Bai, JihongHassinan, Cera2025-08-012025-08-012025-08-012025Hassinan_washington_0250E_27629.pdfhttps://hdl.handle.net/1773/53708Thesis (Ph.D.)--University of Washington, 2025Locomotion is a fundamental component of behavior that is established and refined throughout development into adulthood. The model organism Caenorhabditis elegans is a powerful model to study the development of rhythmic locomotion due to its well-defined timecourse of development, powerful genetic tools, a fully resolved connectome of both sexes, and an array of naturalistic behaviors. C. elegans perform crawling, swimming and transitions between these gaits, readily adapting to their environmental conditions. Here, I comprehensively investigate the establishment and maintenance of rhythmic locomotor behaviors–swimming and crawling–in wild-type hermaphrodite C. elegans across various developmental stages. To do this, I assayed rhythmic locomotor behavior of young L1, late L1, L2, L3, L4, and adult hermaphrodite worms and applied principal component analysis (PCA) to transform both swimming and crawling postural data into a low-dimensional space. My research revealed that, similar to crawling, swimming behavior in C. elegans can be distilled into four principal components, referred to as ‘eigenworms’. However, the characteristic eigenworm shapes associated with swimming differ from crawling. Further, I analyzed the progression of coordination of locomotor behavior over the course of development. My findings reveal that young L1 animals can perform adult-like swimming and crawling behaviors but struggle to maintain an organized rhythm. By the time animals reach the late L1 stage, rhythmic locomotion stabilizes for both swimming and crawling. From these discoveries, I speculate that the neural circuits in young L1 stage C. elegans are immature, limiting their ability to fully integrate sensorimotor feedback in the rhythmic networks required for stable, smooth motor output. Remarkably, we observed juvenile C. elegans generate coordinated rhythmic locomotion during this period of rapid growth into adulthood, managing to withstand substantial restructuring of neuronal networks demonstrating a striking example of circuit degeneracy. To study the emergence of sexual dimorphism in locomotor development, I compared findings in hermaphrodite swimming development to their male counterparts. My analysis revealed differences in adult male swimming, reflected in a more complex higher-dimensional behavior. These differences coincide with the development of neural circuitry and sensory organs in the male-specific tail, potentially revealing a link between swimming and sexual maturation. Overall, these findings lay a groundwork to investigate the molecular mechanisms underlying the neural dynamics of locomotor behaviors across development and between sexes.application/pdfen-USCC BYC. elegansDevelopmentEigenwormsHermaphroditeLocomotionMaleNeurosciencesMolecular and cellular biologyThesis