Sex pheromones in marine polychaetes: Volatile organic substances (VOS) isolated from Arenicola marina

Volatile organic substances (VOS) were extracted from the coelomic fluid of gravid specimens of the lugworm Arenicola marina through the use of using a closed loop stripping technique and analysed via coupled gas chromatography-mass spectroscopy. VOS detectable in coelomic fluid of mature specimens include aldehydes, n-alkanes, methyl-alkanes, terpenes and ketones. The bouquet of compounds is very similar to nereid volatiles that have been recently described as having sex pheromonal activity. One of the major constituents is the ketone 5-methyl-3-heptanone, the sex pheromone of Platynereis dumerilii and Nereis succinea. Behavioural bioassays with gravid specimens produced no evidence that this substance has any pheromonal function in A. marina. Samples taken at monthly intervals showed an increase in the content of VOS in the coelomic fluid of both sexes during maturation with 1 major peak, 2-ethyl-hexanol, representing up to 50 % of the total amount of VOS in spawning male lugworms. Behavioural assays with ripe females established the existence of a chemical cue inducing the burrow irrigation behaviour during which sea water is pumped through the burrows. This behaviour ensures transport of spermatozoa from the water column into the tube inhabited by the female and increases fertilization success by minimising the dilution effects of the incoming tide. The VOS extract obtained from male spawning water had biological activity in eliciting the 'pumping' behaviour in females, with 16 of 24 worms irrigating continuously upon exposure, whilst controls showed no increase of activity, with 'pumping' occurring at 30 to 40 min intervals.