A CIRCADIAN-RHYTHM OF THERMAL PREFERENCE IN THE ANT CAMPONOTUS MUS - MASKING AND ENTRAINMENT BY TEMPERATURE CYCLES

Along a stable temperature gradient and under a LD 12:12 h cycle, nurs e workers of the ant Camponotus mus Roger 1863 (Hymenoptera: Formicida e) select for the brood two different temperatures daily: 30.8 degrees C at the middle of the light period (circadian phase = 90 degrees), a nd 27.5 degrees C 8 h later, during the dark period (circadian phase = 210 degrees), this rhythm being of endogenous nature. When a 24 h tem perature cycle was superimposed along the thermal gradient, so that th e immobile brood experienced a temperature transition as they receive when translocated by nurses (8 h at 30.8 degrees C and 16 h at 27.5 de grees C), no brood translocations occurred. The thermal cycle masked t he rhythm of brood translocation when temperature fitted the daily pat tern expected by nurses. When the same temperature cycle was presented with a phase-advance, nurses did not tolerate the early thermal incre ase and removed the brood as temperature rose. However, when workers e xperienced this new phase relationship between light and temperature c ycles for more than 10 days, brood translocations were suppressed. Rec ords under constant conditions of light and temperature indicated that the overt rhythm was locked-on to the expected early increase in temp erature, so that the temperature cycle dominated over the LD cycle in resetting brood-carrying activity.