Melatonin secretion in a strictly subterranean mammal, the Damaraland mole‐rat (<i>Cryptomys damarensis</i>)

Abstract

Abstract Subterranean mammals inhabit an environment that is normally devoid of light and are therefore deprived of photoperiodic information that can be used to time important life‐history events. An assessment was made of whether melatonin secretion in a strictly subterranean rodent, the Damaraland mole‐rat Cryptomys damarensis , can be modified by photoperiod. In experiment 1, a clear diurnal rhythm of melatonin secretion in animals housed under a neutral photoperiod (12L:12D) was observed, with significantly higher melatonin concentrations in the dark compared to the light phase. The same diurnal melatonin rhythm was found 1 day after animals were transferred to either continuous light or continuous dark, suggesting that a circadian rhythm was maintained under acute exposure to light and dark. In experiment 2, melatonin secretion was monitored in a long (14L:10D) and short day (10L:14D) photoperiod and was found to be modified by the photoperiodic change. We therefore suggest that the Damaraland mole‐rat possesses a circadian melatonin rhythm that can be physiologically modulated in response to photoperiod.