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Direct Competition (direct + competition)
Selected AbstractsLaminin and fibronectin modulate inner ear spiral ganglion neurite outgrowth in an in vitro alternate choice assayDEVELOPMENTAL NEUROBIOLOGY, Issue 13 2007Amaretta R. Evans Abstract Extracellular matrix (ECM) molecules have been shown to function as cues for neurite guidance in various populations of neurons. Here we show that laminin (LN) and fibronectin (FN) presented in stripe micro-patterns can provide guidance cues to neonatal (P5) inner ear spiral ganglion (SG) neurites. The response to both ECM molecules was dose-dependent. In a LN versus poly- L -lysine (PLL) assay, neurites were more often observed on PLL at low coating concentrations (5 and 10 ,g/mL), while they were more often on LN at a high concentration (80 ,g/mL). In a FN versus PLL assay, neurites were more often on PLL than on FN stripes at high coating concentrations (40 and 80 ,g/mL). In a direct competition between LN and FN, neurites were observed on LN significantly more often than on FN at both 10 and 40 ,g/mL. The data suggest a preference by SG neurites for LN at high concentrations, as well as avoidance of both LN at low and FN at high concentrations. The results also support a potential model for neurite guidance in the developing inner ear in vivo. LN, in the SG and osseus spiral lamina may promote SG dendrite growth toward the organ of Corti. Within the organ of Corti, lower concentrations of LN may slow neurite growth, with FN beneath each row of hair cells providing a stop or avoidance signal. This could allow growth cone filopodia increased time to sample their cellular targets, or direct the fibers upward toward the hair cells. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007 [source] Prey availability influences habitat tolerance: an explanation for the rarity of peregrine falcons in the tropicsECOGRAPHY, Issue 3 2001Andrew R. Jenkins The density and productivity of peregrine falconFalco peregrinus populations correlate positively with distance from the Equator, while habitat specificity increases with proximity to the Equator. Low peregrine densities in the tropics may he a result of competition with similar conveners (e.g. the lanner falcon F. biarmicus in Africa), which replace them in many areas. Alternatively, tropical peregrines may he limited by resource deficiencies that do not affect their close relatives. Data from peregrine and lanner populations in South Africa support the resource deficiency hypothesis, and there is no evidence to suggest direct competition between the two species. In areas where prey are not spatially or temporally concentrated, or otherwise particularly vulnerable to attack, morphological and behavioural specializations of peregrines probably restrict them to optimal foraging conditions. The relative dynamics of.Arctic and temperate vs tropical prey populations is suggested as an important factor determining peregrine distribution globally. Populations of other widespread hut particularly specialized avian predators (e.g. osprey Pandion haliaetus) may he similarly controlled. Food limitation (in terms of a dearth of particularly vulnerable prey) in the tropics has resulted in specialization and rarity in peregrines and generalization and relative abundance in similar congeners. [source] Prey availability influences habitat tolerance: an explanation for the rarity of peregrine falcons in the tropicsECOGRAPHY, Issue 3 2001Article first published online: 30 JUN 200 The density and productivity of peregrine falcon Falco peregrinus populations correlate positively with distance from the Equator, while habitat specificity increases with proximity to the Equator. Low peregrine densities in the tropics may be a result of competition with similar congeners (e.g. the lanner falcon F. biarmicus in Africa), which replace them in many areas. Alternatively, tropical peregrines may be limited by resource deficiencies that do not affect their close relatives. Data from peregrine and lanner populations in South Africa support the resource deficiency hypothesis, and there is no evidence to suggest direct competition between the two species. In areas where prey are not spatially or temporally concentrated, or otherwise particularly vulnerable to attack, morphological and behavioural specializations of peregrines probably restrict them to optimal foraging conditions. The relative dynamics of Arctic and temperate vs tropical prey populations is suggested as an important factor determining peregrine distribution globally. Populations of other widespread but particularly specialized avian predators (e.g. osprey Pandion haliaetus) may be similarly controlled. Food limitation (in terms of a dearth of particularly vulnerable prey) in the tropics has resulted in specialization and rarity in peregrines and generalization and relative abundance in similar congeners. [source] Refuge-mediated apparent competition in plant,consumer interactionsECOLOGY LETTERS, Issue 1 2010John L. Orrock Abstract At the intersection of consumer behaviour and plant competition is the concept of refuge-mediated