Factors affecting seed preference among Old World harvester ants of the genus Messor

Abstract

Abundant literature references suggest that seeds, in order to increase their dispersal capacity, developed elaiosomes in order to attract the ants (myrmecochory). Ants have even been reported to consume the elaiosomes only and to carry the remaining seeds out of the nest. Under standard laboratory conditions, foragers of Messor semirufus—a seed-harvesting ant species—do not discriminate between seeds of a myrmecochorous plant (Luzula multiflora) with elaiosomes and seeds from which the elaiosomes have been artificially removed. If confronted with an equal mass of seeds or of elaiosomes only, the ants regularly prefer the seeds. Elaiosomes glued to very light (≤ 5 mg), artificial seeds (styrofoam spheres coated with flour), elicited no transport into the nest among the ants. The same artificial seeds without elaiosomes but loaded with a 50 mg lead weight elicited a strong transport reaction. To explain these results, the following evolutionary steps are suggested: (1) Plant production of seeds with appendages containing food reserves in order to attract the ants. (2) Ant species broadening their alimentary spectrum to whole seeds and specializing essentially on this diet. (3) Ant ability to colonize xeric areas where seeds represent the main source of food. (4) Plant advantage to have a proportion of their seeds stored at great depths in the soil of desert habitats and the redundancy of the nutrient appendages on the seeds.