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  • 1
    Electronic Resource
    Electronic Resource
    Location of ecdysteroid 22-O-acyltransferase in the larvae ofHeliothis virescens (1994)
    Springer
    Entomologia experimentalis et applicata 70 (1994), S. 263-272 
    Details
    ISSN: 1570-7458
    Keywords: tobacco budworm ; Heliothis virescens ; Noctuidae ; epithelial cell ; brush border membrane ; ecdysteroids ; metabolism ; acyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Larvae of the tobacco budworm,Heliothis virescens, are resistant to high levels of ingested 20-hydroxyecdysone which could cause potential inhibition to the development of many other lepidopteran species. This resistance is attributed to the ability of the larvae to metabolize this molting hormone to its 22-acyl ester forms. When tobacco budworm larvae were fed large quantities of 20-hydroxyecdyone, the hormonal metabolites were found in gut and fat body tissues. When incubated with 20-hydroxyecdysone gut tissue converted 20-hydroxyecdysone into its 22-acyl ester metabolites. Lumen site of the midgut was found to be the major location of this bio-transformation. In contrast, fat body tissue failed to convert 20-hydroxyecdysone to 22-acyl ester metabolitesin vitro. After the oral injection of3H-ecdysone, the major metabolites formed were ecdysone 22-acyl esters whereas the majority of3H-ecdysone was transformed to polar metabolites after it was injected into the hemocoel of the larvae. Similar distributions of ecdysteroid 22-O-acyltransferase and alkaline phosphatase activity in subcellular fractions demonstrates the co-localization of these enzymes in plasma membrane of the gut epithelial cells. These results suggest that gut brush border membrane is the major site of ecdysteroid 22-acyl ester formation inH. virescens larvae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02380560
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  • 2
    Electronic Resource
    Electronic Resource
    Role of bilateral chemosensory input in food discrimination by Manduca sexta larvae (1991)
    Springer
    Entomologia experimentalis et applicata 61 (1991), S. 159-168 
    Details
    ISSN: 1570-7458
    Keywords: Feeding ; behaviour ; chemosensory ablation ; Manduca sexta ; Lepidoptera ; bilateral sensory input ; input redundancy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The function of bilateral chemosensory input in food discrimination was examined using larvae of the tobacco hornworm, Manduca sexta (Johan.) (Lepidoptera: Sphingidae), in 2-choice preference tests. Larvae having three different complements of chemosensory organs remaining after microsurgery were tested: unoperated, unilaterally-ablated, and bilaterally-ablated. Discrimination between Solanum pseudocapsicum (L.) and Pelargonium hortorum (Bailey) was reduced after unilateral removal of chemosensory organs. A similar effect was found in tests offering larvae a choice between one plant species or an ethanolic extract of S. pseudocapsicum and wetted filter paper, indicating an impaired food detection. These results demonstrate that both sets of chemosensory organs are required for normal feeding decisions about these plants. Six additional plant species were each tested against wetted filter paper. The function of bilateral chemosensory input in food discrimination varies with the plant species tested. Bilateral chemosensory input is required for discrimination of Vigna sinensis (Savi) and Raphanus sativus (L.), but not for that of Lycopersicon esculentum (Mill.), Datura innoxia (L.), Brassica napus (L.), and Canna generalis (Bailey). Discrimination of V. sinensis, S. pseudocapsicum, and P. hortorum by unoperated larvae is twice as strong as that by unilaterally-ablated larvae, suggesting algebraic addition of unilateral sensory inputs. For R. sativus unilateral input does not mediate discrimination, but bilateral input does, indicating sensory processing which may be more than additive. These results show that information mediated by bilateral chemosensory organs of M. sexta is not redundant in mediating feeding decisions, but provide the necessary sensory input for normal discrimination. This suggests that, for some plant species, feeding decisions are based on both qualitative and quantitative aspects of chemosensory input. No difference in preferences between left-sided and right-sided operated larvae were observed which suggests functional duplication of each set of unilateral chemosensory organs. Possible neural mechanisms underlying feeding decisions mediated by bilateral versus unilateral chemosensory inputs are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191746
