bluuebunny/crossref_metadata_2025 huggingface dataset:
Biochemical and functional characterization of three activated macrophage populations
Authors: Edwards Justin P , Zhang Xia , Frauwirth Kenneth A , Mosser David M
Published: August 2006

We generated three populations of macrophages (Mφ) in vitro and characterized each. Classically activated Mφ (Ca-Mφ) were primed with IFN-γ and stimulated with LPS. Type II-activated Mφ (Mφ-II) were similarly primed but stimulated with LPS plus immune complexes. Alternatively activated Mφ (AA-Mφ) were primed overnight with IL-4. Here, we present a side-by-side comparison of the three cell types. We focus primarily on differences between Mφ-II and AA-Mφ, as both have been classified as M2 Mφ, distinct from Ca-Mφ. We show that Mφ-II more closely resemble Ca-Mφ than they are to AA-Mφ. Mφ-II and Ca-Mφ, but not AA-Mφ, produce high levels of NO and have low arginase activity. AA-Mφ express FIZZ1, whereas neither Mφ-II nor Ca-Mφ do. Mφ-II and Ca-Mφ express relatively high levels of CD86, whereas AA-Mφ are virtually devoid of this costimulatory molecule. Ca-Mφ and Mφ-II are efficient APC, whereas AA-Mφ fail to stimulate efficient T cell proliferation. The differences between Ca-Mφ and Mφ-II are more subtle. Ca-Mφ produce IL-12 and give rise to Th1 cells, whereas Mφ-II produce high levels of IL-10 and thus, give rise to Th2 cells secreting IL-4 and IL-10. Mφ-II express two markers that may be used to identify them in tissue. These are sphingosine kinase-1 and LIGHT (TNF superfamily 14). Thus, Ca-Mφ, Mφ-II, and AA-Mφ represent three populations of cells with different biological functions.
Fetal spleen stroma drives macrophage commitment
Authors: Bertrand Julien Y. , Desanti Guillaume E. , Lo-Man Richard , Leclerc Claude , Cumano Ana , Golub Rachel
Published: August 2006

The role of the fetal spleen in hematopoeisis remains largely unknown. In this particular environment, we show that hematopoietic stem cells do not proliferate, but that they lose multipotency and differentiate exclusively into mature macrophages. B lymphocytes in the spleen derive from committed B cell precursors that are likely to have immigrated from the fetal liver. We developed fetal spleen stromal cell lines that are unique in their capacity to expand myeloid precursors, resulting in large numbers of mature macrophages. These lines secrete high levels of anti-inflammatory molecules. By phenotype,fetal splenic macrophages are reminiscent of their adult counterparts found in the red pulp. We postulate that F4/80+ splenic macrophages participate in fetal erythropoiesis, as well as in the formation of the splenic architecture.
Dynamic regulation ofDrosophilanuclear receptor activity in vivo
Authors: Palanker Laura , Necakov Aleksandar S. , Sampson Heidi M. , Ni Ruoyu , Hu Chun , Thummel Carl S. , Krause Henry M.
Published: August 2006

Nuclear receptors are a large family of transcription factors that play major roles in development, metamorphosis, metabolism and disease. To determine how, where and when nuclear receptors are regulated by small chemical ligands and/or protein partners, we have used a `ligand sensor'system to visualize spatial activity patterns for each of the 18 Drosophila nuclear receptors in live developing animals. Transgenic lines were established that express the ligand binding domain of each nuclear receptor fused to the DNA-binding domain of yeast GAL4. When combined with a GAL4-responsive reporter gene, the fusion proteins show tissue- and stage-specific patterns of activation. We show that these responses accurately reflect the presence of endogenous and exogenously added hormone, and that they can be modulated by nuclear receptor partner proteins. The amnioserosa,yolk, midgut and fat body, which play major roles in lipid storage, metabolism and developmental timing, were identified as frequent sites of nuclear receptor activity. We also see dynamic changes in activation that are indicative of sweeping changes in ligand and/or co-factor production. The screening of a small compound library using this system identified the angular psoralen angelicin and the insect growth regulator fenoxycarb as activators of the Ultraspiracle (USP) ligand-binding domain. These results demonstrate the utility of this system for the functional dissection of nuclear receptor pathways and for the development of new receptor agonists and antagonists that can be used to modulate metabolism and disease and to develop more effective means of insect control.
Organization of the peripheral fly eye: the roles of Snail family transcription factors in peripheral retinal apoptosis
Authors: Lim Hui-Ying , Tomlinson Andrew
Published: August 2006

