Licht- und elektronenmikroskopische Untersuchungen an den Eihüllen der Elritze (Phoxinus phoxinus [L.];Teleostei,Cyprinidae)

Zusammenfassung Die Oocyten der ElritzePhoxinus phoxinus wurden licht- und elektronenmikroskopisch untersucht. Sie sind im Stadium I nur von der primären Oocytenmembran umgeben, die Mikrovilli zum Follikelepithel hin aussendet. Die Bildung der eigentlichen Eihülle, des Cortex radiatus, beginnt im frühen Stadium II. Der Cortex radiatus differenziert sich bald in den Cortex radiatus externus und den Cortex radiatus internus, wobei der Externus vor dem Internus angelegt wird. Die Differenzierung der Cortex-Schichten ist gegen Ende des Stadiums III abgeschlossen. Aussehen und Aufbau des Cortex radiatus externus der Elritze weichen stark von dem bisher bei anderen Cypriniden-Eizellen gefundenen Schema ab. DiePhoxinus-Eihüllen gleichen mehr denen von Salmoniden. Die Bildung der Rindenvakuolen erfolgt in einfacher Schicht überall gleichzeitig in den Eizellen unterhalb der primären Oocytenmembran. Sie breiten sich zentripetal aus. Die Rindenvakuolen entstehen beiPhoxinus phoxinus wahrscheinlich größtenteils durch Verschmelzung von Vesikeln.

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Light and electron microscopic studies of the envelopes in egg cells of the minnow (Phoxinus phoxinus [L.];Teleostei, Cyprinidae)

Summary The oocytes of the minnowPhoxinus phoxinus were examined by light and electron microscopy. In stage I they are only enveloped by the primary oocyte membrane which extends microvilli towards the follicle epithelium. The development of the actual egg envelope, the cortex radiatus, starts early in stage II. The cortex radiatus differentiates soon into the cortex radiatus externus and the cortex radiatus internus. In the course of this development the externus is formed earlier than the internus. The differentiation of the cortex layers is finished about the end of stage III. The exterior and the structur of the cortex radiatus externus of the minnow differs widely from the scheme found at other cyprinid oocytes. ThePhoxinus egg envelopes resemble more those of salmonids. The development of the cortical alveoli takes place simultaneously in the oocytes beyond the primary oocyte membrane. They expand centripetally. The cortical alveoli ofPhoxinus phoxinus probably derive for the most part from fusion of vesicles.

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Herrn Prof. Dr. Dr. h. c. W. E.Ankel zu seinem 80. Geburtstag gewidmet.     

Clutch size and the rejection of parasitic eggs: a comparative test of the maternal investment hypothesis

Evolutionary Ecology - Obligate brood parasitic birds lay their eggs in the nests of other species, reducing the host’s own reproductive output. To circumvent these fitness costs,...     

Adding depth to line artwork by digital stippling—a step-by-step guide to the method

Vector-based software has revolutionized scientific illustrating and is well established in taxonomy. However, simple line drawings lack depth information. Shading techniques, such as stippling—the application of dots to generate shade—are the methods of choice for simulating shade, structure, shape, and texture. In this paper, a step-by-step guide for digital stippling is presented. Manual stippling offers great flexibility to achieve highly realistic results. A round brush is applied to the line art by tapping. To drastically reduce time consumption and generate homogeneous tinges, a semiautomation was developed: the smallest units of symmetric stippling patterns are stored in a brush library. Using macroinstructions (macros), such stored raw patterns are converted into symmetric repetitive patterns. This way, stippling can be applied quickly and evenly across large areas of the underlying line drawing. These methods come with all the advantages of vector illustrations, such as high scalability, reproducibility and easy correction of strokes that have turned out imperfect.     

Protonische Halbleiter

Ohne Zusammenfassung     

Intermittent breeding is associated with breeding group turnover in a cooperatively breeding bird

Oecologia - Intermittent breeding, in which an adult skips a breeding opportunity, can represent a non-adaptive constraint or an adaptive response to the tradeoff between current and future...     

Effect of culture medium composition on pheromone receptor levels in Achlya ambisexualis

Sexual reproduction in the eukaryotic fungi Achlya is controlled by two steroid pheromones. Antheridiol is the steroid released by female cells that induces male sexual differentiation. The antheridiol-induced response of male cells has been shown to be influenced by the composition of the culture medium. The present study was designed to determine if the composition of the culture media might also affect the levels of antheridiol binding protein in the cytosol of male cells. The mycelial content of cytosolic steroid pheromone binding sites in Achlya ambisexualis E87 males was measured at daily intervals during 6 days of suspension culture in media containing different nitrogen sources. Levels of binding sits increased during the first 2 days in culture to a plateau that was maintained for the next 2-3 days. During the first 3 days in culture, levels were much lower in mycelia cultured in an enriched medium containing lactalbumin hydrolysate compared to mycelia cultured in defined media containing glutamic acid as the nitrogen source. The level of binding sites increased rapidly when mycelia were transferred from an enriched medium to a nutrient-free salt solution and decreased when mycelia were transferred from a defined to an enriched medium. The relative differences in cytosolic binding measured by in vitro radioligand saturation analysis were confirmed by in vivo uptake studies. It is concluded that the mycelial content of antheridiol binding sites can be experimentally manipulated by variations in the composition of the culture medium and/or the time period of incubation in the medium.     

Micropyle of some salmonins and coregonins

Synopsis The micropyle of seven salmonins and four coregonins were examined by a scanning electron microscope. In addition, the micropyle of Coregonus pidschian is described for the first time. The micropyles and the surface pattern may be used for identification of eggs. The studied micropyle belongs to two different types: 1. micropyle with flat pit and long canal (type II) and 2. micropyle with canal but without pit (type III). The sides of the micropyle canal are often reinforced by annular or helicoid thickening.