For the Lion

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Zombie ant controlled by fungus (source)The fungus-controlled zombie ant is one of nature’s greatest wonders. A fungus (e.g.O. Unilateralis) is inhaled by an ant (e.g.Camponotus Leonardi), and begins to grow inside its body.  Eventually the fungus infests the brain of the ant, causing it to drunkenly wander, periodically convulse, climb up a leaf and clamp down on its ridge. Once the ant is securely in place, the fungus devours the brain and innards of the ant and grows out the back of its head often (but not always) releasing its spores onto the ground below. Un-freaking-believable, right?

As if this wasn’t amazing enough, it’s not like it is only one fungus species that infects only one ant species. There are many of these fungi and they infect many different kinds of insect, but somehow maintain a species specificity. In other words, fungus#1 can infect SpeciesX, but not SpeciesY, and Fungus#2 infects SpeciesY, but not SpeciesQ, and so forth. 

So WHY does this happen? and HOW has no one looked at the brain cells of these ants? 

Though no one has looked at the brains of these ants, Last year a paper painstakingly characterized their behavior under ‘fungi control’. The most interesting characteristics are:
  1. The ants display a ‘drunkard’s walk’ (the author’s words)
  2. The ants periodically spasm and fall down (if they are above ground level)
  3. The ants clamp down on the underside main vein of a leaf (never the side of the leaf, never the top) Interestingly they all bite down on the leaf around solar noon.

Figure 1, Hughes et al., 2011
This figure shows the behavior of several ants.  Each ant was observed during the time of the horizontal blue bar.  The black vertical lines and ‘spasms’ which caused the ants to fall down (gray stars), and the red triangles are when the ant bit down on the leaf ridge. 

Because we have no idea how the fungus is manipulating the ant, let’s wildly speculate.

1.The Drunken Walk:
Why: The reason for this is not clear.  The ant doesn’t go far, so the non-directional walking could be to keep it close to more ants.
How: The mechanism is also not clear, but usually an ants directional walking could be following a pheromone trail. The fungus could presumably cause random walking by confusing the ants ability to sense pheromones. It could possibly even cause ‘hallucinatory’ pheromone sensing.

2.The Periodic Spasms:
Why: The authors speculate that the purpose of these spasms is to keep the ant near the ground.  The infect ants spend much more time on the ground level than the uninfected ants, and the spasms are often followed by a fall.
How:A fungus could essentially cause a seizure in the ants brain by manipulating potassium or calcium channels. On the other hand, I suppose the fungus could be acting directly on the muscles, causing them to twitch in an uncontrolled way. 

3.The Clamping:
Why: This has an obvious function, to root the ant for ultimate fungal growth and dispersion. 
How: First of all, biting and evenwalkingon leaves is not something these ants normally do. So the fungus isn’t just hijacking a behavior that the ant already has, it’s basically creating a new one.  The correlation with solar noon indicates that a light or heat signal could contribute to the trigger, but basically nothing else is known about it. Interestingly, the clamping does not always have to be one single event either.  A few of the ants clamped down on the leaf veinmore than once. The authors of this paper spend time discussing fungi’s direct effect on the mandible muscles of the ant.

Figure 3 Hughes et al., 2011They show that the mandible muscles of the normal ant are fat and healthy (B), but the muscles of the infected ant are separated and reduced in size (C). Though this image is of an ant at the moment of biting, the authors suggests that the deterioration of the mandible muscle might be to prevent re-opening of the clamp. They do not speculate on how the clamp is initiated in the first place, or why it occurs at noon.

So please, fellow neuroscientists, somebody stain these brains! It’s just too fascinating to resist exploration. What proteins are altered? What is the receptor composition of behaviorally-specific neurons? Are the dendrites differently shaped?

wear crocs on a regular basis, that would be a deal breaker.

just printed himself a copy of the supplemental all of an hour ago. Shows how much he’s studied it this weekend. Watch, he’ll get an A tomorrow. Pisses me off.

it’s the period thing. Or maybe it’s the finals thing. But, my feelings were hurt. And I know you didn’t mean to. I know that. But they were.

for you to be working on some summer evening. I’ll get up from doing my homework, come over to you, and sit on your lap. You’ll tell me you really have to finish putting the test together, but I’ll kiss you and reposition myself so that my legs are on either side of you. You’ll tell me again that you need to get work done, but I’ll bite your ear and your neck and put my hands on your back underneath shirt as I dig my nails into you ever so slightly. You’ll try to resist but I’ll unbutton your pants, unzip them and slowly make my way down….

you can get your work done later.