The periphery of the fly eye contains a number of concentrically arranged cellular specializations that are induced by Wingless (Wg) signaling from the surrounding head capsule (HC). One of these is the pigment rim (PR), which is a thick layer of pigment cells that lies directly adjacent to the HC and completely circumscribes the rest of the retina. Many of the cells of the PR are derived from presumptive pigment cells that previously surrounded peripheral ommatidia that subsequently died. Here, we describe the Wgelicited expression of Snail family transcription factors in the eye periphery that directs the ommatidial death and subsequent PR formation. These transcription factors are expressed only in a subset of the ommatidial cells not including the photoreceptors. Yet, the photoreceptors die and, thus, a non-autonomous death signal is released from the Snail-family-expressing cells that direct the death of the photoreceptors. In addition, Wg also elicits a similar peripheral expression of Notum, an enzyme that limits the extent of Wg signaling. Furthermore, we describe a later requirement for Snail family proteins in the 2° and 3° pigment cells throughout the main body of the eye.
Deleted in cancer 1 (DICE1) is an essential protein controlling the topology of the inner mitochondrial membrane in C. elegans
Authors: Han Sung Min , Lee Tae Hoon , Mun Ji Young , Kim Moon Jeong , Kritikou Ekaterini A. , Lee Se-Jin , Han Sung Sik , Hengartner Michael O. , Koo Hyeon-Sook
Published: August 2006

DICE1 (deleted in cancer 1), first identified in human lung carcinoma cell lines, is a candidate tumor suppressor, but the details of its activity remain largely unknown. We have found that RNA interference of its C. elegans homolog (DIC-1) produced inviable embryos with increased apoptosis, cavities in cells and abnormal morphogenesis. In the dic-1(RNAi) germ line, ced-3-dependent apoptosis increased, and cell cavities appeared at the late-pachytene/oogenic stage,leading to defective oogenesis. Immunofluorescence microscopy of DIC-1 revealed its ubiquitous expression in the form of cytoplasmic foci, and cryoelectron microscopy narrowed down the location of the foci to the inner membrane of mitochondria. After dic-1 RNAi, mitochondria had an irregular morphology and contained numerous internal vesicles. Homozygous embryos from a heterozygous dic-1 mother arrested at the L3 larval stage, in agreement with the essential role of DIC-1 in mitochondria. In summary, C. elegans DIC-1 plays a crucial role in the formation of normal morphology of the mitochondrial cristae/inner membrane. Our results suggest that human DICE1 may have several functions in multiple intracellular locations.
Gli3-mediated repression of Hedgehog targets is required for normal mammary development
Authors: Hatsell Sarah J. , Cowin Pamela
Published: August 2006

The Hedgehog pathway is vital for the development of many epidermal appendages, but its role in mammary development has been unclear. Here, we show that although Gli2 and Gli3 are expressed during embryonic mammary development, transcriptional reporters of positive Hedgehog signaling are absent. Nevertheless, Gli3xt/xt embryos show aberrant early mammary marker expression and lack two pairs of mammary buds,demonstrating that Gli3 is essential for mammary bud formation and preceding patterning events. Misactivation of the Hedgehog pathway by targeted expression of the constitutive activator Gli1, from the Gli2promoter in Gli3xt/+ mice, also induces mammary bud loss. Moreover, loss of Gli3 expression induces Gli1 misexpression in mammary mesenchyme. These results establish that the essential function of Gli3 during embryonic mammary development is to repress Hedgehog/Gli1-inducible targets. During postnatal mammary development, Gli2 and Gli3 are expressed in stromal and myoepithelial cells, and Gli3 is also found within the lumenal epithelium. Again,transcriptional reporters of positive Hedgehog signaling are absent from these cell types, yet are expressed robustly within mammary lymphatics. Thus,positive Hedgehog signaling is absent throughout mammary development,distinguishing the mammary gland from other epidermal appendages, such as hair follicles, which require Hedgehog pathway activity.
Connexin 43-mediated modulation of polarized cell movement and the directional migration of cardiac neural crest cells
Authors: Xu Xin , Francis Richard , Wei Chih Jen , Linask Kaari L. , Lo Cecilia W.
Published: August 2006

Connexin 43 knockout (Cx43α1KO) mice have conotruncal heart defects that are associated with a reduction in the abundance of cardiac neural crest cells (CNCs) targeted to the heart. In this study, we show CNCs can respond to changing fibronectin matrix density by adjusting their migratory behavior,with directionality increasing and speed decreasing with increasing fibronectin density. However, compared with wild-type CNCs, Cx43α1KO CNCs show reduced directionality and speed, while CNCs overexpressing Cx43α1 from the CMV43 transgenic mice show increased directionality and speed. Altered integrin signaling was indicated by changes in the distribution of vinculin containing focal contacts, and altered temporal response of Cx43α1KO and CMV43 CNCs to β1 integrin function blocking antibody treatment. High resolution motion analysis showed Cx43α1KO CNCs have increased cell protrusive activity accompanied by the loss of polarized cell movement. They exhibited an unusual polygonal arrangement of actin stress fibers that indicated a profound change in cytoskeletal organization. Semaphorin 3A, a chemorepellent known to inhibit integrin activation, was found to inhibit CNC motility, but in the Cx43α1KO and CMV43 CNCs, cell processes failed to retract with semaphorin 3A treatment. Immunohistochemical and biochemical analyses suggested close interactions between Cx43α1,vinculin and other actin-binding proteins. However, dye coupling analysis showed no correlation between gap junction communication level and fibronectin plating density. Overall, these findings indicate Cx43α1 may have a novel function in mediating crosstalk with cell signaling pathways that regulate polarized cell movement essential for the directional migration of CNCs.
Comparative sequence analysis and tissue localization of members of the SLC6 family of transporters in adultDrosophila melanogaster
Authors: Thimgan Matthew S. , Berg Jonathan S. , Stuart Ann E.
Published: August 2006

