Circadian rhythms of locomotor activity in captive eastern rock sengi

Abstract

We investigated locomotor activity rhythms in the little-studied wild-caughteastern rock sengi (Elephantulus myurus) from Goro Game Reserve, LimpopoProvince, South Africa. To assess whether locomotor activity is endogenouslyentrained by the light–dark cycle, animals (n = 13) were subjected to three differentlight-cycle regimes: a 12 h light/12 h darkness (LD) cycle, a total darkness (DD)cycle and an inverse of the LD cycle (DL). Ten animals exhibited strong lightentrainment under LD1 with the total percentage of activity during the light phase(56.5% 11.9%) significantly higher than during the dark phase (43.5% 11.9%).Eleven animals expressed distinct endogenous free-running rhythms under DD(mean t = 23.6 h 0.6 h; range: 22.9 h–24.5 h), with significant inter-individualvariation. Under DL, the total percentage of activity was approximately equalduring the light (50.4%7.8%) and dark phase (49.6%7.8%). E. myurus was onaverage active 25% of the 24-h day with a nocturnal–diurnal ratio of 0.8 underLD1 and exhibited locomotor activity under controlled conditions similar to thatof closely related species in the wild. In 62% of the animals, activity was highestaround dawn, lowest during the afternoon and intermittently expressed throughoutthe night. Little quantitative data are available on the daily locomotor activityrhythms of sengis particularly in response to the light–dark cycle. This studyprovides valuable quantitative data on locomotor activity rhythms in E. myurus.