Secondary seed dispersal by ants of Ricinus communis (Euphorbiaceae) in the Atlantic forest in southeastern Brazil: Influence on seed germination

Abstract

Some seeds rely on fleshy lipid-rich appendages as attractants to ants. By carrying those seeds to their nest, ants play a major role as seed dispersers and can provide suitable conditions for seed germination. Ricinus communis (the commonly known castor) seeds are primarily dispersed by autochory but probably present secondary dispersal by ants, once they bear a lipid-rich elaiosome. The following questions were addressed: (1) are ants legitimate dispersers of castor seeds?; (2) which ant species interact with the seeds?; and (3) is germination success higher in a predicted scenario met by seeds discarded from ant nest? We compared the removal of seeds with and without elaiosome and we determined which ant species interact with castor seeds and whether there was seed predation by ants. We performed experiments under controlled conditions to evaluate seed germination responses to light, temperature and elaiosome. Seeds with elaiosome were removed preferentially and no predation was found, indicating that ants are legitimate seed dispersers. A large coterie of ants (20 species) interacts with castor seeds, especially Myrmicinae species. Elaiosome removal enhanced germination success, as well as alternated temperatures and absence of light. Such conditions are a mixture of two of the three scenarios we assumed for castor seed germination, and are met by seeds discarded from ant nest, but covered by a thin layer of litter, or eventually abandoned inside the nest, but in shallow depths. Therefore, by discarding seeds without elaiosome on the pile mound, ants may submit castor seeds to conditions that enhance germination.