Dr. Jennifer Rudgers
Could Fungi Promote Exotic Grass Invasions?
The grass family (Poaceae) has more weedy and invasive
species than any other plant family. It is currently unknown
whether symbiosis with beneficial fungi may play a role
in the widespread invasiveness of grasses. We can test a
diverse array of native and non-native grasses from around
the world to ask questions such as (a) are endophytes more
(or less) common in non-native than native grasses? (b)
do grass species with high frequencies of endophyte symbiosis
exhibit greater invasiveness than grasses with low levels
of symbiosis? Herbarium collections provide a great resource
for expanding our knowledge of endophyte prevalence in grasses,
because immunological stains can detect endophytes dried
plant tissues.
Cooperation and Conflict Between Fungi
and Plants
Plants can reproduce via seed production or pollen production.
However, their symbiotic endophytes are only inherited through
seeds, thus creating the potential for conflict between
the fungus and host. From the fungal perspective, pollen
production by plants could reduce resources available for
making seeds that carry the endophyte, and thus would be
a waste of resources. For the first time, we will test the
prediction that endophytes reduce plants’ investment
in pollen, thereby increasing their own reproduction through
seed production.
Lifestyles of the Rich and Symbiotic
Symbionts have two primary lifestyles. Horizontal transmission
occurs when symbionts produce infectious elements (e.g.,
spores) that spread contagiously among hosts. In contrast,
vertical transmission occurs when symbionts are directly
inherited by offspring from their parents. Both chloroplasts
and mitochondria were once vertically transmitted symbionts
that became permanently inherited by their hosts. However,
many vertically transmitted symbionts have not become a
fixed part of the host. These associations are widespread
in nature and include gut bacteria in insects, zooxanthellae
in corals, lichen-forming algae and fungi, and fungal endophytes
in plants. Symbionts are expected to reach high frequencies
in host populations when they are beneficial to hosts. However,
observations in nature often find intermediate, rather than
high, levels of symbiosis. One factor that may contribute
to intermediate levels is imperfect vertical transmission,
whereby the symbiont is inherited by less than 100% of the
host’s offspring. We will document the degree of imperfect
vertical transmission of fungi in several rare and common
grass species from Texas.
All Dried Up? Host a Fungus.
Endophytic fungi grow in plant leaves and are widespread
in grasses. Endophytes gain carbon from their host plant
and, in exchange, make the grasses toxic to herbivores,
such as insects and cattle. Another possible benefit of
endophytes is improved drought tolerance, which can occur
because endophyte-produced compounds allow the grass to
draw more water from the soil. This benefit has not been
tested in most endophyte-grass associations. In greenhouse
and growth chamber experiments, we can manipulate the presence
of the endophyte and subject host plants to different water
treatments to test whether drought tolerance is a common
benefit provided by endophytes.
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