bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biological control using sterilizing viruses: host suppression and competition between viruses in non‐spatial models
Authors: Hood G.M. , Chesson P. , Pech R.P. 
Published: March 2003

Summary1. Research is currently underway to develop genetically engineered viruses that can sterilize pest animals. The technique, known as viral‐vectored immunocontraception (VVIC), promises to control mammalian pests such as the European rabbit, the house mouse and domestic cats.2. Using host–parasite models we explored the degree of control of the host population that can be attained when hosts that recover from infection become permanently infertile. The models assume some demographic compensation for reduced fertility in the host population, and are tailored to address issues raised by the use of the myxoma virus as an agent to sterilize rabbits. A ‘pay‐off’ function is developed, which defines the degree to which host density is suppressed by a sterilizing agent.3. The results show that sterilizing viruses can reduce host abundance, and that hosts with low birth rates and moderate mortality rates are the best targets for VVIC. High transmissibility increases the pay‐off from VVIC, but because virulent parasites kill most of the hosts that they infect, the pay‐off is highest if benign parasites are used as the vector of contraceptive antigens. We argue that appropriate pay‐off functions should be developed as a basis for research and development on genetically modified organisms.4. The host–parasite models are extended to include a competing strain of virus that does not sterilize the host. We analysed these models using a general approach to the analysis of competition, which has not often been applied to epidemiological models. The extended model shows that host sterilizationper sedoes not affect the competitive ability of viruses, a result that applies to a broad class of models in which the per capita growth rates of competing parasites are linear functions of limiting competitive factors.
Bee diversity along a disturbance gradient in tropical lowland forests of south‐east Asia
Authors: Liow Lee Hsiang , Sodhi Navjot S. , Elmqvist Thomas 
Published: March 2003

Summary

Bees are believed to be dominant pollen vectors in tropical forests, yet studies specific to bees in south‐east Asia are rare. Regeneration and restoration of the rapidly disappearing lowland forests of this region are reliant on bees, thus there is an urgent need for forest bee data at the community level.
Bee communities of eight forested sites in Johor (Malaysia) and Singapore were surveyed three times each from February to August 1999 at the below‐canopy level. These sites ranged from relatively undisturbed primary lowland dipterocarp forests to late secondary forests and exotic forests, including an oil palm plantation. We attempted to elucidate the environmental factors that correlated with the distribution of bees.
Bee abundance, in particular that of Apidae, was significantly higher in larger primary forests than other types of forests. However, bee species richness was higher in disturbed forests.
The distribution of bees was apparently influenced by variables closely related to forest disturbance and resource abundance, such as the density of big trees (diameter at breast height 30–40 cm), temperature and flowering intensity of trees and shrubs.
More stingless bees (Trigona spp.) were found where trees were larger and ambient conditions more constant but flowering intensities lower.
The differences between the bee communities in forests of urban Singapore and primary forests in Johor may indicate that ecological processes in the forests of Singapore, in particular pollination, may be changing. However, pollination may not be totally intact in the primary forests surveyed, as their bee communities seemed to be depauperate.
The role of important pollinators, especially bees, for the long‐term survival of tropical lowland forests is poorly understood. Our study indicates that we urgently need more thorough understanding of pollination and pollinators, as some bee species appear to be disappearing from disturbed tropical lowland forests.
Meadow pipits, red grouse and the habitat characteristics of managed grouse moors
Authors: Smith A.A. , Redpath S.M. , Campbell S.T. , Thirgood S.J. 
Published: March 2003

