Numerical tests of magnetoreception models assisted with behavioral experiments on American cockroaches

Many animals display sensitivity to external magnetic field, but it is only in the simplest organisms that the sensing mechanism is understood. Here we report on behavioural experiments where American cockroaches (Periplaneta americana) were subjected to periodically rotated external magnetic fields with a period of 10 min. The insects show increased activity when placed in a periodically rotated Earth-strength field, whereas this effect is diminished in a twelve times stronger periodically rotated field. We analyse established models of magnetoreception, the magnetite model and the radical pair model, in light of this adaptation result. A broad class of magnetite models, based on single-domain particles found in insects and assumption that better alignment of magnetic grains towards the external field yields better sensing and higher insect activity, is shown to be excluded by the measured data. The radical-pair model explains the data if we assume that contrast in the chemical yield on the order of one in a thousand is perceivable by the animal, and that there also exists a threshold value for detection, attained in an Earth-strength field but not in the stronger field.

Automated summary

The study found that American cockroaches show increased activity when placed in a periodically rotated Earth-strength magnetic field, whereas this effect diminishes in a stronger field. The magnetite model based on single-domain particles and the assumption that better alignment of magnetic grains yields better sensing and activity in insects is excluded by the data. The radical-pair model explains the results by assuming that a contrast in chemical yield perceivable by the animal and a threshold value for detection exist, with the threshold attained in an Earth-strength field but not in a stronger field.