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  • 3
    Electronic Resource
    Electronic Resource
    Diet-induced food preference by Manduca sexta larvae: acceptable non-host plants elicit a stronger induction than host plants (1992)
    Springer
    Entomologia experimentalis et applicata 63 (1992), S. 3-12 
    Details
    ISSN: 1570-7458
    Keywords: Feeding ; behaviour ; food preference induction ; diets ; Manduca sexta ; Lepidoptera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Diet-induced changes in food preference by fifth instar larvae of the tobacco hornworm, Manduca sexta (Johan.) (Lepidoptera, Sphingidae), were examined. Two groups of larvae with different diet experience were used: larvae reared on a host or on an acceptable non-host plant species. Each group of larvae was offered a choice between leaf discs from each rearing plant species (2-plant choice test) and food preference was measured as the consumption of one plant species relative to that of the other plant species. Diet-induced changes in preferences were larger with the host versus acceptable non-host plant pairs Solanum pseudocapsicum (L.) versus Raphanus sativus (L.), Lycopersicon esculentum (Mill.) versus Vigna sinensis (Savi), and Datura innoxia (L.) versus V. sinensis than with the host versus host plant pairs L. esculentum versus Capsicum annuum (L.) and L. esculentum versus D. innoxia. To examine how much the food preference had been altered for each test plant species alone, two other groups of larvae were offered a choice between leaf discs from a single plant species and filter paper discs laced with distilled water (1-plant choice test). Larvae preferred the dietary plant species more strongly than the non-dietary plant species in tests using the following plant species: for C. annuum with C. annuum and L. esculentum as diets, for V. sinensis with V. sinensis and L. esculentum or D. innoxia as diets, and for R. sativus with R. sativus and S. pseudocapsicum as diets. The preference for the hosts L. esculentum and D. innoxia did not change significantly after rearing larvae on different hosts or on an acceptable non-host. Thus, diet-induction by M. sexta larvae results in an enhancement of preference for the dietary plant species which is much stronger with acceptable non-hosts than with hosts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350341
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  • 4
    Electronic Resource
    Electronic Resource
    Chemoreceptors in the preoral cavity of the tobacco hornworm, Manduca sexta, and their possible function in feeding behaviour (1977)
    Springer
    Entomologia experimentalis et applicata 21 (1977), S. 287-298 
    Details
    ISSN: 1570-7458
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Wie Wirtswahlversuche zeigten, verlieren Larven des Tabakhornwurms nach Antennen- und Maxillenentfernung nicht die Fähigkeit zwischen einer Wirtspflanze (Tomate) und einer Nichtwirtspflanze (Canna) zu unterscheiden. Wenn jedoch auch das Labrum entfernt wurde, konnte kein Unterschied mehr in der Bevorzugung einer der beiden Pflanzen gefunden werden. Dies läßt Chemorezeptoren im Labrum vermuten. Raster-elektronenmikroskopische Bilder des Epipharynx ließen ein Paar von Rezeptoren mit möglicherweise chemorezeptiven Strukturen erkennen. Mit elektrophysiologischen Methoden wurde die Geschmacksfunktion dieser Sensillen nachgewiesen und es wurden einige Eigenschaften untersucht. Dabei wurde die Aktivität von nicht mehr als drei verschiedenen Sinneszellen in jedem Epipharynxsensillum festgestellt. Eine Zelle erwies sich als empfindlich für verschiedene, geschmacklich unangenehme Verbindungen. Saft von Tomaten und Canna stimulierten keine besonderen Sinneszellen; dennoch sind die Verhaltensreaktionen gegenüber diesen Pflanzen völlig verschieden. Es wird vermutet, daß dieses Sinnesorgan Information über die chemische Zusammensetzung der Pflanzen in bestimmten Aktivitätsmustern übermittelt. Die Fraßtests an verschiedenen Diäten zeigten, daß Maxillenektomie die fraßstimulierende Wirkung von Saccharose vermindert, allerdings nicht vollständig. Elektrophysiologisch wurde keine Aktivität eines spezifischen epipharyngalen Zuckerrezeptors in den epipharyngalen Sensillen festgestellt. Jedoch wurde die Reaktion von zwei Zellen auf Salz in Gegenwart von Zucker gehemmt. Die epipharyngalen Chemorezeptoren arbeiten als eine zweite Kontrollstelle nach den maxillaren Chemorezeptoren für fraßabschreckende Verbindungen. Es ist wahrscheinlich, daß die tatsächliche Nahrungsaufnahme bei Larven nach Maxillenentfernung eher durch die Gegenwart von Fraßdeterrentien gesteuert wird als durch die Gegenwart von Fraßstimulantien.
