4.1 | Dispersal of elaiosome-less seeds by ants
In this study, we first verified that M. humile seeds without elaiosomes surely attracted ants. We have confirmed that 9 out of 80 untreated seeds were carried to the ant nest, whereas no treated seeds were carried (Table S1). We also found that by using dummy seeds coated with the odor components of M. humile seeds, those dummy seeds treated with a mixture of 6 major components were carried to the nest by the ants, although the dummy seeds treated with the solvent were not carried away (Table S3). Among the 6 main odor components, linalool and α-terpineol were also identified as floral scents of M. humile , but the other 4 components were not identified (Kubo & Ono, 2014). These results indicate that M. humile seeds attracted ants by their seed or fruit specific odor mixture. In the pepper family plant,Peperomia macrostachya , the mixture of seed odors efficiently attracts the ant, Camponotus femoratus (Youngstead et al., 2007). Since the volatile seed odors would have disappeared in 72 h, the dummy seeds were abandoned outside the nest. Similarly, the seeds are likely to be abandoned after the outer fruity coating components are consumed. Therefore, even in the absence of elaiosomes, some plants, includingM. humile , could disperse their seeds through the ants using a specific blend of odor components.
Hence, ants are thought to participate in the seed dispersal of M. humile, in addition to herbivorous insects, such as cockroaches and camel crickets (Suetsugu 2017; Uehara & Sugiura 2017), and the seed dispersal by ants could be beneficial for the achlorophyllous species. With regards to the seed dispersal by ant, the seed-discards or left-inside-the-nest indicated that dispersal by ants should be important for plant seeds of such achlorophyllous plants as M. humile . The plant does not depend solely on the myrmecochory, as Suetsugu 2017 reported many of seeds have been detected from the herbivorous insects’ excretion. Because the number of seeds carried in our assay is relatively small, myrmecochory of the species could be one aspect of their zoochory.