bluuebunny/crossref_metadata_2025_split huggingface dataset:
Looks are important: parasitic assemblages of agromyzid leafminers (Diptera) in relation to mine shape and contrast
Authors: Salvo Adriana , Valladares Graciela R. 
Published: April 2004

SummaryWe test the hypothesis that leaf mine appearance can affect the risk of leafminers being discovered by parasitoids, and therefore influence parasitic assemblages, using a comparative study of parasitic complexes associated with 28 agromyzid species in Central Argentina. Analyses were based on size, structure (defined as the number of species in host‐range categories) and impact (percentage parasitism) of parasitic complexes on leafminers. Mine appearance was defined in terms of shape (linear, linear‐blotch, blotch) and colour (high or low contrast with the leaf lamina).Irrespective of the agromyzid species involved, significant differences were found in the structure of the parasitoid complexes: specialists were more abundant and generalists rarer than expected in blotch and cryptically coloured mines.There were no differences in average parasitoid species richness and parasitism rates among differently coloured or shaped galleries. However, mine appearance significantly affected parasitic assemblage structure, with shape driving generalist species richness and contrast influencing that of specialists. Mine shape also affected parasitism rates, which were highest for generalists in linear mines, and for specialists in blotch mines. The existence of a gradient of discovery from the cryptically coloured blotch mines to the most apparent highly contrasting linear ones was supported by significant correlations of this gradient with richness and parasitism rates of generalist and specialist parasitoids.Taxonomic composition of parasitic complexes (analysed through parasitoid species abundance) was separated significantly according to host mine shape. An even more significant classification of assemblages was achieved when the combination of mine shape and colour was considered in the discoverability gradient.Our results suggest that despite leaf mines being an ecologically homogeneous resource, their morphology might offer varying degrees of refuge against different parasitoids.
Foraging trip duration and density of megachilid bees, eumenid wasps and pompilid wasps in tropical agroforestry systems
Authors: Klein Alexandra‐Maria , Steffan‐Dewenter Ingolf , Tscharntke Teja 
Published: April 2004

Summary

Most animals have to bridge some distances in space and time to provide all resources necessary for survival. Little is known about how the local and regional management of tropical agroforestry systems, differing in the availability of food resources and suitable nesting sites, determine foraging trip duration and density of bees and wasps (Hymenoptera Aculeata).
In this study, foraging trip duration and brood‐cell density (in trap nests exposed for a 15‐month period) were analysed for three species, which represent three guilds in 24 agroforestry systems in Central Sulawesi (Indonesia): the pollinator Heriades sp. aff. fulvescens (Apidae), the cacao caterpillar‐hunting predator Rhynchium haemorrhoidale umeroatrum (Eumenidae) and the spider‐hunting predator Auplopus levicarinatus (Pompilidae). The agroforestry systems were characterized by plant species richness, blossom cover of herbs, light intensity and distance from the nearest natural forest.
The correlation of foraging time to bee and wasp density showed the relative importance of food and nest‐site availability for the pollinator and the spider‐hunting predator, because both parameters are correlated with light intensity in the agroforestry systems. In contrast, foraging time and nest density of the eumenid predator were not correlated because of the distance between high quantities of food resources (in sites with dense cacao plants) and nesting sites (in adjacent natural forests).
The eumenid response to local and regional agroforestry management illustrates that species may survive only in landscapes that permit access to a multiple set of resources. Accordingly, habitat evaluations using only foraging time may lead to wrong conclusions, as key drivers of population dynamics may not be inside but outside the local systems, emphasizing the need for a landscape approach.
Parasitoid–host metapopulation dynamics: the causes and consequences of phenological asynchrony
Authors: Van Nouhuys Saskya , Lei Guangchun 
Published: April 2004