    Notes: Abstract Feeding preference tests showed that antenna- and maxillectomized larvae of the tobacco hornworm do not lose the ability to discriminate between a host plant (tomato) and a non-host plant (canna). When the labrum was also removed, no difference in acceptability of the two plants could be found. This suggested that chemoreceptors existed on the labrum. Scanning electronmicroscope pictures of the epipharynx revealed one pair of possible chemoreceptive structures. Using electrophysiological methods, the gustatory function of these sensilla was established and some properties were studied. Activity of not more than three different sensory cells of each epipharyngeal sensillum was observed. One cell was found to be sensitive to various distasteful compounds. Saps of tomato and canna do not stimulate particular sensory cells; however, the behavioural responses towards these plants are totally different. It was suggested that these sense organs relay information on the chemical composition of the plants in certain patterns of activity. The feeding tests on different diets showed that maxillectomy reduced the feeding stimulant effect of sucrose, but not completely. No activity of a specific sugar receptor in the epipharyngeal sensilla was observed electrophysiologically. However, the response of two cells to salt was inhibited in the presence of sugar. The epipharyngeal chemoreceptors function as a second checkpoint after the maxillary chemoreceptors for feeding deterrent compounds. It is more likely that the actual food intake in maxillectomized larvae is controlled by the presence of feeding deterrents than by the presence of feeding stimulants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00291791
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  • 5
    Electronic Resource
    Electronic Resource
    Numerical convergence of the dynamics of a GCM (1997)
    Springer
    Climate dynamics 13 (1997), S. 359-374 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract.  Atmospheric general circulation models (GCMs) are characterized by many features but especially by: (1) the manner of discretizing the governing equations and of representing the variables involved at a given resolution, and (2) the manner of parameterizing unresolved physical processes in terms of those resolved variables. These two aspects of model formulation are not independent and it is difficult to untangle their intertwined effects when assessing model performance. The attempt here is to separate these aspects of GCM behaviour and to ask, “Given a perfect parameterization of the physical processes in a model, what resolution is needed to capture the dominant dynamical aspects of the atmospheric climate?” Alternatively, “At what resolution do the dynamics of a GCM converge”? The perfect parameterization approach assumes that the calculation of the physical terms returns the “correct” result at all resolutions. In the idealized case, a time-independent forcing is one of the simplest that satisfies this condition. However, experiments show that it is difficult for the dynamics of a GCM to balance a time-independent forcing with atmosphere-like flows and structures. The model requires, and the atmosphere presumably includes, physical feedback mechanisms which act so as to maintain the kinds of flows and structures that are observed. Resolution experiments are performed with a simplified forcing function for the thermodynamic equation which combines a dominant time-independent specified forcing with a weak linear relaxation feedback. These experiments show that the dynamics of the GCM have essentially converged at T32 and certainly by T63 which is the next resolution considered. This is shown by the constancy of structures, variances, covariances, transports and energy budgets with increasing resolution. Experiments with an alternative forcing proposed by Held and Suarez, which has the form of a linear relaxation, show somewhat less evidence of convergence at these resolutions. In both cases the “physics” are known by assumption. However, the form and nature of the forcing is different, as is the behaviour with resolution. The implication for the real system is that the resolution required for simulating the dynamical aspects of climate is rather modest. The simulated climate does, however, apparently depend on the ability to correctly and consistently parameterize the physical processes in a GCM, involving both forcing and feedback mechanisms, as a function of resolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050171
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  • 6
    Electronic Resource
    Electronic Resource
    Northern Hemisphere atmospheric blocking as simulated by 15 atmospheric general circulation models in the period 1979–1988 (1998)
    Springer
