Moon and sun compasses in sandhoppers rely on two separate chronometric mechanisms

The relationship between the chronometric system of compensation for the ap parent movement of the sun and that for the moon has been the subject of se veral, never proven, hypotheses. Our studies on sand-hoppers have demonstra ted that the chronometric mechanism of the moon compass is separate from th at of the sun compass. They show (i) that a period of seven days in constan t darkness has no influence on the capacity for orientation, either solar o r lunar, and indicates the presence of one or more continuously operating t iming mechanisms; (ii) that two different shifts in the light-dark phase ha ve no effect on the chronometric mechanism of lunar orientation, but they d o affect that of solar orientation; and (iii) that exposure to an artificia l moon delayed by seven days with respect to the natural cycle causes the e xpected change in the mean direction of individuals tested under the natura l moon, but not of those tested under the sun.