Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Simon, Anne F.

Abstract

Social interactions among animals can be complex, and abnormal social behaviours may result in negative fitness consequences for both the individual displaying them, and the entire group. To understand the neural basis of complex social behaviour, we can study simpler behaviours that precede and mediate them. Social spacing, the typical distance between individuals in a group, is an easily quantifiable behaviour in Drosophila melanogaster. Here, I investigated the neural circuitry underlying social spacing through the lens of Autism-candidate gene neuroligin 3. Based on the Nlg3 enrichment pattern in adult fly brains, I hypothesized that nlg3-expressing neurons, along with the mushroom bodies and protocerebral bridge, were involved in this behaviour. I determined that all the aforementioned structures are involved, and there is likely sexual dimorphism in this neural circuitry. This research contributes to understanding the role Nlg3 plays in social spacing and reveals more routes of neural connectivity to be investigated.

Summary for Lay Audience

Social interaction among humans has allowed us to create our modern society. Underlying each social interaction are complex patterns of neural signalling that give us the ability to perceive cues and understand each other; this is called neural circuitry. There is a surprising lack of information regarding the neural circuits that govern our behaviour, and because of that we also lack knowledge pertaining to how abnormal social behaviours occur. Abnormal social interaction can lead to negative consequences for an individual and their social group, so why and how might this occur? To investigate this, we can use the vinegar fly (a.k.a. the fruit fly) Drosophila melanogaster. Flies display numerous social behaviours, from complex courtship songs to simpler behaviours such as social spacing. To better understand the neural circuitry of complex behaviours, we can study simple ones like social spacing because it often precedes and mediates the complex behaviours. Just as we have a preferred social distance, flies will repeatedly choose a to maintain a specific amount of space from each other. Additionally, about 75% of disease-related genes in humans have a similar gene in the fly, and there is a remarkable amount of similarity in how certain parts of our brains function compared to flies. These similarities allow us to study how genes related to abnormal social interactions, such as those seen in autism spectrum disorders, can affect neural circuitry. To investigate social spacing neural circuitry, I used the fly counterpart to a gene associated with autism (autistic individuals often display abnormal social space) in humans called neuroligin 3. This gene is involved in determining how neurons interact with each other, and previous research has shown that mutating this gene affects social spacing. To get a better idea of which neurons are involved in this behaviour, I investigated brain regions that contain the Neuroligin 3 protein. Here I show that brain structures enriched with Nlg3 are involved in social spacing neural circuitry, and that there may be sex differences in the circuitry as well. From here, more studies can be conducted to further specify the neuronal underpinnings of social spacing.

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