The SLC6 family comprises proteins that move extracellular neurotransmitters, amino acids and osmolytes across the plasma membrane into the cytosol. In mammals, deletion of SLC6 family members has dramatic physiologic consequences, but in the model organism Drosophila melanogaster, little is known about this family of proteins. Therefore,in this study we carried out an initial analysis of 21 known or putative SLC6 family members from the Drosophila genome. Protein sequences from these genes segregated into either well-defined subfamilies, including the novel insect amino acid transporter subfamily, or into a group of weakly related sequences not affiliated with a recognized subfamily. Reverse transcription-polymerase chain reaction analysis and in situhybridization showed that seven of these genes are expressed in the CNS. In situ hybridization revealed that two previously cloned SLC6 members, the serotonin and dopamine transporters, were localized to presumptive presynaptic neurons that previously immunolabelled for these transmitters. RNA for CG1732 (the putative GABA transporter) and CG15088 (a member of the novel insect amino acid transporter family)was localized in cells likely to be subtypes of glia, while RNA for CG5226, CG10804 (both members of the orphan neurotransmitter transporter subfamily) and CG5549 (a putative glycine transporter)were expressed broadly throughout the cellular cortex of the CNS. Eight of the 21 sequences were localized outside the CNS in the alimentary canal,Malpighian tubules and reproductive organs. Localization for six sequences was not found or not attempted in the adult fly. We used the Drosophilaortholog of the mammalian vesicular monoamine transporter 2, CG33528,to independently identify monoaminergic neurons in the adult fly. RNA for CG33528 was detected in a limited number of cells in the central brain and in a beaded stripe at the base of the photoreceptors in the position of glia, but not in the photoreceptors themselves. The SLC6 localization observations in conjunction with likely substrates based on phylogenetic inferences are a first step in defining the role of Na/Cl-dependent transporters in Drosophila physiology.
Influence of the muscle-tendon unit's mechanical and morphological properties on running economy
Authors: Arampatzis Adamantios , De Monte Gianpiero , Karamanidis Kiros , Morey-Klapsing Gaspar , Stafilidis Savvas , Brüggemann Gert-Peter
Published: August 2006

The purpose of this study was to test the hypothesis that runners having different running economies show differences in the mechanical and morphological properties of their muscle-tendon units (MTU) in the lower extremities. Twenty eight long-distance runners (body mass: 76.8±6.7 kg, height: 182±6 cm, age: 28.1±4.5 years) participated in the study. The subjects ran on a treadmill at three velocities (3.0, 3.5 and 4.0 m s-1) for 15 min each. The \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{V}}_{\mathrm{O}_{2}}\) \end{document}consumption was measured by spirometry. At all three examined velocities the kinematics of the left leg were captured whilst running on the treadmill using a high-speed digital video camera operating at 250 Hz. Furthermore the runners performed isometric maximal voluntary plantarflexion and knee extension contractions at eleven different MTU lengths with their left leg on a dynamometer. The distal aponeuroses of the gastrocnemius medialis (GM) and vastus lateralis (VL) were visualised by ultrasound during plantarflexion and knee extension, respectively. The morphological properties of the GM and VL(fascicle length, angle of pennation, and thickness) were determined at three different lengths for each MTU. A cluster analysis was used to classify the subjects into three groups according to their \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{V}}_{\mathrm{O}_{2}}\) \end{document}consumption at all three velocities (high running economy, N=10;moderate running economy, N=12; low running economy, N=6). Neither the kinematic parameters nor the morphological properties of the GM and VL showed significant differences between groups. The most economical runners showed a higher contractile strength and a higher normalised tendon stiffness (relationship between tendon force and tendon strain) in the triceps surae MTU and a higher compliance of the quadriceps tendon and aponeurosis at low level tendon forces. It is suggested that at low level forces the more compliant quadriceps tendon and aponeurosis will increase the force potential of the muscle while running and therefore the volume of active muscle at a given force generation will decrease.
Effect of temperature on maximum swimming speed and cost of transport in juvenile European sea bass (Dicentrarchus labrax)
Authors: Claireaux Guy , Couturier Christine , Groison Anne-Laure
Published: August 2006

