and VH4/6 are the most mutated families. CpG stimulation also results in upregulation of VH5 transcripts in proliferating cells. Therefore, early recognition of bacterial DNA preferentially expands VH5-expressing B cells while inducing somatic hypermutations in other families. The mutation frequency, range, and type of substitutions observed in vitro are comparable to those found in memory B cells from the peripheral blood of Hyper IgM type 1 patients and the spleen of normal infants. The process triggered by TLRs may represent a first step leading to additional diversification of the germline repertoire and to the generation of memory B cells that will further refine their repertoire and specificity in the germinal centers.
Amiodarone-Induced Bone Marrow Granulomas: An Unusual Cause of Reversible Pancytopenia
Authors: Erie Andrew J. , McClure Rebecca F. , Wolanskyj Alexandra P.
Published: November 2010

Bone marrow infiltration by granulomas rarely presents with cytopenias and is usually a result of atypical infections, lymphomas, or sarcoidosis. Drugs are also an important but often overlooked causal agent of bone marrow granulomas. Although rare, amiodarone has been associated with bone marrow granuloma formation. This case report describes a 73-year-old male who presented with pancyto­penia during a preoperative evaluation. Amiodarone therapy was suspected to be the causal agent after diagnostic evaluation and exclusion of other causes. After cessation of amiodarone, the patient’s pancytopenia gradually resolved over a period of several months. Our report illustrates an often overlooked yet important cause of reversible pancytopenia owing to suspected amiodarone-induced bone marrow granuloma formation, and guides clin­icians in an expected timeline for blood count improvement after cessation of this drug.
Concomitant Leiomyosarcoma of the Right Kidney and Squamous Cell Carcinoma of the Cervix—An Unusual Clinical Presentation
Authors: Momah Tobe Samuel , Kondamudi Vasantha , Abraham Sherly , Etwaru Dhanan , Meena Ahulwalia , Teo Arnold , Xiao Phillip
Published: November 2010

We report a case of right-sided leiomyosarcoma of the kidney with concomitant poorly differentiated squamous cell carcinoma of the cervix diagnosed one month after radical nephrectomy in a previously healthy female patient. This is the first reported case of concomitant leiomyosarcoma of the kidney and squamous cell carcinoma of the cervix, and the diagnosis, clinical presentation, prognosis, and treatment are discussed.
Colonic Phasic Motor Activity Is Stronger in Patients with Repaired Anorectal Malformations than Patients with Severe Colonic Dismotility
Authors: Demirogullari Billur , Sari Sinan , Egritas Odul , Karakus Cuneyt , Ozen Io , Sonmez Kaan , Dalgic Buket , Kale Nuri , Basaklar A. Can
Published: November 2010

In this study, colonic manometry studies of the patients with repaired anorectal malformations (ARM) were compared with those of patients with severe colonic dismotility due to chronic constipation (CC) and acute pseudo-obstruction (PSO). The patients with repaired ARM were accepted as group #1 (n=10). The patients with CC and acute PSO composed group #2 (n=10). Eight-channel water perfused catheter was inserted into the colon under sedation. Colonic activity was recorded in three phases including fasting, after meal and after bisacodyl installation. The results were assessed by Pearson χ2 test, P<.05 was considered statistically significant. Mean age was 9.6 and 12.1 in groups #1 and #2, respectively. Ninety-five per cent of all patients had propagated contractions (PCs) and 20% and 40% of the patients in group #1 had PCs during fasting and after meal, respectively. These contractions were seen 30% and 70% of the patients in group #2, but no statistical difference was found between the groups. PCs after bisacodyl were observed 90% and 40% of the patients in groups #1 and #2, respectively, and this difference was statistically significant (P=.019). In this study, the prominent difference between the groups was found in response to intraluminal stimulation. This finding may indicate that the colon of the patients with ARM has more capacity to develop PCs by peripheral stimuli and more regular enteric nervous integrity.
Die eenheid van die kerk in gedrang
Authors: Van Wyk Tanya , Buitendag Johan
Published: November 2010

