方舟子写的“苍蝇也爱打架”一文来自《大象为什么不长毛 》，该书 气势磅礴，销量骇人！
《Fruit Fly Fight Club》来自www.sciencemag.org SCIENCE VOL 315 12 JANUARY 2007
another. It took some trial and error to get the setup right, but the arena now consists of a small cup of agar enclosed by Plexiglas. A dab
of yeast paste—a delicacy for Drosophila—in the middle of the cup gives the flies something to fight over. For male flies, the researchers up
the ante by sticking a headless female in the center of the ring. (The males seem to find decapitated females just as attractive as intact
ones, and the headless ones can’t fly away.)
After poring over more than 2000 video-taped interactions between male flies, Kravitz and colleagues identified nine distinct acts of
aggression in a 2002 paper in the Proceedings of the National Academy of Sciences(PNAS).
These moves included “wing threats” in which one fly faces another and suddenly raises both wings, “fencing” in which one fly
pokes a leg at another fly, “lunges” in which one fly stands up on two hind legs and slams down on his opponent, and “boxing,” which
looks about like it does in humans, if you add two limbs and subtract the gloves.
Whichever fly started the fight was most likely to win, especially if his first move was a strong one, the researchers also found. For
example, an instigator that used a slow “approach” move, in which he lowered his body and walked toward his opponent, had
3-to-1 odds of ultimately making his opponent retreat. But flies that started with a more intense move, such as fencing or wing threat,
improved their odds to 16 to 1.
Recent work by Kravitz’s team sheds further light on how flies form and maintain hierarchical relationships. When flies that had lost
their first fight reentered the ring after a 30-minute time-out, they almost never won. First-time losers had a 0-5-5 (win-loss-draw)
record in rematches with their first opponent and a similarly feeble 0-6-6 record against naive opponents who’d never fought another
fly, Kravitz and colleagues reported in the 16 November 2006 PNAS. First-time losers lunged less and retreated more in their second
fights, and they rarely made the first move; they only managed wins against other losers.
The researchers also found that flies appear to remember not just the outcome of their first fight but also the opponent. In sec-
ond fights, familiar opponents had fewer aggressive encounters than did unfamiliar opponents. First-time losers tried out a few
more lunges early on in fights against unfamiliar winners than in fights with the fly they’d lost to previously.
Like males, female fruit flies don’t shy away from conflict. They may not be as easily provoked as males, but given a dab of delicious
yeast to fight over, a pair of females will do their worst. (“They might be interested in headless males,” Kravitz says. “We haven’t
looked.”) Although males and females employ some common moves, female fights never escalate to “boxing” and “tussling” (a
barroom-brawl mix of holding, punching, and rolling around on the ground) as do the most intense fights between males, Kravitz and
colleagues reported in PNAS in 2004. Instead, females frequently head butt and shove—tactics rarely used by males. Females
also showed no evidence of dominance hierarchies. Unlike fights between males, in which a clear victor typically emerges, fights among
females seesaw indefinitely.
More recently, Kravitz’s team has begun to investigate the genetics behind these gender differences. The group’s initial experiments
have focused on a gene called fruitless(fru) that has long been studied for its role in determining sex-specific courtship behavior. The frugene is
spliced differently in males and females, creating distinct messenger RNA transcripts. The male transcript can be used to make protein, but
the female transcript apparently cannot. In 2005, Barry Dickson of the Research Institute of Molecular Pathology in Vienna, Austria, and
colleagues reported in Cell that female flies genetically altered to make the male version of fruperformed courtship behaviors usually seen
in males and courted other females (Science, 3 June 2005, p. 1392). Male flies given female frubarely courted at all. The frugene has a similar effect on fighting
styles, Kravitz, Dickson, and colleagues reported in the December 2006 issue of Nature Neuroscience. Males with the female version of fruwere more likely to fight females than to
court them. The altered males also fought like females, using head butts and shoves; they never boxed. In addition, males with female fru did not appear to form dominance relationships
with other males. Conversely, female flies with the male version of fru tended to fight like males. Overall, the findings suggest that fru establishes the neural circuitry for aggressive
behavior, just as it does for courtship behavior.
To get at that question, he extracted these dauntless flies from the fight cage and mated them with random females from the same gen-
eration. Then he started the process all over. After 21 generations, he’d created a superaggressive line of flies that were quicker to fight
and fought longer and more intensely than a line of flies created by selecting random males from the fight cages. Next, Dierick used DNA
microarrays to look for changes in gene expression in the aggressive flies. In this strain, 42 genes had increased or decreased
their activity by 25% or more, Dierick and Greenspan reported in the September 2006 issue of Nature Genetics. These genes,
they noted, have diverse roles, including muscle contraction, energy metabolism,
and cuticle formation.