Student Theses and Dissertations
Date of Award
2025
Document Type
Thesis
Degree Name
Doctor of Philosophy (PhD)
Thesis Advisor
Daniel Kronauer
Keywords
clonal raider ants, olfaction, antennal lobe, neuroanatomy, connectome, social behavior
Abstract
Ants have been studied extensively due to their advanced social structure and communication strategies. Olfaction plays a crucial role in their social behaviors, with ants using a variety of pheromones produced by different exocrine glands to communicate. For example, ants release alarm pheromones in response to danger to alert their nestmates and to trigger behavioral alarm responses. Despite extensive behavioral studies, the neurobiological mechanisms underlying these behaviors are not well understood. The clonal raider ant, Ooceraea biroi, is an ideal species for investigating the neural circuits involved in social behavior, as it is both experimentally tractable and genetically accessible compared to other ant species. In this thesis, I describe my efforts to bridge the gap between behavior and brain function in hopes of uncovering the neural underpinnings of social behavior in O. biroi. To begin, I focused on studying alarm behavior, as identification of a pheromone that triggers a robust, consistent, and conserved behavior, like the alarm pheromone, provides an avenue to dissect the behavioral and neuronal mechanisms underpinning chemical communication. I began by characterizing the alarm response of the clonal raider ant Ooceraea biroi. During an alarm response, ants quickly become unsettled, leave their nest pile, and are sometimes initially attracted to the source of alarm, but ultimately move away from it. We find that the alarm pheromone is released from the head of the ant and identify the putative alarm pheromone as a blend of two compounds found in the head, 4-methyl-3-heptanone and 4-methyl-3-heptanol. While 4-methyl-3-heptanone and 4-methyl-3-heptanol are known alarm pheromones in other more distantly related ant species, this is the first report of the chemical identity of a pheromone in O. biroi, and the first alarm pheromone identified in the genus Ooceraea. The synthetic alarm pheromone components have been used identify a core set of glomeruli within the antennal lobe of the ant that is active in response to panic alarm-inducing compounds, including 4-methyl-3-heptanone and 4-methyl-3-heptanol. We have also identified age-related changes in alarm behavior and processing of alarm pheromones in the antennal lobe, thereby linking neural function with behavior in the clonal raider ant. To advance neuroscience in the clonal raider ant, a deeper understanding of the brain's gross anatomy is essential. To this end, we performed a comprehensive neuroanatomical analysis of the Ooceraea biroi brain to date, using immunohistochemistry, light microscopy, and advanced image processing techniques. We dissected, immunostained, and imaged the brains of forty age-matched, genetically identical individuals with confocal microscopy. Then, using 3D groupwise registration, we generated the first reference brain for the clonal raider ant. We use this new reference to conduct a 3D structural analysis of key regions putatively involved in regulating sociality and describe the neuroanatomy of major neurotransmitter systems in the clonal raider ant brain. Unexpectedly, we discovered extensive phenotypicstructural plasticity across our collection of brain samples. Half of the ants displayed a left-tilted brain anatomy, while the remaining half possessed a right-tilted 'mirror image' phenotype. In addition, 3D reconstructions revealed substantial variability in total neuropil volume across our dataset, with the most voluminous brains roughly three-fold larger than the smallest. These findings indicate clonal raider ants exhibit varied nervous system phenotypes despite apparent genotypic and experiential homogeneity. This work provides a powerful resource for the clonal raider ant neuroscience community, while simultaneously introducing novel features of the species' neurobiology which may have important significance for social behaviors and colony function. Finally, to further investigate the structural connectivity of the O. biroi brain, we imaged a whole brain at synaptic-level resolution using transmission electron microscopy (TEM). This will allow us to reconstruct neurons, identify synapses, and ultimately create a complete wiring diagram, or connectome, of the clonal raider ant brain. To accelerate the mapping of neural circuits in the EM dataset, we used convolutional neural networks to segment neurons and predict synapses. To facilitate the matching of cells between EM and light microscopy, we have registered the EM volume to the clonal raider ant reference brain atlas. We are now in the process of manual proofreading of these automatic neuron segmentations to reconstruct neural circuits. Given the importance of olfaction in the pheromone-mediated communication of the ant and massive expansion of odorant receptor genes and olfactory glomeruli in the antennal lobe compared to other insects, our initial reconstruction efforts focus on understanding the wiring logic of the ant olfactory system. In summary, this thesis represents early steps toward understanding the neural circuits underlying social behavior in the clonal raider ant. The creation of a reference brain, along with ongoing efforts to map its connectome, contributes to the expanding toolkit for investigating the neural mechanisms that govern the complex social behaviors of ants.
License and Reuse Information
This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 4.0 International License.
Recommended Citation
Lopes, Lindsey Etelvina, "Mapping the Brain of the Clonal Raider Ant: Integrating Behavior, Neuroanatomy and Connectomics" (2025). Student Theses and Dissertations. 813.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/813
Comments
A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy