The response to disturbance chemicals and predator odours of juvenile and adult signal crayfish Pacifastacus leniusculus (Dana)

Many species of crayfish have been shown to use disturbance chemicals to detect the presence of predators and other dangers, yet there have been no investigations in adults or juveniles of Pacifastacus leniusculus, a key species, particularly for invasive species study. Juveniles and adults were exposed to conditioned water from stressed and damaged conspecific males. Both responded to these odours, but did not respond to water from stressed or damaged males with blocked nephropores. Urine from stressed and damaged males also elicited a significant response, which was much stronger than that of conditioned water. Odours from urine and water of damaged individuals induced a greater response than stress odours. We propose that chemicals released by stressed or damaged Pa. leniusculus are the same substance, but quantities released in the urine vary in context-specific circumstances. Predator-odour conditioned water from Perca fluviatilis elicited no response, but conditioned Anguilla anguilla water stimulated significant responses in juveniles and adults. Juveniles exhibited the strongest responses to all odours. These results show that Pa. leniusculus utilises both conspecific and heterospecific sources of info-chemicals to assess risk in the environment, which may contribute to its success as an invasive species and give it a competitive advantage.     

The conversion of S-adenosyl-l-methionine to stipitatic acid by extracts of Penicillium stipitatum

Cell-free extracts prepared from acetone powders of Penicillium stipitatum contain an enzyme system converting [¹⁴CH₃]-S-adenosyl-l-methionine to radioactive stipitatic acid; the estimated molecular weight is 105 000. The incorporated radio-activity is located at C-7 of the tropolone ring. Addition of putative acceptor compounds had little or no influence on tropolone synthesis. Methylation appears to be an early step in tropolone biosynthesis in this organism.     

Discontinuite ecologique et zooplancton (copepodes) en Manche Orientale

In the Dover Strait, coastal waters hug the French coast andthe mixing with open sea waters is relatively limited. A realdiscontinuity has been observed during a cruise between Boulogne-sur-merand Dover (15.10.85). The analysis of zooplankton reveals theexistence of two different populations of Copepoda. Coastalpopulation of Temora longicornis is only comprised of largeadults. In open sea waters, the adults, which are smaller, areless than 55% of the population. The development stage differenceshows that the discontinuity has been established several weeksago. This discontinuity, born in the western Channel, has beenretained during the general flow of water masses to the Straitof Dover. But analysis shows that there is a planktonic transfer,principally from coastal to open sea waters.