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Joint Action (joint + action)
Selected AbstractsSynergistic interaction of endocrine-disrupting chemicals: Model development using an ecdysone receptor antagonist and a hormone synthesis inhibitorENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2004Xueyan Mu Abstract Endocrine toxicants can interfere with hormone signaling through various mechanisms. Some of these mechanisms are interrelated in a manner that might result in synergistic interactions. Here we tested the hypothesis that combined exposure to chemicals that inhibit hormone synthesis and that function as hormone receptor antagonists would result in greater-than-additive toxicity. This hypothesis was tested by assessing the effects of the ecdysteroid-synthesis inhibitor fenarimol and the ecdysteroid receptor antagonist testosterone on ecdysteroid-regulated development in the crustacean Daphnia magna. Both compounds were individually characterized for effects on the development of isolated embryos. Fenarimol caused late developmental abnormalities, consistent with its effect on offspring-derived ecdysone in the maturing embryo. Testosterone interfered with both early and late development of embryos, consistent with its ability to inhibit ecdysone provided by maternal transfer (responsible for early developmental events) or de novo ecdysone synthesis (responsible for late developmental events). We predicted that, by decreasing endogenous levels of hormone, fenarimol would enhance the likelihood of testosterone binding to and inhibiting the ecdysone receptor. Indeed, fenarimol enhanced the toxicity of testosterone, while testosterone had no effect on the toxicity of fenarimol. Algorithms were developed to predict the toxicity of combinations of these two compounds based on independent joint action (IJA) alone as well as IJA with fenarimol-on-testosterone synergy (IJA+SYN). The IJA+SYN model was highly predictive of the experimentally determined combined effects of the two compounds. These results demonstrate that some endocrine toxicants can synergize, and this synergy can be accurately predicted. [source] Do woodlice and earthworms interact synergistically in leaf litter decomposition?FUNCTIONAL ECOLOGY, Issue 1 2005MARTIN ZIMMER Summary 1In laboratory microcosms, we investigated the influence of diversity of both leaf litter and detritivores on decomposition processes. Either woodlice or earthworms, or a combination of woodlice and earthworms, fed on leaf litter of either oak or alder, or oak and alder for 8 weeks. Mass loss of leaf litter, soil microbial respiration and soil nutrient concentrations were determined every 2 weeks. 2For four out of seven decomposition parameters, the joint effects of woodlice and earthworms were stronger than the sum of single-species effects when they had fed on alder litter. When feeding on oak litter, however, woodlice and earthworms together revealed lower decomposition rates than predicted from their single effects. Joint effects of detritivores on decomposition of mixed litter were always lower than predicted from the sum of their effects. 3In mixed-litter assays, we obtained intermediate values of decomposition parameters, indicating that doubling the species richness of leaf litter from one to two species did not promote decomposition processes. Effects of mixing litter were, thus, mostly additive; essentially only when earthworms fed on mixed litter we observed, mostly positive, non-additive effects of diverse litter. 4Our findings provide evidence for a potential effect on ecosystem functioning through joint action of detritivores even at low species diversity, while litter diversity seems to be less significant. On high-quality litter, isopods and earthworms are not functionally redundant but act synergistically on litter decomposition. The effects of detritivore diversity on ecosystem processes, however, are context-specific and depend on the quality and diversity of the available food sources, and on species-specific characteristics of the detritivores. [source] Cumulative effects of in utero administration of mixtures of reproductive toxicants that disrupt common target tissues via diverse mechanisms of toxicityINTERNATIONAL JOURNAL OF ANDROLOGY, Issue 2 2010C. V. Rider Summary Although risk assessments are typically conducted on a chemical-by-chemical basis, the 1996 Food Quality Protection Act required the US Environmental Protection Agency to consider cumulative risk of chemicals that act via a common mechanism of toxicity. To this end, we are conducting studies with mixtures of chemicals to elucidate mechanisms of joint action at the systemic level with the goal of providing a framework for assessing the cumulative effects of reproductive toxicants. Previous mixture studies conducted with antiandrogenic chemicals are reviewed briefly and two new studies are described. In all binary mixture studies, rats were dosed during pregnancy with chemicals, singly or in pairs, at dosage levels equivalent to approximately one-half of the ED50 for hypospadias or epididymal agenesis. The binary mixtures included androgen receptor (AR) antagonists (vinclozolin plus procymidone), phthalate esters [di(n-butyl) phthalate (DBP) plus benzyl n-butyl phthalate (BBP) and diethyl hexyl phthalate (DEHP) plus DBP], a phthalate ester plus an AR antagonist (DBP plus