Insecticides in host-parasitoid interactions

The equilibrium and local stability properties are described of insect host-parasitoid models that include the effects of insecticide application. The models are framed in discrete time making it important to distinguish between different sequences of parasitism and insecticide kill in the host's life cycle. Four possibilities are considered: (1) Insecticides act prior to parasitism and only kill hosts. (2) Insecticides act after parasitism and only kill hosts. (3) Insecticides act after parasitism and also kill parasitized hosts at the same rate. (4) Insecticides act prior to parasitism and also kill adult parasitoids. There is a clear ranking of the different application strategies in terms of their effect on the depression of the host equilibrium and their contribution to stability.     

Nonmuscle myosin phosphorylation sites for calcium-dependent and calcium-independent protein kinases

Thymus myosin, light chains and a synthetic peptide (S-S-K-R-A-K-A-K-T-T-K-K-R-P-Q-R-A-T-S-N-V-F-S) corresponding to the N-terminal sequence of smooth muscle myosin light chains were compared as substrates for calcium/calmodulin-dependent protein kinase (MLCK), calcium/phospholipid-dependent protein kinase (PKC), and a MgATP-activated protein kinase (H4PK) from lymphoid cells. All protein kinases catalyzed phosphorylation of the substrates although H4PK showed higher affinity for isolated light chains and the peptide. Phosphoamino acid analysis and analysis of thermolysin peptides established that PKC catalyzed phosphorylation of threonine-9 or 10. In addition, PKC and H4PK catalyzed phosphorylation at serine-19, the MLCK site. Collectively the data support the hypothesis that myosin filament assembly in nonmuscle cells may be regulated by a variety of calcium-dependent and calcium-independent protein kinases.     

Predation in multi-prey communities

We consider the effect of a top predator on the stability of a system of competing prey species. In the first instance, this is done in detail for two prey species where the predators either behave in a completely random way, interfere with each other or switch to the more abundant prey at any time. The analysis is then extended to the case of n similar prey species, either competing equally or competing with their two nearest neighbours in exploiting a one-dimensional resource spectrum. It is found that predator switching can produce local stability when the prey species overlap completely and even when the competition coefficients are greater than one. This, however, is more difficult to attain for nearest neighbour competition. In either case switching is advantageous to the predators, since it allows them to coexist successfully with their prey over a wider range of conditions.     

Accounting for heterogeneity when estimating stopover duration,timing and population size of red knots along the Luannan Coast of Bohai Bay,China

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The abundance of an invasive freshwater snail Tarebia granifera (Lamarck, 1822) in the Nseleni River,South Africa

The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.     

Environmental stresses inhibit splicing in the aquatic fungus Blastocladiella emersonii

Background  

Exposure of cells to environmental stress conditions can lead to the interruption of several intracellular processes, in particular those performed by macromolecular complexes such as the spliceosome.     

A novel approach to controlling dissolved oxygen levels in laboratory experiments

Hypoxia is a widespread environmental stressor that affects marine, estuarine and freshwater systems worldwide. Investigating the effects of hypoxia on aquatic animals in the natural environment is difficult and expensive. Laboratory experiments provide an alternative that allows manipulation of environmental variables and simulation of altered conditions that are expected in the future. However, controlling dissolved oxygen (DO) levels precisely in laboratory test situations is challenging and generally costly and time intensive. In this paper, we describe a novel chamber design that is capable of maintaining low DO levels precisely for a period of at least 4 days with minimal re-adjustment and nitrogen gas requirement. The system is simple, inexpensive and easy to use, and offers the additional benefit of being portable. The utility of this design is demonstrated with an experiment to test the effects of hypoxia and high salinity on hatch rates and yolk-sac larvae survival in the estuarine fish black bream Acanthopagrus butcheri (Munro, 1949). The results show that early life-stage black bream are sensitive to hypoxia and increased salinity, indicating that deterioration in estuarine environmental conditions may have negative effects on spawning success and recruitment to fish populations. This new laboratory technique will be useful for testing future scenarios for the estuaries of southern Australia as predicted by climate change models. Other potential applications and modifications for further development of this new technique are discussed.