SummaryThe strength of interaction between the specialist parasitoidCotesia melitaearumand the host butterflyMelitaea cinxiais influenced by the coincidence of the adult stage of the parasitoid with the larval stage of the host.We show that there is great variation in this developmental synchrony among local populations and among years, ranging from complete synchrony to complete asynchrony.The causal mechanism is early spring temperature, which affects parasitoid development differently than the development of the host.At cool air temperatures the dark‐coloured and mobile host larvae benefit from basking in the sun, while the white and immobile parasitoid cocoons develop slowly in shaded microclimates, becoming adults after hosts have pupated and are no longer available for parasitism. At warm temperatures many adult wasps emerge in time to parasitize host larvae.We show that the host–parasitoid synchrony influences subsequent parasitoid population size and the rate of colonization of previously uninhabited host populations, contributing to parasitoid metapopulation dynamics.We detected no direct effect of the phenological synchrony on local host population size, but the synchrony is likely to be important for overall host metapopulation dynamics via variation in the rate of colonization by the parasitoid.
Invertebrate community assembly along proglacial chronosequences in the high Arctic
Authors: Hodkinson Ian D. , Coulson Stephen J. , Webb Nigel R. 
Published: April 2004

SummaryInvertebrate community assembly is described for two contrasting proglacial chronosequences (over 1900 years) at Kongsfjord, W. Spitsbergen, Svalbard.Three hypotheses were tested: (1) community assembly is deterministic, directional and predictable; (2) succession is inextricably linked to plant community and soil development; and (3) dispersal is a rate‐limiting factor for community assembly.Communities, dominated by omnivores and detritivores, are more complex than supposed previously. Herbivore species were few but predators, parasitoids and hyperparasitoids were abundant.Species fell within one of eight defined groups with respect to colonization. This relates to ecophysiological tolerances, need for facilitation or dependence on other species. Spiders, surface‐active Collembola and drought‐resistant cryptostigmatic mites arrived before vascular plants established and soils developed. Later colonizers required site facilitation through soil development or host availability.Comparisons between the proglacial area of Midtre Lovénbre, a land‐terminating glacier, and three Lovén Islands, released from beneath a tidewater glacier, showed similarities in community composition and species abundance with respect to successional stage, suggesting determinism and direction in community development.Most common species on Midtre Lovénbre colonized the Lovén Islands rapidly, suggesting that dispersal does not seriously restrict community development on the time scales involved. Some minor species associated with older soils appear not yet to have reached the islands.
Temperature‐dependent interactions explain unexpected responses to environmental warming in communities of competitors
Authors: Jiang Lin , Morin Peter J. 
Published: April 2004

Summary

Predictions about how species will respond to climate warming are based commonly on eco‐physiological models or niche models. One critique of this practice is that it ignores interspecific interactions.
We examined how resource competition affects the responses of two ciliate species, Colpidium striatum Stein and Paramecium tetraurelia Sonneborn, to warming in laboratory microcosms.
We found that warming had a negative effect on Colpidium abundance and a negligible effect on Paramecium abundance in the absence of interspecific competition. When Colpidium and Paramecium competed, however, Paramecium coexisted with Colpidium at low and high temperatures, and was competitively excluded at intermediate temperatures.
Temperature‐dependent strength of the interaction between Colpidium and Paramecium may explain the unexpected responses of Paramecium, which were inconsistent with its response to temperature in the absence of Colpidium.
Our results provide further support for the important role of species interactions in understanding how species respond to environmental warming, and suggest that the complex interplay between species interactions and climate may make it extremely difficult to predict accurately how species embedded in complex communities will respond to climate warming.
Ontogenetic changes in metabolism may determine diet shifts for a sit‐and‐wait predator
Authors: Jackson Angus C. , Rundle Simon D. , Attrill Martin J. , Cotton Peter A. 
Published: April 2004

