THE ASSOCIATION BETWEEN THE POLYMORPHISMS AT THE Adh AND αGpdh LOCI AND THE In(2L)t INVERSION IN DROSOPHILA MELANOGASTER IN RELATION TO TEMPERATURE

Substantial allele-frequency changes were observed at the Adh and αGpdh loci in a seminatural population of Drosophila melanogaster kept in a tropical greenhouse during 1972–1985. Further analysis of the changes at the Adh and αGpdh loci showed that linkage disequilibrium between these loci occurred for a prolonged period due to the presence of In(2L)t, a long inversion on the left arm of the second chromosome. We observed increases in the frequencies of In(2L)t and of short inversions on the left arm of the second chromosome in subpopulations kept at 29.5°C or 33°C. These inversion-frequency increases were accompanied by an increase in Adh^s and a decrease in αGpdh^s frequency. In populations kept at 20°C and 25°C, inversion frequencies decreased, while αGpdh^s allele frequencies decreased at 25°C and increased at 20°C. At 33°C, egg-to-adult survival of individuals possessing In(2L)t, either in the homokaryotypic or the heterokaryotypic state, was higher than that of the other karyotypes of identical allozyme constitution (i.e., Adh^s αGpdh^F). Thus it seems that In(2L)t has a selective advantage at high temperature. We argue that the observed changes in allele frequencies at the Adh and αGpdh loci are, in part, due to genic selection and are not merely the result of selection acting on the chromosome rearrangements and hitchhiking of the allozymes. The results are discussed with respect to the latitudinal clines found for In(2L)t, Adh, and αGpdh.     

Behavioural responses of the vine weevil, Otiorhynchus sulcatus, to semiochemicals from conspecifics, Otiorhynchus salicicola, and host plants

The vine weevil Otiorhynchus sulcatus is a parthenogenetic reproducing species which forages for suitable host plants at night, but is found congregated in dark places during the day. Frass of this weevil species is suspected to contain attractive compounds that are host‐plant related. Using a still‐air olfactometer, we tested adult vine weevils at night for their behavioural response to odours from conspecifics, feeding on a mixture of spindle tree (Euonymus fortunei) and yew (Taxus baccata), and to a sexually reproducing related species (Otiorhynchus salicicola), feeding on a mixture of ivy (Hedera helix) and cherry laurel (Prunus laurocerasus). Their attraction to conspecifics and O. salicicola appeared to be related to frass production. Freshly collected frass from O. sulcatus and from O. salicicola males and females was attractive. Prunus laurocerasus and H. helix have not been observed to be hosts of the vine weevil in the field. However, our tests showed that the vine weevil was attracted to mechanically damaged leaves of both plant species, whereas undamaged leaves were not attractive. Only undamaged young unfolding leaves of H. helix were also attractive. The attraction to odours from mechanically damaged host and non‐host plants suggested the involvement of compounds that are commonly found in many plant species. The involvement of plant compounds and/or aggregation pheromones in attraction to frass of the vine weevil and frass of the related weevil species O. salicicola is discussed.     

First chemical synthesis of a scorpion alpha-toxin affecting sodium channels: the Aah I toxin of Androctonus australis hector.

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.     

Integrated Control of Sclerotium rolfsii on Groundnut in South Africa

Sclerotium rolfsii Sacc. causes disease of numerous crop plants worldwide, including groundnuts. Control of this pathogen is difficult as it produces sclerotia which overwinter in the soil to emerge as inoculum and cause disease the following season. Various chemical, biological and cultural control strategies have been suggested and implemented, some of which have reduced disease incidence in the field. No studies have yet been undertaken in South Africa to control this disease on groundnut, either chemically, biologically or by cultural practices. In this study, several strategies were investigated for the control of S. rolfsii on groundnuts. Difenoconazole was identified as a fungicide that could possibly be applied in combination with Trichoderma harzianum, a biological antagonist of S. rolfsii, above carbendazim and flusilazole, and chlorothalonil. Difenoconazole significantly reduced the growth rate of S. rolfsii but not of T. harzianum. The cultivation of infected fields with an inversion plough significantly reduced infection of groundnuts by S. rolfsii and also improved the quality of the produce, while yield was not increased. Lower plant density increased the incidence of disease in an infected field, and is therefore not considered to be a viable form of cultural control.     

Effect of Planting Unit Size and Sediment Stabilization on Seagrass Transplants in Western Australia

