Der Nucleolus und seine Beziehungen zu den Ribosomen des Cytoplasmas. Eine Untersuchung an den Malpighischen Gefässen von Drosophila melanogaster

Summary The investigation described herein is concerned with the structure and the behavior of the nucleolus of the cells of the Malpighian tubules of Drosophila melanogaster (see Fig. 16).Primarly the nucleolus consists of ribonucleic-acid granules about 150 Å in diameter which, with electron microscope, are not distinguishable from the ribosomes of the cytoplasm; they lie on or within the structural network of the nucleolus (Fig. 9). During the stages of the life history of the insect the nucleolus shows correspondingly characteristic peculiarities in structure which reflect the varying functional stages of the cell: The structure is loose in the cells of the larva (Fig. 2) and imago (Fig. 12), whereas it is compact in the pupa (Fig. 8, 9). In pupa sufficiently mature for emergence, the nucleolus contains a large central vacuole (Fig. 8, 9). The nucleolus of the larva has a similar appearance after a decrease in assimilation induced by starvation (Fig. 10, 11).There are smaller vacuoles in the nucleolus which mostly are filled with parts of the nucleolus-chromosome. In the pupal stage some of the peripheral constituents of the nucleolus separate and move to the nuclear membrane through which they pass via pores into the cytoplasm (Fig. 3, 4).Larger pieces reach the cytoplasm by local dissolution of the nuclear membrane (Fig. 5). During this process the extruded nucleolar material is dispersed into its structural components. Because the cytoplasm becomes richer in ribosomes during the period of nucleolar extrusion (Fig. 1b), it can be assumed, that the nucleolus must be a source of ribosomes, and that through such an extrusion which has been demonstrated to be a natural process (Fig. 7) the cytoplasm can be provided with ribosomes rapidly.The importance of this phenomenon in the synthesis of imaginal body is discussed.In the nucleus there are many vacuoles with a diameter of about 425 Å (Fig. 15a, b) which pass through the pores of membrane in the cytoplasm (Fig. 15c).

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Die Untersuchung wurde mit Unterstützung der Deutschen Forschungsgemeinschaft durchgeführt.     

Untersuchungen zur entwicklungsgeschichte der araneae [Pardosa Hortensis (Thorell)] unter besonderer berücksichtigung des vorderen prosomaabschnittes

Ohne ZusammenfassungDie Untersuchungen warden mit Unterstützung der Deutschen Forschungsgemeinschaft in den Jahren 1965–1966 im Zoologischen Institut der Universität Kiel durchgeführt. Herrn Prof. Dr. R. Siewing möchte ich meinen herzlichsten Dank sagen für die Überlassung des Themas, für seinen freundlichen Rat und seine stote Hilfsbereitschaft während der Durchführung meiner Untersuchungen. Herrn Dr. G. Scholl bin ich sehr verbunden für zwei mir zur Verfügung gestellte Präparate und eine Zeichnung von Carausius, und ich danke ihm ebenfalls für seine Anteilnahme am Gelingen meiner Arbeit.     

Emerging model systems in evo-devo: horned beetles and the origins of diversity

Horned beetles and beetle horns are emerging as a model system suited to address fundamental questions in evolutionary developmental biology. Here we briefly review the biology of horned beetles and highlight the unusual opportunities they provide for evo-devo research. We then summarize recent advances in the development of new approaches and techniques that are now available to scientists interested in working with these organisms. We end by discussing ways to implement and combine these new approaches to explore new frontiers in evo-devo research previously unavailable to reseachers working outside traditional model organisms.     

Developmental capacitance, genetic accommodation, and adaptive evolution

The concept of genetic accommodation remains controversial, in part because it remains unclear whether evolution by genetic accommodation forces a revolution, or merely a shift in emphasis, in our understanding of how evolution produces adaptive new traits. Here I outline a perspective that largely favors the latter view. I argue that evolution by genetic accommodation can easily be integrated into traditional evolutionary concepts. At the same time, evolution by genetic accommodation invites novel empirical and theoretical approaches that may allow biologists to push the boundaries of our current understanding of the process of evolution and to solve some long-standing controversies. Specifically, I discuss the role of developmental mechanisms as natural, and likely ubiquitous, capacitors of cryptic genetic variation, and the role of environmental perturbations as mechanisms by which such variation can become visible to selection on an individual to population-wide scale. I argue that in combination, developmental capacitance and large-scale environmental perturbations have the potential to facilitate rapid evolution including the origin of novel adaptive features while circumventing otherwise powerful genetic and population-biological constraints on adaptive evolution. I end by highlighting several promising avenues for future empirical research to explore the mechanisms and significance of evolution by genetic accommodation.     