procymidone), a mixed mechanism androgen signalling disruptor (linuron) plus BBP, and two chemicals which disrupt epididymal differentiation through entirely different toxicity pathways: DBP (AR pathway) plus 2,3,7,8 TCDD (AhR pathway). We also conducted multi-component mixture studies combining several ,antiandrogens'. In the first study, seven chemicals (four pesticides and three phthalates) that elicit antiandrogenic effects at two different sites in the androgen signalling pathway (i.e. AR antagonist or inhibition of androgen synthesis) were combined. In the second study, three additional phthalates were added to make a 10 chemical mixture. In both the binary mixture studies and the multi-component mixture studies, chemicals that targeted male reproductive tract development displayed cumulative effects that exceeded predictions based on a response-addition model and most often were in accordance with predictions based on dose-addition models. In summary, our results indicate that compounds that act by disparate mechanisms of toxicity to disrupt the dynamic interactions among the interconnected signalling pathways in differentiating tissues produce cumulative dose-additive effects, regardless of the mechanism or mode of action of the individual mixture component. [source] The importance of growth and mortality costs in the evolution of the optimal life historyJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2006D. A. ROFF Abstract A central assumption of life history theory is that the evolution of the component traits is determined in part by trade-offs between these traits. Whereas the existence of such trade-offs has been well demonstrated, the relative importance of these remains unclear. In this paper we use optimality theory to test the hypothesis that the trade-off between present and future fecundity induced by the costs of continued growth is a sufficient explanation for the optimal age at first reproduction, ,, and the optimal allocation to reproduction, G, in 38 populations of perch and Arctic char. This hypothesis is rejected for both traits and we conclude that this trade-off, by itself, is an insufficient explanation for the observed values of , and G. Similarly, a fitness function that assumes a mortality cost to reproduction but no growth cost cannot account for the observed values of ,. In contrast, under the assumption that fitness is maximized, the observed life histories can be accounted for by the joint action of trade-offs between growth and reproductive allocation and between mortality and reproductive allocation (Individual Juvenile Mortality model). Although the ability of the growth/mortality model to fit the data does not prove that this is the mechanism driving the evolution of the optimal age at first reproduction and allocation to reproduction, the fit does demonstrate that the hypothesis is consistent with the data and hence cannot at this time be rejected. We also examine two simpler versions of this model, one in which adult mortality is a constant proportion of juvenile mortality [Proportional Juvenile Mortality (PJM) model] and one in which the proportionality is constant within but not necessarily between species [Specific Juvenile Mortality (SSJM) model]. We find that the PJM model is unacceptable but that the SSJM model produces fits suggesting that, within the two species studied, juvenile mortality is proportional to adult mortality but the value differs between the two species. [source] Language as a Tool for Interacting MindsMIND & LANGUAGE, Issue 1 2010KRISTIAN TYLÉN What is the role of language in social interaction? What does language bring to social encounters? We argue that language can be conceived of as a tool for interacting minds, enabling especially effective and flexible forms of social coordination, perspective-taking and joint action. In a review of evidence from a broad range of disciplines, we pursue elaborations of the language-as-a-tool metaphor, exploring four ways in which language is employed in facilitation of social interaction. We argue that language dramatically extends the possibility-space for interaction, facilitates the profiling and navigation of joint attentional scenes, enables the sharing of situation models and action plans, and mediates the cultural shaping of interacting minds. [source] Conditioning period, CO2 and GR24 influence ethylene biosynthesis and germination of Striga hermonthicaPHYSIOLOGIA PLANTARUM, Issue 1 2000Abdel Gabbar T. Babiker Germination of witchweed (Striga hermonthica [Del.] Benth), an important root parasite on poaceous crops, requires pretreatment ,conditioning' in a warm moist environment and a subsequent exposure to a stimulant. The roles of conditioning period, CO2 and a strigol analogue (GR24) in ethylene biosynthesis and germination of the parasite were investigated. Conditioning increased the seeds' capacity to oxidize exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous CO2 increased the seeds capacity to oxidize ACC by 3- to 9-fold. A combination of GR24 and ACC increased ethylene production by more than 3-fold in comparison with the rates obtained using these compounds separately. Aminoethoxyvinylglycine (AVG) completely inhibited ethylene induction by GR24, but not by ACC. A GR24 treatment, made subsequent to conditioning in GR24, did not induce ethylene. However, seeds conditioned