apparent competition: an indirect interaction whereby plants provide a refuge for a shared consumer, subsequently increasing consumer pressure on another plant species. Here, we use a simple model and empirical examples to develop and illustrate the concept of refuge-mediated apparent competition. We find that the likelihood that an inferior competitor will succeed via refuge-mediated apparent competition is greater when competitors have similar resource requirements and when consumers exhibit a strong response to the refuge and high attack rates on the superior competitor. Refuge-mediated apparent competition may create an emergent Allee effect, such that a species invades only if it is sufficiently abundant to alter consumer impact on resident species. This indirect interaction may help explain unresolved patterns observed in biological invasion, such as the different physical structure of invasive exotic plants, the lag phase, and the failure of restoration efforts. Given the ubiquity of refuge-seeking behaviour by consumers and the ability of consumers to alter the outcome of direct competition among plants, refuge-mediated apparent competition may be an underappreciated mechanism affecting the composition and diversity of plant communities. Ecology Letters (2010) 13: 11,20 [source] Analysing scots pine defence-related transcripts and fungal DNA levels in seedlings single- or dual-inoculated with endophytic and pathogenic Rhizoctonia speciesFOREST PATHOLOGY, Issue 6 2009H. Grönberg Summary Fungal DNA and induction of host defence-related transcripts were monitored by real-time PCR in young Scots pine seedlings inoculated with pathogenic uninucleate (UNR) and endophytic binucleate (BNR) Rhizoctonia species. The UNR (teleomorph Ceratobasidium bicorne) causes root dieback in conifer seedlings following invasion of the vascular cylinder via root apex and destroying apical meristems whilst the BNR, representing anastomosis group AG-I of genus Ceratobasidium, is primarily restricted to the cortex in basal root regions. In the experiment 1 the fungi were simultaneously inoculated on roots, while in experiment 2, BNR was pre-inoculated 168 h before inoculation with UNR. Nucleic acids were extracted from infected roots at intervals up to 192 h post-infection (hpi), and the genomic DNA levels of the host and fungi and the transcript levels of a house-keeping gene (glyceraldehyde-3-phosphate dehydrogenase) and nine putative defence genes were quantified. In simultaneous inoculation UNR was more competitive than BNR whereas pre-inoculation of BNR suppressed but did not completely prevent root colonization by UNR. Stilbene synthase (STS) transcription was significantly up-regulated in single-inoculations with both fungi and in dual inoculation in both experiments. Maximum STS transcript levels were observed in roots single-inoculated with UNR; the peak level at 48 hpi in experiment 2 was significantly higher than in seedlings single-inoculated with BNR or co-inoculated with both fungi, the latter two treatments showing relatively similar STS transcript levels. Similarly, transcript levels of phenylalanine ammonia lyase at 48 hpi in experiment 2 were significantly higher in roots single-inoculated with UNR compared with BNR or in UNR+BNR co-inoculations. The other seven putative defence genes monitored did not show any clear-cut up-regulation following fungal inoculation. We conclude that BNR suppresses UNR in Scots pine roots via direct competition for infection sites, since the studied transcripts showed no evidence of BNR induced resistance against UNR. [source] A molecular approach to detect hybridisation between crucian carp (Carassius carassius) and non-indigenous carp species (Carassius spp. and Cyprinus carpio)FRESHWATER BIOLOGY, Issue 3 2005B. HÄNFLING Summary 1. Releases of non-native fish into the wild is an increasing problem posing considerable ecological and genetic threats through direct competition and hybridisation. 2. We employed six microsatellite markers to identify first generation hybrids and backcrosses between native crucian carp (Carassius carassius) and introduced goldfish (C. auratus) and common carp (Cyprinus carpio) in the U.K. We also investigated the genetic characteristics of the taxonomically controversial gibel carp (Carassius spp.) from sites across Europe. 3. Natural hybridisation between goldfish and crucian carp occurs frequently, although hybrids between all other species pairs were observed. Only 62% of British crucian carp populations (n = 21) consisted exclusively of pure crucian carp. In some populations hybrids were so frequent, that no pure crucian carp were caught, indicating a high competitive ability of hybrids. 4. Most hybrids belonged to the F1 generation but backcrossing was evident at a low frequency in goldfish × crucian carp hybrids and goldfish × common carp hybrids. Furthermore, some local populations had high frequencies of backcrosses, raising the opportunity for introgression. 5. Gibel carp from Germany and Italy belonged to two triploid clonal lineages that were genetically closely related to goldfish, whereas all individuals identified from British populations proved to be crucian carp × goldfish hybrids. 