Juvenile hormone mediates sexual dimorphism in horned beetles

The causes and consequences of sexual dimorphism are major themes in biology. Here we explore the endocrine regulation of sexual dimorphism in horned beetles. Specifically, we explore the role of juvenile hormone (JH) in regulating horn expression in females of two species with regular sexual dimorphism for pronotal horns (females have much shorter horns than males) and a third species with a rare reversed sexual dimorphism for both pronotal and head horns (females have much larger horns in both body regions compared with males). Applications of the JH analog methoprene caused females of the two more typical species to grow significantly shorter pronotal horns than control females, whereas no consistent effect on pronotal horn development was detected in the third, sex-reversed species. Instead, females in this species showed an unexpected and significant increase in head horn expression in response to methoprene treatment. Lastly, horn shape was also affected in females of one of the regularly sexually dimorphic species, but in the opposite direction than horn length. Although methoprene exerted a feminizing effect on female horn length in this species, it significantly masculinized horn shape by inducing a peculiar shape change observed naturally only in males. Our results suggest that JH influences both overall size and shape of female horns, but does so flexibly and as a function of species, sex and horn location. We use our results to review current models on the role of endocrine mechanisms in development and evolution of horned beetle diversity.     

Risk maps for the spread of highly pathogenic avian influenza in poultry

Devastating epidemics of highly contagious animal diseases such as avian influenza, classical swine fever, and foot-and-mouth disease underline the need for improved understanding of the factors promoting the spread of these pathogens. Here the authors present a spatial analysis of the between-farm transmission of a highly pathogenic H7N7 avian influenza virus that caused a large epidemic in The Netherlands in 2003. The authors developed a method to estimate key parameters determining the spread of highly transmissible animal diseases between farms based on outbreak data. The method allows for the identification of high-risk areas for propagating spread in an epidemiologically underpinned manner. A central concept is the transmission kernel, which determines the probability of pathogen transmission from infected to uninfected farms as a function of interfarm distance. The authors show how an estimate of the transmission kernel naturally provides estimates of the critical farm density and local reproduction numbers, which allows one to evaluate the effectiveness of control strategies. For avian influenza, the analyses show that there are two poultry-dense areas in The Netherlands where epidemic spread is possible, and in which local control measures are unlikely to be able to halt an unfolding epidemic. In these regions an epidemic can only be brought to an end by the depletion of susceptible farms by infection or massive culling. The analyses provide an estimate of the spatial range over which highly pathogenic avian influenza viruses spread between farms, and emphasize that control measures aimed at controlling such outbreaks need to take into account the local density of farms.     

Beta-Arrestin1 Prevents Preeclampsia by Downregulation of Mechanosensitive AT1-B2 Receptor Heteromers

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Resistance and tolerance to mixed nematode infections in chicken genotypes with extremely different growth rates

Fast growing broilers are less able to cope with fitness related challenges. As the allocation of metabolic resources may be traded off between performance and defence functions in parasitized hosts, we hypothesized that fast growing broilers are more sensitive to mixed nematode infections compared with slower growing genotypes under the same environmental conditions. Therefore, we compared male birds of genotypes selected for either meat production (Ross-308, R) or egg production (Lohmann Brown Plus, LB) or for both purposes (Lohmann Dual, LD), to assess their resistance and tolerance to mixed nematode infections with Ascaridia galli and Heterakis gallinarum. While infections reduced feed intake in all three genotypes, feed conversion efficiency was not affected. Infections impaired growth performance only in R birds, indicating lower tolerance in the fast growing genotype compared with slower growing LB and LD genotypes. Impaired tolerance in R birds was associated with a relative nutrient scarcity due to an infection-induced lower feed intake. Resistance to experimentally induced infections depended on host genotype as well as on the worm species involved. Overall, the A. galli burden was higher in R than LB, whereas the burden of LD was not different from that of R and LB. In contrast, the H. gallinarum burden of first generation worms was similar in the three genotypes. Susceptibility to re-infection with H. gallinarum was higher in LB than in LD, whereas very low levels of re-infection were observed in R birds. Our data collectively suggest that resistance and tolerance to mixed nematode infections are sensitive to growth rate in chickens. These differences amongst genotypes may partly be associated with a mismatch between the actual nutrient supply and genotype-specific nutrient requirements.