Carabid beetle community composition, body size, and fluctuating asymmetry along an urban-rural gradient

Within the goal of defining indicators (species or combinations of life history traits) for habitat quality in an urban environment we investigated effects of urbanization on the community composition and morphological characteristics of carabid beetles. Between May and July 2000 nine woodlots were sampled along three axes representing urban - rural gradients from the centre of the city of Hamburg to its rural borders. Species richness decreased towards the city centre and with increasing isolation of the sites but was uncorrelated with the size of the site. Species assemblages were highly nested making successive loss of species predictable. Responsivness towards urbanization could not be linked to specific life history traits. Body length of one species (Carabus nemoralis) declined towards the city centre. Four species were found at all sites. These four species showed differences in fluctuating asymmetry (FA) at the different sites that could not be interpreted as an indication of responses to habitat suitability. FA of the remaining species (species negatively affected by urbanization) increased towards the city centre and with increasing isolation of a site. This matched the prediction that FA indicates habitat quality. Thus, urban effects lead to changes of communities through a predictable loss of species, to a reduction in body size in one species, and to increased FA in species which are susceptible to urbanization. The results indicate that the different sites were islands in an urban matrix rather than parts of a green network which would allow free exchange of plants and animals within the city of Hamburg.Wir untersuchten den Einfluss von Verstädterung auf Laufkäfergemeinschaften in Hamburg, Deutschland. Zwischen Mai und Juli 2000 wurden neun Fangorte entlang städtischer Gradienten beprobt. die von relativ ländlichen Gebieten an den Stadtgrenzen, bis hin zu Flächen im Stadtzentrum reichten. Die Artenzahl korrelierte negativ mit dem Grad der Isolierung und der Entfernung des Gebietes von der Peripherie, aber nicht mit der Größe eines Gebietes. Die gefundenen Artengemeinschaften wiesen strenge Schachtelung auf. Der Verlust bestimmter Arten war daher vorhersagbar, konnte aber nicht auf bestimmte Charakteristika (“life history traits”) der Arten zurückgeführt werden. Die Körperlänge von Carabus nemoralis nahm entlang des Gradienten ab. Nur vier Arten kamen im gesamten Stadtgebiet vor. Fluktuierende Asymmetrien (FA) dieser Arten konnten nicht sinnvoll mit Habitatqualitäten oder Verstädterung in Beziehung gesetzt werden. Die anderen Arten, die nach den Ergebnissen der Analysen zu geschachtelten Strukturen durch “Verstädterung” negativ beeinflusst waren (d.h. nicht an allen Orten und vor allem nicht im Stadtzentrum gefunden worden waren) zeigten zunehmende FA zum Stadtzentrum. Verstädterung führte demnach zu vorhersagbaren Verlust an Arten, zu Reduktion der Körperlänge einer Art und zu erhöhten Asymmetrien bei Arten, die durch Verstädterung negativ beeinflusst wurden. Nach diesen Befunden kann das Ziel der offiziellen Politik, in Hamburg negative Effekte der Stadtentwicklung auf die Biodiversität durch einen Verbund von Grünflächen und geschützten Gebieten zu reduzieren, mit den heute noch verfügbaren Flächen nicht erreicht werden.     

Effects of heliotropic movements of flowers of Dryas octopetala L. on gynoecium temperature and seed development

Dryas octopetala has heliotropic flowers, whose petals reflect the light on the pistils, thus warming them up. The effects of this reflection on seed formation and development were studied by measuring the pistil temperature of intact flowers, of flowers with petals removed, of shaded flowers, and of flowers constrained in such a way as always to be directed towards the zenith. In August, the seeds of these flowers were collected, counted and weighed. The temperature differences between the differently treated flowers were greates about noon, the flowers ranking as follows in ascending order of temperature: shaded flowers, flowers without petals, constrained flowers and intact flowers. The mean temperature differences between the gynoecia and the air, in degrees Celsius, were: 1.1, 1.8, 2.5 and 3.2, respectively. The same ranking was obtained for the different treatments, when arranged in order of ascending weight per seed, except that the positions of the shaded flowers and the flowers without petals were interchanged. The mean values of the weight per seed in milligrams were: 0.42, 0.48, 0.53 and 0.61 for the groups flowers without petals, shaded flowers, constrained flowers and intact flowers, respectively.     

Acetylarsenocholine: A Cholinergic Agonist

Abstract: The pharmacological properties of acetylarsenocholine, an arsenic analogue of acetylcholine, were investigated. Acetylarsenocholine behaved as a cholinergic ligand both in the central and peripheral nervous system. It bound to nicotinic receptors in rat medulla-pons with a K _D of 15 μ M and to muscarinic receptors in rat cerebral cortex with a K _D of 10 μ M . It behaved also as an agonist at presynaptic muscarinic receptors in guinea pig ileum myenteric plexus preparation. Arsenocholine is an alternative substrate for choline acetyltransferase and acetylarsenocholine is an alternative substrate for acetylcholinesterase.