    Climate dynamics 14 (1998), S. 385-407 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  As a part of the Atmospheric Model Intercomparison Project (AMIP), the behaviour of 15 general circulation models has been analysed in order to diagnose and compare the ability of the different models in simulating Northern Hemisphere midlatitude atmospheric blocking. In accordance with the established AMIP procedure, the 10-year model integrations were performed using prescribed, time-evolving monthly mean observed SSTs spanning the period January 1979–December 1988. Atmospheric observational data (ECMWF analyses) over the same period have been also used to verify the models results. The models involved in this comparison represent a wide spectrum of model complexity, with different horizontal and vertical resolution, numerical techniques and physical parametrizations, and exhibit large differences in blocking behaviour. Nevertheless, a few common features can be found, such as the general tendency to underestimate both blocking frequency and the average duration of blocks. The problem of the possible relationship between model blocking and model systematic errors has also been assessed, although without resorting to ad-hoc numerical experimentation it is impossible to relate with certainty particular model deficiencies in representing blocking to precise parts of the model formulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050230
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  • 7
    Electronic Resource
    Electronic Resource
    The Canadian Centre for Climate Modelling and Analysis global coupled model and its climate (2000)
    Springer
    Climate dynamics 16 (2000), S. 451-467 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  A global, three-dimensional climate model, developed by coupling the CCCma second-generation atmospheric general circulation model (GCM2) to a version of the GFDL modular ocean model (MOM1), forms the basis for extended simulations of past, current and projected future climate. The spin-up and coupling procedures are described, as is the resulting climate based on a 200 year model simulation with constant atmospheric composition and external forcing. The simulated climate is systematically compared to available observations in terms of mean climate quantities and their spatial patterns, temporal variability, and regional behavior. Such comparison demonstrates a generally successful reproduction of the broad features of mean climate quantities, albeit with local discrepancies. Variability is generally well-simulated over land, but somewhat underestimated in the tropical ocean and the extratropical storm-track regions. The modelled climate state shows only small trends, indicating a reasonable level of balance at the surface, which is achieved in part by the use of heat and freshwater flux adjustments. The control simulation provides a basis against which to compare simulated climate change due to historical and projected greenhouse gas and aerosol forcing as described in companion publications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050339
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  • 8
    Electronic Resource
    Electronic Resource
    A transient climate change simulation with greenhouse gas and aerosol forcing: projected climate to the twenty-first century (2000)
    Springer
    Climate dynamics 16 (2000), S. 427-450 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  The potential climatic consequences of increasing atmospheric greenhouse gas (GHG) concentration and sulfate aerosol loading are investigated for the years 1900 to 2100 based on five simulations with the CCCma coupled climate model. The five simulations comprise a control experiment without change in GHG or aerosol amount, three independent simulations with increasing GHG and aerosol forcing, and a simulation with increasing GHG forcing only. Climate warming accelerates from the present with global mean temperatures simulated to increase by 1.7 °C to the year 2050 and by a further 2.7 °C by the year 2100. The warming is non-uniform as to hemisphere, season, and underlying surface. Changes in interannual variability of temperature show considerable structure and seasonal dependence. The effect of the comparatively localized negative radiative forcing associated with the aerosol is to retard and reduce the warming by about 0.9 °C at 2050 and 1.2 °C at 2100. Its primary effect on temperature is to counteract the global pattern of GHG-induced warming and only secondarily to affect local temperatures suggesting that the first order transient climate response of the system is determined by feedback processes and only secondarily by the local pattern of radiative forcing. The warming is accompanied by a more active hydrological cycle with increases in precipitation and evaporation rates that are delayed by comparison with temperature increases. There is an “El Nino-like” shift in precipitation and an overall increase in the interannual variability of precipitation. The effect of the aerosol forcing is again primarily to delay and counteract the GHG-induced increase. Decreases in soil moisture are common but regionally dependent and interannual variability changes show considerable structure. Snow cover and sea-ice retreat. A PNA-like anomaly in mean sea-level pressure with an enhanced Aleutian low in northern winter is associated with the tropical shift in