Ants Associated with Turnera subulata (Turneraceae): Elaiosome Attraction, Seed Dispersion and Germination

Abstract

Symbiosis between plants and ants include examples in which the plant provides shelter and/or food for ants that, in turn, act in the defense or in the dispersion of seeds from the host plant. Although traditionally referred as mutualistic, the results of these interactions may vary with the ecological context in which patterns are involved. A range of species have facultative association with Turnera subulata (Turneraceae). Here, using behavioral bioassays, we investigated the effects of the most frequent ant species associated with T. subulata (Brachymyrmex sp.1, Camponotus blandus (Smith), Dorymyrmex sp.1, Crematogaster obscurata Emery, and Solenopsis invicta Buren) in the dispersion of plant host seeds and in the number of seedlings around the associated ant nests. We also evaluated the effects of these ant species in the germination of T. subulata seeds, in the consumption of elaiosome, and in the attractiveness to elaiosome odor. Our results showed that the ant species associated with T. subulata presented variation in the attraction by the odor and in the rate of consumption of the elaiosomes. However, none of the ant species studied contributed significantly to the increase of seed germination and seedling growth. Our results suggest that the consumption of the elaiosome by ant species is not a determinant factor to the success of germination of T. subulata. However, such species could contribute indirectly to seed germination by carrying seeds to sites more fertile to germination. In general, our results help to elucidate the results of ecological interactions involving ants and plants.

Seed morphology and germination of <Turnera diffusa> Willd. ex Schult. emulating environmental conditions within ant nest

“…The pre-germination treatment imitating the environmental conditions of an ant nest and the removal of the elaiosome do not promote an increase in the percentage of seed germination in T. diffusa. These results are similar to those of Cuautle [10] and Rocha [19] for T. ulmifolia and T. subulata, in which the species of ants studied were attracted by the elaiosome to consume it, but none of the associated ants actually favored an increase in the germination success of the seeds. The results of our study under laboratory conditions show that the removal of the elaiosome is not a factor that benefits germination, although it should be considered as a mechanism to promote its dispersion by ants.…”

“…From the standpoint of seed handling for the propagation of the species, it is necessary to apply treatments to inhibit fungal growth, since the high content of nutrients contained in the elaiosome favor fungal proliferation. Rocha [19] proposes that during the consumption of the elaiosome, the ants introduce some type of salivary substance that promotes scarification and optimizes germination. However, in the case of T. diffusa, removal of the elaiosome is shown to not benefit germination.…”

Ant mediated dispersal of spiny stick insect (Extatosoma tiaratum) eggs and Acacia longifolia seeds is ant-species dependent

“…The diaspores of these plants possess an elaiosome, a knob-like appendage, which is enriched with essential nutrients (Berg 1975;Hughes and Westoby 1990). This structure acts as an incentive that induces both omnivorous and herbivorous ants to retrieve the seed and transport it back to the nest (Hughes and Westoby 1990;Bologna et al 2017;Rocha et al 2018). Following dispersal, the elaiosome is typically detached, leaving the remainder of the seed intact, before being buried in nest chambers or discarded in refuse piles nearby (Beaumont et al 2013).…”

“…This structure acts as an incentive that induces both omnivorous and herbivorous ants to retrieve the seed and transport it back to the nest (Hughes and Westoby 1990; Bologna et al . 2017; Rocha et al . 2018).…”