Elena A. Osipova

Influence of magnetic field on zebrafish activity and orientation in a plus maze.

We describe an impact of the geomagnetic field (GMF) and its modification on zebrafishs orientation and locomotor activity in a plus maze with four arms oriented to the north, east, south and west. Zebrafishs directional preferences were bimodal in GMF: they visited two arms oriented in opposed directions (east-west) most frequently. This bimodal preference remained stable for same individuals across experiments divided by several days. When the horizontal GMF component was turned 90° clockwise, the preference accordingly shifted by 90° to arms oriented to the north and south. Other modifications of GMF (reversal of both vertical and horizontal GMF components; reversal of vertical component only; and reversal of horizontal component only) did not exert any discernible effect on the orientation of zebrafish. The 90° turn of horizontal component also resulted in a significant increase of fishs locomotor activity in comparison with the natural GMF. This increase became even more pronounced when the horizontal component was repeatedly turned by 90° and back with 1min interval between turns. Our results show that GMF and its variations should be taken into account when interpreting zebrafishs directional preferences and locomotor activity in mazes and other experimental devices.

The response of European Daphnia magna Straus and Australian Daphnia carinata King to changes in geomagnetic field

This study investigates the effects of lifelong exposure to reversed geomagnetic and zero geomagnetic fields (the latter means absence of geomagnetic field) on the life history of Daphnia carinata King from Australia and Daphnia magna Straus from Europe. Considerable deviation in the geomagnetic field from the usual strength, leads to a decrease in daphnia size and life span. Reduced brood sizes and increased body length of neonates are observed in D. magna exposed to unusual magnetic background. The most apparent effects are induced by zero geomagnetic field in both species of Daphnia. A delay in the first reproduction in zero geomagnetic field is observed only in D. magna. No adaptive maternal effects to reversed geomagnetic field are found in a line of D. magna maintained in these magnetic conditions for eight generations. Integrally, the responses of D. magna to unusual geomagnetic conditions are more extensive than that in D. carinata. We suggest that the mechanism of the effects of geomagnetic field reversal on Daphnia may be related to differences in the pattern of distribution of the particles that have a magnetic moment, or to moving charged organic molecules owing to a change in combined outcome and orientation of the geomagnetic field and Earths gravitational field. The possibility of modulation of self-oscillating processes with changes in geomagnetic field is also discussed.

Influence of magnetic field on the spatial orientation in zebrafish (Danio rerio) (Cyprinidae) and Roach (Rutilus rutilus) (Cyprinidae)

Preferred direction of motion under influence of geomagnetic field and its modifications was registered in zebrafish (Danio rerio) raised in laboratory culture and in roach (Rutilus rutilus) from the Rybinsk Reservoir. In the geomagnetic field, specimens of zebrafish prefer two opposite directions oriented towards the north and south, while they prefer towards east and west at 90° turning of the horizontal component of geomagnetic field. The specimens of roach in the geomagnetic field prefer only the direction oriented towards east–northeast. This direction coincides with the direction along the canal where roach was sampled to the main river channel part of the Rybinsk Reservoir. At 90° rotation of the horizontal component of geomagnetic field, the direction turns to the south–southeast. The reasons for selection of certain directions in the geomagnetic field are discussed.

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.

Influence of simulated H component of a typical magnetic storm on early ontogeny of Daphnia magna straus

The influence of simulating the H component of a typical magnetic storm on the early ontogeny of Daphnia magna Straus at 21 and 23°C has been studied. Judging by the rates of early development, the effects of the whole magnetic storm experienced by the egg (from the sudden onset to the end) differ from those produced by only the recovery phase. Moreover, the effects essentially depend on the hatching temperature. Early exposure to the whole simulated magnetic storm has remote effects such as changes in the body length in the first progeny broods from the females exposed at the embryo stage.