Fig. 3. Body size and circadian rhythms in locomotor activity for B. terrestris workers in a constant laboratory environment. Individual workers were monitored from the day they emerged from the pupa. (A) Representative actogram for an individual small bee. The height of the small bars within each day corresponds to the locomotor activity in a 5 min bin. Other details of the actogram are as in Fig. 2A. This individual emerged from the pupa at day 4, and had significant circadian rhythms at 6 days of age (power=273, determined after 6 days of age). There was an alternation in FRP at 13 days of age. (B) Representative actogram for an individual large bee. Details of actogram as in A. This individual is from the same trial as the one in A, emerged from the pupa at day 3, and had significant circadian rhythms for the first time at 3 days of age (power=505). (C) The relationship between body size and the strength of circadian rhythms. The broken line represents the regression for the power of circadian rhythms on the length of the forewing marginal cell (an index for body size; regression analysis; N=41, R²=0.2, P<0.005; y=264x–447). (D) The power of circadian rhythms in small and large bees. Numbers within bars indicate sample size. The differences are statistically significant (unpaired t-test, P=0.0015). (E) Age at onset of circadian rhythms for large (broken line, N=17) and small (continuous line, N=25) workers. The differences between small and large bees were statistically significant (Kaplan–Meier Survival Analysis, Breslow statistic, P<0.025).