Summary

The abundance of meadow pipits appears to be a good indicator of the breeding density of hen harriers on moorland managed for red grouse in Scotland. High densities of hen harriers can limit grouse populations at low density and reduce shooting bags, with repercussions for grouse moor management and conservation. We therefore examined the habitat characteristics of managed grouse moors, asking whether changes in vegetation could alter the ratio of pipits, and thus harriers, to grouse.
We examined grouse abundance and habitat on 69 sites of 1 km2 in upland Britain, of which pipit abundance was studied on 36. Similar data were collected on 73 sites of 25 ha within the Langholm estate in south‐west Scotland, in order to make a within‐estate and among‐moor comparison.
The distribution of pipit abundance on the Langholm estate was similar to that seen in the extensive among‐moor study. Pipit and grouse abundance were related to habitat in similar ways in the two data sets.
Pipits were the most frequent passerine, but their abundance was not related to grouse abundance. Pipit abundance declined with increasing muirburn and heather, but increased with grass cover. In a linear regression model Calluna, Sphagnum and muirburn cover accounted for 42% of the variation in pipit abundance across Britain.
Grouse abundance was influenced by the regional location of the grouse moor and to a lesser extent by its altitude. There were more grouse on English moors with less patchy habitats. Bird species declined with increasing Calluna and Sphagnum cover and habitat patchiness. Bird species diversity increased from west to east and on moors with more muirburn.
This study provides evidence that meadow pipits are influenced by habitat characteristics on moorland managed for grouse. This work also illustrates how habitat management may be able to mitigate human–wildlife conflicts: long‐term increases in heather cover and management of this habitat by muirburn on grouse moors may reduce pipit numbers and thus reduce the ratio of hen harriers to grouse. However, the effects of such vegetation change on other components of the upland bird assemblage requires further investigation.
Predation on livestock by an expanding reintroduced lynx population: long‐term trend and spatial variability
Authors: Stahl P. , Vandel J.M. , Herrenschmidt V. , Migot P. 
Published: March 2003

SummaryIn recent decades, the Eurasian lynxLynx lynxhas recolonized former habitat, bringing it into potential conflict with livestock. We studied the spatial and temporal distribution of lynx attacks on sheep in the French Jura between 1984 and 1998, during and after its population expansion. We estimated the local and regional impact of lynx predation on livestock.The number of attacks increased from three in 1984 to 188 in 1989, concurrently with the colonization of the main sheep range by lynx. During subsequent years, 66–131 attacks were recorded annually (92–194 sheep killed per year).On average, 1·6 sheep were killed per attack. Lynx preyed disproportionately on lambs and subadult sheep. A small percentage of flocks (9·5–22·9%) were attacked, most of which (75·2%) were attacked once or twice a year. At the regional level, annual sheep losses to lynx were 0·14–0·59% of the total number of sheep.The major lynx–livestock problem was due to clustered attacks in a few small areas. Each year, two to six ‘hot spots’ (33–69% of the attacks) were identified. Hot spots covered 0·3–4·5% of the total area where attacks occurred (1835–4061 km2). Roe deer abundance was higher in hot spots and, even here, sheep only made up 3·1% of the lynx diet. These data show that lynx were not killing sheep due to shortages of alternative prey or in response to an increased need for food when rearing young.The concentration of hot spots in only nine small areas between 1984 and 1998 indicated that only a few individual lynx were involved. The reappearance of hot spots at the same sites, after years of interruption and despite the removal of lynx, suggested that the ultimate factors causing hot spots were factors inherent to those sites. Further investigation is needed to identify causal factors with a view to eliminating them. These may relate to landscapes features, animal husbandry practices or the behavioural ecology of lynx.In future, where large predator reintroductions are planned, the potential for concentrated, localized, impact should be evaluated and mitigation measures put in place. For scattered and episodic lynx damage, financial compensation is the only realistic option at present. In hot spots, the cost‐effectiveness of guard‐dogs or the selective removal of some individual lynx should be evaluated.
The selection of stubble fields by wintering granivorous birds reflects vegetation cover and food abundance
Authors: Moorcroft D. , Whittingham M. J. , Bradbury R. B. , Wilson J. D. 
Published: March 2003

