Geographic variations in seed dispersal by ants: are plant and seed traits decisive?

Abstract

The effect of local ant species on the dispersal success of a myrmecochorous plant, Helleborus foetidus, was analyzed in two populations of the Iberian Peninsula (Caurel and Cazorla, respectively). The contribution of the various local ant species to dispersal was very unequal. While 5 and 19 ant taxa visited the plants of Caurel and Cazorla, respectively, most removal activity (67 and 80%) was performed by two species only (Formica lugubris and Camponotus cruentatus, respectively). Visits by dispersers were also unequally distributed between neighboring plants. While some plants were always visited during the period of seed release, others were never visited. A regression model indicated that this pattern might be explained by two plant traits: ants preferred to visit plants that released more seeds and whose elaiosomes were richer in oleic acid. Although it has long been known that this compound triggers removal by ants, it is the first demonstration that quantitative variations in elaiosome traits contribute to variation in dispersal success. Finally, other variables being equal, morphological traits (seed size, elaiosome size, and elaiosome/seed size ratio) did not affect ant behavior. Although myrmecochory has long been considered a diffuse interaction, our results support the idea that, at local scale, a limited number of ant species may be decisive to its evolution.

Signals Can Trump Rewards in Attracting Seed-Dispersing Ants

“…The foraging decicions of A. rudis may only be responsive to a wider range of seed or elaiosome sizes. Other studies have also found that size does not completely predict removal [46], [47].…”

Spatial variation in the fatty acid composition of elaiosomes in an ant-dispersed plant: Differences within and between individuals and populations

“…Nevertheless, variation in the relative concentration of fatty acids between individuals may have important ecological consequences, like has recently been proposed for Helleborus foetidus. In that plant species, Boulay et al (2007) found that the frequency of visits to plants by ant dispersers (and consequently seed removal) was highly correlated with interindividual differences in oleic acid content of elaiosomes. Thus, the chemical composition of elaiosomes seems to be under strong selection by ants and may indirectly play an important role in determining local plant demography.…”

“…Among lipids, fatty acids are major components of elaiosomes and a few of these compounds (e.g., oleic or oleyl-based glycerides) have been identified as mainly responsible for elaiosome attractiveness by ants (Brew et al, 1989;Marshall et al, 1979;Skidmore and Heithaus, 1988). Consequently, some studies have focused in assessing the fatty acid composition of elaiosomes of a plant species, occasionally drawing interspecific comparisons on fatty acid profiles (Lanza et al, 1992;Mackay and Whalen, 1998;Pfeiffer et al, 2010;Soukup and Holman, 1987), but only a few of them have assessed the effects of natural variation in the fatty acid profile within species (Boulay et al, 2006(Boulay et al, , 2007.…”

Niemann–Pick type C2 protein mediating chemical communication in the worker ant

“…The internal organs are rich in long-chain fatty acids derived from triglycerides and cholesterol. Fatty acids that are derived from seed elaiosomes are also used as rewards and/or semiochemicals that help trigger seed-dispersal behavior of ants (26,27). These behaviors indicate that ant antennae are able to detect fatty acids.…”