Sunday, October 20, 2013

Cordyceps: killer fungi

Most of the time, we see what's beautiful, enticing and admirable in the natural world.  However, we are all well aware that there are many challenges to the struggle for live of any living organism—predators, climate change, natural disasters, human activity—as we tend to see more and more of in the media, documentaries, and witness in person in our daily lives.  

Cordyceps wasp
Wasp killed by Cordyceps fungus in Panama
A few weeks ago during a visit to the Canopy Lodge in El Valle, I was walking around the gardens and spotted this unusual creature on a low palm frond.  Upon closer examination, I saw that it was a wasp - but something wasn't right.  This wasp had two large, white projections emerging out of its thorax, and white spines over its legs and other parts of its body.  It was motionless.  I knew exactly what had happened.

In tropical regions, there are some rather unlikely predators, and they kill in rather gruesome ways.  Aside from large cats, raptors, and many other predators out there, there exists the strange and ruthless world of Cordyceps—an endoparasitoid fungi that attacks insect and arthropod hosts.  When this fungus attacks a host, it releases mycelium, which replaces the host tissues.  It also causes a change in behaviour of the host, perhaps an ant or wasp, causing it (if a social insect) to leave its colony and climb up a branch or shrub and attach there before they die.  This change in behaviour ensures that the spores of the fungus will be released in the optimal surroundings to maximize distribution.   Once the host is in position, the mycelium then forms a fruiting body—usually a cylindrical, branched or complex projectionwhich emerges through the exoskeleton of the host.  Spores are released through this fruiting body.  Cordyceps means "club head", referring to the shape of the fruiting bodies.  The spores are very potent, and this killer fungus can wipe out entire colonies of insects.  Check out this video from Planet Earth.  
Cordyceps moth
Moth showing small Cordyceps fruiting bodies in Ecuador, 2010
Cordyceps cricket
Cricket killed by Cordyceps fungus in Ecuador, 2010
Cordyceps Bullet Ant
Bullet Ant - note the elongated fruiting body extending from back of head.  Ecuador, 2010
It sounds (and looks!) like something out of a grotesque sci-fi movie, but this is real.  In the time I have spent living and working in tropical humid environments, I have come across this several times.  I have seen moths, crickets, bullet ants, and other insects parasitized by these unusual killers.  Here are a few photos I have taken in recent years of various Cordyceps attacks. The fruiting bodies take on different forms and colours, depending on the species of Cordyceps (there are approximately 400 described species and many more remain undescribed), and I have never seen two alike. 

So its not just some mammals, birds, reptiles and other animals, even plants that have mastered their roles as predators, but an entire world of predatory and parasitic fungi, which continues to show us the complexity and diversity of the world we live in.  Incredible!

~ Jenn 

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