Socially Adjusted Synchrony in the Activity Profiles of Common Marmosets in Light-Dark Conditions

Abstract

Synchronized state of activity and rest might be attained by mechanisms of entrainment and masking. Most zeitgebers not only act to entrain but also to mask circadian rhythms. Although the light-dark (LD) cycle is the main zeitgeber of circadian rhythms in marmosets, social cues can act as weaker zeitgebers. Evidence on the effects of social entrainment in marmosets has been collected in isolated animals or in pairs where activity is not individually recorded. To characterize the synchronization between the daily activity profiles of individuals in groups under LD conditions, the motor activity of animals from five groups was continuously monitored using actiwatches for 15 days during the 5th, 8th, and 11th months of life of juveniles. Families consisting of twins (4 ♂♀/1 ♂♂) and their parents were maintained under controlled lighting (LD 12:12 h), temperature, and humidity conditions. Synchronization was evaluated through the synchrony between the circadian activity profiles obtained from the Pearson correlation index between possible pairs of activity profiles in the light and dark phases. We also calculated the phase-angle differences between the activity onset of one animal in relation to the activity onset of each animal in the group (ψ_on). A similar procedure was performed for activity offset (ψ_off). By visual analysis, the correlation between the activity profiles of individuals within each family was stronger than that of individuals from different families. A mixed-model analysis showed that within the group, the correlation was stronger between twins than between twins and their parents in all families, except for the family in which both juveniles were males. Because a twin is an important social partner for juveniles, a sibling is likely to have a stronger influence on its twin’s activity rhythm than other family members. Considering only the light phase, the second strongest correlation was observed between the activity profiles of the individuals in the reproductive pair. Regarding the parameters ψ_on and ψ_off, the juvenile/juvenile dyad had lower values than the other dyads, but these differences did not reach statistical significance in relation to all dyads. Comparing the results of the ψ_on and ψ_off, and correlation indices, we suggest that the latter could detect differences between the animals that were not observed in the results of the phase-angle differences. These differences could be related to changes that occur during the active phase but not only in a particular phase, such as the temporal changes during the activity phase that characterize unimodal or bimodal patterns. Based on the differences in the correlations between individuals subjected to the same LD routine, we suggest that social cues modulate the circadian activity profiles of marmosets as a result of interactions between the animals within each group. Future studies are necessary to characterize the mechanisms of synchronization that are involved in this social modulation. (Author correspondence: [email protected])

• Circadian activity rhythm
• correlation
• marmoset
• social cues
• social synchronization

Acknowledgments

We would like to thank our graduate students Henrique James, Fernanda Kolodiuk, Kahena Florentin, Luiz Cândido da Silva Júnior, Deyse Bezerra, Diego Fernandes, Camila Bessa, and Bruna Wanderley for assisting in data collection; Dr. Fidel Ernesto Castro Morales (Consulest/UFRN) and Dr. Altay Alves Lino de Souza for statistical support; Flávio Coutinho, Edinólia Câmara, and Antônio Barbosa for technical support at the Primatology Center of UFRN; and Dr. Maria de Fátima Arruda for suggestions made during the investigation.

We are also grateful to the Federal Agency for the Support and Evaluation of Graduate Education (CAPES) and the Research Support Foundation of Rio Grande do Norte (FAPERN) for financial support.