Summary

Body size is a central parameter in determining prey selection, and where animals exhibit large increases in size, ontogenetic diet shifts are common. Optimal foraging models have proved to be useful tools in predicting changes in diet, but previous applications have been limited to those associated with changes in external drivers such as habitat use.
We conducted laboratory and field experiments to parameterize an optimal foraging model to test whether prey choice can be determined by internal mechanisms such as metabolism.
Model predictions were made for Pomatoschistus microps, the common goby (Pisces: Gobiidae), a sit‐and‐wait predator that exhibits a shift in prey choice independently of external drivers. The model predicted a change in diet at a fish length of 30 mm, which agrees well with existing empirical observations. This is the first time the link between metabolism and prey choice has been considered as a major determinant of diet shifts.
P. microps, using a sit‐and‐wait foraging mode, were expected to act as cost‐minimizers but the model indicated that gobies were typically not time‐limited and that prey selection maximized energy intake rates both before and after the diet shift.
Prey size range and mean prey length were determined primarily by the presence or absence of meiofauna in the diet, supporting the observation that the diet shift occurs between the two ecologically distinct groups of benthic meiofauna and macrofauna.
Interaction strengths in food webs: issues and opportunities
Authors: Berlow Eric L. , Neutel Anje‐Margiet , Cohen Joel E. , De Ruiter Peter C. , Ebenman Bo , Emmerson Mark , Fox Jeremy W. , Jansen Vincent A. A. , Iwan Jones J. , Kokkoris Giorgos D. , Logofet Dmitrii O. , McKane Alan J. , Montoya Jose M. , Petchey Owen 
Published: April 2004

SummaryRecent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory.Much confusion stems from lack of clarity about whether the questions posed relate to community‐level patterns or to species dynamics, and to what authors actually mean by the term ‘interaction strength’. Here, we describe the various ways in which this term has been applied and discuss the implications of loose terminology and definition for the development of this field.Of particular concern is the clear gap between theoretical and empirical investigations of interaction strengths and food web dynamics. The ecological community urgently needs to explore new ways to estimate biologically reasonable model coefficients from empirical data, such as foraging rates, body size, metabolic rate, biomass distribution and other species traits.Combining numerical and analytical modelling approaches should allow exploration of the conditions under which different interaction strengths metrics are interchangeable with regard to relative magnitude, system responses, and species identity.Finally, the prime focus on predator–prey links in much of the research to date on interaction strengths in food webs has meant that the potential significance of non‐trophic interactions, such as competition, facilitation and biotic disturbance, has been largely ignored by the food web community. Such interactions may be important dynamically and should be routinely included in future food web research programmes.
Lateral inhibition and habituation of the human auditory cortex
Authors: Pantev C. , Okamoto H. , Ross B. , Stoll W. , Ciurlia‐Guy E. , Kakigi R. , Kubo T. 
Published: April 2004

AbstractThe goal of this study was to compare the lateral inhibition and the habituation in the human auditory cortex, two important physiological effects during auditory processing that can be reliably measured by means of magnetoencephalography when recording auditory evoked fields. Applying 40‐Hz amplitude‐modulated stimuli allowed us to record simultaneously the slow transient evoked and the steady‐state fields and thus to characterize the lateral inhibition and the habituation effect in primary and non‐primary auditory cortical structures. The main finding of the study is that the lateral inhibition effect of non‐primary auditory areas as measured on the major component of the slow transient auditory evoked field (N1) is significantly stronger than the corresponding habituation effect. By contrast, this effect was not observed for the 40‐Hz steady‐state fields, characterizing the activation of the primary auditory cortex in humans. The results might be interpreted as (i) evidence that the inhibition mediated by lateral connections is stronger than the habituation of excitatory neurons in the non‐primary auditory cortex and (ii) the processing hierarchy in the human auditory cortex is demonstrated by the different behaviour of lateral inhibition and habituation in primary and non‐primary auditory cortical structures.
Comparative analysis of CNS populations in knockout mice with altered growth hormone responsiveness
Authors: Ransome Mark I. , Goldshmit Yona , Bartlett Perry F. , Waters Michael J. , Turnley Ann M. 
Published: April 2004

