Mercurialis annua L. (Euphorbiaceae) seed interactions with the ant Messor structor (Latr.), hymenoptera: Formicidae

Mercurialis annua seeds are shed all year round. In the period early April to mid October they are actively collected by Messor structor. This ant transports the seeds to the nest and removes a seed appendage containing lipid and protein reserves known as caruncle. After this ‘manipulation’ the seeds are able to germinate but they are deposited in small chambers inside the ant nest where they are prevented from germinating. They germinate if experimentally removed from the nest or if disturbed by man or animals. During the experiments the seeds germinated after being washed in running water for 24 h or if the caruncle was physically removed. The seeds of this plant species thus have two ways of terminating dormancy. Ants remove both the mechanical and the chemical inhibitor, water only removes the chemical one.