The winter metabolic depression in Arctic beavers (Castor canadensis Kuhl) with comparisons to California beavers

Abstract

No major seasonal changes were observed in California beavers kept under Vancouver climatic conditions, with a constant ration made available ad libitum, but Arctic beavers kept under the same conditions showed a growth cessation, a 40% reduction in food intake, and a depression in the 131PBI conversion ratio during the winter. These findings strongly indicated that the observed changes in the Arctic form are inherent attributes.Manipulation of light conditions had no detectable effects on California beavers but exposure of Arctic beavers to constant darkness, beginning in October, resulted in a reduction of food intake to zero after 17 and 22 days in two animals respectively, a weight loss, and a complete muscular paralysis of unknown nature. Exposure to constant incandescent light after 24 days of darkness erased these effects.It was concluded that northern beavers possess a winter metabolic depression induced by decreasing light intensity in the autumn. The normal mechanism for reversal is unknown, but restoration of light can accomplish reversal. The metabolic depression is poorly understood, but is characterized by an absence of growth, low thyroid activity, low food intake, a normal body temperature, and possibly a peripheral control of activity. The physiology of the apparent control mechanism is unknown.