The unity of the church in jeopardy This article examines the possible influence that a church’s understanding of ecclesiology could have on its approach to homosexual people, with special reference to the Netherdutch Reformed Church of Africa (NRCA). By referring to recent debates in the NRCA concerning the prominence the Church awards to the tenet of an ‘ethnic church’ (‘volkskerk’) in its ecclesiology, it is argued that the Church’s understanding of the confession of the one, holy, apostolic and catholic church is not reflected in the NRCA’s own ecclesiology and that this has direct implications for the Church’s understanding and accommodation of homosexual people. It is concluded that if the Church maintains an inclusive character as it is meant in the Creeds, the Church has to design and incorporate models of being church that adhere to this character and the abovementioned confession.
Spring‐neap modulation of internal tide mixing and vertical nitrate fluxes at a shelf edge in summer
Authors: Sharples Jonathan , Tweddle Jacqueline F. , Mattias Green J. A. , Palmer Matthew R. , Kim Young-Nam , Hickman Anna E. , Holligan Patrick M. , Moore C. Mark , Rippeth Tom P. , Simpson John H. , Krivtsov Vladimir
Published: November 2010

Measurements of the intra‐tidal and spring‐neap variation in the vertical flux of nitrate into the base of the sub‐surface chlorophyll maximum (SCM) were made at the shelf edge of the Celtic Sea, a region with strong internal mixing driven by an internal tide. The neap tide daily mean nitrate flux was 1.3 (0.9‐1.8, 95% confidence interval) mmol m‐2 d‐1. The spring tide flux was initially estimated as 3.5 (2.3‐5.2, 95% confidence interval) mmol m‐2 d‐1. The higher spring tide nitrate flux was the result of turbulent dissipation occurring within the base of the SCM as compared to deeper dissipation during neap tides and was dominated by short events associated with the passage of internal solitons. Taking into account the likely under‐sampling of these short mixing events raised the spring tide nitrate flux estimate to about 9 mmol m‐2 d‐1. The neap tide nitrate flux was sufficient to support substantial new production and a considerable fraction of the observed rates of carbon fixation. Spring tide fluxes were potentially in excess of the capacity of the phytoplankton community to uptake nitrate. This potential excess nitrate flux during spring tides may be utilized to support new production during the lower mixing associated with the transition toward neap tide. The shelf edge is shown to be a region with a significantly different phytoplankton community as compared to the adjacent Celtic Sea and northeast Atlantic Ocean, highlighting the role of gradients in physical processes leading to gradients in ecosystem structure.
Determining net dissolved organic carbon production in the hydrographically complex western Arctic Ocean
Authors: Mathis Jeremy T. , Hansell Dennis A. , Kadko David , Bates Nicholas R. , Cooper Lee W.
Published: November 2010

Each spring and summer, the Chukchi Sea in the western Arctic Ocean experiences a short but intense phytoplankton bloom that is controlled by sea ice cover, nutrient availability, and river runoff. During the bloom, dissolved inorganic carbon (DIC) concentrations are drawn down in the mixed layer (shelf, ~Δ100 µmol kg−1; shelf‐break, ~Δ50 µmol kg−1; basin, <Δ5 µmol kg−1) and converted to particulate organic carbon (POC) and dissolved organic carbon (DOC). We use δ18O and salinity to estimate DOC inputs by river and sea ice melt, allowing the marine portion of the DOC pool to be compared between seasons and to facilitate estimates of net DOC production in the region. We estimate that ~10% of the DIC consumed during net community production is converted to DOC. The remaining carbon deficit (90% of DIC drawdown) is most likely exported from the mixed layer as POC. In 2002 a carbon (C) mass balance was developed for the Chukchi Sea that showed that rates of vertical export were highest over the Chukchi Shelf near Point Barrow (64 mmol C m− d−1), but more commonly ranged from 10 to 35 mmol C m− d−1 over the remainder of the shelf. At the shelf‐break and in the Canada Basin export production was <10 mmol C m− d−1. DOC plays a relatively small role as a carbon sink in the system, but quantifying its contributions provides more robust estimates of export production in the Arctic.
Sources and sinks of methane in Lake Baikal: A synthesis of measurements and modeling
Authors: Schmid M. , Batist M. De , Granin N. G. , Kapitanov V. A. , McGinnis D. F. , Mizandrontsev I. B. , Obzhirov A. I. , Wüest A.
Published: November 2010

