Abstract
BackgroundMost fatty acids (FAs) making up the adipose tissue in mammals have a dietary origin and suffer little modification when they are stored. However, we propose that some of those FAs, specifically those that can be synthesised or modified by mammals, are also being influenced by thermal forces and used as part of the mechanism to regulate core body temperature. As FA desaturation increases, adipose tissues can reach colder temperatures without solidifying. The ability to cool the superficial fat tissues helps create a thermal gradient, which contributes to body heat loss reduction. Therefore, it is expected that animals exposed to colder environments will possess adipose tissues with higher proportions of desaturated FAs. Here, through a model selection approach that accounts for phylogeny, we investigate how the variation in FA desaturation in 54 mammalian species relates to the thermal proxies: latitude, physical environment (terrestrial, semi-aquatic and fully-aquatic) and hair density.ResultsThe interaction between the environment (terrestrial, semi- or fully-aquatic) and the latitude in which the animals lived explained best the variation of FA desaturation in mammals. Aquatic mammals had higher FA desaturation compared to terrestrial mammals. Semi-aquatic mammals had significantly higher levels of desaturated FAs when living in higher latitudes whereas terrestrial and fully-aquatic mammals did not. To account for dietary influence, a double bond index was calculated including all FAs, and revealed no correlation with latitude in any of the groups.ConclusionsWe propose that FA modification is an important component of the thermoregulatory strategy, particularly in semi-aquatic mammals. Potentially this is because, like terrestrial mammals, they experience the greatest air temperature variations across latitudes, but they lack a thick fur coat and rely primarily on their blubber. Unlike fully-aquatic mammals, extremely thick blubber is not ideal for semi-aquatic mammals, as this is detrimental to their manoeuvrability on land. Therefore, the adipose tissue in semi-aquatic mammals plays a more important role in keeping warm, and the modification of FAs becomes crucial to withstand cold temperatures and maintain a pliable blubber.
Highlights
Most fatty acids (FAs) making up the adipose tissue in mammals have a dietary origin and suffer little modification when they are stored
Fully-aquatic mammals have a mean Desaturation index (Δ9-DI) of 3.08 ± 1.07, whereas semi-aquatic mammals have a Δ9-DI of 3.09 ± 1.75, and terrestrial mammals have a lower Δ9-DI of 1.37 ± 0.70
We show that the ability to modify FAs is an important part of mammalian thermal plasticity, especially for mammals living under adverse thermal conditions
Summary
Most fatty acids (FAs) making up the adipose tissue in mammals have a dietary origin and suffer little modification when they are stored. The ability to cool the superficial fat tissues helps create a thermal gradient, which contributes to body heat loss reduction. In bare-skinned mammals, the cooling of the body surface in contact with air or water is of critical importance in order to reduce the heat lost to the environment. In cold superficial tissues occurs peripheral vasoconstriction, where the flow of warm blood is reduced [8], reducing body heat loss and creating a thermal gradient through the adipose tissue. Cooling the body surface to temperatures similar to those of the ambient could create a potential problem. Low temperatures could cause rigidity and solidification of superficial tissues; potentially it is here when the biochemical structure of fats becomes more important
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