Article Figures & Data
Figures
- Figure 1.
Apparatus for delivering temperature steps to unrestrained worms. A thin agarose film (gray circle) was glued beneath a hole in a Plexiglas plate, forming a trampoline-like arena. The worm was placed on the agarose film, the temperature of which was controlled by means of two insulated fluid-filled chambers containing buffer at different temperatures. Temperature steps were produced by sliding the chambers to the left, as shown by the arrow, with the agar film remaining stationary. Temperature was monitored throughout the experiment by probes placed in contact with the underside of the agarose film.
- Figure 2.
Ethograms for wild-type worms subjected to a downstep plotted on two different time scales. A, A complete experiment. Each row represents the data from one worm; thirty-nine worms are shown. White regions indicate the forward state; black regions indicate the reversal and omega-turn states. B, Expanded view of data near the time of the step in A. Here, black regions indicate the reversal state and gray regions indicate the omega-turn state. The temperature protocol is indicated below each graph.
- Figure 5.
The effect of a temperature step on the six rate constants for transitions between behavioral states in wild-type animals. Each graph shows the effect on the rate constant for the indicated transition (e.g., forward to reversal) as a function of time relative to the temperature step. Rate constants were computed as described in Materials and Methods. Two traces are shown: the rate constant in response to a downstep and the rate constant in a control experiment using a sham step. Regions between the downstep and the control rate constant curves are shaded either black to indicate where the rate constant in the downstep experiment was greater than the rate constant in the control experiment, or gray to indicate where the rate constant in the control experiment was greater than in the upstep experiment. The temperature protocol is shown at the bottom of the figure. Asterisks indicate significant differences from control in the time window indicated by the horizontal line. Note that a different vertical scale is used in each graph. Data are from the experiment shown in Figure 3, A1 and A2.
- Figure 3.
Behavior of wild-type, ttx-3, and unc-86 mutant worms in response to step changes in temperature. The average probability of finding a worm in each of three behavioral states [forward (circles), reversal (triangles), or omega turn (squares)] is plotted in 10 sec bins versus time. Worms were subjected to one of three test conditions: a sham temperature step as described in Materials and Methods (top row), a downward step (downstep) from 20 to 17°C (middle row), or an upward step (upstep) from 20 to 23°C (bottom row). The temperature protocol is indicated below each graph. Within graphs, the shaded region represents the poststimulus period. Data are presented as means ± SEM; n indicates the number of worms in each group.
- Figure 4.
The effect of temperature steps on the frequency of avoidance responses in wild-type, ttx-3, and unc-86 animals. Worms were subjected to one of three test conditions: a sham temperature step (data not shown), a downward step (downstep) from 20 to 17°C (top row), or an upward step (upstep) from 20 to 23°C (bottom row). Avoidance-response frequency, defined as the number of reversal-omega transitions per animal per second, is plotted versus time in 10 sec bins. The temperature protocol is indicated below each graph. Within graphs, the shaded region represents the poststimulus period. The dotted line shows the average frequency in the prestimulus period.
- Figure 6.
Summary of the effects of temperature steps on rate constants in wild-type and ttx-3 mutants. Circles represent behavioral states; shading within circles indicates the effect of the temperature step on the probability of the indicated state (F, forward; R, reversal; Ω, omega turn) as shown in the key. The thickness and line style of arrows indicates the effect of the temperature step on rate constants. The rate constant data of Figure 5 are summarized at the top left; similar data (summarized in Table 2) were used to construct the other three panels. Note that the diagrams on the bottom refer to the run phase of the turn-and-run response, such as the response depicted in Figure 3B3 (20 –200 sec).
Tables
- Table 1.
Responses of wild-type and thermotaxis mutants to temperature steps as predicted by the pirouette hypothesis
Stimulus Wild-type Cryophilic (ttx-3) Thermophilic (unc-86) Downstep Turn Run Turn Upstep Turn Turn Run The term “turn” means an increase in the probability of the reversal and/or the omega states with a decrease in the probability of the forward state; conversely, “run” means an increase in the probability of the forward state with a decrease in the probability of the reversal and/or omega states.
- Table 2.
Effect of temperature steps on average rate constants for behavioral state transitions in wild-type and ttx-3 animals
Transition Experiment Wild type ttx-3 Forward-reversal Control 0.038 ± 0.002 0.059 ± 0.003 Downstep 0.052 ± 0.003* 0.030 ± 0.002* Upstep 0.021 ± 0.001* 0.061 ± 0.002 Forward-omega Control 0.026 ± 0.001 0.029 ± 0.001 Downstep 0.060 ± 0.003* 0.024 ± 0.002 Upstep 0.026 ± 0.001 0.022 ± 0.001* Reversal-forward Control 0.065 ± 0.006 0.120 ± 0.004 Downstep 0.029 ± 0.003* 0.055 ± 0.004* Upstep 0.094 ± 0.011 0.109 ± 0.009 Reversal-omega Control 0.195 ± 0.006 0.232 ± 0.010 Downstep 0.218 ± 0.010 0.128 ± 0.007 Upstep 0.232 ± 0.013 0.275 ± 0.012* Omega-forward Control 0.648 ± 0.016 0.610 ± 0.016 Downstep 0.539 ± 0.010* 0.423 ± 0.013* Upstep 0.687 ± 0.026 0.646 ± 0.019 Omega-reversal Control 0.033 ± 0.005 0.019 ± 0.004 Downstep 0.034 ± 0.004 0.028 ± 0.004 Upstep 0.014 ± 0.004 0.045 ± 0.006* Rate constants were averaged in the time window 20-200 sec after the temperature step (mean ± 1SE). Asterisks indicate significant differences relative to control rate constants averaged across the same time window (Mann-Whitney; p < 0.05). - Table 3.
Behavioral strategies for thermal migration in response to four combinations of direction of locomotion and rate of temperature change
Direction relative to preferred temperature ΔT/dt Experiment Behavioral strategy Away − Downstep wild type Turn Downstep thermophilic Away + Upstep wild type Turn-and-run Upstep cryophilic Toward − Downstep cryophilic No response Toward + Upstep thermophilic Run Plus signs indicate ΔT/dt > 0; minus signs indicate ΔT/dt < 0. Behavioral strategies are defined in the legend of Table 1.