Abstract The effect of increasing planting unit size and stabilizing sediment was examined for two seagrass planting methods at Carnac Island, Western Australia in 1993. The staple method (sprigs) was used to transplant Amphibolis griffithii (J. M. Black) den Hartog and the plug method was used to transplant A. griffithii and Posidonia sinuosa Cambridge and Kuo. Transplant size was varied by increasing the number of rhizomes incorporated into a staple and increasing the diameter of plugs. Planting units were transplanted into bare sand, back into the original donor seagrass bed, or into a meadow of Heterozostera tasmanica, which is an important colonizing species. Sprigs of A. griffithii were extracted from a monospecific meadow; tied into bundles of 1, 2, 5, and 10 rhizomes; and planted into unvegetated areas. Half the units were surrounded by plastic mesh and the remainder were unmeshed. All treatments were lost within 99 days after transplanting, and although larger bundles survived better than smaller ones, no significant differences could be attributed to the effects of mesh or sprig size. Plugs of P. sinuosa and A. griffithii were extracted from monospecific meadows using polyvinyl chloride pipe of three diameters, 5, 10, and 15 cm, and planted into unvegetated areas nearby. Half the units were surrounded by plastic mesh and the remainder were unmeshed. Posidonia sinuosa plugs were also placed within a meadow of H. tasmanica (Martens ex Aschers.) den Hartog. Only 60% of A. griffithii plug sizes survived 350 days after transplanting back into the donor bed; however, survival of transplants at unvegetated areas varied considerably, and analysis of variance indicated a significant two‐way interaction between treatment and plug size. Transplants survived better when meshed (90% survived) and survival improved with increasing plug size. Posidonia sinuosa transplants survived poorly (no plugs survived beyond 220 days in bare or meshed treatments) regardless of size. Survival of 10‐ and 15‐cm plugs was markedly better than the 5‐cm plugs in vegetated areas, including the H. tasmanica meadow. The use of large seagrass plugs may be appropriate for transplantation in high‐energy wave environments.     

Social Behaviour of the Carpenter Bee Xylocopa pubescens (Spinola)

The development of about 20 relatively small nests of Xylocopa pubescens was studied. After the first offspring had become adult, these nests reached a social stage in which there was only one egg-layer per nest. Freshly emerged (teneral) adults eat a lot of food, collected by a forager, before they fly out of the nest. This food appears to be of major importance to these bees in that it makes them fully agile. It seems therefore, that part of the food needed for the development of a young bee is not given at the larval stage, via the beebread, but at the teneral adult stage. As a result of this, a necessary overlap of generations is accomplished. Besides, less pollen has to be collected for the provision of a brood cell, so more cells can be constructed within a short period of time. There is a high degree of nest competition. Many nests were taken over by conspecific individuals (or by females of X. sulcatipes) that were searching for nesting sites within the study area. However, although more than 50% of the solitary nests were taken over sooner or later, strangers hardly ever intruded into social nests, with more than one adult. This illustrates how important it is for a reproducing female to tolerate the presence of nestmates which guard the nest in her absence. Although in most cases the foundress of a nest proceeded to produce new brood in the presence of her offspring, it happened that a daughter took over reproduction from her mother. In two of these cases, it could be observed that a mother started a new nest elsewhere after having been thrown out by her own daughter. At least in these cases, nest competition between mother and daughter started long before the mother had reached the end of her reproductive capacities. Since nesting possibilities are scarce, it seems a logical strategy to stay in the maternal nest and wait for a chance to become the egg-layer if the mother dies or if she loses her dominance. The occurrence of several social interactions among nestmates is discussed: — trophallaxis was observed often, not only under ‘forced’ conditions, but also as a form of ‘voluntary’ feeding; — nestmates were observed to groom each other.     

The interactions with Ro60 and La differentially affect nuclear export of hY1 RNA.

Ro RNPs are evolutionarily conserved ribonucleoprotein particles that consist of a small RNA, known as Y RNA, associated with several proteins, such as La, Ro60, and Ro52. The Y RNAs (Y1-Y5), which are transcribed by RNA polymerase III, have been shown to reside almost exclusively in the cytoplasm as Ro RNPs. To obtain more insight into the nuclear export pathway of Y RNAs, hY1 RNA export was studied in Xenopus laevis oocytes. Injection of various hY1 RNA mutants showed that an intact Ro60 binding site is a prerequisite for nuclear export, whereas the presence of an intact La binding site resulted in strong nuclear retention of hY1 RNA. Competition studies with various classes of RNAs indicated that, in addition to Ro60, another titratable factor was necessary for nuclear export of hY1 RNA. This factor appears also to be involved in nuclear export of tRNA. Because export of hY1 RNA could not be blocked by a synthetic peptide containing the recently identified nuclear export signal of the HIV-1 Rev protein, nuclear export of hY1 RNA does not seem to be dependent on a Rev-like nuclear export signal.     

Mapping of resistance to the potato cyst nematode Globodera rostochiensis from the wild potato species Solanum vernei

A population of diploid potato (Solanum tuberosum) was used for the genetic analysis and mapping of a locus for resistance to the potato cyst nematode Globodera rostochiensis, introgressed from the wild potato species Solanum vernei. Resistance tests of 108 genotypes of a F₁ population revealed the presence of a single locus with a dominant allele for resistance to G. rostochiensis pathotype Ro1. This locus, designated GroV1, was located on chromosome 5 with RFLP markers. Fine-mapping was performed with RAPD and SCAR markers. The GroV1 locus was found in the same region of the potato genome as the S. tuberosum ssp. andigena H1 nematode resistance locus. Both resistance loci could not excluded to be allelic. The identification of markers flanking the GroV1 locus offers a valuable strategy for marker-assisted selection for introgression of this nematode resistance.Abbreviations BSA bulked segregant analysis - RAPD random-amplified polymorphic DNA - RFLP restriction fragment length polymorphism - SCAR sequence-characterized amplified region