Cristiano de Mello Gallep, Daniel Robert, Are cyclic plant and animal behaviours driven by gravimetric mechanical forces?, Journal of Experimental Botany, 2021;, erab462, https://doi.org/10.1093/jxb/erab462
The celestial mechanics of the Sun, Moon, and Earth dominate the variations in gravitational force that all matter, live or inert, experiences on Earth. Expressed as gravimetric tides, these variations are pervasive and have forever been part of the physical ecology with which organisms evolved. Here, we first offer a brief review of previously proposed explanations that gravimetric tides constitute a tangible and potent force shaping the rhythmic activities of organisms. Through meta-analysis, we then interrogate data from three study cases and show the close association between the omnipresent gravimetric tides and cyclic activity. As exemplified by free-running cyclic locomotor activity in isopods, reproductive effort in coral, and modulation of growth in seedlings, biological rhythms coincide with temporal patterns of the local gravimetric tide. These data reveal that, in the presumed absence of rhythmic cues such as light and temperature, local gravimetric tide is sufficient to entrain cyclic behaviour. The present evidence thus questions the phenomenological significance of so-called free-run experiments.
All organisms exhibit cyclical modulations in their levels of activity that are deemed to be of adaptive value. Long-term and short-term cycles are thus ubiquitous and can be regarded as ‘embodied rhythms of life’, a temporally organized homeostatic activity dictated by or even exploiting the cyclic variations of environmental variables. Such variations are diverse and well known; examples are variations in day and night, the passing of the seasons and their associated periods of cold, dark, or wet, or any combination thereof, and also the abundance or lack of resources in ecological niches. Such cyclic variations are ubiquitously found from microorganisms to unicellular and multicellular organisms, including human beings and their socio-economic life, which also crucially depends on natural daily and seasonal rhythms. The 2017 Nobel Prize in Physiology or Medicine was awarded to those who discovered some of the molecular mechanisms underpinning circadian rhythms, providing the first mechanistic insights into how organisms physiologically organize their cyclic activities, in particular to the ~24h period of the Earth’s rotation ( Nobel Assembly, 2017).