Graduate Thesis Or Dissertation
 

Circadian rhythms in Megachile rotundata (Fabricius)

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  • The rhythms of emergence, oxygen consumption, and activity were studied in Megachile rotundata with the object of comparing the results to the major properties of the biological clock such as temperature independence, susceptibility to light synchronization, and entrainment. A further objective was to compare the three rhythms to determine if they were three aspects of the same rhythm or if they were indeed three different rhythms. The emergence rhythm proved to possess a period of 23.7 h in DD and 23.0 h in LL. This difference was not statistically significant. The emergence period displayed a Q₁₀ of 1.02 for a temperature rise of 25 to 30° C and a Q₁₀ of 1.12 for a 30 to 35° C temperature rise. The rhythm was largely refractive to light but very responsive to temperature from the dark-eyed pupa stage through the adult stage. The temperature phase response curve displayed phase advances during the subjective high temperature period and phase delays during the subjective low temperature period. No transients occurred in the response of M. rotundata to a temperature pulse. The oxygen consumption rhythm responded to light and temperature in a manner similar to that of the emergence rhythms. However, no difference was detected in the length of the oxygen consumption period in LL as compared to DD. The rhythm did not respond to light entrainment (LD 12:12). The temperature phase response curve was similar to that of the emergence rhythm. The oxygen consumption rhythm was analyzed in the pre-adult and adult stages using power spectra analyses. The rhythm spectrum appeared to be less stable in the pre-adult stages than in the adult stage. The circadian component was very prominent in the adult while from two to four ultradian components appeared in the pre-adult stages. The activity rhythm proved to be very similar to both the emergence and oxygen consumption rhythms in its response to light and temperature. Again the response to light was very slight and was only detected in the period length in LL compared to the period length in DD. In LL the activity period length was 22.34 h while in DD the period length was 22.86 h. This difference of 0.52 h was significant at the five percent level. The temperature response curve was almost identical to that of the emergence and oxygen consumption response curves. A comparison of the three rhythms is drawn with the conclusion that the emergence and activity rhythms are probably the same basic rhythm. It is possible that the oxygen consumption rhythm is different from the other two but more experimentation is required before a more positive conclusion can be made.
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