AbstractRecently we have shown that growth hormone (GH) inhibits neuronal differentiation and that this process is blocked by suppressor of cytokine signalling‐2 (SOCS2). Here we examine several cortical and subcortical neuronal populations in GH hyper‐responsive SOCS2 null (−/−) mice and GH non‐responsive GH receptor null (GHR−/−) mice. While SOCS2−/− mice showed a 30% decrease in density of NeuN positive neurons in cortex compared to wildtype, GHR−/− mice showed a 25% increase even though brain size was decreased. Interneuron sub‐populations were variably affected, with a slight decrease in cortical parvalbumin expressing interneurons in SOCS2−/− mice and an increase in cortical calbindin and calretinin and striatal cholinergic neuron density in GHR−/− mice. Analysis of glial cell numbers in cresyl violet or glial fibrillary acidic protein (GFAP) stained sections of cortex showed that the neuron : glia ratio was increased in GHR−/− mice and decreased in SOCS2−/− mice. The astrocytes in GHR−/− mice appeared smaller, while they were larger in SOCS2−/− mice. Neuronal soma size also varied in the different genotypes, with smaller striatal cholinergic neurons in GHR−/− mice. While the size of layer 5 pyramidal neurons was not significantly different from wildtype, SOCS2−/− neurons were larger than GHR−/− neurons. In addition, primary dendritic length was similar in all genotypes but dendritic branching of pyramidal neurons in the cortex appeared sparser in GHR−/− and SOCS2−/− mice. These results suggest that GH, possibly regulated by SOCS2, has multiple effects on central nervous system (CNS) development and maturation, regulating the number and size of multiple neuronal and glial cell types.
Hippocampal theta rhythm is reduced by suppression of the H‐current in septohippocampal GABAergic neurons
Authors: Xu Changqing , Datta Subimal , Wu Min , Alreja Meenakshi 
Published: April 2004

AbstractHippocampal learning and memory tasks are tightly coupled to the hippocampal theta rhythm, which is critically dependent on the medial septum/diagonal band of Broca (MSDB) although the underlying mechanisms remain unclear. The MSDB sends both cholinergic and GABAergic projections to the hippocampus. Here we show that: (i) septo‐hippocampal GABAergic but not cholinergic neurons have a pacemaking current, the H‐current, and that its selective blockade by ZD7288 reduces their spontaneous firing in rat brain slices; and (ii), local infusions of ZD7288 into the MSDB reduce exploration and sensory evoked hippocampal theta bursts in behaving rats. Thus, the H‐current in septohippocampal GABAergic neurons modulates the hippocampal theta rhythm.
Purinergic modulation of synaptic input to Purkinje neurons in rat cerebellar brain slices
Authors: Brockhaus Johannes , Dressel Diana , Herold Sabine , Deitmer Joachim W. 
Published: April 2004

AbstractAdenosine triphosphate (ATP) is a cotransmitter and an extracellular neuromodulator in nervous systems, and it influences neural circuits and synaptic strength. We have studied a stimulating effect of ATP (100 µm) on the synaptic input of Purkinje neurons in acute cerebellar brain slices of juvenile rats (p14–19). Bath application of ATP increased the frequency of spontaneous postsynaptic currents (sPSCs) almost twofold, and increased their amplitude. These effects were fully suppressed by the P2 receptor antagonist pyridoxalphosphate‐6‐azophenyl‐2′4′‐disulphonic acid (PPADS; 10 µm), or after blocking action potentials with tetrodotoxin (TTX; 0.5 µm), but were not impaired by inhibiting ionotropic, non‐NMDA glutamate receptors with 2,3‐dioxo‐6‐nitro‐1,2,3,4,‐tetrahydrobenzo[f]quinoxaline‐7‐sulphonamide (NBQX; 5 µm). The frequency of sPSCs was reduced by 35% by PPADS and increased by 50% after inhibiting ectonucleotidase with ARL67156 (50 µm), suggesting intrinsic, ‘tonic’, stimulation of synaptic activity via P2 receptors. The pharmacological profile indicated that the ATP effect was mediated by both P2X and P2Y receptors, most probably of the P2X5– and P2Y2,4–like subtypes. The action potential frequency in the inhibitory basket cells was increased by 65%, and decreased in Purkinje neurons by 25%, in the presence of ATP. Our results suggest that ATP continuously modulates the cerebellar circuit by increasing the activity of inhibitory input to Purkinje neurons, and thus decreasing the main cerebellar output activity, which contributes to locomotor coordination.
Species differences in the localization of cGMP‐producing and NO‐responsive elements in the mouse and rat hippocampus using cGMP immunocytochemistry
Authors: Van Staveren Wilma C. G. , Steinbusch Harry W. M. , Markerink‐van Ittersum Marjanne , Behrends Sönke , De Vente Jan 
Published: April 2004

