bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of Varroa and viral pathogens in the collapse of honeybee colonies: a modelling approach
Authors: Martin Stephen J. 
Published: March 2003

Summary

The ecto‐parasitic mite Varroa destructor is a serious world‐wide pest of the honeybee Apis mellifera and has being linked with the death of millions of colonies, although its role in colony death has remained elusive.
A simulation model was developed to explain the link between the mite and collapse of the host bee colony, given that colony death does not always occur. We investigated the effects of two pathogens, deformed wing virus (DWV) and acute paralysis virus (APV), vectored by the mite, on the host colony.
Two previously published simulation models, a bee and a mite, were combined and adapted for use in temperate climates with a variety of bee diseases. The model was constructed using Modelmaker® software, which allows the progression of a disease in the host colony to be followed daily.
The population dynamics generated by the model were similar to those observed in a natural honeybee colony. When DWV‐ or APV‐transmitting mites were introduced into the colony, its adult worker bee population collapsed either during winter or spring for DWV, or autumn to spring for APV. This corresponds well with field observations of colony death in Europe.
The model revealed that DWV initially had little effect on the colony but during late summer, as the population of DWV‐transmitting mites increased, the virus caused a reduction in the number of healthy young bees entering the overwintering population. This imbalance in the age structure of the overwintering bees resulted in the eventual death of the colony during the winter or spring. As few as 2000–3600 mites in autumn could kill a colony.
In contrast, APV transmitted by Varroa was only able to kill the honeybee colony if a large (10 000+) mite population was already present when an overt APV infection occurred. It was difficult for APV to become established within the bee population due to it causing rapid host death.
The model predicts that the less virulent DWV will become more widely established than the highly virulent APV, and that mite control measures need to be taken prior to the production of overwintering bees.
Effect of forskolin on endothelin‐induced phosphoinositide hydrolysis and calcium mobilization in cultured canine tracheal smooth muscle cells
Authors: Yang C. ‐M. , Pan S. ‐L. , Chiu C. ‐T. , Lin C. ‐C. , Hsu Y. ‐M. 
Published: March 2003

1 The effects of increase in intracellular adenosine 3′:5′‐cyclic monophosphate (cAMP) on endothelin‐1 (ET‐1)‐induced generation of inositol phosphates (IPs) and increase in intracellular Ca2+ ([Ca2+]i) were investigated in canine cultured tracheal smooth muscle cells (TSMCs). 2 Pretreatment of TSMCs with either cholera toxin (CTX; 10 μg ml−−1, 4 h), forskolin (10 μm, 30 min), or dibutyryl cAMP (1 mm, 30 min) inhibited ET‐1‐stimulated Ca2+ mobilization (by 23 ± 5%, n = 8) and IPs accumulation (by 32 ± 6%, n = 4). While after treatment with forskolin for 24 h, the cells retained the ability to respond to ET‐1‐induced Ca2+ mobilization to the same extent as the control group. 3 Forskolin (1–100 μm) inhibited the ET‐1‐induced increase in [Ca2+]i, but the lower concentrations had little effect on this response. The inhibitory effects of these agents produced both depression of the maximal response and a shift to the right of the concentration–response curve of ET‐1 without changing the –logEC50 values. 4 The water‐soluble forskolin analogue L‐858051, 7‐deacetyl‐7β‐(γ‐N‐methylpiperazino)‐butyryl forskolin, significantly inhibited ET‐1‐stimulated IPs accumulation. In contrast, the addition of 1,9‐dideoxy forskolin, an inactive analogue of forskolin, had little effect on stimulated responses. Moreover, SQ‐22536, 9‐(tetrahydro‐2‐furanyl)‐9H‐purin‐6‐amine, an inhibitor of adenylate cyclase, and both H‐89, N‐(2‐aminoethyl)‐5‐isoquinolinesulfonamide, and HA‐1004, N‐(2‐guanidinoethyl)‐5‐isoquinolinesulfonamide, inhibitors of cAMP‐dependent protein kinase (PKA), attenuated the ability of forskolin to inhibit ET‐1‐induced IPs accumulation. These results suggest that activation of cAMP/PKA was involved in these inhibitory effects of forskolin. 5 The locus of this inhibition of forskolin treatment on AlF4−−‐stimulated IPs accumulation was investigated in canine TSMCs. The AlF4−−‐induced IPs accumulation was inhibited by forskolin, supporting that G protein(s) are directly activated by AlF4−− and uncoupled to phospholipase C by forskolin treatment. 6 We conclude that cAMP elevating agents inhibit ET‐1‐stimulated generation of IPs and Ca2+ mobilization in canine cultured TSMCs. Since generation of IPs and increases in [Ca2+]i are very early events in the activation of ET‐1 receptors, attenuation of these events by cAMP elevating agents might well contribute to the inhibitory effect of cAMP on tracheal smooth muscle function.
Myosin light chain kinase inhibitors and calmodulin antagonists inhibit Ca2+– and ATP–dependent catecholamine secretion from bovine adrenal chromaffin cells
Authors: Matsumura C. , Kuwashima H. , Kimura T. 
Published: March 2003

