Circadian clock(s) allow an organism to be in synchrony with the surrounding environment and perform daily and seasonal physiological processes, including hibernation, migration, and reproduction. To cope with adverse environmental conditions, organisms have evolved various strategies. Insects undergo diapause, while some higher animals either migrate or hibernate/aestivate during unfavorable environmental conditions. Hibernation is an energy conservation strategy used to cope with adverse environmental conditions. Limited knowledge is available on the physiology of hibernation in non-mammalian vertebrates. Some studies suggest that metabolism is altered during amphibian hibernation, but nothing is known about the circadian clock. In the present study, we investigated daily oscillation of clock genes in the brain and liver of the terai tree frog (Polypedates teraiensis) during two annual phases of life: breeding and hibernation. Adult male terai tree frogs were procured from their natural habitat on the Mizoram University campus (23°N 92°E) during their breeding and hibernation phases. Body mass and testes weight were recorded. Animals were sacrificed at six time points: ZT1, ZT5, ZT9, ZT13, ZT17, and ZT21 (ZT0, zeitgeber time 0, indicates the sunrise time at the respective time of the year; N = 5 frogs per time point). Quantitative real-time polymerase chain reaction (qPCR) was performed for clock genes (Bmal1, Clock, Per2, and Cry2) in the hypothalamus and liver. Our results showed that body and testes weights decreased during hibernation. Further, the hypothalamus retained daily clock gene oscillations during breeding and hibernation. However, the liver lost this daily oscillation during hibernation. The maintained rhythm in hypothalamus in contrast to other hibernating animals might be the result of the fact that these animals hibernate at a higher temperature and might be more alert. As the animals have no food intake during their hibernation season which might be the reason the animals loose their rhythm in liver clock genes. These results suggest that retaining daily clock gene oscillations in the hypothalamic clock could be important for internal time tracking and post-hibernation emergence.

昼夜节律使生物体与周围环境保持同步，并执行日常和季节性生理过程，包括冬眠，迁移和繁殖。为了应对不利的环境条件，生物体发展了各种策略。昆虫会滞育，而一些较高等的动物会在不利的环境条件下迁移或冬眠/繁殖。休眠是一种节能策略，用于应对不利的环境条件。关于非哺乳动物脊椎动物冬眠生理的知识有限。一些研究表明，在两栖动物冬眠期间，新陈代谢会发生变化，但有关生物钟的信息一无所知。在本研究中，我们调查了terai树蛙（和树蛙teraiensis）在生命的两个年度的阶段：繁殖和冬眠。成年雄性特莱树蛙在繁殖和冬眠阶段从其自然栖息地在米佐拉姆大学校园（23°N 92°E）采购。记录体重和睾丸重量。在六个时间点处死动物：ZT1，ZT5，ZT9，ZT13，ZT17和ZT21（ZT0，zeitgeber时间0，表示一年中各个时间的日出时间；每个时间点N = 5只青蛙）。对时钟基因（Bmal1，Clock，Per2和Cry2）进行了实时定量聚合酶链反应（qPCR））在下丘脑和肝脏中。我们的结果表明，冬眠期间身体和睾丸的重量减少。此外，下丘脑在繁殖和冬眠期间保持每日的时钟基因振荡。但是，在冬眠期间肝脏失去了这种日常振荡。与其他冬眠动物相反，下丘脑保持节律可能是这些动物在较高温度下冬眠并可能更加机警的结果。由于动物在冬眠季节没有食物摄入，这可能是动物放松肝脏时钟基因节奏的原因。这些结果表明在下丘脑时钟中保留每日时钟基因振荡对于内部时间跟踪和休眠后出现可能很重要。