We studied the methane (CH4) budget of Lake Baikal, the most voluminous lake in the world and the only freshwater body with known occurrences of methane hydrates in the sediments. CH4 concentrations were measured in water samples taken during six expeditions between October 2002 and June 2004; these expeditions covered the entire lake volume. A one‐dimensional model was applied to (1) estimate the large‐scale vertical CH4 fluxes within the South Basin of Lake Baikal, (2) determine the exchange with the atmosphere, and (3) constrain the CH4 inputs from seeps and mud volcanoes to the deep water. Fluxes were generally several orders of magnitude below previous estimates. The annual internal source of CH4 to the pelagic surface mixed layer was roughly estimated to be 40 Mg CH4. A large part of this input diffuses downwards and is consumed in the water column, with a CH4 residence time of about 4 yr. The input of CH4 from deep gas seeps and mud volcanoes is less than a few 10 Mg CH4 yr−1, most of which is oxidized before reaching the surface. The net CH4 flux between the atmosphere and the main waterbody distant from shallow areas is negligible and not significantly different from zero. However, occasional high CH4 concentrations, both in the surface water and in the atmosphere, indicate that the region near the Selenga delta is a local CH4 source to the atmosphere. CH4 fluxes in the Central Basin are very similar to those in the South Basin, whereas in the North Basin, the shallow CH4 sources are weaker.
Spatial patterns of flow and their modification within and around a giant kelp forest
Authors: Gaylord Brian , Rosman Johanna H. , Reed Daniel C. , Koseff Jeffrey R. , Fram Jonathan , MacIntyre Sally , Arkema Katie , McDonald Cameron , Brzezinski Mark A. , Largier John L. , Monismith Stephen G. , Raimondi Peter T. , Mardian Brent
Published: November 2010

We present findings from two sets of measurements that quantified currents around and over the full extent of a giant kelp (Macrocystis pyrifera) forest located at Mohawk Reef, Santa Barbara, California. Velocities were damped inside this 200‐m X 300‐m forest, but not to the extent reported for larger (kilometer‐scale) kelp beds, suggesting that alongshore currents may play a greater role in exchange than has often been assumed. Secondary flow features that bear on the performance of forest organisms were observed, including a region along the forest’s outer boundary where velocities exceeded incident speeds by up to 200%. An offshore current on the order of 1 cm s−1 developed within the kelp bed, likely due to pressure gradients established across the forest coupled with topography. Wake recirculations that might have facilitated leeward retention of waterborne subsidies were not apparent. Calculations suggest that kelp beds can interact with (and thus potentially filter) substantial portions of impinging waters; in our study, 40–90% of arriving waters entered the upstream end, and 20–70% reached the center of the forest. Seasonal changes in the size and density of the forest modified the levels of flow damping and filtration. The sum of these effects suggests potential influences on organisms throughout the forest community.
Topographic shading and wave exposure influence morphology and ecophysiology of Ecklonia radiata (C. Agardh 1817) in Fiordland, New Zealand
Authors: Wing S. R. , Leichter J. J. , Perrin C. , Rutger S. M. , Bowman M. H. , Cornelisen C. D.
Published: November 2010