1 We have used stage‐specific assays for ATP‐dependent priming and for Ca2+‐activated triggering in the absence of ATP to examine the effects of myosin light chain kinase (MLCK) inhibitors, ML‐9 and ML‐7, and calmodulin antagonists, W‐7 and trifluoperazine (TFP), on regulated exocytosis in β‐escin‐permeabilized bovine adrenal chromaffin cells. 2 Ca2+ (0.1–30 μm) induced a significantly greater secretion of catecholamines in the presence of MgATP (2 m
m) than in the absence of MgATP. 3 ML‐9 (30 and 100 μm), ML‐7 (30 and 100 μm), W‐7 (30 and 100 μm) and TFP (10 and 30 μm) inhibited the Ca2+‐induced catecholamine secretion in the presence of MgATP, but did not affect the catecholamine response to Ca2+ in the absence of MgATP. 4 In intact cells all these compounds inhibited catecholamine secretion in responses to acetylcholine (100 μm) and high K+ (40 m
m). 5 The results obtained in permeabilized cells suggest that the calmodulin‐MLCK system plays an essential role in the ATP‐requiring priming stage but not in the Ca2+‐triggered fusion step in the exocytotic process in bovine adrenal chromaffin cells.
Adrenergic–purinergic interactions on vasoconstrictor responses to periarterial electric nerve stimulation in canine splenic arteries
Authors: Yang X. ‐P. , Chiba S. 
Published: March 2003

1 Periarterial nerve electrical stimulation caused a double peaked vasoconstriction in isolated perfused canine splenic arterial preparations. At low frequencies (1–3 Hz), the 1st peak responses were significantly inhibited by α,β‐methylene ATP. On the other hand, at high frequencies (8–10 Hz), the responses were not completely inhibited by α,β‐methylene ATP but the remaining response was abolished by an additional treatment of prazosin. 2 Concerning the 2nd peak responses, at low frequencies (1–3 Hz), the response was mostly suppressed by α,β‐methylene ATP, but at high frequencies (6–10 Hz), the response was not significantly modified by it, although the remaining responses were completely blocked by prazosin. Thus, at high frequencies an adrenergic and purinergic interaction may exist presynaptically, to prevent the inhibition by α,β‐methylene ATP. 3 At 1 Hz, rauwolscine, an α2‐adrenoceptor antagonist, caused a potentiation of electrical stimulation‐induced responses (both 1st and 2nd peaked responses) which were inhibited by prazosin, and the remaining ones were abolished by α,β‐methylene ATP. On the other hand, at 10 Hz, rauwolscine did not cause any potentiation of the double peaked responses. 4 The biphasic responses at 1 Hz were strongly inhibited by exogenously applied ATP, and its inhibition was reversed in part by a P1 receptor antagonist 8‐phenyltheophylline (8‐PT). On the other hand, the biphasic vasoconstrictions at 10 Hz were only slightly depressed by ATP, and a subsequent administration of 8‐PT produced a partial recovery of the 1st phase response but not that of the 2nd one. 5 From these results, it is concluded that (1) at low frequencies the double peaked responses are mostly mediated via P2X receptor, presynaptic P1 receptors may also modulate the release of ATP, and presynaptic α2‐adrenergic mechanism may tonically participate in the release of noradrenaline (2) at high frequencies the responses are mostly mediated via α1‐adrenoceptors and presynaptic P2 receptors may exert its action to inhibit the release of noradrenaline from adrenergic nerve terminals.
Inhibition of isolated rat and human detrusor muscle contraction by disopyramide
Authors: Elliott R. A. , Hudman D. , Terry T. , Sandhu D. , Norman R. I. 
Published: March 2003

