Ants and sugar cravings.
Jacob Schor ND FABNO
Denver Naturopathic Clinic
October 1, 2009
I am forever looking for explanations for things I don’t understand. I think I’ve come a step closer today after reading about an obscure fungus that infects obscure ants who live on the other side of the world.
In alternative health circles one of the big things to diagnose in patients is Candidiasis, an overgrowth of the common intestinal inhabitant the yeast Candida. Regular doctors usually scoff at this diagnosis and call Candida just, ‘normal flora’ yet my experience is that occasionally some people feel a great deal better if populations of these yeast are kept as low as possible. I’m not writing to debate this tonight. Rather I’m writing to describe a peculiar symptom that many of these people who are sensitive to yeast overgrowth frequently describe.
They tell me that they crave sugar or starch with a vigor that sounds to be near addiction. Granted that sugar tastes good, so does bread, but the way they talk about this, it’s more than good. It’s like a drug. This is so common to hear that we will often anthropomorphize the experience saying, “That’s just the yeast talking. Yeast needs sugar to grow so it’s telling you to eat some sugar.”
Yet we are talking about yeast and the idea that they can tell a person what to do seems ludicrous. Still every once in awhile something I read seems to support the idea that some little parasite can direct its host's behavior. I wrote several years ago about the parasite Toxoplasma and how at the proper time in its life cycle it eliminated its host rat’s inborn fear of cats.
Link to that article:
Here’s an even better example of a parasite directing its host's behavior.
A report in the September issue of the American Naturalist describes a peculiar fungus, Ophiocordyceps unilateralis, that infects ants living in the rainforests of Thailand. When infected, the ants turn into zombies and climb up the north side of a tree and at approximately 25 cm above the ground, lock their jaws upon bark or a leaf and then quickly die. The humidity and other conditions at this height from the ground provide the perfect growing environment for the fungus, which after feasting on the dead ant’s body, eventually forms a fruiting body that grows out of the dead ant’s neck.
If a fungus can manipulate an ant and tell it to climb to a specific height off the ground and then turn it’s jaws into a set of locking vise-grips, if a fungus can do all that, it’s not hard to think it can tell a person, “Sugar will make us happier.” Add that the fungus communicates its preference for the north facing side of the tree and its surprising that these human Candida infections are not more specific, “Yo, George, on the way home pick up a dozen doughnuts, the double fudge ones with chocolate icing.”
Now I'm not saying that Candida really forces people to eat sugar and other foods that help it grow, but looking at these ant fungi, it's not so impossible to imagine that maybe Candida provided some sort of chemical encouragement suggestion, "Well, just a little nibble won't hurt...."
This dead ant infected with the fungus Ophiocordyceps unilateralis clamped on to a leaf before dying. The stalk growing out of its neck is the fungus. The red ball will soon release spores that will infect other ants.
The life of a dead ant: the expression of an adaptive extended phenotype.
Centre for Social Evolution, Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark. email@example.com
Specialized parasites are expected to express complex adaptations to their hosts. Manipulation of host behavior is such an adaptation. We studied the fungus Ophiocordyceps unilateralis, a locally specialized parasite of arboreal Camponotus leonardi ants. Ant-infecting Ophiocordyceps are known to make hosts bite onto vegetation before killing them. We show that this represents a fine-tuned fungal adaptation: an extended phenotype. Dead ants were found under leaves, attached by their mandibles, on the northern side of saplings approximately 25 cm above the soil, where temperature and humidity conditions were optimal for fungal growth. Experimental relocation confirmed that parasite fitness was lower outside this manipulative zone. Host resources were rapidly colonized and further secured by extensive internal structuring. Nutritional composition analysis indicated that such structuring allows the parasite to produce a large fruiting body for spore production. Our findings suggest that the osmotrophic lifestyle of fungi may have facilitated novel exploitation strategies.