Lipid cues for seed-carrying by ants inHepatica americana.

We investigated the chemical basis for ants carrying the seeds ofHepatica americana, an ant-dispersed plant of eastern North America. A laboratory bioassay of seed and elaiosome extracts was based on the distance test items were carried byPogonomyrmex rugosus. Ants responded equally to isolated elaiosomes and to the diglyceride fraction. Diolein was a major component of the diglyceride fraction, which is consistent with a finding that 1,2-diolein releases seed-carrying byAphaenogaster rudis. Ants' response to the free fatty acid fraction was less intense. Gas chromatography of the fatty acid fraction indicated that oleic acid was a primary component, and oleic acid is known to elicit necrophoric behavior. No evidence supports an earlier suggestion that ricinoleic acid stimulates seed-carrying behavior. Ants failed to respond to seeds from which elaiosomes were removed.