6. Our study suggests that the release of closely related exotic cyprinids not only poses a threat to the genetic integrity and associated local adaptations of native species, but may also contribute to shifts in community structure through competitive interactions. [source] Sex-dependent use of information on conspecific feeding activities in an amphibian urodelianFUNCTIONAL ECOLOGY, Issue 2 2009Pedro Aragón Summary 1Animals can make decisions by observing the behaviour of others. Their decisions vary depending on whether the benefits of using such information exceed the costs. Thus, it is worthwhile to explore the potential costs associated with different sources of information to understand the consequences of sociality. Previous studies focused mainly on the costs inherent to information gathering, whereas sex differences with regard to the costs arising from information use have received less attention. 2To explore this further I performed two complementary experiments. The first experiment aimed to examine individual responses to different combinations of information types that are likely to appear in nature, to test whether there is a sex-dependent response in the Bosca's newt, Lissotriton boscai. I tested the time needed for individuals to eat food items by trial-and-error tactics (personal information), and when a conspecific, which was eating or not, was added to the food cue. The second experiment aimed to evoke social interactions that are likely to arise after the choice of using information on conspecific feeding activities is made. I examined the potential costs associated with direct competition between same-sex pairs in food-limited conditions. 3Results of experiment 1 revealed that in both sexes the latency to eat food items was shorter in the presence of non-feeding conspecifics, but only females took advantage when information related to feeding activities where added to the food cue. Results of experiment 2 showed that when faced with a limited resource of food, females were more prone to engage in costly interactions. 4This study suggests that the balance between costs and benefits associated with the short-term use of information on conspecific feeding behaviour in combination with food cues may differ between sexes. Differential information uses by sexes might have profound consequences in intraspecific relationships and in the evolution of vertebrates' social systems. [source] Site history affects soil and plant 15N natural abundances (,15N) in forests of northern Vancouver Island, British ColumbiaFUNCTIONAL ECOLOGY, Issue 3 2000S. X. Chang Abstract 1.,About 10 years after establishment, plantations of Western Redcedar (Thuja plicata Donn ex D. Don) on northern Vancouver Island, British Columbia become nutrient deficient and chlorotic, grow slowly, and are susceptible to invasion by the ericaceous shrub Salal (Gaultheria shallon Pursh.). 2.,To test the hypothesis that ,15N can be related to site histories (site disturbance, soil N dynamics and plant development), we measured soil and foliar ,15N in the summer of 1992 in 3-year-old (nutrient-sufficient) and 10-year-old (nutrient-deficient) plantations and in old-growth stands. The foliar and soil ,15N values of the plantations and old-growth forests were different and closely reflected site histories. Salal invasion and nutrient deficiency interacted to depress the growth of Redcedar in 10-year-old plantations. 3.,Site preparation destroyed the top soil organic layers (fresh and decaying litter) and forced Salal (ecto- and ericoid mycorrhizal) into the humus layer, where it was in direct competition with Redcedar, thereby disadvantaging arbuscular mycorrhizal/non-mycorrhizal Redcedar in its nutrient acquisition during a period when N and P are severely limited. 4.,There was a large seasonal range of foliar ,15N (5·5 and 4·3, for 10-year-old Redcedar and Salal, respectively), and there was no relationship between foliar ,15N and measured rooting depth, demonstrating that rooting depths cannot be used to explain foliar ,15N variation among coexisting woody taxa. 5.,Foliar and soil ,15N declined with site age and with a presumed change from ,open' to ,closed' N cycling; the 15N-depleting effects of mycorrhizal N transformations contributed to the observed ,15N decline. [source] Effects of hippocampal cholinergic deafferentation on learning strategy selection in a visible platform version of the water mazeHIPPOCAMPUS, Issue 6 2003J.L. Bizon Abstract Recent evidence has suggested that the relative levels of acetylcholine (ACh) between brain structures may be an important factor in the choice of behavioral strategy in settings in which either hippocampal or dorsal striatal brain systems can be employed both effectively and independently (McIntyre and Gold. 1999. Soc Neurosci Abs 25:1388). The current investigation used the neurotoxin 192 IgG-saporin to deplete the hippocampus of ACh selectively, while leaving ACh in other brain regions, including dorsal striatum, intact. Rats were then trained on a version of the Morris water maze, in which behavioral strategies attributed to