Circannual testis and moult cycles persist under photoperiods that disrupt circadian activity and clock gene cycles in spotted munia

摘要

We investigated whether circannual rhythms underlying annual testis maturation and moult cycles are independent of duration and frequency of the light period and circadian clock control in non-photoperiodic spotted munia. Birds were subjected to an aberrant light-dark (LD) cycle (3.5 h L:3.5 h D; T7, where T is the period length of the LD cycle) and continuous light (LL, 24 h L:0 h D), with controls on 12 h L:12 h D (T24, 24 h LD cycle). We measured the behavioural activity pattern of the birds and 24 h mRNA oscillations of circadian clock genes (bmal1, clock, per2, cry1, cry2) in the hypothalamus, the putative site of seasonal timing. Diurnal munia were rhythmic in behaviour with the period of the activity-rest cycle matched to T7 and T24, and became behaviourally arrhythmic with activity scattered throughout 24 h under LL. Similarly, exposure to 3.5 h L:3.5 h D and LL caused arrhythmicity in 24 h clock gene expression, suggesting disruption of internal circadian timing at the transcriptional level; a significant rhythm was found under 12 h L:12 h D. During an exposure of 80 weeks, munia showed two to three cycles of testis maturation and wing primaries moult under all photoperiods, although with a longer period under 12L:12D. Thus, the frequency of light period under 3.5 h L:3.5 h D or LL disrupted circadian clock gene cycles, but did not affect the generation of circannual testis and moult cycles. We conclude that the prevailing light environment and hypothalamic circadian gene cycles do not exert direct control on the timing of the annual reproductive cycle in spotted munia, suggesting independent generation of the circadian and circannual rhythms in seasonally breeding species.