The ticking clock in the dark: Review of biological rhythms in cave invertebrates

ABSTRACT

Circadian clocks, internal mechanisms that generate 24-hour rhythms, play a crucial role in coordinating biological events with day-night cycles. In light-deprived environments such as caves, species, particularly isolated obligatory troglobites, may exhibit evolutionary adaptations in biological rhythms due to light exposure. To explore rhythm expression in these settings, we conducted a comprehensive literature review on invertebrate chronobiology in global subterranean ecosystems, analyzing 44 selected studies out of over 480 identified as of September 2023. These studies revealed significant taxonomic diversity, primarily among terrestrial species like Coleoptera, with research concentrated in the United States, Italy, France, Australia, and Brazil, and a notable gap in African records. Troglobite species displayed a higher incidence of aperiodic behavior, while troglophiles showed a robust association with rhythm expression. Locomotor activity was the most studied aspect (>60%). However, approximately 4% of studies lacked information on periodicity or rhythm asynchrony, and limited research under constant light conditions hindered definitive conclusions. This review underscores the need to expand chronobiological research globally, encompassing diverse geographical regions and taxa, to deepen our understanding of biological rhythms in subterranean species. Such insights are crucial for preserving the resilience of subsurface ecosystems facing threats like climate change and habitat loss.

KEYWORDS:

• Cave
• biological clock
• rhythms
• invertebrates
• cave-dwelling
• arrhythmia

Acknowledgments

This review was prepared as part of a larger project related to the theme. This research was partially funded by Term of Commitment of Speleological Compensation (TCCE) 01/2018, signed between ICMBio and Vale S.A. and with resource management by the Instituto Brasileiro de Desenvolvimento e Sustentabilidade (IABS). Therefore, the authors would like to thank the Centro Nacional de Pesquisa e Conservação de Cavernas (ICMBio/Cecav) for directing resources from the aforementioned TCCE.; the FAPEMIG (CRA APQ 02822-17) for the financial support; CNPq (National Council for Scientific and Technological Development, grant n. 302925/2022-8) for the productivity scholarship provided to RLF. PES additionally acknowledges José Geraldo Gomes de Alvarenga for his assistance in developing the silhouettes.

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Funding

The author(s) reported there is no funding associated with the work featured in this article.