Patterns in morphology, pigment concentration, and light saturation kinetics of Ecklonia radiata reveal great morphological and physiological variability among individuals from sites spanning strong gradients in topographic shading and wave exposure among the 14 fjords in southwestern New Zealand. Morphology of E. radiata varies from relatively narrow (85 ± 4.7 mm) (mean ± standard error), thick (3.2 ± 0.30 mm) blades from the well‐illuminated, wave‐exposed outer coast sites to wide, undulate (460 ± 36.8 mm,) and thin (0.46 ± 0.059 mm) blades from quiescent, topographically shaded inner fjord sites. Chlorophyll a (Chl a) concentration of blades (0.084‐1.34 µg g−1 of tissue) and the ratio of fucoxanthin to Chl a (0.33 to 0.56) also increased along this gradient, indicating photoacclimation within the inner fjord populations. In situ measurements of light saturation kinetics indicate maximum photosynthetic rates at lower irradiance (Imax = 43.7 vs. 257 µmol quanta m−2 s−1) for algae at inner fjord sites relative to well‐lit outer fjord locations. Individuals exhibiting characteristically photoacclimated relative electron transfer rate curves had more deplete δ13C (‐13.35% to ‐22.35%) than individuals with higher Imax. There was no significant association between the kelp morphology or geographic location and the observed recombinant DNA diversity of ITS sequences that would indicate the presence of two Ecklonia species in the fjords. E. radiata occupies a wide range of habitats in Fiordland and displays variability in morphology and photo‐physiological responses to low light that coincide with gradients in wave exposure and topographically shaded light conditions.
Silica banding in the deep‐sea lithistid sponge Corallistes undulatus: Investigating the potential influence of diet and environment on growth
Authors: Ellwood Michael J. , Kelly Michelle , de Forges Bertrand Richer
Published: November 2010

We present detailed records of trace metals and carbon isotopes to understand siliceous spicule formation in the deep‐sea lithistid sponge Corallistes undulatus Levi and Levi, 1983 (Demospongiae: Corallistidae). X‐ray analysis of two longitudinal sections removed from the lamellae of the cup‐shaped sponge revealed 144 and 137 light and dark density band‐pairs, respectively, within the siliceous skeleton. Four portions of silica were removed along one of the sections for silicon‐32 (32Si) dating in order to constrain the overall extension rate of the sponge. Although there was some variability in the 32Si data, the overall age established using these data indicated that the sponge was between 135 and 160 yr old. This agreed well with the counts of density band‐pairs, indicating that these band‐pairs represent an annual deposition of layers of silica in the desma skeleton. Links between silica deposition and growth (food supply) were established using the Δ14carbon (C) and Δ13C signatures of organic material trapped with the spicule matrix and the zinc content of the silica. A carbon budget based on these results indicated that the amount of fresh, labile surface export organic carbon reaching C. undulatus was not sufficient to support its growth. The Δ14C results for organic carbon trapped in the silica desmas, deposited after the 1960s, supports this assertion; only a small atmospheric nuclear weapons ‚bomb’ spike was observed in the Δ14C data. Taken together, the Δ14C, Δ13C, and trace‐metal results all indicate that the organic carbon source to C. undulatus is likely to be a mixture of fresh, labile, surface‐derived material and older, perhaps sediment‐derived material, with the latter being dominant.
In situ mussel feeding behavior in relation to multiple environmental factors: Regulation through food concentration and tidal conditions
Authors: Saurel C. , Gascoigne J. C. , Palmer M. R. , Kaiser M. J.
Published: November 2010

Feeding behavior of mussels (Mytilus edulis) was measured in situ using a video camera and expressed as the mean percentage of valve gape aperture (VA), concomitant with environmental and biological parameters over two tidal cycles. Mussel feeding behavior and the physical parameters responded to three primary tidal components, of which semidiurnal was dominant (12.42 h). VA was synchronized with chlorophyll a (Chl a) concentration (proxy for food) with a strong positive correlation (r = 0.72, p < 0.001). Chl a and suspended particulate matter (SPM) were dependent on tidal advection. The combination of the reconstructed tidal constituents derived from harmonic analysis were used to successfully model mussel feeding behavior (r = 0.90, p < 0.001). In this concentration range (0.6 to 2.5 µg L−1), Chl a, measured at 1 m above the mussel bed, regulates mussel feeding behavior irrespective of the presence of predators, changes in SPM, or flow velocity.
Benthic solute exchange and carbon mineralization in two shallow subtidal sandy sediments: Effect of advective pore‐water exchange
Authors: Cook Perran L. M. , Wenzhöfer Frank , Glud Ronnie N. , Janssen Felix , Huettel Markus
Published: November 2010

