Seed Elaiosome Mediates Dispersal by Ants and Impacts Germination in Ricinus communis

Abstract

Myrmecochory is the ant-mediated secondary dispersal of seeds that depends on the presence of a lipid-rich seed appendage known as "elaiosome." Attractive cues of elaiosomes that drive such an interaction and benefits to the plant are not clearly understood. Here, using Ricinus communis, we establish reward compositions and determine the benefits of myrmecochory to the plant. We also compare elaiosome compositions across ecotypes. Our results show that the elaiosome is essential for seed displacement and olfactory cues are important attractive cues. Nonanal and 2-decenal were found to be the major attractive volatiles in the castor elaiosome. Different ant species showed different behaviors toward elaiosome-bearing seeds. Among them, Pheidole grayi was efficient in dispersal but did not disperse all seed ecotypes tested. Major differences in fatty acid levels were observed between ecotypes. To determine the benefits of myrmecochory, germination rates before and after removal of elaiosome were studied. Seed germination improved upon elaiosome removal and aqueous elaiosome extract inhibited germination indicating water-soluble inhibitory factors. Further, ant nest sites were richer in nitrogen than control sites, revealing a clear benefit of seed displacement. In summary, we demonstrate the ecological significance of the seed elaiosomes in the absence of nutritive rewards for seed dispersers.

Switching roles from antagonist to mutualist: a harvester ant as a key seed disperser of a myrmecochorous plant

“…In conclusion, we have demonstrated that the harvester ant P. naegelii is a key disperser of the seeds of M. serrulata, and this can be attributed to two universal traits of myrmecochorus seeds -the presence of an elaiosome for attracting ants and facilitating seed transport (Sasidharan & Venkatesan, 2019), and a hard seed coat that protects the embryo and endosperm from even a specialist harvester ant (Rodgerson, 1998). These seed traits make P. naegelii switch its role from seed predator for most plant species (Belchior et al, 2012) to seed disperser of M. serrulata.…”

“…Elaiosomes clearly play a key role in the removal of M. serrulata seeds by P. naegelii, as is typically the case for the removal of myrmecocohorus diaspores by ants (Sasidharan & Venkatesan, 2019). More than twice as many seeds with elaiosomes were removed than seeds without elaiosomes, as is the case for seeds of Dendromecon rigida (Papaveraceae) removed by Pogonomyrmex subnitidus in the USA (Carney et al, 2003), and for other euphorb species removed by different ant species in Brazilian Caatinga (Leal et al, 2007).…”

Odor of achlorophyllous plants’ seeds drives seed‐dispersing ants

“…humile attracts ants with fruit and seed odors and that their seeds are carried by the ants (Figure 1). The seeds might then be abandoned after the outer components are consumed (Sasidharan & Venkatesan, 2019). Consequently, the seed may be dispersed to suitable, host‐inhabited sites on the forest floor.…”

“…If the seeds are carried to an ant nest, the elaiosomes are generally consumed inside the nest before the seeds are discarded (Culver & Beattie, 1978;Fokuhl et al, 2007Fokuhl et al, , 2012Giladi, 2006). Various studies have shown that nutritional contents, such as lipids, amino acids, and proteins, in the elaiosome are important for inducing seed dispersal (Anjos et al, 2020;Fischer et al, 2008;Miller et al, 2020;Pizo & Oliveira, 2001;Sasidharan & Venkatesan, 2019). In contrast, some granivorous ants, such as species of the genera Messor, Pheidole, and Tetramorium, lose or abandon their nonmyrmechochorous seeds during transportation and thus disperse seeds without elaiosomes (Clemente & Whitehead, 2020;Kobayashi, 2009;Ohnishi et al, 2008Ohnishi et al, , 2013Retana et al, 2004).…”

Seed germination of the endangered Viola kitaibeliana and other Italian annual pansies (Viola Section Melanium, Violaceae)

“…Elaiosome removal from seeds functions as a germination cue in many ant-dispersed plant species (e.g., Horvitz 1981;Blois & Rockwood 1985;Lobstein & Rockwood 1993;Ohkawara 2005). Elaiosome is also known to inhibit seed germination due to the presence of water-soluble inhibitory substances (Sasidharan & Venkatesan 2019). On the other hand, its removal did not improve germination success in Viola striata Aiton (Lobstein & Rockwood 1993), Viola pedata L. (Gehring & al.…”