PARENT SESSION
Oral Session 67: Mutualism - Parasitism III: Ants.
Presiding: K Mooney
Wednesday, August 4, 8:00 AM to 11:30 AM, Meeting Room D 135.

Fatty acid composition of seeds and elaiosome in three species of Datura.

Marussich, Wendy^*,1, ¹ wendy.marussich@asu.edu, Tempe, AZ, USA

ABSTRACT- Myrmecochory, or mutualistic seed dispersal by ants, is characterized by the presence of a lipid- and protein-rich appendage, or elaiosome, on the seed. The elaiosome is attractive to the ants, while the seed is not. Ants readily gather the seeds, carry them back to the nest, consume the elaiosome, and discard the seed unharmed either in the nest or on a refuse pile. The plants are thought to benefit from effective dispersal away from the parent plant, protection from seed predators, a reduction in seedling competition, protection from fire, or transportation to nutrient-rich microsites. The specific benefits to ants are not well understood, but are thought to be nutritional, as ants require dietary sources of lipids. However, some elaiosomes contain fatty acids that are known to induce corpse- and brood-carrying behaviors in ants (e.g., oleic acid). Thus, plants may be cheating by using behavior-inducing chemicals instead of nutritional rewards to induce ant-dispersal. I extracted fatty acids from the seeds and elaiosomes of three species of Datura (D. wrightii, D. discolor, and D. quercifolia) using gas chromatography and mass spectrophotometry, and calculated the relative proportions of each fatty acid. Both seeds and elaiosomes contained oleic acid, but seeds contained more oleic acid than elaiosomes (33% vs. 11%). The fatty acid composition of Datura seeds was similar across species (means: 46% linoleic, 33% oleic, 16% palmitic, 3% stearic), but Datura elaiosomes varied both within and between species. As oleic acid can induce carrying behaviors in ants, its presence in Datura seeds and elaiosomes may be a form of cheating.

Key words: myrmecochory, seed chemistry, Datura, fatty acids