Browsing by Subject "Eierstock"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Publication Geschlechtsspezifische Unterschiede in der Fötalentwicklung beim Schwein(2007) Häußler, Susanne; Claus, RolfBasic mechanisms of sexual differentiation in higher mammals are well established. The development of the testes is controlled by genetic mechanisms and initiated by the Y-chromosome. Further differentiation of the ?Anlagen? is performed by the presence of testicular androgens but requires no specific signal in females (basic femaleness). Speculation exists during the fetal development of pigs, because androgens are also measurable in female fetuses. In addition, the male gonad is able to synthesize remarkably high levels of estrogens. The aim of the present study was to follow up concentrations of steroids in peripheral plasma throughout fetal development, starting with week 6, and in particular to analyze changes in testicular cell populations (spermatogonia, Leydig cells) and to correlate them with testicular androgens, estrogens, 19-nortestosterone and cortisol. The expression of steroid converting enzymes such as 11beta-HSD 2 and aromatase as well as receptors were determined by immunocytochemistry and quantitative PCR. Altogether each of the stages of gestation (weeks 6, 10, 13, and 15 of pregnancy) was represented by 4 sows, so that a total of 158 fetuses were collected. Testicular steroid synthesis (testosterone, estradiol) could be demonstrated as early as week 6, but was independant of gonadotropine. 19-nortestosterone, which is formed during estrogen synthesis, was detected in amniotic fluid using a new established enzymeimmunoassay in this study. Aromatase activity clearly correlated with a wave-like pattern of cell development. Therefore the activity was elevated both during an alternating rise of Leydig cells or spermatogonia mitosis. During the rise of spermatogonia development Leydig cells remained quiescent and during the Leydig cell mitosis spermatogonia remained inactive. An increased aromatase activity was observed both during the rise of spermatogonia and Leydig cell mitosis, and in consequence an elevated concentration of estradiol was found. But during an increased Leydig cell formation aromatase expression and thus estradiol synthesis was taken over by spermatogonia. It is therefore reasonable to resume that estrogens are important mitogenic signals as it was also found earlier in mature boars. The expression of glucocorticoid receptors by spermatogonia could be demonstrated for the first time in fetal pig testes. As also shown for other tissues, its likely role in testes is the differentiation of new cells. This important role also explains the expression of the enzyme 11beta-HSD 2 both by Leydig cells and spermatogonia. This enzyme is a well known fine-tuning mechanism which indicates cortisol and thus the ligand for the glucocorticoid receptor. Its expression in parallel to the rise of estrogens suggests a dependancy on estrogens. Investigating this was, however, not the topic of the present study. The demonstration of androgens both in blood plasma and amniotic fluid in female fetuses seems to contradict the principle of basic femaleness. It was shown however, that concentrations of testosterone in males increase up to 2.01 ng/ml plasma during the main period of sexual differentiation whereas female levels remain at 0.2 ng/ml so that it is simply the concentration which decides where the male differentiation does occur. It can not be ruled out, however, that low concentrations in female fetuses may have an effect on follicular differentiation, as was also demonstrated in mature sows. At the same time androgens could have a mitotic effect caused by insulin-like growth factors (IGF I + II). Thus the present investigation was able to clarify of several new mechanisms and basic data of fetal pig development. Further confirmation of the mechanisms suspected in this study may be served by an aromatase inhibitor.Publication Overwintering and reproduction biology of Drosophila suzukii Matsumura (Diptera: Drosophilidae)(2018) Zerulla, Florian Niklas; Zebitz, Claus P. W.Drosophila suzukii (Matsumura) was introduced to southern Europe and the United States of America in 2008 through fruit imports from Southeast Asia and spread in the following years all over Europe, as well as South and North America. D. suzukii is a polyphagous pest which infests fruits of soft-skinned wild and cultivated plants. In contrast to the well-known D. melanogaster, healthy and ripe fruits are preferred. The infestation is caused by female D. suzukii who damage the fruit skin to deposit eggs underneath with the help of their serrated ovipositor. The feeding of hatching larvae and secondary infections, which can easily penetrate through the damaged fruit, can lead to complete yield losses. A short reproductive period, a large range of host plants and infestation of the fruits, shortly before harvesting makes it extremely difficult to control the pest. Due to comparatively late infestation, the possible period of application during ripening and harvesting is limited. The same applies to the frequency of application of insecticides at this time. Possible residues on the harvested products also carry the risk of rejection of the fruit on the market. Furthermore, an incomplete knowledge of the biology, especially overwintering biology under European environmental conditions makes an effective control of this invasive pest extremely difficult. Therefore, the main research topics are the induction and refraction of the postulated diapause, the detection of any possible hibernation sites and the influence of temperature on the oviposition behaviour of D. suzukii. Based on field experiments it could be shown that successful wintering could probably only take place in forest areas. After freezing, the forest was the only place where D. suzukii could resume its flight activity at warmer temperatures. It has also been confirmed that female flies are more resistant to temperatures below freezing than male flies. Accordingly, after a frost period, hardly any male D. suzukii were caught in bait traps. Similar results have also been obtained in laboratory tests, showing that D. suzukii adapted to low temperatures and shortday conditions had lower temperature preferences and a decreased mortality after changing environmental conditions. It can therefore be assumed that overwintering D. suzukii can spread better in spring due to a lower temperature preference and a higher physical activity under cold environmental conditions than flies without adaptation to winter conditions. Bait traps were also used to determine the developmental status of the ovaries by dissecting the abdomens of weekly captured D. suzukii. This enabled a correlation between microclimatic conditions of individual habitats and the reproductive status of females to be established. In winter, the majority of female D. suzukii had “immature ovaries”, whereas in the summer most females had “mature eggs” in their abdomen. For this reason, it can be assumed that D. suzukii entered a reproductive diapause, which is apparently influenced by winter climatic conditions, nutritional status and the availability of food. In addition, it was found that the developmental status of ovaries correlates positively with oviposition. Laboratory tests were carried out to determine the highest number of egg depositions at 20 °C. Most females with “mature eggs” were also documented under these simulated conditions. We detected that the preferred surface temperature for egg depositing was very similar to the preferred ambient temperature of D. suzukii. Most of the eggs were deposited on fruits with a surface temperature of 22 °C. At this temperature, the highest net reproductive rate and intrinsic rate of population increase was found, too. Temperatures below 15 °C and above 35 °C were not preferred, which represented the thresholds for a successful development of D. suzukii. Temperatures between 10 and 15 °C and shortday conditions were the most important key stimuli for entering the reproductive diapause. Therefore, temperature had a stronger influence on oviposition behaviour than daylength. A complete disruption of diapause occurred at higher temperatures (20 °C) and longday conditions after 72 hours. The data presented in this work on the possibility of adapting D. suzukii to environmental conditions and key temperatures, which influence the development of ovaries and egg deposition, can provide an important contribution to the development of prediction and population dynamics models and can be used for long-term control strategies against D. suzukii. According to current knowledge and observations, overwintering is obviously a critical period for the survival of the populations. Therefore, the characterisation and identification of additional hibernation sites is of great importance. There, a targeted and environmentally friendly control of D. suzukii populations could be particularly efficient.