Summary

Fields left fallow after harvest (i.e. stubble fields) support high wintering densities of many species of granivorous bird. We examined correlates of use by eight such species of different types of intensively managed wheat and barley stubble fields, organic wheat fields and set‐aside fields on mixed lowland farmland in central England. Field occupancy was studied in relation to the physical characteristics of fields and seed abundance.
Higher seed abundance was associated with greater occupancy by linnet Carduelis cannabina, grey partridge Perdix perdix, chaffinch Fringilla coelebs, yellowhammer Emberiza citrinella, reed bunting Emberiza schoeniclus and corn bunting Miliaria calandra. Larger areas of bare earth within stubble fields were associated with greater occupancy by linnet, yellowhammer, reed bunting and corn bunting, but lower occupancy by woodpigeon Columba palumbus.
On conventional intensively farmed sites, seed abundance and area of bare earth were significantly greater on barley stubbles than on wheat stubbles.
Seed numbers fell throughout the winter in all stubble types, although reductions were greatest on intensive barley stubbles, intermediate on intensive wheat stubble and lowest on undersown organic wheat stubbles.
Within fields occupied by linnets, areas used for feeding had significantly greater quantities of seeds known to be important in their diet. Feeding areas also had a greater area of bare earth than randomly selected ‘non‐feeding areas’.
Linnets and reed buntings were rarely found on fields where densities of weed seeds important in their diets fell below 250 seeds m−2. In autumn, yellowhammers and grey partridges rarely fed on fields where cereal grain density was below 50 m−2. However, in spring, both species fed on these fields irrespective of grain density, perhaps indicating a switch to other food sources.
We suggest that land managers wishing to maximize the value of overwinter stubble fields for granivorous birds locate such fields where there is a substantial natural regeneration of weed flora and where previous cropping (e.g. barley) is likely to offer a sparse stubble with substantial areas of bare ground.
Functional identification of β3‐adrenoceptors in the guinea‐pig ileum using the non‐selective β‐adrenoceptor antagonist (±)‐bupranolol
Authors: Horinouchi T. , Koike K. 
Published: March 2003

1 To clarify whether there is a species difference or a tissue difference in β3‐adrenoceptors, the β3‐adrenoceptors mediating relaxations to catecholamines ((–)‐isoprenaline, (–)‐noradrenaline and (–)‐adrenaline), a selective β3‐adrenoceptor agonist BRL37344 and a non‐conventional partial β3‐adrenoceptor agonist (±)‐CGP12177A (a potent β1‐ and β2‐adrenoceptor antagonist with a partial β3‐adrenoceptor agonist property) were investigated in the guinea‐pig ileum. 2 Catecholamines and β3‐adrenoceptor agonists induced concentration‐dependent relaxations of pre‐contracted strips of the guinea‐pig ileum. The rank order for their relaxing potency was (–)‐isoprenaline (pD2: 7.60) > BRL37344 (7.05) > (–)‐noradrenaline (6.38) > (±)‐CGP12177A (6.25) > (–)‐adrenaline (6.07). 3 In the presence of the non‐selective β1‐ and β2‐adrenoceptor antagonist (±)‐propranolol (1 μM), only small rightward shifts of the concentration–response curves (CRCs) to these agonists were observed and the rank order of potency of agonists was BRL37344 (pD2: 7.00) > (±)‐CGP12177A (6.17) > (–)‐isoprenaline (6.01) > (–)‐noradrenaline (5.69) > (–)‐adrenaline (5.41). 4 In the presence of (±)‐propranolol (1 μM), the additional presence of (±)‐bupranolol (3–30 μM), a non‐selective β1‐, β2‐ and β3‐adrenoceptor antagonist, caused a concentration‐dependent rightward shift of the CRCs to catecholamines and β3‐adrenoceptor agonists. Schild plot analyses of (±)‐bupranolol against these agonists gave pA2 values of 6.02 ((–)‐isoprenaline), 6.03 ((–)‐noradrenaline), 6.01 ((–)‐adrenaline), 6.56 (BRL37344) and 5.74 ((±)‐CGP12177A), respectively. All Schild plot slopes were not significantly different from unity. The pA2 values of (±)‐bupranolol obtained for the guinea‐pig β3‐adrenoceptors were about one log unit less than the values obtained for the rat β3‐adrenoceptors and about two log units less than the values obtained for dog β3‐adrenoceptors. 5 These results confirm that functional β3‐adrenoceptors are present in the guinea‐pig ileum and that the relaxations of these agonists are mainly mediated via β3‐adrenoceptors in this tissue. The differential antagonistic potency of (±)‐bupranolol may suggest that there is a species difference between the three species (guinea‐pig, dog and rat) in their β3‐adrenoceptors.
The effects of thiol compounds and ebselen on nitric oxide activity in rat aortic vascular responses
Authors: Kim H. R. , Kim J. W. , Park J. Y. , Je H. D. , Lee S.‐Y. , Huh I. H. , Sohn U. D. 
Published: March 2003

