Circadian rhythms of locomotor activity in the Lesotho mole-rat, Cryptomys hottentotus subspecies from Sani Pass, South Africa

Jul 29, 2006Physiology & behavior

Daily activity patterns in Lesotho mole-rats from Sani Pass, South Africa

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Abstract

91.7% of Lesotho mole-rats adjusted their activity patterns to a 12L/12D light cycle.

The majority of mole-rats displayed a monophasic nocturnal activity preference.
In constant darkness, 83.3% of mole-rats exhibited a free-running circadian rhythm with an average duration of 24.07 hours.
The timing of activity rhythms remained consistent when transitioning from light to dark conditions.
Mole-rats took an average of 9.4 days to readjust to a new light-dark cycle after initial exposure.
91.7% of the mole-rats adapted to an inverted light regime and maintained significant nocturnal activity.

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The Lesotho mole-rat is a social subterranean rodent that occurs at altitude in the Drakensberg mountain range. As a consequence of living permanently underground these animals rarely if ever are exposed to light. The visual system of African mole-rats is particularly regressed whereas the circadian system is proportionately conserved. This study investigated the locomotor activity patterns of 12 Lesotho mole-rats maintained under a range of different lighting regimes. The majority (91.7%) of mole-rats entrained their activity patterns to a LD photoperiod of 12L/12D. The mole-rats displayed a monophasic nocturnal activity preference. Under constant dark (DD) most of the mole-rats (83.3%) showed a free running circadian activity pattern with a tau of 23.8 h to 24.4 h (mean+/-S.E.M.: 24.07 h+/-0.07 h; n=10). The phase of the activity rhythms each mole-rat exerted during the previous LD-cycle did not change when the animals started free-running after being placed in constant conditions. The duration of re-entrainment to a second bout of LD 12:12 amounted to 9.4+/-2.03 days (mean+/-S.E.M., n=10). Eleven mole-rats (91.7%) adjusted their locomotor activity rhythms to an inversed light regime DL 12:12 and displayed significant nocturnal activity preference. The animals required 9.73+/-2.01 days (mean+/-S.E.M., n=11) to adjust to the DL-photoperiod. The Lesotho mole-rat thus possesses a functional circadian clock that responds to a photic zeitgeber.

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Circadian rhythms of locomotor activity in the Lesotho mole-rat, Cryptomys hottentotus subspecies from Sani Pass, South Africa

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