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Project titleInfluence of slow magnetic variations on the rhythms of locomotor activity of the blind cave tetra Astyanax mexicanus (Pisces, Characidae)

AffiliationI.D. Papanin Institute for Biology of Inland Waters Russian Academy of Sciences,

KeywordsAstyanax mexicanum, locomotor activity, behavior, magnetic field, circadian rhythm

Annotation
The ability to coordinate behavior and physiological processes in response to external stimuli is essential for the success and survival of animals. Circadian rhythms underlie the adaptation of living organisms, causing the most beneficial use of environmental resources. The issues of synchronization of circadian behavior of fish with external pacemakers are urgent problems of modern science. Recently, a hypothesis was developed that in addition to the primary synchronizer, the day-night illumination cycle, fish can use diurnal geomagnetic variation as a secondary external driver of circadian biological rhythms. As an external driver of biorhythms, this factor may be essential for aquatic organisms living in caves under aphotic conditions. However, research in this direction has not been carried out. Data on the response of the cave species to the effects of magnetic fields will contribute to understanding the interaction of various external drivers of biorhythms and their effect on living organisms. The project is aimed at studying changes in circadian rhythms of behavioral indicators of the blind cavefish Astyanax mexicanus during long-term exposure in three variants of magnetic influences: 300 nT, 13.23 μHz; 300 nT, 11.57 μHz; 300 nT, 10.29 μHz. The amplitude of these fluctuations corresponds to the intensity of natural strong geomagnetic oscillations, and the frequency corresponds to the period of 21, 24, and 27 hours. The experimental conditions will be close to natural for this species: no illumination and constant water temperature. Evaluation of locomotor activity rhythms in groups of fish exposed to these magnetic fields will confirm or refute the assumption that natural diurnal geomagnetic variation may be the driver of circadian rhythms for some species living in aphotic conditions.

Expected results
For the first time, the project will yield experimental data on the effect of slow magnetic fluctuations on near-circadian rhythms of locomotor activity and associated behavioral indicators in Astyanax mexicanus. The results of the work will confirm or refute the hypothesis that natural diurnal geomagnetic variation may be the driver of circadian rhythms for some species living in aphotic conditions. The expected data will contribute to understanding the synchronization of biological rhythms with different external drivers. The potential of using Astyanax mexicanus as a model species for studying the biological effects of magnetic fields will be assessed since, due to the reduction of the visual analyzer, these fish may be more sensitive to magnetic influences.

Annotation of the results obtained in 2023
Experiments were conducted to investigate the impact of slow magnetic variations on the rhythmic behavior of the blind cave tetra, Astyanax mexicanus (Characidae). Video recordings captured the movement of fish exposed to both natural 24-hour diurnal geomagnetic variation and slow magnetic fluctuations with a period differing from the diurnal variation by 3 hours (21 hours and 27 hours) in both vertical and horizontal planes. The behavior of each of the 64 individuals was recorded over 10 days. Remarkably, alterations in the period of slow magnetic variations did not affect the locomotor activity of A. mexicanus, evaluated based on time series of average swimming speed. In contrast to similar experiments conducted with Danio rerio, magnetic fluctuations failed to entrain rhythms in the motor activity of blind cavefish. High individual variability manifested in the presence/absence of rhythm and diversity in the values of locomotor activity periods was identified among different individuals. It was demonstrated that the rhythmicity of locomotor activity in A. mexicanus becomes apparent at a relatively low swimming speed. Non-rhythmic fish exhibited faster movements, presumably indicative of heightened stress levels. Our data on the correlation between locomotor activity period values and freezing, active swimming, and angular velocity suggest that individual rhythmicity in blind cavefish within our experiment likely did not adhere to circadian zeitgebers. Instead, it appeared to be contingent upon the nuances of neuron activity governing motor function, potentially influenced by feeding or exploratory behavior. Consequently, this rhythmicity emerges as specific to each unique individual.

Publications

1. Krylov V.V., Osipova E.A. Molecular Biological Effects ofWeak Low-Frequency Magnetic Fields: Frequency–Amplitude EfficiencyWindows and Possible Mechanisms International Journal of Molecular Sciences, 24, 10989 (year - 2023) https://doi.org/10.3390/ijms241310989

2. Pavlova V.V., Krylov V.V. Cavefishes in Chronobiological Research: A Narrative Review Clocks & Sleep, 5, 62–71 (year - 2023) https://doi.org/10.3390/clockssleep5010007

Annotation of the results obtained in 2022
Experiments were carried out to reveal the effect of slow magnetic variations on the rhythmic behavior of the blind cave tetra Astyanax mexicanus (Characidae). The fish were subjected to natural geomagnetic variation with a period of 24 h and slow magnetic fluctuations with periods differing from the geomagnetic by 3 hours (21 h and 27 h). Illumination was constant. 10-day video records of fish behavior were obtained for 64 individuals. At present, these video records are processed. The coordinates of each fish location are defined on each frame. Fish movement trajectories and the indicators of locomotor activity will be obtained based on these coordinates. Next, circadian and near-circadian rhythms with a period of 20-28 hours will be assessed in fish locomotor activity. After analysis, conclusions will be drawn about the effect of slow magnetic fluctuations on the circadian rhythms of motor activity and related behavioral parameters in Astyanax mexicanus.

Publications