Patterns of body temperature, activity, and reproductive behavior in a tropical murid rodent, Arvicanthis niloticus

Nile grass rats (Arvicanthis niloticus), are murid rodents from tropical Africa that exhibit diurnal patterns of wheel-running. In the present paper we describe the temporal organization of several other behaviors in these animals, as well as daily rhythms in their body temperature. In the first experiment, we characterized rhythms of gross motor activity and core body temperature in four adult females implanted with telemetry transmitters and kept on a 12:12 light:dark (LD) cycle. In all animals body temperature and gross motor activity were clearly diurnal, with peaks often occurring around dawn and dusk. In the second experiment we recorded the times of mating and parturition in eight mating couples housed in a 12:12 LD cycle. We monitored animals 24 h a day using a time-lapse video recording system, beginning when males and females were paired, and ending after the birth of the second litter and the associated post-partum copulation. Mating almost always began just before the lights came on, and parturition generally occurred in an "anticrepuscular" pattern, outside of the periods around dawn and dusk. Thus, these animals exhibit an interesting mosaic of temporal adaptations, with some crepuscular tendencies expressed within a predominantly diurnal pattern.