The effects of groove height and substrate stiffness on C. elegans locomotion.

The physical environment surrounding an animal has a significant impact on its behavior. The nematode Caenorhabditis elegans (C. elegans) has proved to be an excellent choice for understanding the adaptability of organisms crawling on soft surfaces. In this work, we investigate the modulation of C. elegans' behavioral kinematics in response to changes in the stiffness of the substrate and study the effect of grooves incised by the worms on their locomotion speed and efficiency. We measure the height of the grooves created by the animals on surfaces with different rigidity using confocal microscopy. Our results indicate that the kinematic properties of C. elegans, including amplitude (A), wavelength (λ) and frequency (f) of head turns depend strongly on surface properties and the height of the grooves created by them. During crawling, we observe that the animal assumes two distinct shapes depending on the stiffness of substrates. As the stiffness increases, the worm's body shape changes gradually from a 'W' shape, which is characterized by low amplitude curvature to the more common 'S' shape, which is characterized by high amplitude curvature, at intermediate values and back to 'W' on stiffer substrates. Although the efficiency is found to vary monotonically with surface stiffness, the forward velocity shows a non-monotonic behavior with the maximum on a surface, where the animal makes the 'S' shape.

Durotaxis in Nematode Caenorhabditis elegans.

Durotaxis is a process where cells are able to sense the stiffness of substrates and preferentially migrate toward stiffer regions. Here, we show that the 1-mm-long nematode, Caenorhabditis elegans are also able to detect the rigidity of underlying substrates and always migrate to regions of higher stiffness. Our results indicate that C. elegans are able to judiciously make a decision to stay on stiffer regions. We found that the, undulation frequency, and wavelength of worms, crawling on surfaces show nonmonotonic behavior with increasing stiffness. A number of control experiments were also conducted to verify whether C. elegans are really able to detect the rigidity of substrates or whether the migration to stiffer regions is due to other factors already reported in the literature. As it is known that bacteria and other single-celled organisms exhibit durotaxis toward stiffer surfaces, we conjecture that durotaxis in C. elegans may be one of the strategies developed to improve their chances of locating food.

Effect of temperature pre-exposure on the locomotion and chemotaxis of C. elegans.

The effect of temperature pre-exposure on locomotion and chemotaxis of the soil-dwelling nematode Caenorhabditis elegans has been extensively studied. The behavior of C. elegans was quantified using a simple harmonic curvature-based model. Animals showed increased levels of activity, compared to control worms, immediately after pre-exposure to 30 °C. This high level of activity in C. elegans translated into frequent turns by making 'complex' shapes, higher velocity of locomotion, and higher chemotaxis index (CI) in presence of a gradient of chemoattractant. The effect of pre-exposure was observed to be persistent for about 20 minutes after which the behavior (including velocity and CI) appeared to be comparable to that of control animals (maintained at 20 °C). Surprisingly, after 30 minutes of recovery, the behavior of C. elegans continued to deteriorate further below that of control worms with a drastic reduction in the curvature of the worms' body. A majority of these worms also showed negative chemotaxis index indicating a loss in their chemotaxis ability.