precipitation regime. The interannual variability of mean sea-level pressure generally decreases with largest decreases in the tropical Indian ocean region. Changes to the ocean thermal structure are associated with a spin-down of the Atlantic thermohaline circulation together with a decrease in its variability. The effect of aerosol forcing, although modest, differs from that for most other quantities in that it does not act primarily to counteract the GHG forcing effect. The barotropic stream function in the ocean exhibits modest change in the north Pacific but accelerating changes in much of the Southern Ocean and particularly in the north Atlantic where the gyre spins down in conjunction with the decrease in the thermohaline circulation. The results differ in non-trivial ways from earlier equilibrium 2 × CO2 results with the CCCma model as a consequence of the coupling to a fully three-dimensional ocean model and the evolving nature of the forcing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050338
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  • 9
    Electronic Resource
    Electronic Resource
    Climate change and the regulation of the surface moisture and energy budgets (1993)
    Springer
    Climate dynamics 8 (1993), S. 225-239 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The increase in the vigor of the hydrological cycle simulated in a 2 × CO2 experiment with the Canadian Climate Centre general circulation model is smaller than that obtained by other models which have similar increases in mean surface temperature. The surface energy budget, which encompasses also the moisture budget for the oceans, is analyzed. Changes in the net radiative input to and sensible heat flux from the surface act to warm it. This is balanced, at the new equilibrium, by a change in the latent heat flux which acts to cool it. Although this same general behavior is seen in other models, the increase in radiative input to the surface in the CCC GCM is smaller than in other models while the change in the sensible heat flux is of similar size. As a consequence, the latent heat flux required for balance is smaller. The comparatively small increase in the net radiative input at the surface occurs because of a decrease in the solar component. On average the decrease in solar input in the tropical region outweighs the higher latitude increase associated with the snow/ice albedo feedback. The notable tropical decrease in solar input occurs because the albedo of the clouds increase enough in this region to outweigh a small decrease in cloud amount. The increase in cloud albedo in the warmer and moister tropical atmosphere is a consequence of the parameterized cloud optical properties in the model which play an important role in the regulation of the surface energy and moisture budgets. The results demonstrate some of the consequences of the negative feedback mechanism associated with increasing cloud albedo in the model. They also suggest that the simulated change in the vigor of the hydrological cycle is not a simple function of the average increase in surface temperature but is a consequence of all of the processes in the model which control the available energy at the surface as a function of latitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198617
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  • 10
    Electronic Resource
    Electronic Resource
    A study of atmosphere-ocean predictability on long time scales (2000)
    Springer
    Climate dynamics 16 (2000), S. 469-477 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  Two different methods, one diagnostic and the other prognostic, are used to investigate the predictability of the coupled atmosphere-ocean system on time scales of months to decades. The diagnostic approach analyzes the output of a 200 year coupled model simulation for evidence that the long time scale variability of annual, pentadal, and decadal means of surface air temperature are “potentially predictable”. The prognostic “perfect model” approach analyzes predictability of the system by calculating the rate of separation of a small set of coupled model simulations in terms of monthly and annual means of surface air temperature over the globe. Both approaches give reasonably coherent results. At the shorter of the time scales considered, there is little predictability over land but some evidence of predictability over the tropical Pacific, the Southern Ocean and to some extent the extratropical northern Pacific. At longer time scales there is some slight evidence of predictability over certain land areas and more definite evidence of predictability in the tropical Pacific and Southern Ocean. A new area of predictability emerges in the tropical Atlantic. There are plausible physical mechanisms which may explain these long time scale areas of predictability. Both approaches have the potential of shedding light on the long time scale predictability of the coupled system in more extensive predictability studies of this kind.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050340
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