Saturday, November 25, 2006

Biological basis of aggression

Is it typical in animal species that there are significant, genetic differences between males and females in common behavior? The answer is yes, apparently, for fruit flies. And there is even a single gene whose slightly different forms in males and females produces differing behavior typical of each sex:

Fighting Like a Girl or Boy Determined By Gene in Fruit Flies
Fighting like a girl or fighting like a boy is hardwired into fruit fly neurons, according to a study in the Nov. 19 Nature Neuroscience advance online publication by a research team from Harvard Medical School and the Institute of Molecular Pathology in Vienna. The results confirm that a gene known as “fruitless” is a key factor underlying sexual differences in behavior. The findings mark a milestone in an unlikely new animal model for understanding the biology of aggression and how the nervous system gives rise to different behaviors.

This gene was already known to control courting behavior, which (unsurprisingly) differs between males and females. But the differences go beyound courting:
The fruitless gene is known for its role in male courtship. The large gene makes a set of male-specific proteins found exclusively in the nervous system of fruit flies, in about 2 percent of neurons. The proteins are necessary for normal courting. Males missing the proteins do not court females, and they sometimes court males, other research groups have shown. Females with a male version of the gene perform the male courting ritual with other females.

The same gene directs another sex-specific behavior – fighting patterns, the new study shows. Female fighting, for example, largely involves head butts and some shoving. Males prefer lunges; they rear up on their back legs and snap their forelegs down hard – sometimes nailing an opponent that is slow to retreat.

The flies undergo a major role reversal when the male and female gene versions are switched. With a feminine fruitless gene, male flies adopt more ladylike tactics, mostly the head butt and some shoving. With the masculine fruitless gene, females instinctively lunge to the exclusion of their usual maneuvers.

Can such results be extrapolated to more complex animals like, say, humans? Of course not, at this early stage. But it's a start. The next step is to investigate just how the fruit fly gene tweaks the fly's nervous system to yield specific behavior:
The findings provide a welcome guidepost to help enable future research to track down the underlying neural circuitry, said Bruce Baker, a biology professor at Stanford who first linked the fruitless gene to male-specific courtship behavior. “That’s a pretty big thing,” Baker said. “We can think about understanding in molecular detail how we go from the initial genes and the proteins they encode to the nervous system that causes our body to respond in certain ways.” More generally, he said, such studies form a potential bridge between systems neuroscience studies of behavior and modern molecular neuroscience research into individual neurons and synapses.

Once that is understood in fruit flies, researchers can approach analogous behavior in more complex animals. As another account of the research explains,

Gender-bending boy fruit flies fight like girls
It is important to learn about such complex behaviors in a simple organism, and then apply this knowledge to higher and higher forms while ultimately trying to gain insight into human behavior, Kravitz said.

People do not have an exact equivalent to the "fruitless" gene, Kravitz added, but probably have other human genes serving similar functions.

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