We conducted four field campaigns to evaluate benthic O2 consumption and the effect of advective pore‐water flow in nearshore permeable sediments in the North Sea and Baltic Sea. Advective pore‐water transport had a marked effect on the benthic exchange of O2 and TCO2 in benthic chamber incubations, with the rates of exchange increasing by a factor of up to 2.5 when imposing flushing rates of 100‐300 L m−2 d−1, compared to settings with diffusive exchange only. Estimates of in situ exchange rates using oxygen penetration and volumetric O2 consumption and TCO2 production rates were within the range measured in the chambers. The contribution of advection to solute exchange was highly variable and dependent on sediment topography. Advective processes also had a pronounced influence on the in situ distribution of O2 within the sediment, with characteristic two‐dimensional patterns of O2 distribution across ripples, and also deep subsurface O2 pools, being observed. Mineralization pathways were predominantly aerobic when benthic mineralization rates were low and advective pore‐water flow high as a result of well‐developed sediment topography. By contrast, mineralization proceeded predominantly through sulfate reduction when benthic mineralization rates were high and advective pore‐water flow low as a result of poorly developed topography. Previous studies of benthic mineralization in shallow sandy sediments have generally ignored these dynamics and, hence, have overlooked crucial aspects of permeable sediment function in coastal ecosystems.
Discontinuities in stream nutrient uptake below lakes in mountain drainage networks
Authors: Arp Christopher D. , Baker Michelle A.
Published: November 2010

In many watersheds, lakes and streams are hydrologically linked in spatial patterns that influence material transport and retention. We hypothesized that lakes affect stream nutrient cycling via modifications to stream hydrogeomorphology, source‐waters, and biological communities. We tested this hypothesis in a lake district of the Sawtooth Mountains, Idaho. Uptake of NO3− and PO4−3 was compared among 25 reaches representing the following landscape positions: lake inlets and outlets, reaches >1‐km downstream from lakes, and reference reaches with no nearby lakes. We quantified landscape‐scale hydrographic and reach‐scale hydrogeomorphic, source‐water, and biological variables to characterize these landscape positions and analyze relationships to nutrient uptake. Nitrate uptake was undetectable at most lake outlets, whereas PO4−3 uptake was higher at outlets as compared to reference and lake inlet reaches. Patterns in nutrient demand farther downstream were similar to lake outlets with a gradual shift toward reference‐reach functionality. Nitrate uptake was most correlated to sediment mobility and channel morphology, whereas PO4−3 uptake was most correlated to source‐water characteristics. The best integrated predictor of these patterns in nutrient demand was % contributing area (the proportion of watershed area not routing through a lake). We estimate that NO3− and PO4−3 demand returned to 50% of pre‐lake conditions within 1‐4‐km downstream of a small headwater lake and resetting of nutrient demand was slower downstream of a larger lake set lower in a watershed. Full resetting of these nutrient cycling processes was not reached within 20‐km downstream, indicating that lakes can alter stream ecosystem functioning at large spatial scales throughout mountain watersheds.
Spatial analysis of ice phenology trends across the Laurentian Great Lakes region during a recent warming period
Authors: Jensen Olaf P. , Benson Barbara J. , Magnuson John J. , Card Virginia M. , Futter Martyn N. , Soranno Patricia A. , Stewart Kenton M.
Published: November 2010