AbstractThe aim of the study was to compare the localization of the nitric oxide (NO)–cGMP pathway in hippocampus of mice and rats using cGMP‐ and soluble guanylyl cyclase (GC) immunocytochemistry and in situ hybridization of the cGMP‐hydrolysing phosphodiesterase types 2, 5 and 9. In vitro incubation of hippocampus slices in the absence of a guanylyl cyclase stimulator or a phosphodiesterase inhibitor resulted in cGMP‐positive astrocytes mainly in the CA1 area in mouse slices. In contrast, no cGMP immunoreactivity was observed under these conditions in the rat hippocampus. Treatment with an NO synthase inhibitor or inhibitors of soluble or particulate GC did not abolish cGMP immunoreactivity in astrocytes. Incubation with the NO donors sodium nitroprusside or diethylamino NONOate, or with the NO‐independent activators of soluble GC, YC‐1 and BAY 41‐2272, in combination with phosphodiesterase inhibitors, resulted in an increase in cGMP immunoreactivity in numerous astrocytes throughout the mouse hippocampus. In contrast, under these conditions cGMP immunoreactivity was primarily observed in varicose fibers in rat hippocampus. Comparison of the cellular localization of the β1 subunit of soluble GC and the mRNAs of PDE2, PDE5 and PDE9 revealed that in both species the β1 subunit was observed in pyramidal and granule cells, which also expressed the mRNAs of the three phosphodiesterase families. Although the β1 subunit was observed in astrocytes, none of the phosphodiesterases were detected in these cells. We conclude that, although the expression profiles of the soluble GC β1 subunit and cGMP‐hydrolysing phosphodiesterase mRNAs were identical, the cellular patterns of cGMP immunoreactivity differ between rat and mouse hippocampus.
Transgenic approach reveals expression of the VPAC2 receptor in phenotypically defined neurons in the mouse suprachiasmatic nucleus and in its efferent target sites
Authors: Kalló Imre , Kalamatianos Theodosis , Wiltshire Nzinga , Shen Sanbing , Sheward W. John , Harmar Anthony J. , Coen Clive W. 
Published: April 2004

AbstractCircadian rhythms in mammals depend on the properties of cells in the suprachiasmatic nucleus (SCN). The retino‐recipient core of the mouse SCN is characterized by vasoactive intestinal peptide (VIP) neurons. Expression within the SCN of VPAC2, a VIP receptor, is required for circadian rhythmicity. Using transgenic mice with β‐galactosidase as a marker for VPAC2, we have phenotyped VPAC2‐expressing cells within the SCN and investigated expression of the VPAC2 marker at sites previously shown to receive VIP‐containing SCN efferents. In situ hybridization and immunohistochemistry demonstrated identical distributions for VPAC2 mRNA and β‐galactosidase and coexpression of the two signals in the SCN. Double‐label confocal immunofluorescence identified β‐galactosidase in 32% of the VIP and 31% of the calretinin neurons in the SCN core. Of the arginine‐vasopressin neurons that characterize the SCN shell, 45% expressed β‐galactosidase. In contrast, this marker was not apparent in astrocytes within the SCN core or shell. Cell bodies containing β‐galactosidase were detected at sites reportedly receiving VIP‐containing SCN efferents, including the subparaventricular zone and lateral septum and the anteroventral periventricular, preoptic suprachiasmatic, medial preoptic and paraventricular hypothalamic nuclei. The detection of a marker for VPAC2 expression in the SCN in almost one‐third of the VIP and calretinin core neurons and nearly half of the arginine‐vasopressin shell neurons and also in cell bodies at sites receiving VIP‐immunoreactive projections from the SCN indicates that VPAC2 may contribute to autoregulation and/or coupling within the SCN core and to the control of the SCN shell and sites distal to this nucleus.