Upon watching a clip on entomopathogenic fungi, specifically Cordyceps unilateralis in my Evolution Psychology class, it set me thinking if all behaviour as exhibited by animals are indeed as “fitness” directed as we think.
Horror buffs would be familiar with the idea of possession, which is quite literally what we see with Cordyceps unilateralis and its host – the carpenter ant. Upon infection, the fungus enters the body of the ant, and when it is ready to sporulate, affects the ant’s perception of pheromones through chemicals released by the fungus into the ant’s brain. The ant then exhibits highly atypical behaviour and climbs to the top of a plant stem where it anchors its mandibles and dies. The fungus feeds on the brain of the ant and sprouts as a stalk from the ant’s head which once mature, would explode, spreading its deadly spores yet again.
Straight out of a science fiction movie, whenever a colony member is discovered to be infected, it is immediately removed to a far away location from the rest. Such measures, while seemingly drastic, are necessary to prevent the death of entire colonies.
Perhaps more sinister would be the gordian worm, or Spinochordodes tellinii, which induces its host to “jump off the deep end”, literally drowning itself such that the worm, which may only emerge in water, can do so.
We’ve learnt of how genes may affect an individual’s behaviour, most saliently seen in psychological disorders such as schizophrenia. In the animal and plant world, the genes of such parasites as the gordian worm and the cordyceps fungus, while encoded in their own genome, have a direct effect on their hosts’ behaviour; in what Richard Dawkins dubbed the extended phenotype. This then begs the question. The next time you sneeze while having the flu, are you sneezing as a reflex commonly thought to serve a “fitness” purpose in getting rid of an irritation in your nose? Or are you sneezing for the propagation of the virus?
Biron, D. G., et al. (2005). Behavioural manipulation in a grasshopper harbouring hairworm: a proteomics approach. Proc. R. Soc. B., 272, 2117-2126.
“Brainwashed by a parasite,” by Mo. Neurophilosophy, 20 November 2006. URL: http://neurophilosophy.wordpress.com/2006/11/20/brainwashed-by-a-parasite/ (accessed on 3rd Apr 2010).
“Cordyceps: attack of the killer fungi – Planet Earth Attenborough BBC wildlife,” by BBCWorldwide Youtube Channel, 3rd November 2008. URL: http://www.youtube.com/watch?v=XuKjBIBBAL8 (accessed on 3rd Apr 2010).
“Gordian Worm and Friend,” by VB Films, 2002.