Chemical differences between seeds and elaiosomes indicate an adaptation to nutritional needs of ants

Abstract

Ant-dispersed plants usually produce seeds with appendages (elaiosomes) as reward for ants. Plants that produce high-quality elaiosomes benefit because ants preferentially disperse their diaspores. We therefore hypothesized that seeds and elaiosomes differ in chemical composition in ways that make elaiosomes of high nutritional quality for ants, capable of providing essential dietary components that explain the increased fitness and higher gyne production documented for colonies with elaiosome consumption. To test the hypothesis we analysed the content and composition of lipids, amino acids, soluble carbohydrates, proteins and starch in seeds and elaiosomes of 15 central European ant-dispersed plants. After separating the different fractions, total lipids were determined gravimetrically, fatty acids and soluble carbohydrates were detected by gas chromatography (GC) and GC-mass spectrometry, free amino acids by an amino acid analyser while starch and protein were analysed photometrically. Seeds accumulated high molecular weight compounds such as proteins and starch, whereas elaiosomes accumulated more easily digestible low molecular weight compounds such as amino acids and monosaccharides. Analysis of similarities and similarity percentages analysis demonstrated that the composition of fatty acids, free amino acids and carbohydrates differed markedly between elaiosomes and seeds. The most important difference was in total amino acid content, which was on average 7.5 times higher in elaiosomes than in seeds. The difference was especially marked for the nitrogen-rich amino acid histidine. The availability of essential nutrients and, in some species, the higher nitrogen content in elaiosomes suggest that their nutritional value for larvae plays a key role in this interaction.

Egg Dispersal in the Phasmatodea: Convergence in Chemical Signaling Strategies Between Plants and Animals?

“…Seed elaiosomes contain large amounts of fatty acids that are an important food resource for ants (Fischer et al 2008). These fatty acids often are present in elaiosomes as lipid species rather than free fatty acids.…”

Dispersal of non-myrmecochorous plants by a “keystone disperser” ant in a Mediterranean habitat reveals asymmetric interdependence

“…Studies of seed dispersal by ants have paid much attention to true myrmecochory. Myrmecochory sensu stricto generally refers to the dispersal of seeds bearing a lipid and nutrient-rich elaiosome (Brew et al, 1989;Hughes et al, 1994;Boulay et al, 2006;Fischer et al, 2008;Pfeiffer et al, 2010). This appendage elicits ants to transport the elaiosomebearing diaspores back to their nest.…”

Testing the directed dispersal hypothesis: are native ant mounds (Formica sp.) favorable microhabitats for an invasive plant?

“…Elaiosomes are a nutrient-rich resource (Fischer et al 2008) that provides fat and protein to ants (Pemberton 1988) and may ultimately inXuence ant colony growth and development (Morales and Heithaus 1998;Bono and Heithaus 2002). Ants also abundantly visit nectar glands located near the Xowers of E. esula (M. Berg-Binder, personal observations).…”

“…Occurring in over 11,000 plant species in at least 77 families (Lengyel et al 2009), myrmecochores typically produce seeds with a lipid-rich structure (elaiosome) that serves as a nutrient-rich food source for ants (Fischer et al 2008). Ants can serve as secondary seed dispersers (e.g., Beaumont et al 2009), collecting seeds on the ground and moving them away from the parent plant.…”