On the circadian rhythm of animals in high polar latitudes

Abstract

Even in the highest polar latitudes where animals and plants are able to live, a perception of the changing abiotic parameters in the course of the day is possible. And these factors are used for the setting of the physiological clock, so that animals are synchronized not only with the rotation of the earth but also among the members of a population. The prominent Zeitgeber is the changing spectral composition of light. Even if current experiments are restricted to passerine birds the results may be extended to insects and plants. For instance, an animal which cannot perceive long-wave light should react to this diurnal change of colour temperature as if it were a change of dark and light, and we may expect the same phenomenom for plants with their phytochrome system. Whether the colour temperature may be responsible for photo-periodic inductions is not yet clear. Stross [22, 23] in the Canadian arctic observed Daphnia middendorfiana which always produced resting eggs at the same time of the year, and was able to demonstrate that in an experiment this may be induced by short days. This observation points in the same direction but the spectral composition of the light has not been tested yet.