Worm Breeder's Gazette 13(5): 44 (February 1, 1995)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Nematode Gymnastics: Do They Run and Tumble?

Nicol Fitzhugh, James H. Thomas

Department of Genetics, University of Washington, Seattle, WA 98195

In an effort to elucidate the behavioral mechanism governing
the chemotaxis response in C. elegans, we performed and
analyzed the results from a series of single-animal chemotaxis
assays. We hypothesized that the movement toward attractants
by C. elegans might include a component analogous to the
"run and tumble" phenomenon that occurs in bacteria in
response to chemical attractants. This response is characterized
by the suppression of tumbles (reorientation movements),
in favor of runs (continuous movement in one direction),
when a bacterium is traveling up an attractive chemical
gradient. C. elegans has movements that are somewhat analogous:
continuous forward movement (runs) occasionally interrupted
by bouts of backing and reorienting (tumbles). Based on
our hypothesis, we predicted that the length of each nematode
run would increase if the animal were traveling up an attractive
gradient, and that the frequency of tumbles would increase
if the animal were traveling down an attractive gradient.
In order to assay chemotaxis behavior, we followed an experimental
protocol similar to that devised by Bargmann et al. I, except
that we directly recorded movement of one animal in an assay.
We performed two types of assays: those with 7 microL of
isoamyl alcohol as attractant, and those without attractant.
We used keystrokes interpreted by a computer program to
record such qualities as direction of movement, times
and lengths of tumble bouts and runs, speed of movement,
etc. After running a series of both types of assays, all
data were compiled, and the run lengths and tumble frequencies
that occurred in the absence of attractant and in the presence
of attractant when moving up or down the attractive gradient
were compared.
Contrary to our hypothesis, our data indicate that run
length does not seem to be affected by the presence or absence
of attractant or orientation of movement on the gradient.
Additionally, preliminary evidence suggests that the
animals' initial choice of direction following reorientation
was not strongly biased by the gradient of attractant.
We conclude that the chemotaxis response to this odorant
by C. elegans does not include a significant component
analogous to the run and tumble response in bacteria. We
infer that another type of orientation mechanism must
control the response to attractant. We posit that this
alternate mechanism is one that allows the animal to adjust
its direction of movement while running based on information
about the gradient.
Bargmann, C. I., Hartweig, E.. and Horvitz, H. R., Cell
74: 515-527, 1993