Dissection of Behavioral Components and the Role of Omega/Delta Turns for the Chemotaxis of C. elegans

The chemotactic mechanism of the nematode Caenorhabditis elegans primarily consists of two components: the pirouette mechanism and the weathervane mechanism. The pirouette mechanism is a form of klinokinesis that regulates the frequency of rapid reorientation behaviors called pirouettes, which include omega/delta turns, while the weathervane mechanism involves gradual directional adjustments. Furthermore, previous studies have shown that in pirouettes, not only is the frequency of reorientation regulated, but the reorientation angle is also adjusted. However, conventional centroid-based analyses have left the postural dynamics during turns unresolved. In this study, we tracked the movement of individual worms during chemotaxis and determined the centerlines representing worm postures. From these data, we extracted turning behaviors, classified postural patterns, and quantified directional changes during turns. Our results indicate that the reorientation angle is modulated during turns to orient the animal toward the desired chemical concentrations. Additionally, we found the diversity of postural dynamics and directional changes in turn sequences. A detailed classification of turn sequences revealed that directional turning is achieved by selection of specific sequence types and adjustment of turning angles. This study provides the most detailed and quantitative analysis to date of the turning behaviors as a fundamental component of C. elegans chemotaxis.