1 Thiols have been implicated to play a role in a variety of aspects of nitric oxide (NO) generation and activity. Thiol dependence of nitric oxide synthase (NOS) has remained controversial and its mechanism is not clear. This study investigates possible mechanisms between thiol (SH group) and NOS activation, through thiol compounds (glutathione, dithiothreitol, N‐acetyl‐L‐cysteine) and Ebselen [2‐phenyl‐1,2‐benzisoselenazole‐3(2H)‐one] on rat aortic vascular responses. 2 In rat thoracic aorta, acetylcholine (10–6–10–9 M) induced a relaxation of phenylephrine (PE) (10–7 M)‐induced tone, which was inhibited dose dependently by increasing concentration of ebselen (1–10 μM). 3 In rings of rat thoracic aorta, ebselen and NOS inhibitors (NG‐monomethyl‐L‐arginine, NG‐nitro‐L‐arginine methyl ester) produced an augmentation of phenylephrine (10–7 M)‐ induced tone and acetylcholine induced a relaxation of PE (10–7 M)‐induced tone in rat thoracic aorta, which was inhibited by ebselen (10 μM) like NOS inhibitor. 4 The thiol compounds (glutathione, dithiothreitol, and N‐acetyl‐L‐cysteine) alone did not change vascular tone in rat thoracic aorta. Pretreatment with thiol compounds before ebselen treatment, however, reversed the inhibitory effect of ebselen which acts like the NOS inhibitor in rat thoracic aorta. Posttreatment with thiol compounds after ebselen treatment did not reverse the inhibitory effect of ebselen by as much as pretreatment. 5 Calcium ionophore A23187 (10–7 M)‐induced vasodilation was inhibited in ebselen pretreated rat thoracic aorta, but sodium nitroprusside (SNP, 10–7 M)‐induced relaxation was not inhibited by ebselen. This suggests that NOS is involved in the inhibitory effect of ebselen on rat thoracic aorta relaxation. 6 These results suggest that ebselen exerts an inhibitory action on the nitric oxide synthesis in rat thoracic aorta by interacting with thiol groups.
Arrhythmogenesis in isolated rat hearts with enhanced α‐adrenoceptor‐mediated responsiveness
Authors: Chess‐Williams R. , Milton H. L. 
Published: March 2003

1 It has been postulated that stimulation of myocardial α‐adrenoceptors is one of the primary mediators of the dysrhythmias which occur during periods of myocardial ischaemia and reperfusion. This study examines arrhythmogenesis during coronary artery occlusion and reperfusion in isolated perfused rat hearts from control animals and from rats with enhanced myocardial α‐adrenoceptor responsiveness. 2 Rats were administered propylthiouracil (PTU) in their drinking water for 8 weeks. This treatment resulted in an enhanced responsiveness of isolated left atria to the α‐adrenoceptor agonist phenylephrine compared with atria from control animals. 3 In Langendorff‐perfused isolated hearts, the spontaneous rate of contraction was significantly lower in the PTU‐pretreated group than in either age‐matched or weight‐matched controls. Occlusion of the left anterior descending artery (LAD) for 25 min resulted in ventricular tachycardia (VT) of similar incidence and duration in all groups and ventricular fibrillation (VF) in both control groups but not the PTU‐pretreated group. 4 Following the 25‐min ischaemic period the myocardium was reperfused for 10 min. The incidence and duration of VT and VF during this period was similar in all groups except that the duration of VF in the PTU‐pretreated group was significantly lower than in controls. 5 In perfused hearts paced at 4 Hz, the incidence and duration of dysrhythmias during ischaemia and reperfusion was again similar in all groups, only the duration of VF being affected (reduced) by PTU‐pretreatment. 6 In conclusion, this study does not lend support to the hypothesis that myocardial α‐adrenoceptors have a primary role in arrhythmogenesis, but the data would support a role for these receptors in myocardial protection.
Modulation of M‐channel conductance by adenosine 5′ triphosphate in bullfrog sympathetic B‐neurones
Authors: Chen H. , Kurennyi D. E. , Smith P. A. 
Published: March 2003

