One of the fundamental environmental factors in space is the low magnetic flux density, while on earth the geomagnetic field is permanently present.
Two experiments were performed. In the first experiment, adult frogs were kept for one week in a magnetically shielded room with a magnetic flux density below 200 nT. After fertilization, embryos were incubated in the same magnetic shielding room (n > 30) or kept under similar conditions in an incubator while exposed to the normal environmental magnetic field (ca. 22 µT) as a control group (n > 10). Embryos were examined in the two-, four- and eight-cell-stage (cleavage furrows) or after 2 or 4 days (malformations, mortality).
In a second experiment, fertilized frog eggs (parents were kept under normal geomagnetic field conditions) were incubated in a hypo-geomagnetic field environment below 150 nT (n = 30), while the control group (n = 30) was incubated on the same platform at about 52 µT. Blastomeres were examined in the two-, four- and eight-cell-stage (cleavage furrows, spindle orientation).
Exposure duration: continuous for up to 2 hours (up to eight-cell-stage)
|Setup||shielding room (2 x 3 x 2 m³) was constructed of six layers of permalloy, temperature 18.8 ± 0.8°C; embryos were placed on a wooden shelf in the center of the shielding room (50 x 50 x 50 cm³)|
|Sham exposure||A sham exposure was conducted.|
|Additional info||embryos from the control group were incubated at 19.1 ± 0.2°C in an incubator, magnetic flux density approx. 22 µT|
In the four-cell-stage of blastomeres incubated under hypo-geomagnetic field conditions, reoriented spindles were found compared to blastomeres incubated under the normal magnetic environment (experiment 2). Additionally, in the eight-cell-stage, the horizontal third cleavage furrows were significantly decreased when incubated in the hypo-geomagnetic field in comparison to incubation in the normal magnetic environment (experiment 1 and 2). No differences between the groups were found in the two- and four-cell-stage.
In the group exposed to the hypo-geomagnetic field, the malformation percentage was significantly higher than in the group kept under normal magnetic field conditions, while no significant difference was found regarding mortality (experiment 1).
The authors conclude that the exposure to hypo-geomagnetic fields (< 200 nT) could affect the development of frog embryos in the early cleavage stages.