the hippocampus and dorsal striatum are placed in direct competition. It was predicted that rats with hippocampal ACh depletion would display a cue bias. Contrary to this prediction, depleting hippocampal ACh did not bias against and, in fact, promoted use of a hippocampal place strategy in this task, as indicated by choice in competition tests and performance on hidden platform training trials. These data add to a growing literature demonstrating that the septohippocampal cholinergic system is not required for accurate spatial learning and suggest a complex role for basal forebrain projections in processing information about the spatial environment. © 2003 Wiley-Liss, Inc. [source] Dissociation mechanisms and implication for the presence of multiple conformations for peptide ions with arginine at the C-terminus: time-resolved photodissociation studyJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2010So Hee Yoon Abstract Time-resolved photodissociation (PD) patterns of singly protonated peptides with arginine at the C-terminus (C-arg peptide ions) have been used to classify the dissociation channels into two categories, i.e. high-energy channels generating v, w and x and low-energy ones generating b, y and z. x + 1 formed by C,CO cleavage seems to be the intermediate ion in high-energy channels just as a + 1 is for N-arg peptide ions. Difference in time-resolved pattern indicates that the two sets of channels, high- and low-energy ones, are not in direct competition. Noncompetitive dissociation is also indicated by the observation of anomalous effect of matrix used in matrix-assisted laser desorption ionization, a cooler matrix generating more high-energy product ions both in spontaneous dissociation and in PD. Results from detailed investigation suggest that the two sets of channels start from two (or more) different conformations. Copyright © 2010 John Wiley & Sons, Ltd. [source] trans -Resveratrol Protects Embryonic Mesencephalic Cells from tert -Butyl HydroperoxideJOURNAL OF NEUROCHEMISTRY, Issue 1 2000Electron Param Abstract : In recent years, the antioxidant and other pharmacological properties of resveratrol, a natural product present in grapes and wine, have attracted considerable interest from the biomedical research community. In an examination of the potential neuroprotective properties of the compound, we have investigated the ability of resveratrol to protect rat embryonic mesencephalic tissue, rich in dopaminergic neurones, from the prooxidant tert -butyl hydroperoxide. Using the electron paramagnetic resonance (EPR) spin-trapping technique, the main radicals detected in cell suspensions were the tert -butoxyl radical and the methyl radical, indicating the one-electron reduction of the peroxide followed by a ,-scission reaction. The appearance of EPR signals from the trapped radicals preceded the onset of cytotoxicity, which was almost exclusively necrotic in nature. The inclusion of resveratrol in incubations resulted in the marked protection of cells from tert -butyl hydroperoxide. In parallel spin-trapping experiments, we were able to demonstrate the scavenging of radicals by resveratrol, which involved direct competition between resveratrol and the spin trap for reaction with the radicals. To our knowledge, this is the first example in which cytoprotection by resveratrol has been demonstrated by EPR spin-trapping competition kinetics to be due to its scavenging of the radicals responsible for the toxicity of a prooxidant. [source] Experiments on growth interactions between two invasive macrophyte speciesJOURNAL OF VEGETATION SCIENCE, Issue 1 2004Marie-Hélène Barrat-Segretain Tutin et al. (1980) Abstract. The success of invasive species has been attributed to the ability to displace other species by direct competition. We studied growth and possible competition between the two macrophyte species Elodea nuttallii and E. canadensis, because the former has been observed to replace the latter in the field. Additional experiments were conducted in aquaria with mixed plantings of Elodea species. Species growth was measured and competitive abilities of each species determined by applying the reciprocal yield model to mean plant weight and length. In monocultures the growth rates of the two species were similar, while in mixtures the growth rate of E. canadensis was significantly lower than that of E. nuttallii. E. canadensis was more sensitive to intraspecific than to interspecific neighbours, whereas E. nuttallii was indifferent to the presence of neighbours. Differential growth characteristics of Elodea species can explain the displacement of E. canadensis by E. nuttallii under eutrophic field conditions. [source] Dynamics Behind Standoff Interactions in Three Reef Sponge Species and the Coral Montastraea cavernosaMARINE ECOLOGY, Issue 3-4 2000Lisanne A. M. Aerts Abstract. Benthic organisms compete for space, and standoff interactions, i. e. interactions with no clearly observable outcome such as win or loss, are very common in marine hard substratum communities. Standoffs were more common than overgrowths among all sponge-coral interactions observed in a coral reef community off