Titre |
Chronobiological background to cathemerality: circadian rhythms in Eulemur fulvus albifrons (Prosimii) and Aotus azarai boliviensis (Anthropoidea). |
Résumé |
Proximate and ultimate factors responsible for this behaviour are still being debated. However, the chronobiological background of the behaviour has largely been ignored. We studied E. fulvus albifrons and A. a. boliviensis under controlled laboratory conditions to assess whether their activity rhythm is endogenously regulated by a circadian timing system that obeys general rules found in other mammals, or whether there are characteristic differences. To this end, we carried out long-term activity recordings on individuals of both subspecies kept under constant light and various light-dark cycles (LDs) using a PC-controlled electro-acoustic device in combination with telemetric body temperature measurements. Both subspecies developed free-running circadian activity and body temperature rhythms with periods deviating from 24 h in constant light, and LDs turned out to be the most efficient Zeitgeber synchronizing this endogenous rhythmicity to the external 24-hour day. The luminosity prevailing during the dark time of the LD had a decisive effect on levels of activity in the lemurs and induced strong masking effects on their circadian activity pattern. The results indicate that, from a chronobiological viewpoint, both species should be considered as dark active primates. |