This study is an attempt to gain an integrated understanding of the interactions between temperature, locomotion activity and metabolism in the European sea bass (Dicentrarchus labrax). To our knowledge this study is among the few that have investigated the influence of the seasonal changes in water temperature on swimming performance in fish. Using a Brett-type swim-tunnel respirometer the relationship between oxygen consumption and swimming speed was determined in fish acclimatised to 7, 11, 14, 18, 22, 26 and 30°C. The corresponding maximum swimming speed(Umax), optimal swimming speed (Uopt),active (AMR) and standard (SMR) metabolic rates as well as aerobic metabolic scope (MS) were calculated. Using simple mathematical functions, these parameters were modelled as a function of water temperature and swimming speed. Both SMR and AMR were positively related to water temperature up to 24°C. Above 24°C SMR and AMR levelled off and MS tended to decrease. We found a tight relationship between AMR and Umax and observed that raising the temperature increased AMR and increased swimming ability. However, although fish swam faster at high temperature, the net cost of transport (COTnet) at a given speed was not influence by the elevation of the water temperature. Although Uopt doubled between 7°C and 30°C (from 0.3 to 0.6 m s-1), metabolic rate at Uopt represented a relatively constant fraction of the animal active metabolic rate (40-45%). A proposed model integrates the effects of water temperature on the interaction between metabolism and swimming performance. In particular the controlling effect of temperature on AMR is shown to be the key factor limiting maximal swimming speed of sea bass.
Visual and tactile learning of ground structures in desert ants
Authors: Seidl Tobias , Wehner Rüdiger
Published: August 2006

Place defining landmarks that have been studied intensively in insect navigation are large, voluminous objects visible to the insect from quite some distance. Here, we show that in desert ants, Cataglyphis fortis,local variations in ground properties can also serve as landmarks. The ants were trained to forage within a linear channel, in which the floor adjacent to the nest entrance was altered in optical and tactile properties. When ants were later tested within a test channel that ran parallel to the training channel, they recognized this landmark and centred their search on the part of the ground structure during training that was closest to the nest entrance. Hence, physical properties of the ground can be learnt and used as cues defining, for example, the position of the nest. In a second series of experiments the ants were presented with ground structures that differed in their visual and tactile properties from the training structure. We show that the absence of either the correct tactile properties or the correct optical properties of the ground structure make the ants reject the previously accepted structure. Hence small ground structures are recognized by the ants as familiar landmarks only if both visual and tactile information coincides with what the ants have experienced during training.
Integrating two-dimensional paths: do desert ants process distance information in the absence of celestial compass cues?
Authors: Ronacher B. , Westwig E. , Wehner R.
Published: August 2006

When performing foraging trips desert ants of the genus Cataglyphis continuously process and update a `home vector' that enables them to return to their nest on the shortest route. This capacity of path integration requires two types of information: (i) information about the travelling directions, and (ii) odometric information about the distances travelled in a particular direction. We have investigated how these two necessary pieces of information interact within the path integration processor. The specific question is: how do the ants process distance information if there is no simultaneous input from the sky compass available. Ants were trained to forage in a `Z'-shaped channel system, the three segments of which joined at right angles. Individual animals were transferred from the feeder to a test field where their homing paths could be observed. In the crucial tests the middle segment of the maze was covered by orange Perspex that did not transmit the UV part of the spectrum, and thus precluded the perception of polarization patterns. Changes of the ant's processing of odometric information within this channel segment directly translate into a change in homing direction on the test field. The results indicate that the odometric information about travelling distance is largely ignored for path integration if there is no simultaneous input from the sky-view-based compass. They further show that idiothetic information cannot adequately substitute for the polarization compass to infer travelling directions.
Light and electron microscopic study of the thyroid gland in rats exposed to power-frequency electromagnetic fields
Authors: Rajkovic Vesna , Matavulj Milica , Johansson Olle
Published: August 2006

The effect of 50 Hz electromagnetic field (EMF) on thyroid gland was studied using light and transmission electron microscopes. Two-month-old male rats were exposed to an EMF (100-300 μT, 54-160 V m-1) for 4 h a day, 5 days a week for 1 month. A predominance of microfollicles with less colloid content and dilated blood capillaries was found in the EMF group. Stereological counting showed a statistically significant increase of the volume density of follicular epithelium, interfollicular tissue and blood capillaries as well as the thyroid activation index, as compared to the controls. The volume density of colloid significantly decreased. Ultrastructural analysis of thyroid follicular cells in the EMF group revealed the frequent finding of several colloid droplets within the same thyrocyte with the occasional presence of large-diameter droplets. Alterations in lysosomes, granular endoplasmic reticulum and cell nuclei compared to the control group were also observed. Taken together, the results of this study show the stimulative effect of power-frequency EMF on thyroid gland at both the light microscope and the ultrastructural level.
Juvenile plaice (Pleuronectes platessa) produce camouflage by flexibly combining two separate patterns
Authors: Kelman Emma J. , Tiptus Palap , Osorio Daniel
Published: August 2006

Plaice (Pleuronectes platessa) is a flatfish well-known for the ability to vary its body pattern, probably for camouflage. This study investigates the repertoire of patterns used by juvenile plaice, by describing how they respond to shifts between three artificial backgrounds. Two basic patterns are under active control, fine `spots' and coarser `blotches'. These patterns are superimposed on a fairly uniform ground. For the six plaice studied, the levels of expression of the spot and blotch patterns varied continuously and independently according to the visual background, and in a manner consistent with their being cryptic. The repertoire of plaice appears to be intermediate between the tropical flatfish Bothus ocellatus,which has three separate basic patterns, and two temperate species Paralichthys lethostigma and Pseudopleuronectes americanus,which have one each. It is interesting to consider how mixing a small number of coloration patterns is effective for camouflage, and why the demands of this task may lead to differences between species.
Study of calcification during a daily cycle of the coralStylophora pistillata: implications for `light-enhanced calcification'
Authors: Moya Aurélie , Tambutté Sylvie , Tambutté Eric , Zoccola Didier , Caminiti Natacha , Allemand Denis
Published: August 2006