We examined spatial patterns of trends in ice phenology and duration for 65 waterbodies across the Great Lakes region (Minnesota, Wisconsin, Michigan, Ontario, and New York) during a recent period of rapid climate warming (1975‐2004). Average rates of change in freeze (3.3 d decade−1) and breakup (22.1 d decade−1) dates were 5.8 and 3.3 times more rapid, respectively, than historical rates (1846‐1995) for Northern Hemisphere waterbodies. Average ice duration decreased by 5.3 d decade−1. Over the same time period, average fall through spring temperatures in this region increased by 0.7°C decade−1, while the average number of days with snow decreased by 5.0 d decade21, and the average snow depth on those days decreased by 1.7 cm decade−1. Breakup date and ice duration trends varied over the study area, with faster changes occurring in the southwest. Trends for each site were compared to static waterbody characteristics and meteorological variables and their trends. The trend toward later freeze date was stronger in large, low‐elevation waterbodies; however, freeze date trends had no geographic patterns or relationships to meteorological variables. Variability in the strength of trends toward earlier breakup was partially explained by spatial differences in the rate of change in the number of days with snow cover, mean snow depth, air temperature (warmer locations showed stronger trends), and rate of change in air temperature. Differences in ice duration trends were explained best by a combination of elevation and the local rate of change in either temperature or the number of days with snow cover.
Dissolved oxygen response to wind‐inflow interactions in a stratified reservoir
Authors: Botelho Daniel A. , Imberger Jörg
Published: November 2010

Results of a field campaign and numerical simulations are used to show how physical mechanisms impose length scales and timescales that determine the dominant biogeochemical process. As an example, the dynamics of the Snake River inflows into Brownlee Reservoir is investigated to explain the onset and maintenance of an oxygen‐depleted region (the oxygen block) in the surface layer of the upstream part of the reservoir. The oxygen block was located in a region of the reservoir in which the surface layer was warmer as a result of smaller wind stresses and reduced evaporation rates. Numerical simulations reproduced the hydrodynamic field observations resulting from inflow, outflow, wind stress, and atmospheric heat fluxes. When the wind stress opposed the inflow, the surface layer was arrested, forming a zone of convergence, stagnating the fluid and allowing the biological oxygen demand in the water to deplete the dissolved oxygen (DO) in the surface water; direct measurements showed that vertical mixing was small and contributed only marginally to the oxygen depletion. Net DO production in the water column was consistent with the observed variation with the buoyant inflow pattern, that is, a sink during overflows and overcast days and a source during interflows and intense sunlight. These observations provided further evidence that the water in this region was biologically isolated as confirmed by a scaling analysis. Modern numerical hydrodynamic simulations have reached a level of accuracy where they may be used to identify and quantify ecological niches.
Nutrient limitation of primary producers affects planktivorous fish condition
Authors: Malzahn Arne Michael , Aberle Nicole , Clemmesen Catriona , Boersma Maarten
Published: November 2010

We investigated whether nutrient limitations of primary producers act upward through food webs only in terms of density effects or if there is a second pathway for nutrient limitation signals channelled upward to higher trophic levels. We used tritrophic food chains to assess the effects of nutrient‐limited phytoplankters (the cryptophyte Rhodomonas salina) on herbivorous zooplankters (the calanoid copepod Acartia tonsa) and finally zooplanktivores (larval herring Clupea harengus) living on the herbivores. The primary producers’ food quality had a significant effect on fish condition. Our experimental phosphorus‐limited food chain resulted in larval fish with a significantly poorer condition than their counterparts reared under nitrogen‐limited or nutrient‐sufficient conditions. Our results show that mineral nutrient requirements of consumers have to be satisfied first before fatty acids can promote further growth. This challenges the match/mismatch hypothesis, which links larval fish survival probability solely to prey availability, and could imply that reduced nutrient releases into the environment may affect fish stocks even more severely than previously believed.
Plastic phenotypes of antennule shape in Bosmina longirostris controlled by physical stimuli from predators
Authors: Sakamoto Masaki , Chang Kwang-Hyeon , Hanazato Takayuki
Published: November 2010

