Time management in a co-housed social rodent species (Arvicanthis niloticus)

Alexandra Castillo-Ruiz,Premananda Indic,William J Schwartz

doi:10.1038/s41598-018-19365-3

Abstract

Sociality has beneficial effects on fitness, and timing the activities of animals may be critical. Social cues could influence daily rhythmic activities via direct effects on the circadian clock or on processes that bypass it (masking), but these possibilities remain incompletely addressed. We investigated the effects of social cues on the circadian body temperature (Tb) rhythms in pairs of co-housed and isolated grass rats, Arvicanthis niloticus (a social species), in constant darkness (DD). Cohabitation did not induce synchronization of circadian Tb rhythms. However, socio-sexual history did affect circadian properties: accelerating the clock in sexually experienced males and females in DD and advancing rhythm phase in the females in a light-dark cycle. To address whether synchronization occurs at an ultradian scale, we analyzed Tb and activity rhythms in pairs of co-housed sisters or couples in DD. Regardless of pair type, co-housing doubled the percentage of time individuals were simultaneously active without increasing individual activity levels, suggesting that activity bouts were synchronized by redistribution over 24 h. Together, our laboratory findings show that social cues affect individual “time allocation” budgets via mechanisms at multiple levels of biological organization. We speculate that in natural settings these effects could be adaptive, especially for group-living animals.

Highlights

Sociality has beneficial effects on inclusive fitness[1], and it would follow that natural selection could have favored the evolution of mechanisms that allow individuals within a group to adjust their activity patterns to one another
We report our systematic analysis of daily time management in a social rodent species, the Nile grass rat (Arvicanthis niloticus), in the laboratory
Femalefemale and male-male sexually naïve sibling pairs (n = 12 and 10 pairs, respectively; housed together up to the beginning of the experiment) and female-male sexually experienced couples (n = 12 couples; prior to the experiment these animals had formed a breeding pair for ~4 months) underwent the protocol shown in Fig. 1A: after the animals were initially separated and implanted with ibuttons, one member of each dyad was exposed to a reversed light-dark (LD) cycle (DL, phase-shifted) before all animals were released into constant dim red light (DD), co-housed in DD for about 2 months, and separated

Summary

Introduction

Sociality has beneficial effects on inclusive fitness (e.g., cooperation for resource acquisition or predator defense)[1], and it would follow that natural selection could have favored the evolution of mechanisms that allow individuals within a group to adjust their activity patterns to one another. We view the grass rat, native to Sub-Saharan Africa, as an ideal model to study socially-mediated temporal organization This species is highly social[8,9], and breeding pairs show affiliative behaviours (e.g., sitting together, grooming, and caring for pups). Grass rats express a diurnal activity pattern, but individuals can exhibit plasticity of chronotype (i.e., when provided free access to a running wheel, a subset of animals, becomes night-active while the rest remain day-active)[10]. This is a desirable characteristic that can be used as a tool to explore behavioural and physiological plasticity of circadian rhythms. The use of different lighting conditions allowed us to assess effects of social cues on circadian rhythm parameters (period, entrainment phase) as well as on masking

Methods

Results

Conclusion