Circadian activity rhythms in the solitary cape molerat (Georychus capensis: bathyergidae) with some evidence of splitting.

Circadian activity patterns were measured in the solitary, subterranean Cape molerat, Georychus capensis, under fixed 12:12 LD, constant dark DD, and constant light LL photoperiods for 250 consecutive days using passive infra-red activity sensors. The molerats displayed significant nocturnal activity rhythms under 12:12 LD and free-running rhythms (23.5 h < tau > 25.8 h) under constant conditions. In one individual evidence was found of splitting of the activity rhythm under constant dark; the split rhythms free-ran with short- and long-periods of 23.6 h and 24.7 h, respectively. These data show that, despite degenerate retinae, G. capensis (i) are capable of perceiving light at the level of the circadian pacemaker; (ii) can entrain endogenous activity oscillators to fixed photoperiods; and (iii) display evidence of a free-running activity oscillator.