Abstract
Seed dispersal by ants is one of the important means of migration for
adherent plants. Although many myrmecochorous plants have seed with
elaiosome which is nutritional reward for ants, some seeds without
elaiosomes are also dispersed by ant species. We tested seed dispersal
by ants using the achlorophyllous and myco-heterotrophic herbaceous
plant Monotropastrum humile , whose seeds
do not have elaiosome, and require
a fungal host for germination and ultimately survival. 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 them to their nest.
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 towards locations
with moisture conditions conducive to germination. We concluded that
seeds of the myco-heterotrophic, herbaceous species were dispersed by
the ants, and that seed odors were sufficient to induce directed
dispersal even without elaiosomes. The flesh-fruit producing genusMonotropastrum have probably evolved from the related
anemochorous genus Monotropa , which produces capsule fruit. This
transformation from anemochory to myrmecochory, presents a novel
evolutionary pathway towards ant-mediated seed dispersal in an
achlorophyllous plant.