This work, performed on the scleractinian coral Stylophora pistillata, aims at providing new information on the `light-enhanced calcification' process. In a first step, in controlled conditions of culture and constant light supply, we studied the diurnal cycle of calcification. We determined that calcification rates are constant during the day and the night with a 2.6-fold difference between day and night calcification rates. We also showed that the photosynthetic rate is constant throughout the day when a constant light intensity is applied. Our results on free-running experiments in prolonged conditions of light or dark suggest that calcification is not regulated by an endogenous circadian rhythm. In a second step, using a kinetic isotopic approach with 45Ca, we characterized the transition stages between day and night and vice versa. Under our experimental conditions, the lag-phase necessary to switch from the light to the dark calcification rate is the same as the lag-phase necessary to switch from the dark to the light calcification rate. We discuss our results in the context of two hypotheses of the light-enhanced calcification process: (1) the role of photosynthesis on the pH in the coelenteron and (2) the role of photosynthesis in supplying precursors of the organic matrix.
The pressures of suction feeding: the relation between buccal pressure and induced fluid speed in centrarchid fishes
Authors: Higham Timothy E. , Day Steven W. , Wainwright Peter C.
Published: August 2006

Suction feeding fish rapidly expand their oral cavity, resulting in a flow of water directed towards the mouth that is accompanied by a drop in pressure inside the buccal cavity. Pressure inside the mouth and fluid speed external to the mouth are understood to be mechanically linked but the relationship between them has never been empirically determined in any suction feeder. We present the first simultaneous measurements of fluid speed and buccal pressure during suction feeding in fishes. Digital particle image velocimetry (DPIV)and high-speed video were used to measure the maximum fluid speed in front of the mouth of four largemouth bass and three bluegill sunfish by positioning a vertical laser sheet on the mid-sagittal plane of the fish. Peak magnitude of pressure inside the buccal cavity was quantified using a transducer positioned within a catheter that opened into the dorsal wall of the buccal cavity. In both species the time of peak pressure preceded the time of peak fluid speed by as much as 42 ms, indicating a role for unsteady flow effects in shaping this relation. We parameterized an existing model of suction feeding to determine whether the relationship between peak pressures and fluid speeds that we observed could be predicted using just a few kinematic variables. The model predicted much higher fluid speeds than we measured at all values of peak pressure and gave a scaling exponent between them (0.51) that was higher than observed (0.36 for largemouth bass, 0.38 for bluegill). The scaling between peak buccal pressure and peak fluid speed at the mouth aperture differed in the two species, supporting the recent conclusion that species morphology affects this relation such that a general pattern may not hold.
Na+/H+ antiporter, V-H+-ATPase and Na+/K+-ATPase immunolocalization in a marine teleost(Myoxocephalus octodecemspinosus)
Authors: Catches Justin S. , Burns Julie M. , Edwards Susan L. , Claiborne James B.
Published: August 2006

Long-term pH compensation in a marine teleost requires the transepithelial excretion of H+ across the gill epithelium. H+ efflux in the longhorn sculpin (Myoxocephalus octodecemspinosus) is dependent on external sodium ion concentration and is inhibited by known inhibitors of Na+/H+ exchangers. Our model for proton transport suggests acid-excreting cells in the gill with an apical Na+/H+ antiporter and basolateral Na+/K+-ATPase. This model is similar to mammalian kidney and elasmobranch gill epithelium in which a basolateral electrogenic-vacuolar proton pump (V-H+-ATPase) localizes to base-excreting cells. The objective of this study was to detect the presence and location of membrane transporters in marine fish gills using immunohistochemical staining. Our data indicate the presence of an apical and subapical Na+/H+-exchanger 2 (NHE2) in the sculpin gill. NHE2 is present in large, ovoid chloride cells and often colocalizes in the same cells as Na+/K+-ATPase. We also detected V-H+-ATPase immunoreactivity, predominantly in cells at the base of the lamellae, with staining patterns indicative of a basolateral location. The 85 kDa protein detected on immunoblots with anti-NHE2 antibodies was found in both control and acid-infused animals and did not change following a large acute acidosis over 8 h.
Freezing or supercooling: how does an aquatic subterranean crustacean survive exposures at subzero temperatures?
Authors: Issartel Julien , Voituron Yann , Odagescu Valentina , Baudot Anne , Guillot Geneviève , Ruaud Jean-Pierre , Renault David , Vernon Philippe , Hervant Frédéric
Published: August 2006

