Master of Science
The genetic tools that exist in Drosophila melanogaster make it possible to assess the influence of specific regions of the brain on complex behaviour. Examples of such behaviours include female aggression and receptivity to male courtship. Silencing a candidate region called the mushroom body (MB) was found to decrease female receptivity. Additionally, silencing a specific subset of the MB, the alpha/beta lobes, was also found to decrease receptivity. SIFamide neurons are known to effect receptivity, though manipulation of SIFamide signaling in the MB produced no such changes in receptivity. Aggression, another complex behaviour in Drosophila, was also affected by genetically controlled neural manipulation. More specifically, hyperactivation of a subset of neurons expressing the doublesex gene was found to incite high amounts of aggression in females but not males. Furthermore, the aggression demonstrated by these females differed based on the stimulus presented by the partners, with locomotion being a major elicitor of aggression.
Summary for Lay Audience
The model organism Drosophila melanogaster is highly useful in understanding the neural basis of complex behaviours. Through use of genetic tools unique to D. melanogaster, specific areas of the brain can be manipulated to assess their potential roles in facilitating behaviour. This thesis uses this strategy to explore the influence of various brain regions on female responses to partner flies, namely courtship receptivity and aggression.
Manipulation of an area of the brain called the Mushroom Body brain was found to produce reductions in female receptivity to courtship. Further assessment of this region revealed that manipulation of specific sub regions within the Mushroom Body (the alpha/beta lobes and the alpha prime/beta prime lobes) are also sufficient to influence female receptivity.
Additionally, manipulation of a small group of neurons expressing the doublesex gene was found to incite high levels of aggression in females, but not in males. This demonstrates that in D. melanogaster, the neural circuitry controlling aggression may be different between males and females. Interestingly, the aggression demonstrated by these transgenic females is variable depending on the nature of the partner fly. For example, less aggression is directed toward female partners than male partners. In an attempt to understand why males received more aggression, new partner types were introduced to the aggressive females. Females which were transgenically made to move more frequently received much higher amounts of aggression than wildtype females. This implies movement is an important stimulus for inciting the observed female aggression. However, the aggressive females also demonstrate aggression toward immobile headless males, meaning movement is not the exclusive cause of aggression. Headless males may incite aggression through chemical stimuli, though this remains to be confirmed.
This is the first known identification of neurons effecting female specific aggression and will provide a novel avenue for exploring this poorly understood behaviour. Additionally, the observation that aggressive the behaviours demonstrated are contextually specific provides new considerations for designing future experiments.
Charles, Brendan S., "Neural Regions Affecting Female Aggression and Receptivity in Drosophila melanogaster" (2019). Electronic Thesis and Dissertation Repository. 6453.