What are elaiosomes for? Effects of elaiosomes on ant attraction, seed removal and germination in wild chaya (Cnidoscolusaconitifolius)

Abstract

Seed dispersal by ants is common in arid lands. The seeds of myrmecochorous plants bears an elaiosome, an appendage that acts as a reward for ants. Once an ant identifies an elaiosome-bearing seed, it carries the diaspore to the nest, removes the elaiosome and discards the seed. During elaiosome removal, ants also scarify the seed, which may favor seed germination or facilitate pathogen attack. Some elaiosomes are hygroscopic and therefore, this could increase water intake and retention. We assessed the effect of elaiosome removal, seed scarification and fungal infection on germination in Cnidoscolus aconitifolius, a plant species common in the arid tropics of the Americas. The effects of elaiosome removal on ant attraction and seed removal were also assessed. According to the results, the elaiosome of C. aconitifolius increases the attractiveness of its seeds to ants, but did not affect seed removal or seed germination. Also, the elaiosome significantly increased the chance of pathogen attack on the seed. The benefits of elaiosome removal on seed germination were mediated by physical scarification, with greater germination in scarified seeds without elaiosomes. Seed scarification did not affect the likelihood of fungal attack.