Nucleolus size varies with sex,ploidy and gene dosage in insects

The nucleolus constitutes a cytologically visible phenotype for ribosomal DNA (rDNA). Nucleolar size, as determined by silver staining, is a good indicator of cell proliferation rate and biosynthetic activity. Nevertheless, the relationship between rDNA content and sexual dimorphism for nucleolar size is not well documented. In the present study, the impact of sex and ploidy level on nucleolar size is investigated in three haplo/diploid and three diplo/diploid species of insect. Nucleolar sizes are found to be proportional to ploidy level in the haplo/diploid hymenopterans Trypoxylon albitarse and Nasonia vitripennis. Conversely, in the ant Messor barbarus, nucleolar sizes are larger in haploid males (winged) than diploid females (apterous). Among the diplo/diploid species, evidence for gene dosage compensation on nucleolar activity is suggested by the absence of sex differences in Drosophila simulans, a species in which rDNA is limited to the X chromosome. By contrast, in the grasshopper Stenobothrus festivus, another species with rRNA genes restricted to the X chromosome, the size of the nucleolus is significantly larger in females than in males. Additionally, in the grasshopper Chorthippus parallelus, where rDNA is distributed evenly on several autosomes of males and females, the females also show larger nucleoli than males. In both grasshopper species, the magnitude of the female/male ratio for nucleolus area is very similar to the body size ratio, suggesting that body size, as well as sex, ploidy, gene dosage and physiological activity, may be an important determinant of nucleolus area.     

Studies on sharp eyespot disease of cereals: Effects of the disease on the wheat host and the incidence of disease in the field

Greenhouse and field experiments showed that sharp eyespot disease can reduce establishment in wheat seedlings. Increasing disease severity caused a decrease in height and dry weight of surviving seedlings. Infection by the pathogen caused a reduction in tillering. Experiments also showed that a high incidence of disease can cause a reduction in the yield of grain of mature plants, but the disease level necessary for such effects is far higher than that usually encountered in the field. Survey work in the East of Scotland in 1963-65 showed a high percentage of crops infected with the disease. But even in 1964, a year of comparatively high disease incidence, there were few crops with a level of infection as high as that shown to affect yield.     

An Abscisic Acid-like Substance in Dry and Soaked Phaseolus vulgaris Seeds Determined by the Lemna Growth Bioassay

An acid inhibitor, probably abscisic acid (ABA) in low concentrations was found to be present in bean seeds. The evidence is based on data from paper electrophoresis, chromatography, UV absorption and growth inhibition in the Lemna bioassay, sensitive down to a concentration of 10^-11M ABA or 0.02–0.03 ng/flask. The inhibitor level as measured by this bioassay decreases considerably with increasing soaking time. Acid ether-soluble inhibitors could even be detected in the soaking water from the soaked seeds.     

Ontogeny of cephalic volatile patterns in queens and mating biology of the neotropical stingless bee,Scaptotrigona postica

Summary

Chemical communication is an ancient yet still immensely important part of reproduction. Amongst all invertebrates, the most sophisticated “chemical languages” are used by social insects. Here the sex- and caste-specific pheromonal messages consist of multicomponent mixtures. In the neotropical stingless bee Scaptotrigona postica, an inhabitant of dense tropical rain forests, the cephalic volatiles of a queen transmit information on her reproductive status to males. A distinct ontogenetic pattern of the queen pheromone composition allows drones to discriminate receptive virgins which are then chased during the short nuptial flight through the forest understorey. By means of gas chromatographic/mass spectroscopic analyses, the numerous volatile compounds found in pentane extracts of individual bee heads could be identified. Qualitative as well as quantitative changes of these volatiles in the course of imaginal development could be determined, and bioassays with synthetic compounds were undertaken in order to decode the chemical signals used during the short encounter of a young queen and her mate.