ResultsÂ
In the marking experiment, the main prediction of the Division of Labor
Hypothesis was not supported, as we found no difference in thermal
persistence between foragers that forage near the thermal maxima and
those foraging near the thermal minima (Figure 1; Table 1). However,
foragers demonstrated a higher thermal persistence than non-foragers,
which is consistent with the Thermal Acclimation Hypothesis. Ants found
in lower chambers of the nest had a lower thermal persistence than those
collected from the higher chambers of the nest (Figure 2; Table 1),
which could potentially be explained by either Acclimation or Division
of Labor. There was not a strict division of labor between ants foraging
during thermal maxima and those foraging during thermal minima, as
several workers were marked at both time points (Figure 1). Nonetheless,
their frequency was far lower than expected by random temporal
distribution (Fisher’s Exact Test, p<0.0001). We separately
tested for differences in thermal persistence among the 11 colonies in
this experiment. One colony had an appreciably greater thermal
persistence, and this difference was manifested in the whole model
analysis (Table S1; Figure S2; Wald test X2 = 19.04,
df=10, p<0.04; N=399).
In the circadian rhythm experiment, results indicated short-term colony
thermal acclimation as well as circadian regulation of thermal
persistence (Figure 3; Table 2). Colonies kept at temperatures above
ambient demonstrated greater thermal persistence than those maintained
at ambient, and colonies maintained at a cooler constant temperature
demonstrated lower thermal persistence. Thermal persistence was
different between the thermal maxima and the thermal minima, in all
treatments, and particularly so under constant conditions. This effect
of time of day was not found in field-collected foragers. The
performance of workers removed from colony fragments every 12 hours over
the time series did not atrophy over the duration of trials for up to
four days, indicating that the results are not a spurious consequence of
performance during captivity (Figure S1). As in the marking experiment,
we separately tested for differences in thermal persistence among the 11
colonies in the experiment. Two colonies had an appreciably lower
thermal persistence than the others (Table S2; Figure S3; Wald test
X2 = 21.7=, df=10, p<0.01; N=402).