Abstract:
The circadian rhythm of locomotory activity in the Arabian spiny mouse, a desert living species, was
investigated under controlled laboratory conditions. Ten individuals were subjected to successive light
cycles. When subjected to a 12L:12D light cycle, locomotor activity was confined mainly to the dark
phase (mean 94.2% 1.6%). During a period of constant darkness (DD), all animals expressed free
running rhythms of locomotor activity (mean 23h49 0h04). Following a second LD cycle, the light and
dark phases were inversed (12D:12L). Activity shifted with the lights and was masked during the light
phase, re-entrainment was rather slow (up to 10 days). The effect of varying ambient temperature (20
e35 C) on the locomotor activity under a 12L:12D cycle revealed that temperature had no distinct effect
on the level of locomotor activity. When the dark component of the day was lengthened to 8L:16D, the
mean percentage of activity during the dark increased to 96.0 0.8%, while a significant decrease in
night time activity was observed when the dark phase length was decreased to 16L:8D (78.29 2.52%).
The Arabian spiny mouse therefore behaves as other desert dwelling rodents and can be described as
truly nocturnal.
