Daily rhythms enable organisms to adapt to daily fluctuations in environmental factors. Do organisms still exhibit 24-h rhythms when living in habitats without obvious daily cycles in external signals? To answer this question, we measured the heart rates of six Adélie penguin (Pygoscelis adeliae) chicks on Inexpressible Island during the polar day between 15 and 21 January 2019. Averaged heart rates were between 186 and 233 beats/min for individual chicks. Both fast Fourier transformation and autocorrelation were employed to assess the daily rhythmicity. Based on fast Fourier transformation, a significant contribution of daily rhythm in heart rate variation was found only in one individual. Small effect size of significant autocorrelation coefficients was found in two individuals, while there was no significant autocorrelation coefficient for 24-h time lag in four other individuals. In summary, no prevailing daily rhythm of heart rate was found in these Adélie penguin chicks. We propose that the lack of daily rhythm in Adélie penguin chicks could be an adaptation to the local environment in the polar regions, but that the adaptive value thereof remains to be investigated.

中文翻译：

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极地日期间阿德利企鹅幼鸟缺乏每日心率节律

每日节律使生物体能够适应环境因素的每日波动。当生活在没有明显日常外部信号周期的栖息地时，生物体是否仍然表现出 24 小时的节律？为了回答这个问题，我们测量了六只阿德利企鹅的心率（螳螂) 在 2019 年 1 月 15 日至 21 日的极昼期间，无法表达的岛上的小鸡。单个小鸡的平均心率在 186 至 233 次/分钟之间。快速傅立叶变换和自相关都被用来评估日常节律性。基于快速傅立叶变换，仅在一个个体中发现每日节律对心率变化的显着贡献。在两个个体中发现了显着自相关系数的小效应，而在其他四个个体中没有显着的 24 小时时滞自相关系数。总之，在这些阿德利企鹅小鸡中没有发现普遍的每日心率节律。我们认为阿德利企鹅幼鸟缺乏日常节奏可能是对极地地区当地环境的适应，