Inducible defences in daphinia depend on latent alarm signals from conspecific rey activated in predators

摘要

Some water fleas (Daphnia spp.) undergo phenotypic changes when exposed to chemical signals from predators.The chemical signals have been assumed to be of predator origin (i.e.kairomones),since juices of crushed Daphnia have been found ineffective.We speculated that latent alarm signals could be present in Daphnia,to be activated in predators following ingestion.Accordingly,fish predators were fed earthworms for 10 weeks to remove Daphnia remains from their gastrointestinal tracts.Following another 6 days of earthworm feeding,water conditioned by fish induced no morphological changes in D.galeata.When fish were alternatively fed Daphnia for 6 days,changes were induced with fish-conditioned water.Extracts made from intestines of earthworm-fed fish,homogenized with earthworms,gave no morphological canges,but intestines of the same origin homogenized with Daphnia did.Similar results were found when earthworms and Daphnia were homogenized with fish liver.Freshly frozen extracts of homogenized Daphnia no detectable changes at first instar stage in test animals,whereas extracts of Daphnia that had been kept at room temperature did induce such changes.Our rsults suggest that Daphnia respond to latent conspecfic alarm signals that are activated by intestinal or bacterial enzymes in predators or in the water.