Three antennule morphotypes in the small cladoceran Bosmina longirostris have been considered to be hereditarily rigid phenotypes. However, we found that monoclonal populations of Bosmina collected from a Japanese lake were composed of individuals with all three antennule types when grown under laboratory conditions. This suggests that each of the morphotypes represents a phenotype of the species. A morphotype named ‚‚pellucida’’ observed in the monoclonal cultures has been considered to be effective in avoiding copepod predations. We therefore hypothesized that the morphotype is induced by factors from the predator, cyclopoid copepod. To test this hypothesis, a laboratory experiment was conducted in which the monoclonal individuals were exposed to the kairomones of the copepod Acanthocyclops with or without physical contacts with the predator. The morphotype was not altered when Bosmina was exposed to the predator kairomone alone, but to direct predation by the copepod. This suggests that the antennule type of B. longirostris is controlled by physical stimuli from the copepod. The individual death rate of B. longirostris resulting from a copepod strike is low, even though the population dynamics of the animals are often governed by copepod predation. This may have made the physical stimuli of attempted predations useful factors for the prey Bosmina.
Asexuality and polyploidy in Daphnia from the tropical Andes
Authors: Aguilera Ximena , Mergeay Joachim , Wollebrants An , Declerck Steven , Meester Luc De
Published: November 2010

We assessed genetic variation at microsatellite loci within and among populations of the planktonic crustacean Daphnia pulex in 12 Bolivian Andean lakes, located above 4,000 m above sea level. Genetic analyses show that all populations consisted of obligately asexual lineages, a fact that was confirmed by observations from laboratory cultures. Moreover, microsatellite phenotypes indicate that these tropical lineages are polyploid. Levels of genetic diversity were comparable to those found in polyploid Daphnia from arctic regions, indicating a local origin rather than an accidental colonization from arctic regions. This is the first record of polyploid cladocerans in a tropical region. We suggest that their origination and abundance have probably been facilitated by the extreme environmental conditions in Andean lakes. Our analysis of multilocus genotype frequencies in relation to variation in environmental conditions indicates lineage sorting along a food availability and fish predation gradient.
Newly discovered reproductive phenotypes of a marine copepod reveal the costs and advantages of resistance to a toxic dinoflagellate
Authors: Avery David E. , Dam Hans G.
Published: November 2010

We document for the first time toxin‐resistant reproductive phenotypes of copepods and we describe a novel procedure to identify these phenotypes. Individual copepods of the species Acartia hudsonica were raised on two diets: a standard nontoxic diet and a diet containing the toxic dinoflagellate Alexandrium fundyense, both offered at nonlimiting concentrations. Resistant individuals were defined as those that survived on the toxic diet. We examined several life‐history characters including survivorship, age at metamorphosis, age at maturity, fecundity, and fitness. During this study, we discovered five resistance‐related reproductive phenotypes that appeared as discrete classes in a frequency distribution of fecundity. After grouping the data according to these phenotypes, we calculated the fitness of each phenotype on each diet. We also calculated the cost and advantage associated with resistance. On the standard diet, one phenotype had 46% lower fitness than the phenotype with the highest fitness, indicating that possessing resistance alleles can carry a substantial cost. A different phenotype showed maximum relative fitness on the toxic diet and reduced relative fitness on the standard diet. From these results, we argue that resistance is conferred by a simple genetic system showing heterozygote advantage and leading to a polymorphism for resistance. Such a polymorphism will prevent the fixation of resistance alleles in natural populations. It may also confound the interpretation of typical experiments that measure average population responses.
Growth rate versus biomass accumulation: Different roles of food quality and quantity for consumers
Authors: Andersen Tom , Færøvig Per J. , Hessen Dag O.
Published: November 2010

Population growth and biomass accumulation of Daphnia magna was studied in a two‐stage continuousculture system with light‐ and phosphorus‐limited green algae (Selenastrum capricornutum) as food source. Selenastrum grown at saturating light conditions (70 µmol quanta m−2 s−1) had on average 68% higher biomass yield and 103% higher C: P than algae grown under reduced light (10 or 36 µmol quanta m−2 s−1). Initial Daphnia population response was affected by food quality, showing faster growth in the low‐light treatments where food C: P was low and food quality was correspondingly high. When herbivore biomass became sufficiently high to deplete phytoplankton biomass to the threshold for net positive growth, the Daphnia carrying capacity appeared nevertheless to be determined primarily by the quantity of food. Thus, the high‐light treatments, which yielded the highest algal biomass production, also gave twice as high asymptotic Daphnia biomasses as those with low light. This study demonstrates how short‐term growth rate and long‐term sustainability of populations may be affected differently by the quantity and quality aspects of their food. While high growth rate and reproduction require a diet that is balanced in terms of the grazer’s demand for elements and macromolecules, a higher biomass of nongrowing individuals may still be sustained on a sufficiently plentiful supply of nutritionally deficient food.
Importance of detrital algae, bacteria, and organic matter to littoral microcrustacean growth and reproduction
Authors: Maria Lemke A. , Lemke Michael J. , Benke Arthur C.
Published: November 2010

