The first comprehensive molecular analysis of aggressive behavior in any laboratory species is reported in a study to be published in the September 2006 issue of Nature Genetics. Herman Dierick and Ralph Greenspan developed an original set of assays to record and quantify aggression in the fruit fly Drosophila melanogaster.
Most laboratory strains of D. melanogaster rapidly lose the aggressiveness that is common to strains in the wild, suggesting that aggressive behavior might be recoverable in laboratory strains by deliberately selecting for it. Dierick and Greenspan devised a new 'two-male arena assay', in which twenty pairs of males were placed in a chamber containing separate arenas, and assessed for several parameters related to aggression, including the frequency, intensity, and total amount of time spent fighting (see video and still image). More aggressive males were then selected and mated to random females, a procedure which was repeated for more than twenty generations. Flies in the final generation were thirty times as aggressive as those in the first generation.
The authors report that approximately eighty genes were significantly differentially expressed between the more aggressive and less aggressive flies. One of the genes, Cyp6a20, when mutated, alone had a significant effect on aggressive behavior. Although it is not yet possible to generalize from these preliminary data, the assay and approach used should set a new standard for the genetic analysis of aggressive behavior.
Ralph Greenspan (The Neurosciences Institute, San Diego, USA)
Abstract available online.
(C) Nature Genetics press release.
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