Behavioral study of fruit flies

The fruit fly genome is fully sequenced by researchers, which has shown us that their genetic makeup is fairly similar to human. Unlike the human genome, the fruit fly genome is easily manipulated to create genetically different strains, which allow us to learn more about the effects of certain genes on behavior. In particular, assessing movement-based parameters (speed, angle, and mobility) is of interest, and fortunately these are easily and efficiently monitored with video tracking. However, some studies assess behavioral outcomes such as courtship behavior, which requires a more detailed look at specific behavioral elements. This pages shows some examples of how detailed behavioral scoring is used in these types of studies. 

What makes a male court a female?

Mating behavior in fruit flies is sex specific. Basically, the male fruit fly does all the work, showing a series of courtship rituals while the female remains mainly inactive. Kido and Ito (Ochanomizu University, Japan) have carried out in-depth studies on Drosophila courtship behavior, using The Observer to assess detailed courtship behaviors in different strains of genetically modified flies. 

Can you switch off the male brain? 

Olfactory cues are very important in Drosophila courtship displays.  This has led to a great deal of research into the olfactory sensory organs (located in the antennae) and specific parts of the brain, including specialized cells that seem to be connected to olfaction in courtship behavior (such as the dorso-posterior region and mushroom bodies). By ‘feminizing’ these specific parts, researchers could investigate the role these olfactory organs in courtship behavior. Interestingly, although parts of the male flies were technically female, the male flies still acted male. 

What makes a male act like a male?

So Asami Kido and Kei Ito thought it was time to figure out what exactly makes the male act as it does during courtship. To do this, they used a genetic modification known as GAL4, which feminizes specifically targeted parts of the fly brain. The researchers were then able to carry out a large-scale behavioral screening on several GAL4 strains.

Several brain regions were studied using GAL4 feminized males; none of the regions seems to be solely responsible for sex differences in the brain. However, in strains in which almost all neurons were feminized, male courtship behavior was suppressed, suggesting that the neurological background of this behavior is distributed throughout several brain regions, and not localized to any specific region. 

What makes a male remember rejection? 

Another interesting fact about courtship behavior: male fruit flies remember rejection. Therefore, when a male fruit fly has repeatedly been rejected by potential female mates, he is less likely to court another female. This is an interesting finding that could be relevant in long term memory research. 

Gene expression changes

Winbush and colleagues from the University of Southern California, LA used RNA sequencing to identify specific genes involved in courtship, and to investigate whether transcription of these genes changes after experiences of rejection in Drosophila. To assess courtship, researchers used The Observer XT. With this software tool, courtship behaviors of male flies were quantified. The ethogram included behaviors such as attempted copulation, successful copulation, pursuit of the female, wing extension, and more. 

They indeed found that certain genes that were previously confirmed to be necessary for the formation of memory also show differential regulation, suggesting that these genes play a courtship-specific role in the memory maintenance.