LUNAR-DAY VARIATIONS IN SPONTANEOUS ACTIVITY OF THE MONGOLIAN GERBIL

¹ Department of Biology, San Diego State University, San Diego, California 92115

1. Spontaneous activity of male gerbils, Meriones unguiculatus, kept in actographs was recorded continuously from May 1, 1968, through March 15, 1969, in Evanston, Illinois. Gerbil activity was studied under two lighting conditions: constant illumination (LL) and 12-12 LD.

2. For those gerbils kept in 12-12 LD a lunar-day periodism of spontaneous activity was disclosed for each of three seasons (summer, fall, and winter). The mean three-season cycle in 12-12 LD exhibited maxima around times of rising and setting of the moon and minima at lunar lower and upper transits.

3. For those 5 animals in LL a lunar-day cycle of activity was reported for each animal over a period averaging 179 days. When the lunar-day cycles for each of the 5 gerbils in LL were averaged together, a mean periodism with cycle form and phase relationship very similar to that of the three-season cycle for gerbils in 12-12 LD was found. The range of this cycle was 16%.

4. All lunar-day cycles studied had maxima and minima locked to the approximate hours of moonrise, moonset, lunar upper and lower transits. There was a strong tendency for lunar inversion, but the cycles appeared to be interrelated with one another in degrees of inversion.

5. These results give support to the hypothesis that the gerbils are responsive to weak geoelectromagnetic fields with period lengths of 24.8 hours from which they are not shielded in the laboratory.