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1. Repeated evolution of circadian clock dysregulation in cavefish populations

   https://doi.org/10.1371/journal.pgen.1009642  

   Mack, Katya L.; Jaggard, James B.; Persons, Jenna L.; Roback, Emma Y.; Passow, Courtney N.; Stanhope, Bethany A.; Ferrufino, Estephany; Tsuchiya, Dai; Smith, Sarah E.; Slaughter, Brian D.; et al (July 2021, PLOS Genetics)

   Fay, Justin C. (Ed.)

   Circadian rhythms are nearly ubiquitous throughout nature, suggesting they are critical for survival in diverse environments. Organisms inhabiting largely arrhythmic environments, such as caves, offer a unique opportunity to study the evolution of circadian rhythms in response to changing ecological pressures. Populations of the Mexican tetra, Astyanax mexicanus , have repeatedly invaded caves from surface rivers, where individuals must contend with perpetual darkness, reduced food availability, and limited fluctuations in daily environmental cues. To investigate the molecular basis for evolved changes in circadian rhythms, we investigated rhythmic transcription across multiple independently-evolved cavefish populations. Our findings reveal that evolution in a cave environment has led to the repeated disruption of the endogenous biological clock, and its entrainment by light. The circadian transcriptome shows widespread reductions and losses of rhythmic transcription and changes to the timing of the activation/repression of core-transcriptional clock. In addition to dysregulation of the core clock, we find that rhythmic transcription of the melatonin regulator aanat2 and melatonin rhythms are disrupted in cavefish under darkness. Mutants of aanat2 and core clock gene rorca disrupt diurnal regulation of sleep in A . mexicanus , phenocopying circadian modulation of sleep and activity phenotypes of cave populations. Together, these findings reveal multiple independent mechanisms for loss of circadian rhythms in cavefish populations and provide a platform for studying how evolved changes in the biological clock can contribute to variation in sleep and circadian behavior. 

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2. Convergent latitudinal erosion of circadian systems in a rapidly diversifying order of fishes

   https://doi.org/10.1101/2025.05.28.656707  

   Wright, Daniel B; Zhang, Yanfan; Daane, Jacob M (May 2025, bioRxiv)

   Abstract Biological clocks enable organisms to anticipate cyclical environmental changes. Some habitats, such as those at high latitudes or deep sea, experience seasonally diminished or absent diel cues upon which species entrain their circadian rhythms. Fishes of the order Perciformes have rapidly diversified and adapted to these arrhythmic ecosystems, raising the possibility that evolutionary modifications to their circadian biology contributes to their success as one of the most species-rich orders of vertebrates. Here, we used a comparative genomic approach to investigate patterns of biological clock gene loss and circadian rhythms across 33 perciform and six outgroup species. We found both widespread and lineage-specific loss and relaxed selection in core clock genes, particularly in the convergently evolving polar and deep-sea Notothenioidei and Cottioidei suborders. This trend of circadian gene loss was significantly correlated with latitude, with higher-latitude species showing greater loss. Whether these losses and relaxed selection lead to changes in circadian rhythms is unknown for most perciforms. To address this, we performed metabolic phenotyping on three notothenioid species and found no circadian metabolic oscillations during the late austral fall, including in the sub-AntarcticEleginops maclovinus, sister to the Antarctic adaptive radiation. We propose that diminished reliance on endogenous biological clocks may be an adaptive feature that facilitates the survival and diversification of perciform fishes in polar and arrhythmic environments. 

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3. The circadian clock controls temporal and spatial patterns of floral development in sunflower

   https://doi.org/10.7554/eLife.80984  

   Marshall, Carine M; Thompson, Veronica L; Creux, Nicky M; Harmer, Stacey L (January 2023, eLife)

   Biological rhythms are ubiquitous. They can be generated by circadian oscillators, which produce daily rhythms in physiology and behavior, as well as by developmental oscillators such as the segmentation clock, which periodically produces modular developmental units. Here, we show that the circadian clock controls the timing of late-stage floret development, or anthesis, in domesticated sunflowers. In these plants, up to thousands of individual florets are tightly packed onto a capitulum disk. While early floret development occurs continuously across capitula to generate iconic spiral phyllotaxy, during anthesis floret development occurs in discrete ring-like pseudowhorls with up to hundreds of florets undergoing simultaneous maturation. We demonstrate circadian regulation of floral organ growth and show that the effects of light on this process are time-of-day dependent. Delays in the phase of floral anthesis delay morning visits by pollinators, while disruption of circadian rhythms in floral organ development causes loss of pseudowhorl formation and large reductions in pollinator visits. We therefore show that the sunflower circadian clock acts in concert with environmental response pathways to tightly synchronize the anthesis of hundreds of florets each day, generating spatial patterns on the developing capitulum disk. This coordinated mass release of floral rewards at predictable times of day likely promotes pollinator visits and plant reproductive success. 

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4. Efficient assessment of real-world dynamics of circadian rhythms in heart rate and body temperature from wearable data

   https://doi.org/10.1098/rsif.2023.0030  

   Kim, Dae Wook; Mayer, Caleb; Lee, Minki P; Choi, Sung Won; Tewari, Muneesh; Forger, Daniel B (August 2023, Journal of The Royal Society Interface)

   Laboratory studies have made unprecedented progress in understanding circadian physiology. Quantifying circadian rhythms outside of laboratory settings is necessary to translate these findings into real-world clinical practice. Wearables have been considered promising way to measure these rhythms. However, their limited validation remains an open problem. One major barrier to implementing large-scale validation studies is the lack of reliable and efficient methods for circadian assessment from wearable data. Here, we propose an approximation-based least-squares method to extract underlying circadian rhythms from wearable measurements. Its computational cost is ∼ 300-fold lower than that of previous work, enabling its implementation in smartphones with low computing power. We test it on two large-scale real-world wearable datasets: $\sim 600\hspace{0.17em}\mathrm{days}$of body temperature data from cancer patients and ∼ 184 000 days of heart rate and activity data collected from the ‘Social Rhythms’ mobile application. This shows successful extraction of real-world dynamics of circadian rhythms. We also identify a reasonable harmonic model to analyse wearable data. Lastly, we show our method has broad applicability in circadian studies by embedding it into a Kalman filter that infers the state space of the molecular clocks in tissues. Our approach facilitates the translation of scientific advances in circadian fields into actual improvements in health. 

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5. Potential bidirectional communication between the liver and the central circadian clock in MASLD

   https://doi.org/10.1038/s44324-025-00058-1  

   Gachon, Frédéric; Bugianesi, Elisabetta; Castelnuovo, Gabriele; Oster, Henrik; Pendergast, Julie S; Montagnese, Sara (April 2025, npj Metabolic Health and Disease)

   Most aspects of physiology and behaviour fluctuate every 24 h in mammals. These circadian rhythms are orchestrated by an autonomous central clock located in the suprachiasmatic nuclei that coordinates the timing of cellular clocks in tissues throughout the body. The critical role of this circadian system is emphasized by increasing evidence associating disruption of circadian rhythms with diverse pathologies. Accordingly, mounting evidence suggests a bidirectional relationship where disruption of rhythms by circadian misalignment may contribute to liver diseases while liver diseases alter the central clock and circadian rhythms in other tissues. Therefore, liver pathophysiology may broadly impact the circadian system and may provide a mechanistic framework for understanding and targeting metabolic diseases and adjust metabolic setpoints. 

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