BIO 203

Reproduction and Life History

The life cycle of Ohiocordyceps unilateralis can be divided into approximately four parts: infection, death grip, stalk growth, and dispersal. Fungal spores of O. unilateralis specifically target host ants of the species Camponotus leonardi foraging on the forest floor. Observations conclude that spores attach to the cuticle of a target ant and secrete digestive enzymes to break through the exoskeleton and begin infecting the host (Evans, et al., 2011). Yeast-like growth within the host progresses until the manipulation of the host by the fungal parasite causes the host ant to fall from the canopy to a lower elevation optimal for fungal growth. Further manipulation by the host directs the ant to a leaf, whereupon the ant is cued to bite the middle vein in a characteristic death-grip like form preventing the ant from falling. Following the ant’s death, further growth consumes the ant’s internal tissue while maintaining a protective exoskeleton on the outside (Evans, et al. 2011). The characteristic growth of the fungal stalk (stroma) from the base of the neck, eventually develops into a mature fungal body capable of releasing spores. Spores released complete the cycle until an unfortunate ant below becomes the target and begins the cycle yet again.


Recent analysis of 48 million year old leaves of Messel, Germany by researchers David P. Hughes, Torsten Wappler and Conrad C. Labandeira led to the discovery of biting patterns typical of infected host ants by the parasitic fungus Ophiocordyceps unilateralis (Hughes, et al. 2010). This research is notable both in that it suggests historic biogeographic parallels between mid-eastern Europe and recent Southeast Asia, but also in that it suggests the past history of O. unilateralis.

Ophiocordyceps unilateralis requires few but critical conditions in order to transition from hyphal growth to the formation of a stroma. It is interesting to think that the fungus knows that any death inside the ant colony will lead to its removal by other worker ants that perceive a threat to the colony (BBC America 2006). As a result, observations of infected ants have shown that they will periodically fall from leaves to a lower portion of the tree canopy optimal for fungal growth and away from other ants. The synchronization of leaf biting around the noon hour as observed by researchers is evident of clock genes being expressed by O. unilateralis (Hughes, et al. 2011). The use of clock genes in addition to the “drunkards walk” of infected ants by O. unilateralis suggests that these are critical steps in directing the host towards a location suited for optimal growth.

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