December 12, 2006

Controlling the Mind and Body

In reference to his book Parasite Rex, Carl Zimmer has been blogging about parasites that change the behavior of hosts as a function of reproduction (he also has a great clip from David Attenborough's Planet Earth, one of Cordyceps fungi invading and "sprouting" from an ant's body).

I was reviewing some ecology material for my final tomorrow, and I thought I would share another strange, behavior altering relationship between the European starling, an acanthocephalan (spiny-headed worm) Plagiorhyncus, and a pill bug, Armadillidium vulgare.

Plagiorhyncus infects the pill bug, growing until it reaches a vertebrate infection stage called a cystacanth. The starling eats the infected pill bug and becomes infected itself, allowing the parasite to complete its life cycle by releasing eggs into the bird's digestive tract. I'm sure you can fill in the blanks from here. A hint: Armadillidium likes to eat bird poop.

This cycle is pretty standard in parasite-host relationships. What is unique about Plagiorhyncus is the way it exploits both the pill bug and the starling.

Plagiorhyncus drives Armadillidium out of its usual haunts, moist dark areas under rocks or flower pots. Armadillidium, chemically altered, is suddenly out in the open, and more susceptible to attack from above.

The neat thing is, this only happens when Plagiorhyncus has reached its cystacanth stage. Even more interesting, think about the evolution of such a relationship, how many parameters had to be aligned in order to produce such a situation.

It's mind boggling to be sure, but not so startling, considering the close proximity and vast diversity of life on earth. Relationships of all kinds are to be expected in an interactive global community so large. It's kind of nice that we haven't found them all; we certainly are unsure of all the mechanisms and phylogenies. Yet.

Aside: I want to be David Attenborough when I grow up.

1 comment:

  1. Fascinating story! A very nice and concise essay.

    ReplyDelete