Crystallization temperature (Tc), resistance to inoculative freezing (IF), ice contents, bound water, protein and glycogen body contents were measured in the aquatic subterranean crustacean Niphargus rhenorhodanensis and in the morphologically close surface-dwelling aquatic crustacean Gammarus fossarum, both acclimated at 12°C, 3°C and -2°C. Cold acclimation induced an increase in the Tc values in both species but no survival was observed after thawing. However, after inoculation at high sub-zero temperatures, cold-acclimated N. rhenorhodanensis survived whereas all others, including the 3°C and -2°C acclimated G. fossarumdied. In its aquatic environment, N. rhenorhodanensis is likely to encounter inoculative freezing before reaching the Tc and IF tolerance appears as a highly adaptive trait in this species. Bound water and glycogen were found to increase in the 3°C and -2°C acclimated N. rhenorhodanensis, whereas no variation was observed in G. fossarum. Considering the hydrophilic properties of glycogen, such a rise may be correlated with the increased bound water measured in cold-acclimated N. rhenorhodanensis, and may be linked to the survival of this species when it was inoculated. The ecological significance of the survival of the aquatic subterranean crustacean to inoculative freezing is paradoxical, as temperature is currently highly buffered in its habitat. However, we assume that past geographical distribution and resulting life history traits of N. rhenorhodanensis are key parameters in the current cold-hardiness of the species.
In situmuscle power differs without varyingin vitromechanical properties in two insect leg muscles innervated by the same motor neuron
Authors: Ahn A. N. , Meijer K. , Full R. J.
Published: August 2006

The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situmeasurements under in vivo running conditions of muscle 178 to a previously examined muscle (179) demonstrate that the same inputs (e.g. neural signal and kinematics) can result in different mechanical outputs. The same neural signal and kinematics, as determined during running, can result in different mechanical functions, even when the two anatomically similar muscles possess the same contraction kinetics, force-velocity properties and tetanic force-length properties. Although active shortening greatly depressed force under in vivo-like strain and stimulation conditions, force depression was similarly proportional to strain, similarly inversely proportional to stimulation level, and similarly independent of initial length and shortening velocity between the two muscles. Lastly, passive pre-stretch enhanced force similarly between the two muscles. The forces generated by the two muscles when stimulated with their in vivo pattern at lengths equal to or shorter than rest length differed, however. Overall, differences between the two muscles in their submaximal force-length relationships can account for up to 75% of the difference between the two muscles in peak force generated at short lengths observed during oscillatory contractions. Despite the fact that these muscles act at the same joint, are stimulated by the same motor neuron with an identical pattern, and possess many of the same in vitro mechanical properties, the mechanical outputs of two leg extensor muscles can be vastly different.
Isometric contractile properties of sexually dimorphic forelimb muscles in the marine toad Bufo marinus Linnaeus 1758: functional analysis and implications for amplexus
Authors: Lee Clark Douglas , Peters Susan E.
Published: August 2006

It has been shown in the bullfrog, Rana catesbeiana Shaw 1802,that certain forelimb muscles in males have different contractile properties when compared with females, which may result from adaptation for amplexus. We extended this study to a distantly related species, Bufo marinusLinnaeus 1758, by testing the isometric contractile properties of three muscles, abductor indicus longus (AIL), and flexor carpi radialis (FCR) (both dimorphic muscles), and extensor carpi ulnaris (ECU) (non-dimorphic control). In males the dimorphic muscles had greater wet mass and cross-sectional area than in the females, and also produced significantly greater isometric force. As in bullfrogs, however, the maximum tetanic force per cm2 of muscle cross-section did not differ between the sexes. In spite of this similarity in maximum force, the two dimorphic muscles were much less fatigable in the males than in the females. Lower fatigability in males correlated with exceptionally elongated relaxation times that maintained high levels of force between stimulus trains. This sustained force was negligible in the females, suggesting that this feature may allow males to maintain amplexus for prolonged periods. The same sustained force response was observed in the earlier study of Rana catesbeiana. Because this response is similar in Bufo and Rana, muscular properties correlated with amplexus may be shared across anurans by inheritance of this response from a common ancestor.
Body density affects stroke patterns in Baikal seals
Authors: Watanabe Yuuki , Baranov Eugene A. , Sato Katsufumi , Naito Yasuhiko , Miyazaki Nobuyuki
Published: August 2006

