Theory of oviposition strategy of parasitoids. I. Effect of mortality and limited egg number

The optimal oviposition strategies of parasitoids, the host range, and the number of eggs laid per host which result in the maximum lifetime performance of reproduction, are investigated. To study the effects of parasitoid mortality and of limiting total number of eggs laid by a parasitoid, a standard criterion used in previous theories of optimal diet and optimal patch use, the maximization of the foraging rate, is no longer suitable. The model is solved analytically by using dynamic programming. The results are as follows: The host preference of solitary parasitoids depends on the mortality during handling times; i.e., the forager tends to avoid hosts with high risk of foraging mortality. If the total number of eggs produced by a parasitoid is limited, and if the mortality during handling is negligible, the host range is wider when a larger number of eggs remains in the parasitoid's body. In general, however, the mortality-cost of forager and the egg-cost interplay, because the loss of future reproduction by mortality increases with the number of available eggs. In an example with two host types, host range is widest with an intermediate number of eggs available in the body. The optimal number of eggs per host laid by a gregarious parasitoid is also affected by the differential mortality of the forager, and by the number of available eggs.     

Storage of Hg in the ileum of Blatella germanica: biochemical characterization of metallothionein

Cockroach ileum has a high capability to concentrate mercury compared with other tissues. Part of the mercury contained in the soluble phase of this organ is bound to metallothionein. It is suggested that mercury of the insoluble phase is stored in lysosomes under a polymerized metallothionein form.     

Expression of mosquitocidal crystal protein genes in non-insecticidal Bacillus thuringiensis subsp. israelensis

Bacillus thuringiensis NTB-1 isolated from soil samples in Korea produces ovoidal parasporal inclusions with proteins of approximately 24–40 kDa in size. Although serological study indicated that the isolate has a flagella (H) antigen identical with subsp. israelensis , it seemed to be non-insecticidal against Lepidoptera and Coleoptera as well as Diptera. To investigate the activity of non-insecticidal B. thuringiensis transformed with insecticidal crystal protein genes, cryIVD and cytA genes of B. thuringiensis subsp. morrisoni PG-14, highly toxic to mosquito larvae, were introduced into the isolate NTB-1. The expression of mosquitocidal crystal protein genes in NTB-1 was characterized by SDS–PAGE analysis and electron microscopy. The results showed that crystalline inclusions of host, CryIVD and CytA were stably expressed in the transformant. However, the mosquitocidal activity of transformant was similar to that of B. thuringiensis subsp. kurstaki Cry⁻ B harbouring cryIVD and cytA genes, demonstrating that a synergistic effect by an interaction of both introduced insecticidal and resident non-insecticidal crystal proteins was not observed.     

Changes in Membrane Fluidity and Protein Composition during Release of Cucumber Seeds from Dormancy by a Higher Temperature Shift

Dormancy of seeds of cucumber (Cucumis sativus L.) was inducedby imbibing in -1.8 MPa polyethylene glycol 6000 (PEG) solutionand pulsing with far red light for 15 min prior to washing anddrying. When re-imbibed with water at 20 °C, dormancy wasbroken by raising the temperature to 30 °C for 6 h. Thistreatment was also effective when -0.9 MPa PEG was present duringre-imbibition and high temperature. Seeds with broken dormancywere found to germinate in water over a smaller temperaturerange than seeds in which dormancy had not been induced. Whenthe duration of the temperature shift to 30 °C was varied,germination percentage increased from 7 to 60% after 6 h, butlonger exposures up to 12 h had no further promoting effect.The time course of germination after transfer to water following6 h at 30 °C in PEG showed piercing of the perisperm-endospermenvelope after 9–12 h and radicle protusion after 12–15h. If PEG was retained after high temperature treatment no visiblegermination was observed. Thus, to study membrane fluidity andthe protein content associated with germination, seeds weresampled 9 h after high temperature treatment. To study the germinablebut not germinating state, seed held in PEG for 9 h rather thanin water was used. Dormant seed was sampled before the hightemperature treatment. Membrane fluidity was assessed usingfluorescence polarization of membrane fractions treated withDPH (1,6-diphenyl-1,3,5-hexatriene) or its derivatives. Membraneproteins were compared using one-dimensional SDS-PAGE electrophoresis.Intracellular membrane fluidity was not increased in the transitionfrom the dormant to germinable state, but did increase in thetransition to germination. There were no detected changes inintracellular membrane proteins during either transition. Inplasma membrane fractions, fluidity increased during both transitions,while a marked increase in 21, 18 and 17 kD proteins was observedin the transition from germinable to germinating state. Thusmodification of plasma membrane fluidity rather than changesin protein profile is associated with the high temperature releaseof cucumber seeds from dormancy. Copyright 2000 Annals of BotanyCompany     

Consumption of aquatic subsidies by soil invertebrates in coastal ecosystems

Routes of aquatic allochthonous inputs (aquatic subsidies) to detrital food webs are studied, as is the effect of aquatic subsidies on the functional and taxonomic structure of soil invertebrate communities in coastal ecosystems. The study took place in the coastal zone of an oxbow lake of the Pra River in the Oka Reserve. The results indicate a strong dependence of soil animals in the coastal habitats on aquatic subsidies. Isotopic analysis shows that aquatic resources enter soil food webs not only via predators feeding on flying insects or aquatic prey, but also via saprophages decomposing organic debris of aquatic origin. The contribution of aquatic subsidies to the energy balance of soil invertebrates decreases rapidly with increasing distance from the lake. The fraction of aquatic carbon in tissues of collembolans and saprophages is negligible already a few meters from the water edge. The dependence of predatory invertebrates on aquatic resources can be traced at somewhat greater distance (tens of meters).     

Unbalanced ribosome assembly in Saccharomyces cerevisiae expressing mutant 5 S rRNAs.

Mutant 5 S rRNA genes were expressed in Saccharomyces cerevisiae to further define the function of the ribosomal 5 S RNA. RNA synthesis and utilization were assayed using previously constructed markers which have been shown to be functionally neutral and easily detected by gel electrophoresis. Most mutations were found not to affect the growth rate because they were poorly expressed or could be accommodated effectively in the ribosomal structure. Two of the mutants, Y5A99U56U57 and Y5U90i5 adversely affected cell growth as well as protein synthesis in vitro. Polyribosome profiles in both of these mutants were substantially shorter, and an analysis of the ribosomal subunit composition revealed a significant imbalance with a 25-35% excess in 40 S subunits. Kinetic analyses of RNA labeling indicated very low cellular levels of mutant RNA either because it was poorly expressed (Y5U90i5) or rapidly degraded before being incorporated into mature 60 subunits (Y5A99U56U57). The results suggest that the 5 S RNA is required for the assembly of stable ribosomal 60 S subunits and raise the possibility that this RNA or, more likely, its corresponding ribonucleoprotein complex is critical for subunit assembly or even RNA processing.     

Ultrastructural study of enzymes in reactive astrocytes: Clarification of astrocytic activity

Summary Enzymes in reactive astrocytes of the corebral cortex were examined at the ultrastructural level in an attempt to resolve some conflicting aspects of astrocytic activity. Correlations between morphological and enzyme changes after injury established that the apparent increase in oxidative enzyme activity was exclusively mitochondrial and not an artefactual reaction product resulting from anoxic cellular damage. Pronounced glucose-6-phosphatase activity within cisternae of an increased amount of the granular endoplasnie reticulum was related to increased glycogen. Further evidence from acid phosphatase activity indieated that astrocytes played a minimal role in phagocytosis.