SOCIAL INFLUENCES ON BIOLOGICAL RHYTHMS

Little attention has been given to the influence that social factors may have on biological rhythms. We maintain that this neglect stems from historical and technological circumstances in that most research in chronobiology has been aimed to discover the physiological basis for rhythmicity and that it is very difficult to study the rhythms of interacting animals. We review selected elements of the somewhat scattered literature that deals with social influences on circadian, ultradian and infradian rhythms. We find that social factors have been shown to result in the synchronization, desynchronization and disruption of biological rhythms in a wide range of organisms. By employing a time-lapse video tape recording system we were able to study the individual activity of interacting tegu lizards (Tupiranmbis teguixin). We found that some individuals demonstrated (1) social synchronization, (2) the formation of "time-territories", (3) free-running rhythms against a LD 12:12 lighting schedule, and (4) apparent arrhythmicity. We related these phenomena to the social hierarchy of the lizards. Lizards ranked intermediate often occupied time-territories separate from the dominant lizard, and under certain conditions the lowest ranking lizard exhibited a free-running rhythm that was completely uncoupled from the lighting cycle. Under other conditions the lowest ranking lizard was socially synchronized. Also using closed circuit television techniques, we studied the running wheel rhythms of three individually marked female laboratory rats housed in the same cage in continuous dim red light. The rats could compete for the running wheel by synchronizing their activity or minimize competition by desynchronizing their activity. An inspection of the raw activity data revealed that omega X was displaced from D and S, thus occupying a separate time-territory, while D and S were closely ranked socially and closely synchronized in time. Cosine curves were fit by computer to the data of each rat using the least squares method. The percent rhythm (the percent of the total variability explained by the cosine curve) and the period length (the duration of one complete cycle of the rhythmic variation) proved to be particularly useful. We found that the free-running period lengths of D and S were nearly identical while that of omega X was quite different. So omega X's rhythm was not only displaced but also uncoupled from D and S. While housed with D and S, omega X's percent rhythm was very low and erratic. However, when D and S were temporarily removed from the activity cage, the percent rhythm of omega X rose markedly and its period length increased to a value nearly identical to that of D and S from before. Upon reintroduction of D and S to the home cage, omega X became displaced from the latter : its percent rhythm dropped dramatically and its free-running period length was again much different from D and S. We explore the possibilities (1) that disturbances of the timing of rhythms could affect individual fitness at the level of ecological and social intergration, (2) that crowding may cause rhythm reschedulings and disruptions that produce effects similar to those documented in "jet-lag", (3) that time-territoriality could be a mechanism involved in the partitioning of resources among individuals in natural populations. Finally, (4) commonly housed animals even in controlled laboratory environments can modify one another's activity and perhaps physiological rhythms. This could confound attempts to control for biological rhythmicity using controlled lighting schedules. Thus, an awareness of the interaction of social behavior with rhythms may help physiologists and behaviorists to collect more reproducible data in the future.