Agarwal Neha, Mishra Ila, Komal Ruchi, Rani Sangeeta, Kumar Vinod
IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi 110 007, India.
Department of Zoology, University of Lucknow, Lucknow 226 007, India.
J Exp Biol. 2017 Nov 15;220(Pt 22):4162-4168. doi: 10.1242/jeb.167809. Epub 2017 Sep 15.
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 (, , , , ) 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.
我们研究了非光周期斑纹文鸟中,每年睾丸成熟和换羽周期背后的年周期节律是否独立于光照期的时长和频率以及昼夜节律时钟控制。将鸟类置于异常的明暗(LD)周期(3.5小时光照:3.5小时黑暗;T7,其中T是LD周期的时长)和持续光照(LL,24小时光照:0小时黑暗)条件下,对照组为12小时光照:12小时黑暗(T24,24小时LD周期)。我们测量了鸟类的行为活动模式以及下丘脑(季节性定时的假定部位)中昼夜节律时钟基因(、、、、)的24小时mRNA振荡。日行性文鸟的行为具有节律性,活动-休息周期的时长与T7和T24相匹配,在LL条件下活动在24小时内分散,行为变得无节律。同样,暴露于3.5小时光照:3.5小时黑暗和LL条件下会导致24小时时钟基因表达无节律,表明在转录水平上内部昼夜节律定时受到破坏;在12小时光照:12小时黑暗条件下发现了显著的节律。在80周的暴露期间,文鸟在所有光周期下都表现出两到三个睾丸成熟和初级飞羽换羽周期,尽管在12L:12D条件下周期更长。因此,3.5小时光照:3.5小时黑暗或LL条件下的光照期频率破坏了昼夜节律时钟基因周期,但不影响年周期睾丸和换羽周期的产生。我们得出结论,占主导地位的光照环境和下丘脑昼夜节律基因周期不会对斑纹文鸟年度繁殖周期的定时施加直接控制,这表明季节性繁殖物种的昼夜节律和年周期节律是独立产生的。