Odor of achlorophyllous plants’ seeds

Seed dispersal by ants is an important means of migration for plants. Many
myrmecochorous plants have specialized appendages in their seeds called
elaiosome, which provide nutritional rewards for ants, and enable
effective seed dispersal. However, some non-myrmecochorous seeds without
elaiosomes are also dispersed by ant species suggesting that additional
mechanisms other than elaiosomes for seed dispersal by ants. The seeds of
the achlorophyllous and myco-heterotrophic herbaceous plant Monotropastrum
humile are very small without elaiosomes, we investigated whether odor of
the seeds could mediate seed dispersal by ants. We performed a bioassay
using seeds of M. humile and the ant Nylanderia flavipes to demonstrate
ant-mediated seed dispersal. We also analyzed the volatile odors emitted
from M. humile seeds and conducted bioassays using dummy seeds coated with
seed volatiles. Although elaiosomes were absent from the M. humile seeds,
the ants carried the seeds to their nests. They also carried the dummy
seeds coated with the seed volatile mixture to the nest, and left some
dummy seeds inside the nest and discarded the rest of the dummy seeds
outside the nest with a bias toward specific locations, which might be
conducive to germination. We concluded that, in M. humile seeds, volatile
odor mixtures were sufficient to induce seed carrying behavior by the ants
even without elaiosomes.