Chemical ecology of predator-prey interactions in ctenophores

Two species of ctenophores coexist in the north-east Atlantic, one (Bolinopsis infundibulum) forages on crustaceans, while the other (Beroe; cucumis) feeds exclusively on the former. Some introductory aspects on the chemical ecology of this predator-prey relationship are reported here. In laboratory experiments, Bolinopsis demonstrated an escape response to mechanical stimuli directed towards the frontal lobes, as well as to direct attack from the predator. Chemical stimuli, in the form of water conditioned by the predator, or extract of homogenised conspecifics, gave no detectable responses. This suggests that chemically mediated predator-induced responses, as well as fright reactions induced by alarm signals, are absent in Bolinopsis. On the other hand, a detectable increase in search behaviour of Beroe, measured as an increase in swimming activity, was observed after both stimulation with water conditioned by Bolinopsis and stimulation with extracts of homogenised specimens of the prey. Beroe turns towards mechanical stimuli on the sides of the body, such as that initiated by the wake of a passing prey, as demonstrated by weak water jets from pipettes. A turn towards prey mostly caused the ''lips'' to make direct contact, which initiated a rapid feeding response in which of the mouth opened and the prey was ingested. There was no mouth extension following contact with glass pipettes whereas mouth extension occured on the wall of a glass beaker when tissue from Bolinopsis was present, which confirms the importance of chemical contact stimuli in the final stage of prey selection.