Sleep in the wild: the anatomy and physiology of sleep in free-roaming blue wildebeest (Connochaetes taurinus)

Abstract

Comparative methods of evolutionary biology are useful tools for investigating the function/s of sleep as these still remains elusive. In the present thesis, the global aim was to investigate sleep in blue wildebeest (Connocheates taurinus) from a neuroanatomical, physiological and behavioural point of view. Furthermore, it also set out to understand how this species sleeps in its natural environment and the effects that natural behaviours can have on sleep, specifically investigating the influence of the rut on sleep/rest phasing and architecture in dominant breeding males of this species. Neuroanatomically, a detailed qualitative description of the organization of the somnogenic systems of the blue wildebeest is provided, along with a quantitative analysis of the pontine cholinergic and noradrenergic neurons, and the hypothalamic orexinergic neurons. From the basal forebrain to the pons, the nuclear organization of the cholinergic, catecholaminergic, serotonergic and orexinergic systems for the most part, showed a corresponding nuclear organization to that reported in other mammals and more specifically the Cetartiodactyla. Furthermore, the description and distribution of the GABAergic system, which was examined through immunostaining for the calcium binding proteins calbindin, calretinin and parvalbumin, was also similar to that seen in other mammals. Physiologically, sleep in the blue wildebeest was recorded, in a naturalistic setting, by means of two different measures of sleep, polysomnography (PSG) and actigraphy (ACT). The blue wildebeest were found to be polyphasic sleepers, sleeping mostly during the dark period of the day. PSG showed that total sleep time in the blue wildebeest for a 24-hour period was 4.53 h, with 4.26 h spent in non-REM sleep and 0.28 h spent in REM sleep, the remainder of the day (19.47 h) spent in Wake. Similarly, ACT showed that the blue wildebeest spent 19.23 h Active and 4.77 h Inactive. For both animals studied, Cohen’s κ showed a fair agreement between the two techniques for sleep vi measurement, although differences were observed between individual days and animals. Behaviourally, the daily activity and inactivity patterns of dominant male blue wildebeest were examined by means of actigraphy for a period of three months, which included the time of the rut. It was observed that there were no changes to the sleep phasing and architecture of the blue wildebeest during the rut, but there were changes to the total time spent in a state of inactivity. The studies presented in this thesis form the baseline for further studies of the influence of the environment and natural behaviours on sleep in the blue wildebeest. More broadly, these studies establish a framework from which studies of sleep in other large mammals in their natural environment can be established and compared in a fully quantitative manner.