Locomotory rates of well-fed and food deprived animals both on and off bacteria. In all species, the baseline locomotory rate or frequency (mean ± SEM) is represented by the first column and was calculated for well-fed worms transferred to an empty agar plate (no bacteria). Second column - locomotory rate for well-fed worms transferred to a bacterial lawn. Third column - locomotory rate for previously food-deprived worms transferred to a bacterial lawn. (A-E) C. elegans, C. briggsae, Caenorhabditis sp. 3, O. myriophila, and Pellioditis typica all exhibited basal and enhanced slowing responses. For all these species, there were statistically significant differences among the groups by 1-factor ANOVA (P << 0.001). Asterisks indicate statistically significant differences in planned pairwise comparisons between 'no food' and '+bacteria (well-fed)' [asterisks over this column] or 'no food' and '+bacteria (food-deprived)' *P < 0.05, ** P < 0.01, *** P < 0.001. (F-H) R. axei, Pristionchus pacificus and Panagrellus redivivus did not exhibit either basal slowing or enhanced slowing responses. There were no statistically significant differences among the groups (1-factor ANOVA, P > 0.05) for R. axei. Panagrellus and Pristionchus moved significantly faster on bacteria than off bacteria, but there was no significant difference between well-fed or food-deprived worms (P > 0.05). (A-F) Manual counting of body bends was used . The numbers of worms tested varied in each column: C. elegans (n = 60-72); C. briggsae (n = 87-109), C. sp. 3 (n = 54-80), O. myriophila (n = 139-146), P. typica (n = 101-145), R. axei (n = 62-89) (G, H) Automated tracker scoring of locomotory rate was used. Number of worms scored per column: P. pacificus (n = 14-17), P. redivivus (n = 21). Both manual and automated tracker methods were used to quantify locomotory rate for all species other than Pristionchus pacificus and Panagrellus redivivus (automated only) and Pellioditis typica (manual only); results were comparable and yielded the same statistical significance.