Buoyancy is one of the primary external forces acting on air-breathing divers and it can affect their swimming energetics. Because the body composition of marine mammals (i.e. the relative amounts of lower-density lipid and higher-density lean tissue) varies individually and seasonally,their buoyancy also fluctuates widely, and individuals would be expected to adjust their stroke patterns during dives accordingly. To test this prediction, we attached acceleration data loggers to four free-ranging Baikal seals Phoca sibirica in Lake Baikal and monitored flipper stroking activity as well as swimming speed, depth and inclination of the body axis(pitch). In addition to the logger, one seal (Individual 4) was equipped with a lead weight that was jettisoned after a predetermined time period so that we had a set of observations on the same individual with different body densities. These four data sets revealed the general diving patterns of Baikal seals and also provided direct insights into the influence of buoyancy on these patterns. Seals repeatedly performed dives of a mean duration of 7.0 min(max. 15.4 min), interrupted by a mean surface duration of 1.2 min. Dive depths were 66 m on average, but varied substantially, with a maximum depth of 324 m. The seals showed different stroke patterns among individuals; some seals stroked at lower rates during descent than ascent, while the others had higher stroke rates during descent than ascent. When the lead weight was detached from Individual 4, the seal increased its stroke rate in descent by shifting swimming mode from prolonged glides to more stroke-and-glide swimming, and decreased its stroke rate in ascent by shifting from continuous stroking to stroke-and-glide swimming. We conclude that seals adopt different stroke patterns according to their individual buoyancies. We also demonstrate that the terminal speed reached by Individual 4 during prolonged glide in descent depended on its total buoyancy and pitch, with higher speeds reached in the weighted condition and at steeper pitch. A simple physical model allowed us to estimate the body density of the seal from the speed and pitch(1027-1046 kg m-3, roughly corresponding to 32-41% lipid content,for the weighted condition; 1014-1022 kg m-3, 43-47% lipid content,for the unweighted condition).
On the equivalence between Kalman smoothing and weak‐constraint four‐dimensional variational data assimilation
Authors: Fisher M. , Leutbecher M. , Kelly G. A.
Published: August 2006

The fixed‐interval Kalman smoother produces optimal estimates of the state of a system over a time interval, given observations over the interval, together with a prior estimate of the state and its error covariance at the beginning of the interval. At the end of the interval, the Kalman smoother estimate is identical to that produced by a Kalman filter, given the same observations and the same initial state and covariance matrix.

For an imperfect model, the model error term in the covariance evolution equation acts to reduce the dependence of the estimate on observations and prior states that are well separated in time. In particular, if the assimilation interval is sufficiently long, the estimate at the end of the interval is effectively independent of the state and covariance matrix specified at the beginning of the interval. In this case, the Kalman smoother provides estimates at the end of the interval that are identical to those of a Kalman filter that has been running indefinitely.

For a linear model, weak‐constraint four‐dimensional variational data assimilation (4D‐Var) is equivalent to a fixed‐interval Kalman smoother. It follows that, if the assimilation interval is made sufficiently long, the 4D‐Var analysis at the end of the assimilation interval will be identical to that produced by a Kalman filter that has been running indefinitely.

The equivalence between weak‐constraint 4D‐Var and a long‐running Kalman filter is demonstrated for a simple analogue of the numerical weather‐prediction (NWP) problem. For this nonlinear system, 4D‐Var analysis with a 10‐day assimilation window produces analyses of the same quality as those of an extended Kalman filter. It is demonstrated that the current ECMWF operational 4D‐Var system retains a memory of earlier observations and prior states over a period of between four and ten days, suggesting that weak‐constraint 4D‐Var with an analysis interval in the range of four to ten days may provide a viable algorithm with which to implement an unapproximated Kalman filter. Whereas assimilation intervals of this length are unlikely to be computationally feasible for operational NWP in the near future, the ability to run an unapproximated Kalman filter should prove invaluable for assessing the performance of cheaper, but suboptimal, alternatives. Copyright © 2005 Royal Meteorological Society
Evaluation of new estimates of background‐ and observation‐error covariances for variational assimilation
Authors: Buehner Mark , Gauthier Pierre , Liu Zhuo
Published: August 2006

In this study new estimates for the observation‐ and background‐error covariances in a three‐dimensional variational analysis system at the Canadian Meteorological Centre are evaluated. In the current system, the observation errors are assumed uncorrelated with the variances estimated following a more or less ad hoc approach for each instrument type. The background‐error covariances are computed using the so‐called NMC method. The new estimate for the observation error variances is obtained using a practical approach developed at Météo‐France that computes the maximum likelihood estimate of the variances. Two new estimates for the stationary background‐error covariances are evaluated. The first simply involves tuning the variances in the operational background‐error covariances. For the second, the NMC method is replaced by a Monte Carlo approach applied to the existing analysis system.

Both the variances and spatial covariances of the innovations are computed and compared with the corresponding quantities derived from each set of error covariances used by the analysis system. This comparison shows a significantly improved consistency for radiosonde data when using the new error covariances, especially with the Monte Carlo approach. In contrast, the interchannel innovation covariances for ATOVS AMSU‐A observations are more consistent when using background‐error covariances obtained with the NMC method. In addition, modest forecast improvements are obtained by using the new observation‐ and background‐error covariance estimates, most notably for the tropics. © Crown copyright, 2005
Operational multivariate ocean data assimilation
Authors: Cummings James A.
Published: August 2006