Santa Marta, NE Colombia. The dynamics of these standoffs and the role played by each of the interacting organisms were examined in a series of standard observations of sponge-coral interactions involving the sponge species Niphates erecta, Rhaphidophlus venosus, Scopalina ruetzleri and the coral Montastraea cavernosa. Most sponge-coral standoffs in this study displayed rapid changes in number of polyps along the coral border, sponge area and sponge-coral distance. The outcome of sponge-coral standoffs depended on the ecological stategy (e.g., growth) of the sponge species. Scopalina ruetzleri and N. erecta did not show any signs of direct competition with Montastraea cavernosa. R. venosus, however, was often observed to take over vacant space formed by dead coral polyps (54 % of interactions). The impact of coral damage (lesions) on the interaction process between R. venosus and M. cavernosa was shown by a significant increase in coral polyp death in damaged compared with undamaged M. cavernosa colonies (22.7 % versus 6.9 %). This study demonstrates that (1) sponge-coral standoffs are actually quite dynamic because of the continually changing distance between the organisms, (2) the dynamic nature of sponge-coral standoffs depends on growth-related strategies (growth form, growth rate) of the competing sponge species, (3) the actual frequency of coral overgrowth by (thinly encrusting) sponge species can only be determined by means of intermittent observations; space gained at the cost of coral tissue cannot be seen by single observations, (4) coral damage (lesions) on reefs may enhance deterioration of corals by increasing their susceptibility to sponge overgrowth. [source] Competition as a structuring force in leaf miner communitiesOIKOS, Issue 6 2009Ayco J. M. Tack The role of competition in structuring communities of herbivorous insects is still debated. Despite this, few studies have simultaneously investigated the strength of various forms of competition and their effect on community composition. In this study, we examine the extent to which different types of competition will affect the presence and abundance of individual leaf miner species in local communities on oak trees Quercus robur. We first use a laboratory experiment to quantify the strength of intra- and interspecific competition. We then conduct a large-scale field experiment to determine whether competition occurring in one year extends to the next. Finally, we use observational field data to examine the extent to which mechanisms of competition uncovered in the two experiments actually reflect into patterns of co-occurrence in nature. In our experiment, we found direct competition at the leaf-level to be stronger among conspecific than among heterospecific individuals. Indirect competition among conspecifics lowered the survival and weight of larvae of T. ekebladella, both at the branch and the tree-level. In contrast, indirect competition among heterospecifics was only detected in one out of three species pairs examined. In the field experiment, the presence of a given moth species in one year affected the relative abundance of leaf miner species in the next year. Nevertheless, patterns of competition observed in these experiments did not translate into repulsion among free-ranging leaf miners: conspecific larvae of four leaf-mining species were aggregated on the same trees, shoots and leaves. In contrast, heterospecific larvae were only aggregated at the tree-level. We propose that despite the fact that leaf miners do compete and that such effects extend through time, the incidence and strength of competition is relatively small at realistic densities. Hence, competition will likely be of minor importance in shaping the distribution of leaf miners in a natural setting. [source] Smaller Microtus vole species competitively superior in the absence of predatorsOIKOS, Issue 1 2007Elina Koivisto Interspecific competition is assumed to generate negative effects on coexisting species, possibly including slower population growth and lower survival. The field vole (Microtus agrestis) and the sibling vole (M. rossiaemeridionalis) are sympatric close relatives which compete for similar resources. Previous non-experimental studies suggest that the smaller sibling vole is a superior competitor, yet more vulnerable to predation than the larger field vole. We studied the effects of coexistence on population densities, reproductive parameters, and survival in these two species by means of experimentation in large, predator-free outdoor enclosures. While populations of both species reached higher densities in the absence of the other, field voles appeared to suffer more from interspecific competition than sibling voles. The proportion of young individuals in the population was higher in the sibling vole than in the field vole at the end of the experiment. The presence of a coexisting species reduced the survival of field voles. Sibling voles, on the other hand, appeared to suffer more from intraspecific competition than interspecific competition. On a population level, the sibling vole seems to be a superior competitor in the absence of predators