1 The aim of this study was to investigate the effect of in vitro and in vivo disopyramide treatment on human and rat isolated detrusor muscle contractile response. Muscle strips were suspended in an organ bath chamber containing Kreb’s solution at 37 °C aerated with 95% oxygen and 5% carbon dioxide. 2 Disopyramide antagonized significantly the contractile response of isolated human detrusor muscle to carbachol stimulation, shifting the concentration–response curve to the right in a parallel manner. The pA2 for competitive inhibition was estimated to be 6.4 with a slope of 0.64 for disopyramide. 3 Rat detrusor muscle contractile response to electrical field stimulation (EFS) was inhibited by 28% (P < 0.01) after in vitro administration of disopyramide (7.5 × 10−6 M). Disopyramide had no effect on the atropine‐resistant component of the response to EFS or on spontaneous contractions of isolated rat detrusor muscle strips. The concentration–response curve to carbachol was competitively antagonized by disopyramide with a pA2 of 6.3 and a Schild curve a slope of 0.85. 4 Disopyramide (7.5 × 10−6 M) had no effect on rat detrusor contractile response to low concentrations of KCl but at high concentrations contraction was reduced significantly by 16% (P < 0.01). 5 In vivo treatment of rats with disopyramide for 8 days or with a single dose had a significant inhibitory effect on the contractile response of detrusor muscle strips. 6 In conclusion, disopyramide had a significant anticholinergic effect on isolated human and rat detrusor muscle contraction.
The relative importance of the time‐course of receptor occupancy and response decay on apparent antagonist potency in dynamic assays
Authors: Corsi M. , Kenakin T. 
Published: March 2003

1 The potency of the β1‐adrenoceptor antagonist atenolol was measured as an inhibitor of responses to isoprenaline in guinea‐pig left atria. Measurements were made in two ways, firstly, by pre‐incubating the atria with a given concentration of atenolol followed by an isoprenaline dose–response curve and, secondly, by measuring the response to isoprenaline followed by addition of atenolol. 2 It was found that the estimation of atenolol potency as an antagonist of β1‐adrenoceptors by these two methods gave divergent results. Specifically, it was found that the isoprenaline‐induced increased rate of myocardial relaxation was resistant to receptor blockade. Thus, the rate‐limiting step in the relaxation response was dissociated from receptor activation and therefore, could not be used for the measurement of receptor occupancy. 3 In contrast, the positive inotropic response was very responsive to receptor occupancy. However, when atenolol was used to block a steady‐state isoprenaline response, there was a complicating depression of basal inotropy after receptor blockade that obfuscated measurement of receptor blockade. 4 In general, these data indicated that the blockade of a steady‐state agonist response to measure the potency of an antagonist might in some cases yield erroneous results. These studies indicate some caution in the interpretation of blockade responses in pre‐contracted or pre‐stimulated pharmacological preparations.
Fossil pollen as a record of past biodiversity
Authors: Odgaard Bent Vad 
Published: March 2003

