Life cycle and characteristics of Ophiocordyceps UnilateralisCRAIG WILT

Ophiocordyceps Unilateralis

• Found in tropical forests.• Originally discovered in 1865 and

was named Torrubia Unilateralis by the Tulsane brothers. (Tulsane 1865).• It is commonly known as the

“zombie fungus”.• Alters ants behavior for the

reproductive benefit of the fungus through a series of complex chemical reactions.

ophiocordyceptae

• Described by British Mycologist Tom Petch in 1931.• 140 known species and they are

characterized by their growth on insects (Kirk 2008).• Result of millions of years of

coevolution between the two species.

Camponotus leonardi

• O. unilateralis specificity targets Camponotus leonardi.• Found throughout the world on

many continents. • Build their homes in dead

hollowed out tress rather than dirt. • Black or brown in color. • Size ranges from 0.64 to 2.5 cm.

(Hahn 2008).

Environment

• O. Unilateralis has been found in the tropical forests of Brazil and Thailand. • Require an environment which includes the presence of Carpenter

ants. • Prefer high humidity and warm temperatures. • One study found that the fungus operates in a seasonal pattern. Peaks

for infections were found in both rainy and dry seasons. The data suggests the heavy rainfall at the beginning and end of the rainy season promotes fungal growth. (Kobmoo 2013).

Infection

• Spore release: Fungus releases spores that scatter across the ground.• Contact: As ants walk along the forest floor spores attach to their

cuticles.• Invasion: Through enzymes and mechanical pressure spores force

themselves into ants body.• Behavior: Fungus invades ants CNS causing ant to wander in random

patterns and begin to convulse.

Infection (cont.)

• Fungus encourages ant to climb nearby plants and attach to leaves. • Mycelia growth throughout the ant’s body as well as the tarsus portion

of the legs which aids in attachment to the underside of leaves. • Around solar noon the fungus forces the ants to bite into the main vein

of a leaf. Followed by separating muscles in the ant’s mandible causing its jaw to become locked and unable to separate from the leaf. • Rapid hypheal growth further anchoring the ant to the leaf. The fruiting

body erupts and spreads spores putting any nearby ants in significant danger.

Stroma and perithecial pad

Infection (cont.)

• As the fungus grows in the dead ants it has been found to form an orange tube like structure rich in carbon that extends throughout the ants body. It is thought this structure may play a role in energy storage (Anderson 2009).• The hyphae and fungus of the stroma exhibit a brown and red or

purple color respectively due to pigments made from naphthoquinones. This substance exhibits anti-microbial properties and is thought to provide protection against competing bacteria. (Anderson 2012).

Infection (cont.)

SEM of dead infected ant

Longitudinal dissections of infected ant.

Preferred conditions for reproduction

• As the fungus grows within the ant it encourages it to move to a location best suited for the fungus’ reproduction.

• Directs the ants up a plant to a north facing leaf at a height of about 25 cm above the ground.

• Prefer temperature of 20 to 30 degrees Celsius with 94 to 95 percent humidity. (Attenborough 2006).

• Grip the primary vein of the north-west side of the plant. (Anderson 2009).

Reproduction

• Dead ant stage which describes infected ants often found on the underside of leaves. • Stroma stage characterized by the rod like structure that emerges

from the ants back. • Perithecial pad stage which involves the formation of the spore

dispersion structure. • Their observations found that O. Unilateralis can undergo the DA-S-P

cycle as many as five times and found the fungus could consecutively produce the stroma three times and the perithecial pads twice. (Kobmoo 2013).

Life Cycle

Reproduction (cont.)

• When ready to reproduce the sac-like structures known as asci build up pressure and launch ascospores (Anderson 2009).

• spores are spread throughout the forest floor to be picked up by another ant.

• The fungus’ spores are typically released at night. When dispersed cover an area of 1 meter-squared below the host.

• Spores are not well protected. infection must occur shortly after reproduction before spores degrade.

• Fungus is limited to infection only members of C. Leonardi. Spores must be release often and for long durations of time to compensate (Anderson 2012).

Life Cycle

Summary

• Ophiocordyceps Unilateralis undergoes a complex parasitic lifecycles based around infecting and altering the behavior of Camponotus leonardi for its own reproductive advantage.

Citations

• Andersen S, Ferrari M, Evans H, Elliot S, Boomsma J, Hughes D. Disease Dynamics in a Specialized Parasite of Ant Societies. Plos ONE [serial online]. May 2012;7(5):1-8. Available from: Academic Search Complete, Ipswich, MA. Accessed October 20, 2013.

• Tulasne LR, Tulasne C (1865) Selecta Fungorum Carpologia III. Paris Museum. 1-221:

• Kirk PM, Cannon PF, Minter DW, Stalpers JA. (2008). Dictionary of the Fungi (10th ed.). Wallingford, UK: CABI. p. 483. ISBN 978-0-85199-826-8.

• KOBMOO N, MONGKOLSAMRIT S, TASANATHAI K, THANAKITPIPATTANA D, LUANGSA-ARD J. Molecular phylogenies reveal host-specific divergence of Ophiocordyceps unilateralis sensu lato following its host ants. Molecular Ecology [serial online]. June 15, 2012;21(12):3022-3031. Available from: Academic Search Complete, Ipswich, MA. Accessed October 20, 2013.

• Attenborough, David. "Cordyceps: attack of the killer fungi - Planet Earth Attenborough BBC wildlife". BBC Worldwide. Retrieved 4/21/13.

• Andersen S, Gerritsma S, Hughes D, et al. Natural History Note: The Life of a Dead Ant: The Expression of an Adaptive Extended Phenotype. American Naturalist [serial online]. September 2009;174(3):424-433. Available from: Academic Search Complete, Ipswich, MA. Accessed October 20, 2013.