Latitudinal changes in blubber fatty acids of the South American sea lion along the Southeast Pacific Coast

The composition of marine mammal blubber is influenced by factors such as diet and environmental conditions. Here, we investigate the thermal influence on fatty acid composition and degree of unsaturation in the blubber of 151 South American sea lions (Otaria byronia). Samples were collected at ten locations along the Chilean coast and spanned a latitudinal range of approximately 2500 km, an arc of 23 degrees. We found a significant latitudinal gradient in the biochemical composition of sea lion blubber. At higher colder latitudes the endogenous fatty acids in the blubber were more unsaturated, as indicated by the desaturation index. In cold conditions the modification of fatty acids from saturated to unsaturated improves fluidity of cell membranes, which is important for thermal insulation. Thus, the higher degree of unsaturated endogenous fatty acids at higher latitudes may help sea lions maintain thermal balance in colder environments. For the dietary-sourced fatty acids however, we found the opposite latitudinal pattern, here the overall degree of unsaturation decreases with latitude. The lower proportion of polyunsaturated fatty acids in blubber at higher latitudes may be influenced by the sea lion's dietary choices. Additionally, the presence of extremely high levels of 18:2n-6 in some sea lions south of 40 degrees S, values more typical of terrestrial origin, suggests they consumed farmed salmon. The observed variation in fatty acid profiles across the latitudinal gradient implies that differences in fatty acid composition are not solely attributed to dietary variation, but potentially also to endogenous metabolism in response to environmental conditions.