It seems to go against logic to think that suppressed metabolic energy would lead to increased aggression, but that is exactly what researchers at the University of Illinois at Urbana-Champaign found in insects.
The study looked at fruit flies and honey bees and examined the link between brain metabolism (energy generation in neurons) and aggression. To measure aggressive behavior, the researchers closely studied how the insects faced down intruders.
A previous University of Illinois study had found that honey bees that had recently faced down an intruder had suppressed metabolic genes. These genes were specifically important for a process in energy generation called oxidative phosphorylation.
Gene Robinson, director of the Institute for Genomic Biology and lead researcher of the previous study as well as this recent one, said that the findings seemed counterintuitive, since one would "tend to think of aggression as requiring more energy, not less."
Clare Rittschof, postdoctoral researcher at University of Illinois, worked with Robinson and researchers to look further into this phenomenon. She suppressed the most important steps of oxidative phosphorylation in bee brains and examined the response. Aggression increased in a dose-responsive manner--in other words, the more suppression-inducing drugs the bees were given, the higher their levels of aggression.
Interestingly, however, this response was not seen in chronically stressed bees.
"Something about chronic stress changed their response to the drug," Robinson said. The chronically stressed bees exhibited no increase in aggression when oxidative phosphorylation was suppressed.
Postdoctoral researcher Hongmei Li-Byarlay found a similar response in fruit flies. However, they were able to isolate exactly where the suppressed oxidative phosphorylation induced this effect and where it didn't. It turns out the metabolic suppression only increased aggression when it was reduced in neurons. The effect was not seen when oxidative phosphorylation was reduced in glia, which surprised the researchers, since glia (neighboring cells in the brain) are considered active "energy storehouses".
The findings highlight some of the interesting brain responses that occur when organisms are exposed to threats, both immediate and long-term. Robinson believes the findings suggest that the metabolic changes, which take longer to occur than urgent aggressive responses, likely make the organisms more cautious of future threats.
Furthermore, the idea that this mechanism is well-established and effective is even more convincing since it was found in both bees and fruit flies--two species that diverged 300 million years ago.