A fully three‐dimensional, multivariate, optimum‐interpolation ocean data assimilation system has been developed that produces simultaneous analyses of temperature, salinity, geopotential and vector velocity. The system is run in real‐time, and can be executed as a stand‐alone analysis or cycled with an ocean forecast model in a sequential incremental update cycle. Additional capabilities have been built into the system, including flow‐dependent background‐error correlations and background‐error variances that vary in space and evolve from one analysis cycle to the next. The ocean data types assimilated include: remotely sensed sea surface temperature, sea surface height, and sea‐ice concentration; plus in situ surface and sub‐surface observations of temperature, salinity, and currents from a variety of sources, such as ships, buoys, expendable bathythermographs, conductivity–temperature–depth sensors, and profiling floats. An ocean data quality‐control system is fully integrated with the multivariate analysis, and includes feedback of forecast fields and prediction errors in the quality control of new observations. The system is operational at the US Navy oceanographic production centres both in global and in regional applications. It is being implemented as the data assimilation component of the Hybrid Coordinate Ocean Model as part of the US contribution to the Global Ocean Data Assimilation Experiment, and in a limited‐area ensemble‐based forecasting system that will be used in an adaptive sampling, targeted observation application. Copyright © 2005 Royal Meteorological Society
Tropical Pacific Ocean model error covariances from Monte Carlo simulations
Authors: Alves O. , Robert C.
Published: August 2006

As a first step towards the development of an Ensemble Kalman Filter (EnKF) for ocean data assimilation in the tropical oceans, this article investigates a novel technique for explicitly perturbing the model error in Monte Carlo simulations.

The perturbation technique involves perturbing the surface zonal stress. Estimates of the characteristics of the wind stress errors were obtained from the difference between zonal wind fields from the NCEP and ECMWF re‐analyses. In order to create random zonal wind stress perturbations, an EOF analysis was performed on the intraseasonally time‐filtered difference between the two re‐analysis products. The first 50 EOFs were retained and random wind stress fields for each ensemble member were created by combining random amounts of each EOF.

Ensemble runs were performed using a shallow‐water model, with both short forecasts and long simulations. Results show covariance patterns characteristic of Kelvin wave and Rossby wave dynamics. There are interesting differences between covariances using short forecasts and those using long simulations. The use of the long simulations produced non‐local covariances (e.g. negative covariances between east and west Pacific), whereas short forecasts produced covariances that were localized by the time it takes Kevin and Rossby waves to travel over the forecast period and the scales of spatial covariance in the wind stress errors.

The ensembles of short forecasts produced covariances and cross‐covariances that can be explained by the dynamics of equatorial Rossby and Kevin waves forced by wind stress errors. The results suggest that the ensemble generation technique to explicitly represent the model error term can be used in an EnKF. Copyright © 2005 Royal Meteorological Society
A multivariate balance operator for variational ocean data assimilation
Authors: Weaver A. T. , Deltel C. , Machu E. , Ricci S. , Daget N.
Published: August 2006

It is common in meteorological applications of variational assimilation to specify the error covariances of the model background state implicitly via a transformation from model space where variables are highly correlated to a control space where variables can be considered to be approximately uncorrelated. An important part of this transformation is a balance operator which effectively establishes the multivariate component of the error covariances. The use of this technique in ocean data assimilation is less common. This paper describes a balance operator that can be used in a variable transformation for oceanographic applications of three‐ and four‐dimensional variational assimilation. The proposed balance operator has been implemented in an incremental variational data assimilation system for a global ocean general‐circulation model. Evidence that the balance operator can explain a significant percentage of background‐error variance is presented. The multivariate analysis structures implied by the balance operator are illustrated using single‐observation experiments. Copyright © 2005 Royal Meteorological Society
A pre‐operational variational data assimilation system for a non‐hydrostatic model at the Japan Meteorological Agency: formulation and preliminary results
Authors: Honda Y. , Nishijima M. , Koizumi K. , Ohta Y. , Tamiya K. , Kawabata T. , Tsuyuki T.
Published: August 2006

A new variational data assimilation system for a non‐hydrostatic model is being developed at the Japan Meteorological Agency (JMA) for operational use. Known as the JMA non‐hydrostatic model variational data assimilation (JNoVA) system, it mainly functions as a four‐dimensional variational data assimilation system, although it has an option to be used as a three‐dimensional system.

The set of control variables consists of initial conditions of unbalanced horizontal winds, large‐scale components of potential temperature and surface pressure, unbalanced temperature and pseudo relative humidity. In the control variable transformation, hydrostatic balance and geostrophic balance are considered explicitly and the effect of the surface friction is also considered implicitly. When calculating the background‐error covariances by the NMC method, a low‐pass filter is introduced to remove noise in potential temperature and surface pressure that degrades the quality of the balanced winds. The cut‐off wavelength of the low‐pass filter is set to 300 km, which is the scale at which the model's kinetic energy spectrum transits to the shallower slope characterizing mesoscale motions.

An adjoint model of the JMA non‐hydrostatic model has been developed from scratch by hand for this system. Although some of the physics are simplified, all physical processes except the radiation are considered.

A preliminary data assimilation experiment with the JNoVA has been done for a heavy rainfall event. The results show that the quantitative precipitation forecast (in terms of the intensity, timing and position of the event) from the analysis by the JNoVA is improved over the forecast from the analysis by a four‐dimensional variational system that employs the JMA hydrostatic spectral model. Copyright © 2005 Royal Meteorological Society