The influence of essential fatty acids on hibernation and energy budgets of Alpine marmots in their natural habitat

This research project focused on the role of the essential fatty acids linoleic acid and a-linolenic acid on hibernation in free living marmots. Feeding experiments in the laboratory suggested that hibernators fed during summer fattening with a diet rich in essential fatty acids tolerated during subsequent hibernation deeper body temperatures, interrupted hibernation less frequently, and hence had lower energy expenditure. However, these experiments primarily investigated the role of linoleic acid, and particularly high or low concentrations had been supplied. Hence the role of a-linolenic acid remained unclear as well as whether the effects of linoleic acid found in the laboratory had any ecological relevance. This research project thus investigated with free-living alpine marmots whether essential fatty acids are a limiting factor in the natural habitat, which effects they have on hibernation, whether they influence diet selection of marmots, and how these substances are used in the body. The study was performed in a high alpine valley in the Swiss Canton Grisons (2100m a.s.l.). Temperature sensitive radio transmitters were implanted into the peritoneal cavity of 57 marmots and the course of their body temperature was registered throughout three winters. In addition, marmots were observed while foraging in a second adjacent study site four times a year between spring and autumn, and subsequently shot by game wardens of the Grisons` game agency within a regular population control program. The stomach content of these animals was analysed botanically and chemically and compared with the available food plants. Furthermore, fat samples were obtained from all shot and captured marmots for gaschromatographic analysis of fatty acid composition. The content of linoleic and a-linolenic acid in the fat depot accumulated for overwintering differed substantially between individuals. On average, the body fat in autumn contained 9.6% linoleic acid and 20.3% a-linolenic acid. The higher the content of linoleic acids in autumn in a marmot`s fat was, the deeper sank body temperature during bouts of hibernation and the longer lasted individual bouts. The associated lower energy expenditure became evident in a lower body mass loss during winter. However, analysis of the influence of a-linolenic acid revealed that this fatty acid had rather negative effects on hibernation. The higher the content of a-linolenic acid was in the body fat, the higher were the lowest body temperatures tolerated by the animals during individual bouts of hibernation. Marmots achieved enrichment of linoleic acid through selective feeding. Preferred food plants during fattening were characterised by high energy content, good digestibility, relatively low content of a-linolenic acid, but a high content of linoleic acid. The functional significance of linoleic acid can be assumed in its usage as phospholipid in cell membranes ensuring proper membrane function at low body temperatures. Although a-linolenic acid could fulfil this function as well, it was apparently avoided as much as possible, and rapidly removed from the body. A possible explanation could be that fatty acids containing a high number of double-bonds are more prone to lipid peroxidation thereby producing highly toxic peroxiradicals.