Cumulative incorporation of radiolabeled algal (NaH14CO3) and bacterial (14C‐acetate) carbon associated with benthic organic matter (BOM) was measured at timed intervals to determine the relative importance of algal, bacterial, and detrital components of BOM to the growth and reproduction of Eurycercus vernalis (Chydoridae). Five times more algal than bacterial carbon was incorporated, which corresponded to relative amounts of algal and bacterial carbon quantified from the BOM. Algal and bacterial carbon provided 38% and 8% of the carbon required for Eurycercus growth and reproduction, respectively. Approximately 54% of the carbon required for Eurycercus growth was presumably provided by nonlabeled microbes (e.g., fungi, protists) or detritus. Parallel studies were conducted to measure the growth and reproduction for Eurycercus fed diets varying in amounts of algae, bacteria, and detritus. Effects of diet were especially noticeable in early instar growth and reproduction. Individuals fed diets with high algal and bacterial biomass relative to detrital content exhibited higher maximum somatic growth rates (75‐89% d21) than those fed aggregate and particulate detritus (51‐60%). Egg production and net reproductive rate were highest for females fed nutrient‐supplemented algae and corresponded to increased survivorship, early reproduction, and larger clutches. Survivorship was highest for females fed aggregate detritus; however, the percentage of total growth allocated toward egg production was similar for individuals fed aggregate detritus and cultured algae (67‐82%). Relative trophic importance of algae and bacteria as constituents of BOM likely depends on their relative abundance, but the two in combination can be substantially more important than the detritus alone.
Does terrestrial organic carbon subsidize the planktonic food web in a clear‐water lake?
Authors: Pace Michael L. , Carpenter Stephen R. , Cole Jonathan J. , Coloso James J. , Kitchell James F. , Hodgson James R. , Middelburg Jack J. , Preston Nicholas D. , Solomon Christopher T. , Weidel Brian C.
Published: November 2010

Allochthonous organic carbon can subsidize consumers in aquatic systems, but this subsidy may only be significant in relatively small systems with high organic matter loading. We tested the importance of allochthonous carbon to consumers in a relatively large (258,000 m2) clear‐water lake by adding H13CO3 daily for 56 d. Dissolved inorganic carbon (DIC) was substantially enriched in 13C by the addition, but it was also variable over diel cycles because of exchange with the atmosphere and photosynthesis. By measuring the δ13C value of a physically separated phytoplankton concentrate as well as the δ13C of phospholipid fatty acids, we were able to follow 13C‐labeling dynamics of specific groups of phytoplankton and bacteria. The δ13C values of particulate organic carbon (POC), dissolved organic carbon (DOC), phytoplankton, bacteria, zooplankton, and the invertebrate predator, Chaoborus spp. all increased to a maximum during the addition and declined once the addition ceased. Autochthony (% C derived from internal primary production) of carbon pools (POC, DOC) and consumers was assessed by fitting dynamic models to time series of δ13C. Autochthonous carbon was the dominant source (88‐100%) for POC, gram‐positive bacteria, a copepod, zooplankton biomass, and Chaoborus spp. Autochthonous carbon provided a lower fraction (<70%) of carbon to DOC, gram‐negative bacteria, and cladoceran zooplankton. In comparison to smaller and more humic lakes, terrestrially derived allochthonous C was less significant to the pelagic food web in this larger, clear‐water lake. Among lakes, the relative importance of autochthonous versus allochthonous carbon to planktonic consumers is positively correlated to the ratio of color (absorbance of light at 440 nm, an indicator of terrestrially derived organic carbon) to chlorophyll.