Intensives Wachstum von Ricciocarpus natans (Lebermoos) in Durchlüftungskultur

Das Lebermoos Ricciocarpus natans wurde nichtaxenisch in Durchlüftungskulturen (etwa 2% CO₂ in Luft) im Lichtthermostaten angezogen und seine morphologischen Merkmale beschrieben. Als optimal für eine hohe Produktivität erwiesen sich bei der verwendeten Nährlösung 29 C, ein Licht-Dunkel-Wechsel von 14:10 Stunden und eine Beleuchtungsstärke von maximal 10000 Lux. Unter diesen Bedingungen ist das Wachstum bei relativ kleinen Schwankungen sehr gleichmäß. Die Verdopplungszeit für Masse und Individuen beträgt 48 Stunden. In eine 300 ml-Kulturröhre wurde 1 g Frischgewicht in 200 ml Nährlösung eingeimpft (Trockengewichtsanteil etwa 4 %). NH₄ (bei Konstanthalten des pH-Wertes) und NO₃ sind als Stickstoffquelle gleich gut geeignet. Bei Mangel an Stickstoff nimmt die Thallusgröße stark ab, die Ventralschuppen werden auffällig lang und violett gefärbt. Das Lebermoos eignet sich gut für eine standardisierte, effektive Laborkultur zum Zwecke physiologischer und biochemischer Untersuchungen.     

The impact of local population genetic background on the spread of the selfish element Medea‐1 in red flour beetles

Selfish genetic elements have been found in the genomes of many species, yet our understanding of their evolutionary dynamics is only partially understood. A number of distinct selfish Medea elements are naturally present in many populations of the red flour beetle (Tribolium castaneum). Although these Medea elements are predicted by models to increase in frequency within populations because any offspring of a Medea‐bearing mother that do not inherit at least one Medea allele will die, experiments demonstrating an increase in a naturally occurring Medea element are lacking. Our survey of the specific Medea element, M¹, in the United States showed that it had a patchy geographic distribution. From the survey, it could not be determined if this distribution was caused by a slow process of M¹ colonization of discrete populations or if some populations lacked M¹ because they had genetic factors conferring resistance to the Medea mechanism. We show that populations with naturally low to intermediate M¹ frequencies likely represent transient states during the process of Medea spread. Furthermore, we find no evidence that genetic factors are excluding M¹ from US populations where the element is not presently found. We also show how a known suppressor of Medea can impair the increase of M¹ in populations and discuss the implications of our findings for pest‐management applications of Medea elements.     

Altered tracheal smooth muscle activities in an animal model of human myotonic dystrophy.

Although the 20,25 Diazacholesterol-treated rat exhibits several pathological changes involving skeletal muscle and other tissues resembling those seen in human myotonic dystrophy patients, this animal has not hitherto been examined as a model for studying smooth muscle involvement in this human disease. Rats were therefore treated chronically with 20, 25-D and comparisons made with control animals of dose-response curves of tracheal strip preparations to carbamylcholine, before and after partial irreversible blockade of cholinergic receptors by Dibenamine. Tracheas from myotonic animals exhibited diminished contractility and an increased ED₅₀. The dissociation constant for the carbamylcholine-cholinergic receptor interaction was decreased and the percentage receptor occupancy for a given contractile response was increased. These results indicate that tracheal smooth muscle function is altered after 20,25-D administration and suggest that such animals may constitute a model for studying smooth muscle function in human myotonic dystrophy.     

Effects of access restrictions and stocking on small water body fisheries in Laos

Four different management regimes were identified in small water bodies in Laos: open-access fisheries, both with and without stocking of exotics (mainly Nile tilapia Oreochromis niloticus ); community fisheries with restricted access and regular stocking; and fisheries rented out to corporate entities, based on indigenous stocks only. These regimes represent all possible combinations of the two management measures, access (open/restricted) and stocking of exotic species (no/yes) and a test fishing experiment assessed their effects on stock abundance, richness and diversity. The combination of access restrictions and stocking had a strong positive effect on total standing stocks. Stocks of indigenous fish were significantly increased by access restrictions, while stocking of exotics had no effect on indigenous standing stocks. Community fisheries targeted large sizes of exotic species while reducing the exploitation of smaller size groups, which accounted for much of the indigenous stocks. This suggests that stocking can promote active effort regulation and reduce the exploitation of natural stocks. Data on yields and effort were too limited to allow the use of inferential statistics, but indicated that community fisheries were exploited with much lower effort and gave lower yields than open access fisheries, while providing higher returns to fishing effort. This suggests that active management is effective in increasing standing stocks and the efficiency of exploitation, but does not necessarily increase yields unless optimal management regimes can be identified and implemented by the management institutions. No significant effects on wild stock richness or diversity were detected in the test fishing experiment, but wide confidence limits indicated a low statistical power of the test and therefore no definitive conclusions could be drawn.