Master of Science
Moehring, Amanda J.
In behaviourally isolated species, preferential mate choice for conspecifics over heterospecifics is a primary isolating barrier for reducing interspecific gene flow. Drosophila males court heterospecific females more frequently than females are sexually receptive to courting heterospecific males, emphasizing the importance of female mate preference in reproductive isolation. The neurogenetic bases of female mate preference have been elusive historically, but recent research identified the D. melanogaster fruitless (fru) P2 exon to influence both conspecific and heterospecific female receptivity. I have expanded on these findings by creating a transgenic line that expresses Gal4 under fruP2 regulation. Driving a fluorescent reporter using this line revealed fruP2-neurons in the optic tissues, brain, and ventral nerve cord. Hyperactivating or silencing these neurons significantly decreased female receptivity to conspecific male courtship. The diverse distribution of fruP2-neurons and their strong modulating role in female receptivity implies that complex multimodal signalling is integrated to control female copulatory decision-making.
Summary for Lay Audience
Speciation, the splitting of one species into two or more, underlies much of the biological diversity observed on Earth. For speciation to occur, barriers must prevent the exchange of genetic material between speciating groups. Decreased genetic exchange leads to increased differences between groups over time and eventually leads to their complete and irreversible divergence, such that they cannot reunite into a single group. Changes in mate preferences may be one of the first barriers to arise for preventing mating between speciating groups with geographical overlap. In fruitflies, males readily attempt to mate with females of other species, while females more likely reject males from other species, showing that females are the “choosier” sex. However, it is not clear how females decide if they should mate with a prospective male. Decision-making requires information processing in the brain, and development of the brain and central nervous system is dependent on instructions encoded by genes. Thus, investigating how female mating decisions arise requires consideration of both neural and genetic components.
In this project, I used gene editing to make a custom mutant fruitfly for studying neurons expressing a specific gene product, fruP2. Disrupting a genomic location unique to fruP2 was previously found to affect how often females accept mating attempts from males. I predicted that the neurons expressing fruP2 influence female mating decisions. First, I manipulated these neurons to fluoresce, which allowed them to be mapped in the central nervous system. Second, I manipulated these neurons to increase or decrease in activation, which allowed assessment of their role in female mating decisions. Neurons expressing fruP2 were found in the eyes, brain, and ventral nerve cord (fruitfly equivalent of a spinal cord). In the ventral nerve cord, neurons expressing fruP2 were found in regions connecting to the legs, wings, and reproductive organs. Increasing or decreasing activation of these neurons caused females to reject males at significantly higher rates than usual. These findings suggest that neurons expressing fruP2 transmit sensory information from the eyes, legs, wings, and/or reproductive organs to the brain and influence a female’s decision to accept or reject a prospective male mate.
Yeung, William, "Neuroanatomical characterization of fruitless P2 neurons and assessment of their role in female mate receptivity" (2021). Electronic Thesis and Dissertation Repository. 8350.