CIRCADIAN PATTERNS OF LOCOMOTOR-ACTIVITY AND BODY-TEMPERATURE IN BLIND MOLE-RATS, SPALAX-EHRENBERGI

A wide variety of organisms exhibit circadian rhythms, regulated by in ternal clocks that are entrained primarily by the alternating cycle of light and darkness. There have been few studies of circadian rhythms in fossorial species that inhabit a Microenvironment where day-night v ariations in most environmental parameters are minimized and where exp osure to light occurs only infrequently. In this study daily patterns of locomotor activity and body temperature (T-b) were examined in adul t blind mole-rats (Spalax ehrenbergi). These fossorial rodents lack ex ternal eyes but possess rudimentary ocular structures that ape embedde d in the Harderian glands and covered by skin and fur Most individual mole-rats exhibited circadian rhythms of locomotor activity, but some animals were arrhythmic. Individuals that did exhibit robust rhythms o f locomotor activity also showed rhythms of T-b. In most cases, T-b wa s highest during the phase of intense locomotor activity. Locomotor ac tivity rhythms could be entrained to light:dark cycles, and several mo le-rats exhibited entrainment to non-24-h light cycles (T-cycles) with period lengths ranging from T = 23 h to T = 25 h. Some individuals al so showed entrainment to daily cycles of ambient temperature. There wa s considerable interindividual variation in the daily patterns of loco motor activity among mole-rats in virtually all the conditions of envi ronmental lighting and temperature employed in this study. Thus, where as it appears likely that photic cues have a significant role in the e ntrainment of circadian rhythms in mole-rats, the amount of variabilit y in rhythm patterns among individuals appears to be much greater than for most species that have been studied.