The rhythms of activity in all living things are known to be affected by gravity, such as the gravitational pull of a full moon, yet this phenomenon has been largely neglected in the field of scientific research.
In a new study from the University of Campinas (UNICAMP), experts have confirmed that the gravitational tides generated by the moon and sun influence the behavior of plants and animals, regardless of other factors such as light or darkness.
“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,” wrote the study authors.
“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.”
The researchers explained that all organisms exhibit cyclical variations in their levels of activity that are necessary for survival. These cycles are aligned with variations in day and night, or the passing of the seasons.
“All matter on Earth, both live and inert, experiences the effects of the gravitational forces of the sun and moon expressed in the form of tides,” said study co-author Cristiano de Mello Gallep.
“The periodic oscillations exhibit two daily cycles and are modulated monthly and annually by the motions of these two celestial bodies. All organisms on the planet have evolved in this context.”
“What we sought to show in the article is that gravitational tides are a perceptible and potent force that has always shaped the rhythmic activities of these organisms.”
The three previously published cases analyzed fly the study were focused on: the swimming activity of isopods that emerged at least 300 million years ago, reproduction among corals, and growth modulation in sunflower seedlings inferred from autoluminescence.
“The data shows that in the absence of other rhythmic influences such as lighting or temperature, local gravitational tides are sufficient to organize the cyclical behavior of these organisms,” said Gallep.
“This evidence questions the validity of so-called free-run experiments, in which several environmental factors are controlled but gravitational oscillations are not taken into consideration. These oscillations continue to exist, and may modulate the behavior of living organisms.”
Many rhythmic patterns such as circadian rhythms are linked to the day-night or light-dark cycle. However, some rhythmic cycles are maintained even under controlled laboratory conditions.
The researchers considered coastal organisms such as crustaceans, among which the influence of tidal cycles persists when they are removed from their natural habitats.
“These animals modulate their behavior in tune with the ebb and flow of the tides, in a cycle of approximately 12.4 hours that derives from lunisolar dynamics, even when they’re moved to a laboratory with stable and controlled aquatic conditions,” explained Gallep. “The pattern persists for several days, matching lunisolar tidal timing at the site where the organisms were collected in nature.”
“The brief analysis presented here highlights a possible caveat in the phenomenological significance of so-called free-run experiments in the laboratory,” wrote the study authors.
“Free-running seems to assume that constant light, constant darkness, or constant humidity or temperature imply overall constant conditions and an absence of temporal cues to the organism under test. This is evidently not the case, as several other and distinct physical quantities can vary, and do so with their own cyclic patterns.”
The study is published in the Journal of Experimental Botany.
By Chrissy Sexton, Earth.com Staff Writer