Social forces can impact the circadian clocks of cohabiting hamsters

Abstract

A number of field and laboratory studies have shown that the social environment influences daily rhythms in numerous species. However, underlying mechanisms, including the circadian system's role, are not known. Obstacles to this research have been the inability to track and objectively analyse rhythms of individual animals housed together. Here, we employed temperature dataloggers to track individual body temperature rhythms of pairs of cohabiting male Syrian hamsters (Mesocricetus auratus) in constant darkness and applied a continuous wavelet transform to determine the phase of rhythm onset before, during, and after cohabitation. Cohabitation altered the predicted trajectory of rhythm onsets in 34% of individuals, representing 58% of pairs, compared to 12% of hamsters single-housed as 'virtual pair' controls. Deviation from the predicted trajectory was by a change in circadian period (t), which tended to be asymmetric-affecting one individual of the pair in nine of 11 affected pairs-with hints that dominance might play a role. These data implicate a change in the speed of the circadian clock as one mechanism whereby social factors can alter daily rhythms. Miniature dataloggers coupled with wavelet analyses should provide powerful tools for future studies investigating the principles and mechanisms mediating social influences on daily timing.

Persistence, Entrainment, and Function of Circadian Rhythms in Polar Vertebrates

“…Thus effects of these nonphotic cues on rhythmicity in polar vertebrates are likely occurring through masking and/or the entrainment of peripheral circadian oscillators. Field and laboratory studies also indicate that the social environment can influence daily and circadian rhythms in numerous species (5,80,93), although the mechanisms that underlie social entrainment have yet to be identified.…”

Temporal behaviour profiles of Mus musculus in nature are affected by population activity

“…In hamsters, physiological and behavioural processes are influenced by both the circadian clock and social stimuli, although these influences act independently [15]. Strong evidence of social influence on the clock has been found in the gregarious Nile grass rat Arvicanthis niloticus [9], in hamsters [50] and in social insects [5]. For some species, social behaviour may have an important influence on the clock, whereas for other species, it does not [14].…”

Social synchronization of circadian rhythmicity in female mice depends on the number of cohabiting animals

“…We have previously reported that social influences on t likely depend on individuals being housed unrestrained in direct physical contact for a relatively long period of time [8]. A survey of the literature and the results from this experiment suggest that another crucial element is the number of individuals in the group-with 25 fish [3], 100 bees [5], 40 flies [6], many bats [4], and, in this experiment, five mice.…”

“…Notably, pair-housing naturally solitary male Syrian hamsters can alter the t's of the cohabitants but does not lead to significant synchronization [8]. The effects of housing hamsters in greater numbers, and whether the result would be temporal segregation [15] rather than synchronization, have yet to be tested.…”

“…To ensure a spread of rhythm phases when later grouped, mice were housed in one of two opposite LD cycles, sp., lights went off at noon local time for half of the mice and at midnight for the other half. At eight weeks of age, mice were implanted with intraperitoneal temperature dataloggers (ibuttons; Dallas Semiconductor DS1922, Maxim Integrated Products, Inc., Sunnyvale, CA, USA; as in [8]) and then single-housed in their pre-surgical LD cycle. One week later, all mice were single-housed in constant darkness (DD).…”