in GR24 and then given 1 mM ACC produced 293 nl l,1 ethylene. ACC oxidase (ACCO) activity in crude extracts was increased by conditioning and CO2. The enzyme displayed an absolute requirement for ascorbate. Absence of exogenous Fe2+ reduced enzyme activity only by 14%. GR24 applied during conditioning reduced germination in response to a subsequent GR24 treatment. ACC was, invariably, less effective in inducing S. hermonthica germination than GR24 even at concentrations which induce more ethylene than concurrent GR24 treatments. The results are consistent with a model in which conditioning removes a restriction on the ethylene biosynthetic pathway in S. hermonthica seeds. GR24 modulates the key enzymes in ethylene biosynthesis. The stimulant suppresses ethylene biosynthesis in unconditioned seeds and promotes it in conditioned ones. Germination of S. hermonthica results from the joint action of GR24 and the ethylene it induces. [source] American Federalism and the Search for Models of ManagementPUBLIC ADMINISTRATION REVIEW, Issue 6 2001Robert Agranoff Changes in the United States federal system mean that managers must operate by taking into account multiple interacting governments and nongovernmental organizations; dealing with numerous programs emanating from Washington and state capitols; and engaging in multiple intergovernmental transactions with an expanding number of intergovernmental instruments. Four models of management within this changing system are identified. The top-down model emphasizes executive-branch control and is embedded in enforcement and exchange related to the laws, regulations, funding rules, program standards, and guidelines associated with federal/state grant, procurement, and regulation programs. The donor-recipient model emphasizes mutual dependence or shared program administration, where two-party bargaining or reciprocal interactions among government officials is the norm. The jurisdiction-based model is defined by the initiated actions of local officials and managers who seek out program adjustments and other actors and resources to serve the strategic aims of their governments. The network model highlights the actions of multiple interdependent government and nongovernmental organizations pursuing joint action and intergovernmental adjustment. Although the first two models are long-standing and the latter two are emergent, all appear to be alive and well on the intergovernmental scene, posing complex challenges for public managers. [source] A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systemsANNALS OF APPLIED BIOLOGY, Issue 1 2007A. Milne Abstract A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose,response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance. [source] Learning for sustainable development in tourism networksBUSINESS STRATEGY AND THE ENVIRONMENT, Issue 2 2001Minna Halme The present study investigates learning toward sustainable development in multi-stakeholder public,private networks. The evidence is grounded in the data from six tourism networks in four European countries. The process of cooperation appears more important vis-à-vis achievements regarding sustainable tourism than the structure of networks. This process will determine the network's ability to become adept at explicating tacit knowledge among its actors, and to develop the network so it can facilitate the creation of sustainability outcomes. A leading public actor may assume a ,teacher's' role in the network. In these instances, the network runs a risk of becoming merely an information dissemination tool. This involves a trap of one-way communication and under-used knowledge utilization opportunities. Receptivity of the teacher actor is low and the partners do not really collaborate. The teacher actor should make a special effort to create feedback loops leading to two-way communication, so that a learning strategy of collaboration can take place. The findings also imply that in some networks with a public leader there is an overly high belief in the ability of information dissemination and classroom education to promote learning about sustainable development although learning about sustainability in the practical level requires concrete results and joint action. Copyright © 2001 John Wiley & Sons, Ltd and ERP Environment [source] Shifting voices, oppositional discourse, and new visions for communication studiesJOURNAL OF COMMUNICATION, Issue 1 2001L L Putnam This address, delivered at ICA's 50th anniversary conference, calls on the association to take stock of where we are and how we should come together. It reviews 3 periods in the field's recent past: fermentation, fragmentation, and legitimation. Then, drawing from several of Bahktin's notions of dialogue, it summons scholars to come together by engaging in alternative modes of discourse - ones that center on multiple and shifting voices and oppositional discourse. It advocates using the construct of voice rather than paradigms, theories, and academic divisions, to develop complementary ways of understanding. In particular, it calls on the field to take inventory of multiple and shifting voices in reviews and critiques of the literature, to connect with each other through exploring shifting concepts and theories, and to engage in joint actions in ways that embrace and preserve differences. [source] | |||||||||||||