due to better survival and possibly a higher reproductive capacity. However, predation probably has a profound influence on the interspecific dynamics of these two species indicating that in natural surroundings apparent competition (i.e. competition via shared predators) is stronger than direct competition. [source] Nitrogen balance in forest soils: nutritional limitation of plants under climate change stressesPLANT BIOLOGY, Issue 2009H. Rennenberg Abstract Forest ecosystems with low soil nitrogen (N) availability are characterized by direct competition for this growth-limiting resource between several players, i.e. various components of vegetation, such as old-growth trees, natural regeneration and understorey species, mycorrhizal fungi, free-living fungi and bacteria. With the increase in frequency and intensity of extreme climate events predicted in current climate change scenarios, also competition for N between plants and/or soil microorganisms will be affected. In this review, we summarize the present understanding of ecosystem N cycling in N-limited forests and its interaction with extreme climate events, such as heat, drought and flooding. More specifically, the impacts of environmental stresses on microbial release and consumption of bioavailable N, N uptake and competition between plants, as well as plant and microbial uptake are presented. Furthermore, the consequences of drying,wetting cycles on N cycling are discussed. Additionally, we highlight the current methodological difficulties that limit present understanding of N cycling in forest ecosystems and the need for interdisciplinary studies. [source] Ecological distribution and phenology of an invasive species, Cardamine hirsuta L., and its native counterpart, Cardamine flexuosa With., in central JapanPLANT SPECIES BIOLOGY, Issue 1 2003YOSHINORI YATSU Abstract Cardamine hirsuta is a European species that was recently introduced into Japan and its wide distribution has been confirmed in the Kanto district. To understand mechanisms of the recent spread of C. hirsuta in Japan, a comparative study of the alien species and its native congeneric species, C. flexuosa, was conducted. Habitat preferences, phenology and seed germination were examined. Cardamine hirsuta and C. flexuosa showed distinctive habitat-preferences; the former was most common in open habitats created by recent man-made constructions, and the latter was common in rice paddy fields and surrounding areas. The results indicate that C. flexuosa is a year-long annual, with a mixed phenology of summer and winter germination and growth. Seed dormancy during summer was relatively weak for C. flexuosa, and some plants that germinated early in summer reproduced during the same summer,autumn period. Plants that germinated in late summer and autumn behaved as winter annuals. In rice paddy fields, C. flexuosa is a winter annual because germination is prevented by submergence during summer. Plants flower during the following spring and complete their life cycle before the fields are flooded for rice cultivation. Cardamine hirsuta showed strong seed dormancy during summer and behaved as a typical winter annual. Seeds of C. hirsuta were intolerant to submergence in water, a condition that breaks seed dormancy of C. flexuosa. The results explain the absence of C. hirsuta from rice paddy fields. It was concluded that the spread of C. hirsuta is attributable to the recent expansion of urban habitats created by human activity and has occurred without direct competition with C. flexuosa. Considering recent urbanization in many areas, it is suggested that C. hirsuta has been spreading rapidly in Japan. [source] Correlates of body mass evolution in primatesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2006Christophe Soligo Abstract Body mass is undoubtedly central to the overall adaptive profile of any organism. Despite this, very little is known of what forces drive evolutionary changes in body mass and, consequently, shape patterns of body mass distribution exhibited by animal radiations. The search for factors that may influence evolutionary processes in general frequently focuses on environmental parameters such as climate change or interspecific competition. With respect to body mass, there is also the suggestion that evolutionary lineages may follow an inherent trend toward increased body mass, known as Cope's rule. The present paper investigates whether overall directional trends of body mass change, or correlations between patterns of body mass evolution and environmental factors have influenced the evolution of body mass in plesiadapiforms and primates. Analyses of the global fossil record of plesiadapiforms and primates suggest that the former did indeed follow an overall trend toward increased body mass compatible with the predictions of Cope's rule. In contrast, neither primates as a whole, nor a number of individual primate radiations (Adapiformes, Omomyiformes, and Anthropoidea), show any indication of overall directional patterns of body mass change. No correlations of primate body mass change with either the latitudinal distribution of fossil species, or with