SummaryQuaternary pollen records may contribute uniquely to the understanding of present plant diversity. Pollen assemblages can reflect diversity at community and landscape scales but the time resolution of most studies does not match that of modern ecological studies. Because of the complicating effects of differential pollen productivity and dispersal, pollen records do not directly reflect equitability aspects of vegetation diversity. Vegetation diversity indices other than S (the total number of taxa) are therefore not appropriate for pollen assemblages. As a measure of the species richness palynological richness is biased by the lack of taxonomic precision, by a possible interference on pollen dispersal from vegetation structure and by pollen representation. The nonlinear relationship between species richness and pollen‐taxa richness may be used in attempts to estimate past floristic richness from fossil pollen assemblages. Using a hypothetical example the strong effect of cover shifts in the vegetation affecting taxa with different representation (Rrel) values on observed palynological richness is demonstrated. It is suggested that estimates of relative pollen productivity should be used to guide the pollen sum on which pollen‐type richness is estimated by rarefaction techniques and this approach is illustrated using a paired site study of late Holocene diversity dynamics. The need for a modern training set relating pollen‐type richness to species richness, pollen productivity and vegetation structure is emphasized.
Habitat relationships of forest birds on Tutuila Island, American Samoa
Authors: Freifeld H. B. 
Published: March 2003

Summary Aim Our knowledge of landbirds on tropical Pacific islands is often comprised of brief, one‐time surveys. We know little of species’ habitat preferences, and this information is critical for understanding the resource requirements or population status of native species and the impacts of human activity on island birds. LocationTutuila Island, American Samoa. Methods The spatial patterns in forest birds were investigated. This island harbours large tracts of native forest, a variety of disturbed and non‐native forests, and some relatively healthy bird populations. The distribution of birds was correlated with forest types using habitat data collected at fifty‐seven sites and avian census data collected monthly for 1–4 years at these sites. ResultsDifferences in location and in vegetation structure and composition between native and non‐native habitats are important influences on the distribution of birds on Tutuila. Among native species, for example, the purple‐capped fruit‐dove (Ptilinopus porphyraceus Temminck) is dependent upon native habitat, the Samoan starling (Aplonis atrifusca Peale) occurs in all habitats, and the cardinal honeyeater (Myzomela cardinalis Gmelin) is more abundant in low elevation, non‐native habitat. ConclusionsThis research reinforces the importance of quantitative assessment of habitat relationships in the study and conservation of Pacific birds.
Making a mark: two thousand years of ecology, economy and worldview
Authors: Simmons Ian 
Published: March 2003

AbstractWe can make a history of the world as an ecological history of an empirical nature. But parallelling that is the history of human thought about nature. The two interact at both pragmatic and abstract levels but in essence the outcome is unpredictable and more akin to chaos theory than to environmental or technological determinism. So the pursuit of either environmentalist or cornucopian Utopias seems not only doomed to failure but likely to cause destruction along the way; a step by step improvisatory strategy seems the best we can do.
Using between‐model comparisons to fine‐tune linear models of species ranges
Authors: Cumming Graeme S. 
Published: March 2003

AbstractAim To offer an objective approach to some of the problems associated with the development of logistic regression models: how to compare different models, determination of sample size adequacy, the influence of the ratio of positive to negative cells on model accuracy, and the appropriate scale at which the hypothesis of a non‐random distribution should be tested.Location Test data were taken from Southern Africa.Methods The approach relies mainly on the use of the AUC (Area under the Curve) statistic, based on ROC (threshold Receiver Operating Characteristic) plots, for between‐model comparisons. Data for the distribution of the bont tick Amblyomma hebraeum Koch (Acari: Ixodidae) are used to illustrate the methods.Results Methods for the estimation of minimum sample sizes and more accurate hypothesis‐testing are outlined. Logistic regression is robust to the assumption that uncollected cells can be scored as negative, provided that the sample size of cells scored as positive is adequate. The variation in temperature and rainfall at localities where A. hebraeum has been collected is significantly lower than expected from a random sample of points across the data set, suggesting that within‐site variation may be an important determinant of its distribution.Main conclusions Between‐model comparisons relying on AUCs can be used to enhance objectivity in the development and refinement of logistic regression models. Both between‐site and within‐site variability should be considered as potentially important factors determining species distributions.
Families with highest proportions of rare species are not consistent between floras
Authors: Edwards Will , Westoby Mark 
Published: March 2003

