Monday, 17 January 2011

Ophiocordyceps unilateralis: Horrifying ant parasite

Ant infected with Ophiocordyceps unilateralis (stroma visible)
Ant infected with Ophiocordyceps unilateralis
The ball-like structure is the stroma,
the fruiting body of the fungus
Kingdom: Fungi
Phylum: Ascomycota
Class: Sordariomycetes
Order: Hypocreales
Family: Ophiocordycipitaceae
Genus: Ophiocordyceps
Species: Ophiocordyceps unilateralis (Synonym: Cordyceps unilateralis)
Hosts: Camponotus leonardi and on lesser degree other closely- related ants

Ophiocordyceps unilateralis is a truly frightening parasitic fungus, at least if you are an ant!

In short, it turns ants into zombies and makes them climb tall plants. Next, the zombified ant uses its mandible to affix itself on something, usually a leaf, and then dies. However, the fungus continues to grow inside it and eventually, the fruiting body of the fungus emerges from the back of its head to release new spores, capable of zombifying more ants!

The good news is that O. unilateralis affects only ants. Don't expect a O. unilateralis zombie-apocalypse anytime soon!


Video about Ophiocordyceps unilateralis from BBC documentary 'Planet Earth'


Life cycle & Hosts
Ophiocordyceps unilateralis is an entomopathogenic fungus, with its main host being the Camponotus leonardi ant. However, it also parasitizes on numerous other, closely related ants, although with less reproductive success and a lessened host manipulation.

The fungus cycle begins once its spores attach to the external surface of an ant. There, they germinate and enter the body either through the tracheae or via breathing holes on the exoskeleton called spiracles. There the fungus starts to first consume the non-vital soft tissues. Next, it starts spreading all over the body. It is hypothesized that it is at this stage that it starts to produce certain compounds that affect the ant's brain and thus its behavioral patterns. We still don't know much about the exact mechanisms behind this behavioral alteration.

Now, the ant has lost control and has entered a "zombie-like" mode. It will leave its nest, climb to the top of a plant stem and use its mandibles to secure its place and die. On the other hand, the fungus is still alive and well, continuing to produce more and more mycelia, until some of them sprout out of the ants head! Finally, the fruiting bodies start to develop and the spores are released. With a bit of luck and some help from gravity and wind, some of the spores will find their place on new hosts.

Each cycle takes anywhere from 4 to 10 days to complete.

It's worth mentioning that the ants use abnormally strong force to secure their place, leaving characteristic dumbbell-shaped marks on the plants.This final grip is commonly known as "the death grip" and occurs in very precise locations, most commonly on the underside of leaves.

Image showing Ophiocordyceps unilateralis at the flowering stage

Description
The fungus is visible during the latest stage of its lifecycle, when its reproductive structure has started to protrude from the back of the dead host’s head. This structure is comprised of a wiry, yet pliant darkly pigmented stroma stalk, with the perithecia just below the tip.

Ophiocordyceps unilateralis can be found in the tropical forests of Thailand and the rainforests of Brazil.

Medicinal and other Uses
Recent studies have shown that the fungus contains many known and untapped bioactive metabolites that may be used in the future as a source of making immunomodulatory, antitumor, hypoglycemic and hypocholesterolemic drugs.

The fungus also produces certain red naphthoquinone pigments, which may have cosmetic, food, and pharmaceutical applications in the manufacturing sector. Six of these bioactive naphthoquinone derivatives are:
  • rythrostominone
  • deoxyerythrostominone
  • 4-O-methyl erythrostominone
  • epierythrostominol
  • deoxyerythrostominol 
  • 3,5,8-trihydroxy-6-methoxy-2-(5-oxohexa-1,3-dienyl)-1,4-naphthoquinone

Defensive mechanisms
There are many reported cases in which the fungus has actually exterminated entire ant colonies. To combat this, the ants protect themselves by carefully grooming each other and by carrying infected members of the colony as far away as possible from their nests.

Anti-fungus.. fungus
Interestingly enoughO. unilateralis suffers from an unidentified fungal hyperparasite. Hyperparasites are parasites whose host are other parasites, in this case O. unilateralis. The still unidentified hyperparasite attacks O. unilateralis at the flowering stage, preventing the stalk from releasing its spores. According to research by David Hughes, only 6 to 7% of the fungi’s spores remain viable, greatly limiting the damage O. unilateralis would otherwise inflict on ant colonies.