1 Adenosine 5′ triphosphate (ATP) (0.5–500 μM) or muscarine (0.1–1.0 μM) suppressed M‐current/conductance (IM/gM) in B‐cells of bullfrog sympathetic ganglion. Both agonists suppressed steady‐state M‐conductance (gM) at –30 mV and there was either no change or a slight increase in the time constants for gM activation (τa at –30 mV) and deactivation (τd at –50 mV). 2 It has previously been shown that experimental elevation of intracellular Ca2+ concentration ([Ca2+]i) suppresses gM and this is associated with decreases in both τa and τd. As these changes in kinetics differ from those we observe with agonist application, our results cast doubt on the hypothesis that elevation of [Ca2+]i is involved in the transduction mechanism for ATP‐ or muscarine‐induced gM suppression.
Effects of natural tachykinins on ovine lower urinary tract smooth muscle
Authors: Tucci P. , Bolle P. , Severini C. 
Published: March 2003

1 Numerous studies have demonstrated that the urinary bladder is particularly sensitive to tachykinins; rat, rabbit and guinea pig bladders, besides human detrusor, have been the most extensively studied, whereas very little is known about most large animal detrusors. The aim of this work was to study natural tachykinin activity on the lower urinary tract of ovine to make a comparison with data obtained in laboratory animals. 2 As in other animal species, tachykinins are also able to contract ovine bladder smooth muscle. 3 The results reported in this study indicate that in ovine bladder, neurokinin 2 (NK2) receptors are expressed most. In fact, on lamb and sheep bladder neurokinin A (NKA), a NK2‐ almost selective peptide, was shown to be > 100% more active than the natural tachykinins kassinin (KASS) and eledoisin (ELED). Eledoisin was shown to be 50% less active than KASS, which is typical behaviour for an almost exclusively NK2 receptor population. Moreover, NK1‐ preferential peptides, namely substance P (SP) and physalaemin (PHYS), showed a lack of activity even when applied at high concentrations. 4 The results reported in this study show that lamb and sheep detrusor represent a good alternative model for the characterization of NK2‐selective tachykinins.
Functional effects of dextran sulphate sodium (DSS) treatment on the longitudinal muscle of rat distal colon
Authors: Börjesson L. , Aldenborg F. , Delbro D. S. 
Published: March 2003

1 The current study addressed how acute colitis, induced in male Sprague–Dawley rats by the administration of dextran sulphate sodium (DSS) in their drinking water, may affect some functional properties of the longitudinal muscle layer of the distal colon. 2 Dextran sulphate sodium was provided at a concentration of 3% for 3 or 7 days, or 5% for 7 days, and the rats were thereafter killed. Specimens of the distal colon were taken for histology or for organ bath experiments. 3 The colitis score increased significantly with increasing dose of DSS administered. At 5% concentration, there was sometimes even transmural inflammation. Functionally, there was a progressive increase in optimal preload (Po) for the contractile response to carbachol (1 μM), in relation to the severity of the colitis. At 5% DSS, the magnitude of the response to carbachol at Po was significantly increased compared with control rats. Such an effect could not be verified when, instead, K+ (60 mM) was used as a spasmogen. 4 It is concluded, that the colitis score increased in severity progressively with increasing amounts of DSS administered. The longitudinal muscle layer was functionally affected by the inflammation. Thus, there was a progressive increase in optimal preload for muscle contraction. Moreover, severe colitis resulted in an increase of the contractile response to carbachol, while a significant increase in the response to depolarization with K+ could not be found.
A morpholinocatechol compound (UK42620) with clonidine‐ and tyramine‐like actions
Authors: Thaina P. , Nott M. W. , Rand M. J. 
Published: March 2003

1 The actions of a morpholinocatechol (UK42620) were studied in rat isolated atria preparations consisting of spontaneously beating left and right atrial pairs. 2 UK42620 produced positive inotropic and chronotropic responses and, in atria that were incubated with [3H]‐noradrenaline, it also produced a massive increase in the release of radioactivity. 3 These actions of UK42620 were similar to those of tyramine and were blocked by the β‐adrenoceptor antagonist propranolol (0.3 μM) and by the neuronal uptake blocker desipramine (1 μM). 4 In the presence of desipramine, UK42620 but not tyramine produced a decrease in the stimulation‐induced efflux of radioactivity that was antagonized by idazoxan. 5 Thus, UK42620 had prejunctional α2‐adrenoceptor activity like that of clonidine‐ and tyramine‐like activity releasing large amounts of noradrenaline.