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

Abstract

We investigated if circannual rhythms underlying annual testis maturation and moult cycles were independent of the duration and frequency of light period and the circadian clock control in non-photoperiodic spotted munia. Birds were subjected to an aberrant light-dark (LD) cycle (3.5L:3.5D; T7, T=period length of LD cycle) and continuous light (LL, 24L:0D), with controls on 12L:12D (T24, 24 h LD cycle). Initial experiment measured the activity pattern and 24 h mRNA oscillations of circadian clock genes (bmal1, clock, per2, cry1, cry2) in the hypothalamus, putative site of the seasonal timing. Diurnal munia were rhythmic in behaviour with period of activity-rest cycle matched to T7 and T24, and became behaviourally arrhythmic with activity scattered througout 24 h under LL. Similarly, exposure to 3.5L:3.5D and LL caused arrhythmicity in 24 h clock gene expressions suggesting disruption of internal circadian timing at the transcriptional level; a significant rhythm was found under 12L:12D. In subsequent exposure of 80 weeks, munia showed 2–3 cycles of testis maturation and wing primaries moult under all photoperiods, although with a longer period length under 12L:12D. Thus, the frequency of light period under 3.5L:3.5D, or continuous light 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 a direct control on the timing of annual reproductive cycle in spotted munia, and suggest independent generation of the circadian and circannual rhythms in seasonally breeding species.