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331.
Parasite alteration of the host (predator) functional response provides a mechanism by which parasites can alter predator–prey population dynamics and stability. We tested the hypothesis that parasitic infection of a crab (Eurypanopeus depressus) by a rhizocephalan barnacle (Loxothylacus panopei) can modify the crab’s functional response to mussel (Brachidontes exustus) prey and investigated behavioral mechanisms behind a potential change in the response. Infection dramatically reduced mussel consumption by crabs across mussel densities, resulting in a decreased attack rate parameter and a nearly eightfold reduction in maximum consumption (i.e. the asymptote, or inverse of the handling time parameter) in a type II functional response model. To test whether increased handling time of infected crabs drove the decrease in maximum consumption rate, we independently measured handling time through observation. Infection had no effect on handling time and thus could not explain the reduction in consumption. Infection did, however, increase the time that it took crabs to begin handling prey after the start of the handling time experiment. Furthermore, crabs harboring relatively larger parasites remained inactive longer before making contact with prey. This behavioral modification likely contributed to the reduced mussel consumption of infected crabs. A field survey revealed that 20 % of crabs inhabiting oyster reefs at the study site (North Inlet estuary, Georgetown, South Carolina, USA) are infected by the barnacle parasite, indicating that parasite infection could have a substantial effect on the population level crab-mussel interaction. 相似文献
332.
Douglas E. Soltis Clayton J. Visger D. Blaine Marchant Pamela S. Soltis 《American journal of botany》2016,103(7):1146-1166
Investigators have long searched for a polyploidy paradigm—rules or principles that might be common following polyploidization (whole‐genome duplication, WGD). Here we attempt to integrate what is known across the more thoroughly investigated polyploid systems on topics ranging from genetics to ecology. We found that while certain rules may govern gene retention and loss, systems vary in the prevalence of gene silencing vs. homeolog loss, chromosomal change, the presence of a dominant genome (in allopolyploids), and the relative importance of hybridization vs. genome doubling per se. In some lineages, aspects of polyploidization are repeated across multiple origins, but in other species multiple origins behave more stochastically in terms of genetic and phenotypic change. Our investigation also reveals that the path to synthesis is hindered by numerous gaps in our knowledge of even the best‐known systems. Particularly concerning is the absence of linkage between genotype and phenotype. Moreover, most recent studies have focused on the genetic and genomic attributes of polyploidy, but rarely is there an ecological or physiological context. To promote a path to a polyploidy paradigm (or paradigms), we propose a major community goal over the next 10–20 yr to fill the gaps in our knowledge of well‐studied polyploids. Before a meaningful synthesis is possible, more complete data sets are needed for comparison—systems that include comparable genetic, genomic, chromosomal, proteomic, as well as morphological, physiological, and ecological data. Also needed are more natural evolutionary model systems, as most of what we know about polyploidy continues to come from a few crop and genetic models, systems that often lack the ecological context inherent in natural systems and necessary for understanding the drivers of biodiversity. 相似文献
333.
Interactions between multiple predator species are frequent in natural communities and can have important implications for
shared prey survival. Predator density may be an important component of these interactions between predator species, as the
frequency of interactions between species is largely determined by species density. Here we experimentally examine the importance
of predator density for interactions between predator species and subsequent impacts on prey. We show that aggressive interactions
between the predatory shore crabs Carcinus maenas and Hemigrapsus sanguineus increased with predator density, yet did not increase as fast as negative interactions between conspecifics. At low density,
interactions between conspecific and heterospecific predators had similar inhibitory impacts on predator function, whereas
conspecific interference was greater than interference from heterospecifics at high predator density. Thus the impact of conspecific
interference at high predator density was sufficient in itself that interactions with a second predator species had no additional
impact on per capita predation. Spatial and temporal variability in predator density is a ubiquitous characteristic of natural
systems that should be considered in studies of multiple predator species. 相似文献
334.
335.
336.
Microscopic and Thermal Characterization of Hydrogen Peroxide Killing and Lysis of Spores and Protection by Transition Metal Ions, Chelators, and Antioxidants 总被引:2,自引:2,他引:2 下载免费PDF全文
Soon-Young Shin Elizabeth G. Calvisi Teofila C. Beaman H. Stuart Pankratz Philipp Gerhardt Robert E. Marquis 《Applied microbiology》1994,60(9):3192-3197
Killing of bacterial spores by H2O2 at elevated but sublethal temperatures and neutral pH occurred without lysis. However, with prolonged exposure or higher concentrations of the agent, secondary lytic processes caused major damage successively to the coat, cortex, and protoplast, as evidenced by electron and phase contrast microscopy. These processes were also reflected in changes in differential scanning calorimetric profiles for H2O2-treated spores. Endothermic transitions in the profiles occurred at lower temperatures than usual as a result of H2O2 damage. Thus, H2O2 sensitized the cells to heat damage. Longer exposure to H2O2 resulted in total disappearance of the transitions, indicative of major disruptions of cell structure. Spores but not vegetative cells were protected against the lethal action of H2O2 by the transition metal cations Cu+, Cu2+, Co2+, Co3+, Fe2+, Fe3+, Mn2+, Ti3+, and Ti4+. The metal chelator EDTA was also somewhat protective, while o-phenanthroline, citrate, deferoxamine, and ethanehydroxydiphosphonate were only marginally so. Superoxide dismutase and a variety of other free-radical scavengers were not protective. In contrast, reducing agents such as sulfhydryl compounds and ascorbate at concentrations of 20 to 50 mM were highly protective. Decoating or demineralization of the spores had only minor effects. The marked dependence of H2O2 sporicidal activity on moderately elevated temperature and the known low reactivity of H2O2 itself suggest that radicals are involved in its killing action. However, the protective effects of a variety of oxidized or reduced transition metal ions indicate that H2O2 killing of spores is markedly different from that of vegetative cells. 相似文献
337.
