The effect of a temporal shift in diurnal geomagnetic variation on roach Rutilus rutilus L. embryos: A comparison with effects of simulated geomagnetic storms

A study was made of the effects that 6- and 12-h shifts in diurnal geomagnetic variation relative to the night–day light cycles exert on roach Ritulus ritulus L. embryos. Either temporal shift in diurnal geomagnetic variation stimulated blastomere proliferation and early prelarval hatching in exposed embryos compared to controls. Underyearlings developing from exposed embryos displayed higher locomotor activity in a plusshaped maze, a lower number of rays in the anal fin, a redistribution of vertebrae through sections of the vertebral column, and a higher number of seismosensory system openings in the mandibular and preopercular bones. The effects were similar to those described previously for roaches exposed to a simulated geomagnetic storm during embryonic development. The results support the hypothesis that animals perceive geomagnetic storms as a dramatic disturbance that occurs in the habitual diurnal geomagnetic variation at an unusual time relative to the night–day light cycle, which acts as a primary zeitgeber of circadian biological rhythms.

     

Circadian rhythms in zebrafish (Danio rerio) behaviour and the sources of their variability

Over recent decades, changes in zebrafish (Danio rerio) behaviour have become popular quantitative indicators in biomedical studies. The circadian rhythms of behavioural processes in zebrafish are known to enable effective utilization of energy and resources, therefore attracting interest in zebrafish as a research model. This review covers a variety of circadian behaviours in this species, including diurnal rhythms of spawning, feeding, locomotor activity, shoaling, light/dark preference, and vertical position preference. Changes in circadian activity during zebrafish ontogeny are reviewed, including ageing-related alterations and chemically induced variations in rhythmicity patterns. Both exogenous and endogenous sources of inter-individual variability in zebrafish circadian behaviour are detailed. Additionally, we focus on different environmental factors with the potential to entrain circadian processes in zebrafish. This review describes two principal ways whereby diurnal behavioural rhythms can be entrained: (i) modulation of organismal physiological state, which can have masking or enhancing effects on behavioural endpoints related to endogenous circadian rhythms, and (ii) modulation of period and amplitude of the endogenous circadian rhythm due to competitive relationships between the primary and secondary zeitgebers. In addition, different peripheral oscillators in zebrafish can be entrained by diverse zeitgebers. This complicated orchestra of divergent influences may cause variability in zebrafish circadian behaviours, which should be given attention when planning behavioural studies.