When you imagine zombies, you probably do not imagine zombie caterpillars. Although zombies are only fantasy, “zombie caterpillars” are in fact real, and they play a key role in helping researchers to better understand how human brains work.
So what are zombie caterpillars, and what can they teach us about brains? Research by Dr. Shelley Adamo from Dalhousie University is providing some of the answers.
Dr. Adamo is an expert on how parasites manipulate the behaviour of their hosts. Her most recent studies look at the interactions between the parasitic Cotesia wasp (Cotesia congregata), and the tobacco hornworm (Manduca sexta) caterpillar. She coined the term “zombie caterpillar” to explain what happens once these insects become hosts to the parasitic wasps.
Dr. Adamo revealed that the parasitic wasps live inside their host until they are ready to form cocoons. They then break through the body wall of the caterpillar. The cocooned wasps remain attached to the host for four to five days. To ensure the wasps’ survival, during this time the caterpillars are prevented from feeding, their primary behaviour. The caterpillars also function as bodyguards for the wasps by protecting against other predators.
If the parasites can supress the primary and most robust behaviour of the caterpillars—feeding—Dr. Adamo reasoned, clearly they can teach us something about how to improve control of a brain.
“These parasites can alter behaviours often permanently and much more elegantly than humans can,” stated Dr. Adamo. “If we figure out how they are manipulating behaviours we can gain some insight into how brains work more generally.”
In the beginning, Dr. Adamo expected to find that the parasites would use one of the three methods used by neurobiologists to alter behaviour. These include selectively removing the area of the brain controlling the behaviour in question, using drugs to interact with the neural transmitter system, or altering gene expression, a method that is not yet well understood.
What Dr. Adamo and colleagues discovered, however, was that the parasitic wasps used slightly different methods in combination to produce the desired outcome.
The first change triggered is a massive immune response caused while the wasps are breaking through the body wall of their hosts. Dr. Adamo explained that pretty much all animals decrease feeding when the immune system becomes activated. “By exploiting a pre-existing connection, the caterpillars’ immune systems, the parasitic wasps are able to shut down the feeding behaviour of the caterpillar entirely.”
The second change is an alteration of gene expression. This is an area that Dr. Adamo is studying in greater detail to see if it explains why the caterpillars act as bodyguards to the parasites, even after their immune levels start to come back down. The specific genes that the parasites manipulate during this process are still unknown, but Dr. Adamo believes they are ones we would not necessarily target in neurobiology.
These are exciting discoveries, not only for Dr. Adamo and her colleagues but also for neurobiologists. Her research offers the potential to find new ways of manipulating minds; ways that may never have been considered if not for the parasitic wasps and zombie caterpillars.
“I think parasites offer a unique perspective. When we figure out how they’re doing what they are doing and exactly what genes they are manipulating we can find new ways of changing behaviour.”
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