Directional Locomotion of C. elegans in the Absence of External Stimuli

Abstract

Many organisms respond to food deprivation by altering their pattern of movement, often in ways that appear to facilitate dispersal. While the behavior of the nematode C. elegans in the presence of attractants has been characterized, long-range movement in the absence of external stimuli has not been examined in this animal. Here we investigate the movement pattern of individual C. elegans over times of ∼1 hour after removal from food, using two custom imaging set-ups that allow us to track animals on large agar surfaces of 22 cm×22 cm. We find that a sizeable fraction of the observed trajectories display directed motion over tens of minutes. Remarkably, this directional persistence is achieved despite a local orientation memory that decays on the scale of about one minute. Furthermore, we find that such trajectories cannot be accounted for by simple random, isotropic models of animal locomotion. This directional behavior requires sensory neurons, but appears to be independent of known sensory signal-transduction pathways. Our results suggest that long-range directional behavior of C. elegans may not be driven by sensory cues.

Modeling the ballistic-to-diffusive transition in nematode motility reveals variation in exploratory behavior across species

“…A non-zero drift magnitude k ψrms = 0 indicates that in addition to purely random (diffusive) changes in orientation, there is an underlying bias (i.e. directional persistence) in the worms' turning over 100 s windows, consistent with previous studies in larger arenas [23].…”

Modelling the ballistic-to-diffusive transition in nematode motility reveals variation in exploratory behaviour across species

“…A non-zero drift magnitude k crms = 0 indicates that in addition to purely random (diffusive) changes in orientation, there is an underlying bias (i.e. directional persistence) in the worms' turning over 100 s windows, consistent with previous studies in larger arenas [23].…”

“…The worm's behavioural repertoire [16,17] is commonly characterized in terms of forward motion occasionally interrupted by brief reversals [18][19][20], during which the undulatory body wave that drives its movement [21] switches direction. In addition, worms reorient with a combination of gradual curves in the trajectory (weathervaning) [22,23] and sharp changes in body orientation (omega-turns [19] and delta-turns [24]). These elementary behaviours are combined in exploring an environment [22,25].…”

A role for Ras in inhibiting circular foraging behavior as revealed by a new method for time and cell-specific RNAi

“…Under poor environmental conditions in which C. elegans is far from food resources, it crawled around the field to search for food resources. A previous study quantitatively characterized this behavior and reported that a locomotory behavior under these conditions has a long-range directionality and cannot be explained by a simple random isotropic model of locomotion [ 19 ]. Wild-type animals moved in an apparently unbiased manner when placed on a plate without any chemicals or food (Figure 1 A).…”

“…In addition, to quantitatively measure the extent to which animals made directional tracks, we performed the analysis based on fractal analysis as described previously [ 19 ]. Briefly, the trajectory of each animal was divided into segments with length of size δ (mm), and the sum of linear distances of adjacent dividing points was computed as L δ (mm).…”