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Twilight and Photoperiod Affect Behavioral Entrainment in the House Mouse (Mus musculus)Department of Chronobiology, Center for Life Sciences, University of Groningen, Haren, The Netherlands
Department of Chronobiology, Center for Life Sciences, University of Groningen, Haren, The Netherlands, r.a.hut{at}rug.nl
The effect of twilight transitions on entrainment of C57BL/6JOlaHsd mice (Mus musculus) was studied using light-dark cycles of different photoperiods (6, 12, and 18 h) and twilight transitions of different durations (0, 1, and 2 h). Phase angle differences of the onset, center of gravity, and offset of activity, activity duration (
Key Words: circadian clock • twilight • photoperiod • entrainment • Mus musculus
Journal of Biological Rhythms, Vol. 24, No. 5,
403-412 (2009) |
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), as well as free-running period (
) in continuous darkness were analyzed. The main finding was that for all conditions the onset of activity was close to dusk or lights-off except for the short photoperiod with 2 h of twilight where activity onset was on average 5.3 (SEM 1.07) h after lights-off. This finding contrasts with the results of Boulos and Macchi for Syrian hamsters where a 5.9-h earlier activity onset was observed when similar photoperiod and twilight conditions are compared with a rectangular LD cycle. The authors suggest the opposite effects of 2 h of twilight in the 2 species may be related to their different free-running periods under DD conditions following entrainment to short photoperiod with 2-h twilight conditions. Since the authors observed larger variation in phase angle of entrainment in longer twilight conditions, twilight does not necessarily form a stronger zeitgeber.