Bacterial spore heat resistance correlated with water content, wet density, and protoplast/sporoplast volume ratio. 总被引:6,自引:8,他引:6 下载免费PDF全文
T C Beaman J T Greenamyre T R Corner H S Pankratz P Gerhardt 《Journal of bacteriology》1982,150(2):870-877
Five types of dormant Bacillus spores, between and within species, were selected representing a 600-fold range in moist-heat resistance determined as a D100 value. The wet and dry density and the solids and water content of the entire spore and isolated integument of each type were determined directly from gram masses of material, with correction for interstitial water. The ratio between the volume occupied by the protoplast (the structures bounded by the inner pericytoplasm membrane) and the volume occupied by the sporoplast (the structures bounded by the outer pericortex membrane) was calculated from measurements made on electron micrographs of medially thin-sectioned spores. Among the various spore types, an exponential increase in the heat resistance correlated directly with the wet density and inversely with the water content and with the protoplast/sporoplast volume ratio. Altogether with results supported a hypothesis that the extent of heat resistance is based in whole or in part on the extent of dehydration and diminution of the protoplast in the dormant spore, without implications about physiological mechanisms for attaining this state. 相似文献
338.
Xiang Y Seemann J Bisel B Punthambaker S Wang Y 《The Journal of biological chemistry》2007,282(30):21829-21837
In mammalian cells the Golgi apparatus undergoes an extensive disassembly process at the onset of mitosis that is believed to facilitate equal partitioning of this organelle into the two daughter cells. However, the underlying mechanisms for this fragmentation process are so far unclear. Here we have investigated the role of the ADP-ribosylation factor-1 (ARF1) in this process to determine whether Golgi fragmentation in mitosis is mediated by vesicle budding. ARF1 is a small GTPase that is required for COPI vesicle formation from the Golgi membranes. Treatment of Golgi membranes with mitotic cytosol or with purified coatomer together with wild type ARF1 or its constitutive active form, but not the inactive mutant, converted the Golgi membranes into COPI vesicles. ARF1-depleted mitotic cytosol failed to fragment Golgi membranes. ARF1 is associated with Golgi vesicles generated in vitro and with vesicles in mitotic cells. In addition, microinjection of constitutive active ARF1 did not affect mitotic Golgi fragmentation or cell progression through mitosis. Our results show that ARF1 is active during mitosis and that this activity is required for mitotic Golgi fragmentation. 相似文献
339.
Osmotic stress induces activation of an adaptive mitogen-activated protein kinase pathway in concert with disassembly of the actin cytoskeleton by a mechanism that is not understood. We have previously shown that the conserved actin-interacting MAP kinase kinase kinase Ssk2p/MEKK4, a member of the high-osmolarity glycerol (HOG) MAPK pathway of Saccharomyces cerevisiae, mediates recovery of the actin cytoskeleton following osmotic stress. In this study, we have employed in vitro kinase assays to show that Ssk2p kinase activity is activated for the actin recovery pathway via a noncanonical, Ssk1p-independent mechanism. Our work also shows that Ssk2p requires the polarisome proteins Bud6p and Pea2p to promote efficient, polarized actin reassembly but that this requirement can be bypassed by overexpression of Ssk2p. Formin (BNI1 or BNR1) and tropomyosin functions are also required for actin recovery but, unlike for Bud6p and Pea2p, these requirements cannot be bypassed by overexpression of Ssk2p. These results suggest that Ssk2p acts downstream of Bud6p and Pea2p and upstream of tropomyosin to drive actin recovery, possibly by upregulating the actin nucleation activity of the formins. 相似文献
340.
Boghigian BA Armando J Salas D Pfeifer BA 《Applied microbiology and biotechnology》2012,93(5):2063-2073
Taxadiene is the first dedicated intermediate in the biosynthetic pathway of the anticancer compound Taxol. Recent studies
have taken advantage of heterologous hosts to produce taxadiene and other isoprenoid compounds, and such ventures now offer
research opportunities that take advantage of the engineering tools associated with the surrogate host. In this study, metabolic
engineering was applied in the context of over-expression targets predicted to improve taxadiene production. Identified targets
included genes both within and outside of the isoprenoid precursor pathway. These targets were then tested for experimental
over-expression in a heterologous Escherichia coli host designed to support isoprenoid biosynthesis. Results confirmed the computationally predicted improvements and indicated
a synergy between targets within the expected isoprenoid precursor pathway and those outside this pathway. The presented algorithm
is broadly applicable to other host systems and/or product choices. 相似文献