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31.
Hideo Ezoe 《Evolutionary ecology》1995,9(3):328-339
Summary I study the evolutionarily stable seasonal patterns of hatching and pupation for herbivorous insects that engage in exploitative competition for a renewable resource. A longer larval feeding period enhances female fecundity, but also causes a higher mortality by predation and parasitism. Previously, it was shown that the evolutionarily stable population exhibits asynchronous starting and ending of the larval feeding period in a model in which larval growth rate decreases with the total larval biomass in the population due presumably to interference competition. Here I study the case in which resource availability changes not only with environmental seasonality but with the depletion by the feeding of larvae. I find that if the impact of the herbivory is strong, both hatching and pupation should occur asynchronously in the evolutionarily stable population. And if the favourable season for the host plant is short the ESS population may include synchronous timing of pupation. If the timing of hatching and pupation occurs asynchronously, in the first day of each interval some fraction of the population hatch or pupate, respectively and the rest do so gradually over the interval. In addition, if the environmental variable changes as a symmetric function of time, the length of the period in which hatching occurs tends to be much shorter than the period in which pupation occurs. 相似文献
32.
Cholera toxin (CT) stimulated phospholipase activity and caused [3H]arachidonic acid (3H-AA) release in a murine macrophage/monocyte cell line. Pretreatment of cells with dexamethasone, a phospholipase A2 (PLA2) inhibitor, did not affect CT-induced 3H-AA release. In contrast, aspirin, which is an inhibitor of phospholipase C (PLC), blocked CT-induced 3H-AA release and subsequent prostaglandin (PC) synthesis. The inhibitory effect of aspirin was dose dependent, with 4 mM reducing the CT response by approximately 50%. Similarly, inhibition was time dependent, occurring when the drug was added to the culture medium as late as 30 min after CT. Brief exposure (30 min) of the cells to aspirin did not alter their subsequent response to CT, but 3H-AA release from cells exposed to aspirin for 2.5 h was irreversibly inhibited. The data suggested that CT stimulation of AA metabolism may involve increased PLC activity. 相似文献
33.
Nitric oxide (NO) is a chemical weapon within the arsenal of immune cells, but is also generated endogenously by different bacteria. Pseudomonas aeruginosa are pathogens that contain an NO-generating nitrite (NO2−) reductase (NirS), and NO has been shown to influence their virulence. Interestingly, P. aeruginosa also contain NO dioxygenase (Fhp) and nitrate (NO3−) reductases, which together with NirS provide the potential for NO to be metabolically cycled (NO→NO3−→NO2−→NO). Deeper understanding of NO metabolism in P. aeruginosa will increase knowledge of its pathogenesis, and computational models have proven to be useful tools for the quantitative dissection of NO biochemical networks. Here we developed such a model for P. aeruginosa and confirmed its predictive accuracy with measurements of NO, O2, NO2−, and NO3− in mutant cultures devoid of Fhp or NorCB (NO reductase) activity. Using the model, we assessed whether NO was metabolically cycled in aerobic P. aeruginosa cultures. Calculated fluxes indicated a bottleneck at NO3−, which was relieved upon O2 depletion. As cell growth depleted dissolved O2 levels, NO3− was converted to NO2− at near-stoichiometric levels, whereas NO2− consumption did not coincide with NO or NO3− accumulation. Assimilatory NO2− reductase (NirBD) or NorCB activity could have prevented NO cycling, and experiments with ΔnirB, ΔnirS, and ΔnorC showed that NorCB was responsible for loss of flux from the cycle. Collectively, this work provides a computational tool to analyze NO metabolism in P. aeruginosa, and establishes that P. aeruginosa use NorCB to prevent metabolic cycling of NO. 相似文献
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36.
Rice straw decomposition in rice-field soil 总被引:1,自引:0,他引:1
Rice straw, buried in a rice-field during the dry season decomposed at a rate of 0.0075 day-1. Seventy five percent of the biomass, 70 percent carbon, 50 percent nitrogen and 30 percent phosphorus remained after 139 days of decomposition. Rice straw decomposition furnished 33% N and 8% P of the total nitrogen and phosphorus provided by man. 相似文献
37.
Satiation and the functional response: a test of a new model 总被引:1,自引:0,他引:1
N. J. MILLS 《Ecological Entomology》1982,7(3):305-315
Abstract. 1. A model of the functional response to prey density is derived to include the reduction in time available for search, Ts , resulting from predator satiation.
2. For larger prey items predator satiation occurs at each prey capture and Ts is reduced by the attack time and digestive pause of a series of attack cycles. For small prey items predator foraging is continuous at low densities with Ts reduced solely by attack time. At higher densities predator satiation occurs after the capture of several small prey items and Ts is reduced by the attack time and digestive pause of a series of foraging cycles.
3. A comparison of the predicted asymptotic level of prey capture using experimentally estimated parameter values, with the maximum consumption of aphids by larval and adult coccinellids provides a test of the satiation model.
4. The limitation of prey capture by predator satiation is discussed with reference to handling time and the success of coccinellids in biological control. 相似文献
2. For larger prey items predator satiation occurs at each prey capture and T
3. A comparison of the predicted asymptotic level of prey capture using experimentally estimated parameter values, with the maximum consumption of aphids by larval and adult coccinellids provides a test of the satiation model.
4. The limitation of prey capture by predator satiation is discussed with reference to handling time and the success of coccinellids in biological control. 相似文献
38.
MICHAEL D. BAKER CHARLES R. VOSSBRINCK JAMES J. BECNEL JOSEPH V. MADDOX 《The Journal of eukaryotic microbiology》1997,44(3):220-225
ABSTRACT. Sequences of the small subunit rRNA genes of Amblyospora californica and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp, respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced. 相似文献
39.
The application of porous graphitic carbon as adsorbing phase for direct separation of enantiomeric acids and amines using chiral ion-pair chromatography is described. The enantiomeric amines were separated as diastereomeric ion pairs with N-benzyloxycarbonylglycyl-L -proline, N-benzyloxycarbonylglycylglycyl-L -proline, or captopril as the chiral counterion. High enantioselectivities were obtained for amines having a hydrogen bonding function in the vicinity of the asymmetrical carbon atom. Quinine was the chiral counterion used to separate the enantiomeric acids. The strongly UV-absorbing quinine improved detection of solutes having low UV-absorbing properties, e.g., (R,S)-2-chloropropionic acid, by “indirect detection.” Retention and stereoselectivity of enanticmeric acids were regulated by the quinine concentration and by the addition of carboxylic acids as well as polar modifiers, e.g., methanol and 2-propanol, to the mobile phase. © 1992 Wiley-Liss, Inc. 相似文献
40.