AbstractAimIn this study we compare the incidence of rarity within lineages between three floras: Australia, North America and New Zealand.MethodsWe used published data for absolute numbers of species and for numbers of rare species to ask three questions: 1. Do families have similar proportions of rare species in different floras? 2. Can proportions of rare species within families be interpreted with reference to biogeographic history of particular floras? and 3. Is the proportion of rare species consistent between families and genera within each flora?ResultsWithin families in each flora, genera usually had similar proportions of rare species; indicating processes determining rarity are in general not operating differentially within families. However, in comparisons within‐family between floras, approximately 62% of comparisons showed significant differences in the proportion of rare species.Main conclusionsThese results imply that there are no general rules whereby the particular traits a family possesses are conducive to rarity wherever they occur. Rather, such attributes must exert influence conditionally, in conjunction with the biogeographical and competitive setting where speciation and extinction or persistence has occurred.
Pollen‐based biomes for Beringia 18,000, 6000 and 0 14C yr bp†
Authors: Edwards M. E. , Anderson P. M. , Brubaker L. B. , Ager T. A. , Andreev A. A. , Bigelow N. H. , Cwynar L. C. , Eisner W. R. , Harrison S. P. , Hu F.‐S. , Jolly D. , Lozhkin A. V. , MacDonald G. M. , Mock C. J. , Ritchie J. C. , Sher A. V. , Spear R. W. , Williams J. W. , Yu G. 
Published: March 2003

AbstractThe objective biomization method developed by Prentice et al. (1996)
for Europe was extended using modern pollen samples from Beringia and then applied to fossil pollen data to reconstruct palaeovegetation patterns at 6000 and 18,000 14C yr
bp.The predicted modern distribution of tundra, taiga and cool conifer forests in Alaska and north‐western Canada generally corresponds well to actual vegetation patterns, although sites in regions characterized today by a mosaic of forest and tundra vegetation tend to be preferentially assigned to tundra. Siberian larch forests are delimited less well, probably due to the extreme under‐representation of Larix in pollen spectra.The biome distribution across Beringia at 6000 14C yr
bp was broadly similar to today, with little change in the northern forest limit, except for a possible northward advance in the Mackenzie delta region. The western forest limit in Alaska was probably east of its modern position.At 18,000 14C yr bp the whole of Beringia was covered by tundra. However, the importance of the various plant functional types varied from site to site, supporting the idea that the vegetation cover was a mosaic of different tundra types.
Biomes of western North America at 18,000, 6000 and 0 14C yr bpreconstructed from pollen and packrat midden data
Authors: Thompson Robert S. , Anderson Katherine H. 
Published: March 2003

AbstractA new compilation of pollen and packrat midden data from western North America provides a refined reconstruction of the composition and distribution of biomes in western North America for today and for 6000 and 18,000 radiocarbon years before present (14C yr bp).Modern biomes in western North America are adequately portrayed by pollen assemblages from lakes and bogs. Forest biomes in western North America share many taxa in their pollen spectra and it can be difficult to discriminate among these biomes. Plant macrofossils from packrat middens provide reliable identification of modern biomes from arid and semiarid regions, and this may also be true in similar environments in other parts of the world. However, a weighting factor for trees and shrubs must be used to reliably reconstruct modern biomes from plant macrofossils.A new biome, open conifer woodland, which includes eurythermic conifers and steppe plants, was defined to categorize much of the current and past vegetation of the semiarid interior of western North America.At 6000 14C yr bp, the forest biomes of the coastal Pacific North‐west and the desert biomes of the South‐west were in near‐modern positions. Biomes in the interior Pacific North‐west differed from those of today in that taiga prevailed in modern cool/cold mixed forests. Steppe was present in areas occupied today by open conifer woodland in the northern Great Basin, while in the central and southern Rocky Mountains forests grew where steppe grows today. During the mid‐Holocene, cool conifer forests were expanded in the Rocky Mountains (relative to today) but contracted in the Sierra Nevada. These differences from the forests of today imply different climatic histories in these two regions between 6000 14C yr bpand today.At 18,000 14C yr bp, deserts were absent from the South‐west and the coverage of open conifer woodland was greatly expanded relative to today. Steppe and tundra were present in much of the region now covered by forests in the Pacific North‐west.