estimates of global temperature trends, were found. There is evidence, however, that direct competition between omomyiforms and adapiforms (the two main primate radiations known from the Paleogene) influenced processes of body mass evolution in omomyiforms. Am J Phys Anthropol, 2006. © 2006 Wiley-Liss, Inc. [source] Conservation genetics of the endangered Shenandoah salamander (Plethodon shenandoah, Plethodontidae)ANIMAL CONSERVATION, Issue 2 2001Daniel W. Carpenter The Shenandoah salamander (Plethodon shenandoah) is restricted to three isolated talus outcrops in Shenandoah National Park, VA, USA and has one of the smallest ranges of any tetrapod vertebrate. This species was listed as endangered under the US Endangered Species Act in 1989 over concern that direct competition with the red-backed salamander (Plethodon cinereus), successional habitat changes, and human impacts may cause its decline and possible extinction. We address two issues herein: (1) whether extensive introgression (through long-term hybridization) is present between the two species and threatens the survival of P. shenandoah, and (2) the level of population structure within P. shenandoah. We provide evidence from mtDNA haplotypes that shows no genetic differentiation among the three isolates of P. shenandoah, suggesting that their fragmentation is a geologically recent event, and/or that the isolates are still connected by occasional gene flow. There is also no evidence for extensive introgression of alleles in either direction between P. cinereus and P. shenandoah, which suggests that P. shenandoah may not be in danger of being genetically swamped out through hybridization with P. cinereus. [source] Mechanisms driving the specificity of a myrmecophyte,ant associationBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009JULIEN GRANGIER In the understory of pristine Guianese forests, the myrmecophyte Hirtella physophora almost exclusively shelters colonies of the plant-ant Allomerus decemarticulatus in its leaf pouches. We experimentally tested three non-mutually exclusive hypotheses concerning phenomena that can determine the species specificity of this association throughout the foundation stage of the colonies: (1) interspecific competition results in the overwhelming presence of A. decemarticulatus queens or incipient colonies; (2) exclusion filters prevent other ant species from entering the leaf pouches; and (3) host-recognition influences the choice of founding queens, especially A. decemarticulatus. Neither interspecific competition, nor the purported exclusion filters that we examined play a major role in maintaining the specificity of this association. Unexpectedly, the plant trichomes lining the domatia appear to serve as construction material during claustral foundation rather than as a filter. Finally, A. decemarticulatus queens are able to identify their host plant from a distance through chemical and/or visual cues, which is rarely demonstrated in studies on obligatory ant,plant associations. We discuss the possibility that this specific host-recognition ability could participate in shaping a compartmentalized plant-ant community where direct competition between ant symbionts is limited. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 90,97. [source] Antagonistic lipopolysaccharides block E. coli lipopolysaccharide function at human TLR4 via interaction with the human MD-2 lipopolysaccharide binding siteCELLULAR MICROBIOLOGY, Issue 5 2007Stephen R. Coats Summary Lipopolysaccharides containing underacylated lipid A structures exhibit reduced abilities to activate the human (h) Toll-like receptor 4 (TLR4) signalling pathway and function as potent antagonists against lipopolysaccharides bearing canonical lipid A structures. Expression of underacylated lipopolysaccharides has emerged as a novel mechanism utilized by microbial pathogens to modulate host innate immune responses. Notably, antagonistic lipopolysaccharides are prime therapeutic candidates for combating Gram negative bacterial sepsis. Penta-acylated msbB and tetra-acylated Porphyromonas gingivalis lipopolysaccharides functionally antagonize hexa-acylated Escherichia coli lipopolysaccharide-dependent activation of hTLR4 through the coreceptor, hMD-2. Here, the molecular mechanism by which these antagonistic lipopolysaccharides act at hMD-2 is examined. We present evidence that both msbB and P. gingivalis lipopolysaccharides are capable of direct binding to hMD-2. These antagonistic lipopolysaccharides can utilize at least two distinct mechanisms to block E. coli lipopolysaccharide-dependent activation of hTLR4. The main mechanism consists of direct competition between the antagonistic lipopolysaccharides and E. coli lipopolysaccharide for the same binding site on hMD-2, while the secondary mechanism involves the ability of antagonistic lipopolysaccharide,hMD-2 complexes to inhibit E. coli lipopolysaccharide,hMD-2 complexes function at hTLR4. It is also shown that both hTLR4 and hMD-2 contribute to the species-specific recognition of msbB and P. gingivalis lipopolysaccharides as antagonists at the hTLR4 complex. [source] | |||||||||||||||||||||||||||||||