Variation in the chemical composition of adipose tissue of three species of ursids

Abstract

The relationship between the water content and lipid content of adipose tissue was compared between 25 polar bears (Ursus maritimus) and 25 black bears (Ursus americanus) to determine if it was affected by species differences in the fatty-acid composition of adipose tissue. The adipose tissue of polar bears had a lower water content and a higher proportion of long-chain fatty acids than did the adipose tissue of black bears, when compared at equal lipid content. The relationship between the body water and lipid contents was also compared among 11 polar bears, 18 black bears, and 6 brown bears (Ursus arctos) to determine if this relationship could be affected by species differences in the relationship between the water and lipid contents of adipose tissue. The body-water content in marine (polar) bears was less than that in terrestrial (black and brown) bears, and the differences in body-water content between the two groups became more apparent as the body-lipid content increased. These results suggest that the fatty-acid composition of adipose tissue can affect the body-water content, especially in fat bears. These findings have implications for the use of isotope-dilution models to predict body composition in bears.