Circadian rhythms of locomotor activity in captive eastern rock sengi

Abstract

We investigated locomotor activity rhythms in the little-studied wild-caught eastern rock sengi (Elephantulus myurus) from Goro Game Reserve, Limpopo Province, South Africa. To assess whether locomotor activity is endogenously entrained by the light–dark cycle, animals (n = 13) were subjected to three different light-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 light entrainment 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-individual variation. Under DL, the total percentage of activity was approximately equal during the light (50.4% 7.8%) and dark phase (49.6% 7.8%). E. myurus was on average active 25% of the 24-h day with a nocturnal–diurnal ratio of 0.8 under LD1 and exhibited locomotor activity under controlled conditions similar to that of closely related species in the wild. In 62% of the animals, activity was highest around dawn, lowest during the afternoon and intermittently expressed throughout the night. Little quantitative data are available on the daily locomotor activity rhythms of sengis particularly in response to the light–dark cycle. This study provides valuable quantitative data on locomotor activity rhythms in E. myurus.