Cordyceps unilateralis neutralized by unidentified hyperparasite
This photo shows an ant infected by O. unilateralis. The fungus has been neutralized
by the still unidentified hyperparasite fungus
Credit: David Hughes, Penn State University


Other Interesting Facts about Ophiocordyceps unilateralis
- The fungus was first discovered by British naturalist Alfred Russel Wallace in 1849.
- An investigation through plant fossil databases, led by Dr David P Hughes, revealed similar marks on a fossil leaf from the Messel Pit, which is 48 million years old. It seems like the parasite has been working in the same way for a long, long time.

References & Further Reading
- Andersen, S., Gerritsma, S., Yusah, K., Mayntz, D., Hywel‐Jones, N., Billen, J., Boomsma, J., & Hughes, D. (2009). The Life of a Dead Ant: The Expression of an Adaptive Extended Phenotype The American Naturalist, 174 (3), 424-433 DOI: 10.1086/603640
Hughes, D., Wappler, T., & Labandeira, C. (2010). Ancient death-grip leaf scars reveal ant-fungal parasitism Biology Letters, 7 (1), 67-70 DOI: 10.1098/rsbl.2010.0521
- Andersen, S., Ferrari, M., Evans, H., Elliot, S., Boomsma, J., & Hughes, D. (2012). Disease Dynamics in a Specialized Parasite of Ant Societies PLoS ONE, 7 (5) DOI: 10.1371/journal.pone.0036352
- Wongsa, P., Tasanatai, K., Watts, P., & Hywel-Jones, N. (2005). Isolation and in vitro cultivation of the insect pathogenic fungus Cordyceps unilateralis Mycological Research, 109 (8), 936-940 DOI: 10.1017/S0953756205003321
- Kittakoop, P., Punya, J., Kongsaeree, P., Lertwerawat, Y., Jintasirikul, A., Tanticharoen, M., & Thebtaranonth, Y. (1999). Bioactive naphthoquinones from Cordyceps unilateralis Phytochemistry, 52 (3), 453-457 DOI: 10.1016/S0031-9422(99)00272-1
- Sung, G., Hywel-Jones, N., Sung, J., Luangsa-ard, J., Shrestha, B., & Spatafora, J. (2007). Phylogenetic classification of Cordyceps and the clavicipitaceous fungi Studies in Mycology, 57 (1), 5-59 DOI: 10.3114/sim.2007.57.01
- Hughes, D., Andersen, S., Hywel-Jones, N., Himaman, W., Billen, J., & Boomsma, J. (2011). Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection BMC Ecology, 11 (1) DOI: 10.1186/1472-6785-11-13
- Evans HC, Elliot SL, & Hughes DP (2011). Ophiocordyceps unilateralis: A keystone species for unraveling ecosystem functioning and biodiversity of fungi in tropical forests? Communicative & integrative biology, 4 (5), 598-602 PMID: 22046474
- Andersen SB, Gerritsma S, Yusah KM, Mayntz D, Hywel-Jones NL, Billen J, Boomsma JJ, & Hughes DP (2009). The life of a dead ant: the expression of an adaptive extended phenotype. The American naturalist, 174 (3), 424-33 PMID: 19627240
- Evans, H., Elliot, S., & Hughes, D. (2011). Hidden Diversity Behind the Zombie-Ant Fungus Ophiocordyceps unilateralis: Four New Species Described from Carpenter Ants in Minas Gerais, Brazil PLoS ONE, 6 (3) DOI: 10.1371/journal.pone.0017024
- "The Zombie-Ant Fungus Is Under Attack, Research Reveals". Pennsylvania State University. 2012-05-02. Retrieved 2013-03-04.

3 comments:

  1. woooo scary...!

    ReplyDelete
  2. Wow in contrast to the article I just read that bacteria protects ants, but it's actually the other way around. Thank you for this post, it very educational, I was watching it with my kids, they enjoyed it and they learning too.

    ReplyDelete
    Replies
    1. Hey, nice comment. i realy want to point out that this is a fungus not a bacteria

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