Rearing C. elegans on Parafilm-wrapped NGM Plates Impacts Habituation Behavior

Abstract

Scientists use Parafilm to seal Caenorhabditis elegans cultures on Nematode Growth Media (NGM) petri plates for short-term storage to reduce the likelihood of contamination and improve moisture retention. However, we found that maintaining worms on plates wrapped with Parafilm can affect multiple behavioral metrics when assaying tap-habituation behavior using the Multi-Worm Tracker (MWT). Most notably, worms cultured on parafilm-wrapped NGM plates exhibited slower speed of initial response to tap followed by marked sensitization. These findings suggest that labs should be conscious of the possibility that Parafilm may induce behavioral changes in C. elegans when conducting experiments.

Figure 1. Comparison of habituation behavior in Caenorhabditis elegans reared on Parafilm-wrapped vs non-wrapped plates.

In all panels, the Parafilm-wrapped (P) condition is represented by light grey and the non-wrapped (NP) condition is presented in dark grey. All worms are N2 wild-type, fed with OP50 E. coli , tested at age 96h. Worm length (A) and width (B) were not significantly different between the two conditions. (C) Habituation of speed of reversal of both Parafilm-wrapped and non-wrapped worms, measured in body lengths/s over the course of 30 taps. Error bars denote standard error of the mean. (D) Reversal response speed to only the first five stimuli were statistically different between groups. (E) Speed of movement before the first four taps was measured in the interval beginning 3s before the tap and ending 0.1s before the tap. (F) Speed of movement after the first four taps was measured in the interval beginning 0.1s after the tap and ending 1s after the tap. (G) Population frequency distributions of the bias measure for the two conditions, where an increasing positive value on the X-axis indicates an inclination for forward motion, and an increasingly negative value indicates more backward motion in locomotion behavior. Bias before the first four taps (H) and after the first three taps (I) , and the frequency of direction change before (J) and after (K) the first four taps were also compared between the two conditions. (L) The amount of weight loss in the plates was compared between the two conditions after 11 days. * = p<0.05 ** = p<0.01 *** = p<0.001.