REVIEW article

Front. Physiol.

Sec. Avian Physiology

Volume 16 - 2025 | doi: 10.3389/fphys.2025.1586580

This article is part of the Research TopicEnvironmental Challenges to Avian Populations: A Physiological PerspectiveView all 6 articles

Avian circadian clock genes: ontogeny and role for adaptive programming in avian embryos

Provisionally accepted
  • 1School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Australia
  • 2Institute for Molecular Bioscience, The University of Queensland, St Lucia, Queensland, Australia
  • 3Department of Biomedicine, Faculty of Health, Aarhus University, Aarhus, Capital Region of Denmark, Denmark

The final, formatted version of the article will be published soon.

Circadian clocks are ubiquitous across almost all organisms, from cyanobacteria to humans, due to a highly conserved mechanism involving a network of negative feedback loops. This molecular oscillator underpins rhythmic oscillations in physiology and behaviour at the organismal level. In vertebrates, both cellular processes and the sensory detection mechanisms underlying rhythmic physiology are relatively well understood. But how these processes develop to optimise tissue-specific rhythmic gene expression is much less understood. Birds possess an intricate, multi-oscillatory core circadian system that governs the biological rhythms of all other tissues. Avian studies document rhythmic expression of genes and hormone production prior to hatching, and yet the consequences of the onset of this process and the interactions with embryonic development have rarely been considered. In this review, we summarise the existing literature on clock gene ontogeny in birds and suggest how rhythmic expression of these genes may develop. Then, by also drawing upon evidence from non-mammalian oviparous taxa, we hypothesise how the development of rhythmic clock gene expression may interact with avian developmental processes and events. Specifically, we highlight how rhythmic clock gene expression may adaptively benefit embryos by phasing rhythms in metabolic and neuro-endocrine systems and we suggest that rhythmic gene expression may play a role in coordinating the physiological systems and behavioural outputs required to initiate hatching. Lastly, we highlight the critical avenues of research that will enhance our understanding of the role of clock genes in avian ontogeny and their ecological relevance, particularly in understanding the impacts of anthropogenic light pollution on developing avian clocks.

Keywords: clock gene, circadian, avian ontogeny, hatching, Mitochondria, Melatonin, ALAN

Received: 03 Mar 2025; Accepted: 09 Jun 2025.

Copyright: © 2025 Wellard, Weger, Gachon and Buchanan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence:
Caleb James Wellard, School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Australia
Kate L Buchanan, School of Life and Environmental Sciences, Deakin University, Waurn Ponds, Australia

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