Circadian Synchrony between Mothers and Young in the European Rabbit: Or Not? A Cautionary Tale

The European rabbit Oryctolagus cuniculus, ancestor of all domestic breeds, has an unusual pattern of maternal care in which females briefly nurse their young just once approximately every 24 h, and where the pups anticipate and prepare for their mother’s arrival. Chronobiologists have seen this as a model mammalian system to study the physiological and neurobiological underpinnings of a biologically relevant circadian complex. However, observations of nursing in wild rabbits, together with studies of nursing in domestic breeds allowed free access to their young in laboratory settings, suggest that the rabbit’s pattern of daily nursing visits resembles an hourglass rather than a circadian process, well suited to the sudden starts and stops of natural nursing cycles. We consider whether there might be other such cases in the literature, including in human chronobiology, in which failing to consider the organism’s natural, evolved daily patterns of behaviour and prematurely studying these under artificially imposed laboratory time schedules might have also led to such patterns being erroneously considered circadian.