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Fig. 3. Changes in cryophilic movement are attributed to changes in cryophilic
bias. (A) Scatter plots show the correlation between run orientation and run
duration of the detailed crawling trajectories exhibited by individual
well-fed wild-type (WT) worms navigating a linear spatial thermal gradient at
T>TS (upper plot) and at
T<TS (lower plot). The starting point of all
runs is set to the origin. Each black dot denotes the relative end-point of
each run; duration is indicated by distance from the origin (see scale bar)
and run orientation is indicated by the angle with respect to the thermal
gradient (defined to be 0° for worms crawling up the spatial gradient,
shown by the arrow). For wild-type worms tested at
T>TS (cultivated at 15°C and allowed to
navigate on a gradient between 18–22°C), runs oriented down the
gradient are extended, and runs oriented up the gradient are shortened. By
contrast, for wild-type worms tested at T<TS
(raised at 25°C and allowed to navigate on a gradient between
18–22°C), there is no significant correlation between run
orientation and duration. Each scatter plot represents run statistics
collected from 
1000 runs exhibited by 100 worms. (B) Plots of mean
run duration as a function of run orientation of wild-type animals,
corresponding to the scatter plots in A. Error bars represent 1 s.e.m.
Cryophilic bias at T>TS is represented as
prolonged runs pointed down the gradient (grey data points, fit to a constant
with P<10–5). The weak or undetectable
thermotactic response at T<TS is represented
as invariance of run duration with run orientation (black data points, fit to
a constant with P>0.1). (C) Two measures of cryophilic behavior
– the cryophilic bias, calculated using
Eqn 1, and the mean of cryophilic
migration after 15 min – are plotted for wild-type worms that had been
starved for different durations. Errors bars are 1 s.e.m.
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