THRILLER CHAMPIONSHIPS: Researchers bet on fruit fly fights to expose underlying biology of aggression

Male fruit flies that pick a fight are likely to win the battle. Losing fruit flies don't give up easily, even if it takes them longer to re-engage their foes after a particular bruising encounter. Most fruit fly fights are resolved before they escalate to intense physical contact.

These are some of the results from a study of 75 fruit fly fights staged at a neurobiology laboratory at Harvard Medical School (HMS) in Boston, Mass. USA. The researchers videotaped and analyzed the fights to learn more about aggression. Future studies in the lab will use genetic mutations to investigate the neurobiology of aggression and also explore the gene expression consequences of winners and losers. The first report in the April 16 Proceedings of the National Academy of Sciences establishes the pattern of normal fruit fly fights.

In the half-hour fights, the fruit flies averaged 27 encounters of about 11 seconds each. Each scuffle moved so fast that the researcher-referees needed slow-motion instant replay to score the fights. Harvard University undergraduates Selby Chen and Ann Yeelin Lee scored about 9,000 individual moves in 2,000 skirmishes. In case of doubt or disagreement, HMS neurobiology professor Edward Kravitz determined the final score.

PLACE YOUR BETS 3:1 odds that a fly initiating a fight with the "slow approach" will eventually win 16:1 odds that a fly initiating a fight with a mid-intensity move will win 7:1 odds that a fly that won the last skirmish will win the next skirmish

As it turned out, fruit fly fights were less predictable than lobster fights, which the Kravitz lab has been studying for 20 years. Lobster fights seem to follow a strict choreography, usually beginning with low-intensity moves and countermoves and slowly escalating to higher intensity encounters before the loser retreats for good. Fruit flies fights are more random affairs. Yet, patterns emerged. Fruit flies have a favorite tactic--fencing--but they can also surprise their opponents with wing threats, charging, and even retreating. High-intensity encounters lasted four to five times longer than those of a low level. And it took more than twice as long for fruit flies to re-engage after a high-intensity encounter.

Although fruit flies that pick fights are more likely to win them, especially if they are real bullies, the researchers found no obvious differences in fighting behavior separating the winners and the losers. The decision to retreat can come at any time, after any maneuver, at any level of fighting intensity.

The researchers tallied the sequence of moves by both winners and losers into a fancy statistical chart called a "Markov chain analysis" (above). Bigger boxes show more popular tactics. Smaller boxes show less common maneuvers. Likewise, thicker arrows show the most likely next move, such as the distinct fighting loop that dominates the aggressive behavior: slow approach to a wing threat to a fast approach. There are no boxes or arrows for moves and sequences that occurred less often than chance.

High Intensity

Boxing: Both rear up on hind legs and strike opponent with forelegs

Holding: One grasps the other with forelegs and tries to immobilize it

Mid Intensity

Chasing: One runs after the other

High-level fencing: One or both flies face the other, extend leg forward and push opponent

Low intensity

Low-level fencing: Side by side, one or both extend the leg to the side and tap opponent's leg

Approach: One advances in the direction of the other

Retreat

Defensive wing threat: One flicks wings at 45-degree angle facing away from oppponent

Run away/being chased: One retreats quickly from advance of other

Fly away: Loser flies off food surface

More links:

Video guide to scoring fly fights (with music)