31 August 2010

Cordyceps fungus and zombie ants in the fossil record

I've previously posted this David Attenborough segment about how Cordyceps infects the brains of ants and other insects and influences their behavior.   I'm reposting now because of a discovery reported in Biology Letters - fossil evidence of this fungus/ant interaction.

The evidence comes from the bite marks left by the ants when they cling to a leaf in their death throes (behavior briefly seen in the video above), preserved in fossilized leaves.
Hughes doesn't think the bites could be anything else — such as the vein-cutting behaviour exhibited by some other ants or beetles during feeding — because the location on the leaf vein and shape of the marks are so unusual. "It is not normal ant behaviour to bite into the leaf vein because it has no real nutritional value to the ant and can in fact be toxic in some plant species," he says.
And just for completeness, here is a nice summary of other examples of parasites controlling the behavior of their host:
Many examples of parasites altering host behaviour exist and a few choice ones illustrate the often dramatic effects observed: nematodes and nematomorphs cause various insect hosts (e.g. crickets, ants) to drown themselves so the adult parasite can reproduce in water; parasitoids cause bees to bury themselves alive or spiders to build aerial cocoons so as protect the developing parasitoid pupa and many arthropods, fish and mammals have altered behaviour that makes it much easier for predators to catch them which enables the parasite to be passed on trophically
Tomorrow we'll post something about parasitic wasps.

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