Drivers behind the fatty acid composition in mammals

The adipose tissue of mammals is the main storage site for fatty acids and plays an important role as energy reserve, buoyancy control (in marine animals), and thermal insulation. This study focuses on the last function:... [ view full abstract ]

The adipose tissue of mammals is the main storage site for fatty acids and plays an important role as energy reserve, buoyancy control (in marine animals), and thermal insulation. This study focuses on the last function: adipose tissue as a thermal insulator. Studies of adipose tissues in mammals suggest that when the animal is exposed to cold their fatty acids become more and more unsaturated. Nevertheless, there are other mechanisms through which animals protect themselves from extreme temperatures. Furry animals, for instance, rely on their fur to bear with the cold, so their adipose tissue might not change with temperature variations. On the other hand, bare-skinned mammals, such as whales, rely only on their blubber to keep their body warm. Other factors affecting the way the animals cope with environmental conditions could be body size, body fineness, and environment (aquatic or terrestrial). Are small and large animals affected by cold/heat in the same way? Do adipose tissue fatty acids change according to the environment (aquatic/terrestrial) where the animals live? The aim of our study was to determine what drives the fatty acid composition among mammals. Are the saturation of fatty acids in mammals driven by their 1) Fur density, 2) Body size, 3) Fineness or 3) Environment? We applied a model selection approach to identify which of these four models had the highest support to explain the differences in fatty acid unsaturation among 31 species of mammals. Overall, fur density was the model with the highest support, which means animals with fur do not need to increase the unsaturation of their fatty acids and they rely mostly on fur, rather than adipose tissue, as an insulator. Bared-skinned animals, on the other hand, need to cool their superficial tissues, which reduces heat loss through vasoconstriction. This strategy implies that adipose tissues must be able to resist colder temperatures than the rest of the body, which can be accomplished by increasing the level of unsaturation of fatty acids. Although the animals with highest levels of unsaturation were those without fur, they were also the animals living in the coldest climates.