A deep dive into fat: Investigating blubber lipidomics fingerprint of killer whales and humpback whales in northern Norway

In cetaceans, blubber is the primary and largest lipid body reservoir. Our
current understanding about lipid stores and uses in cetaceans is still
limited and most studies only focused on a single narrow snapshot of the
lipidome. We documented an extended lipidomics fingerprint in two cetacean
species present in northern Norway during wintertime. We were able to
detect 817 molecular lipid species in blubber of killer whales (Orcinus
orca) and humpback whales (Megaptera novaeangliae). The profiles were
largely dominated by triradylglycerols in both species and to a lesser
extent, by other constituents including glycerophosphocholines,
phosphosphingolipids, glycerophosphoethanolamines and diradylglycerols.
Through a unique combination of traditional statistical approaches,
together with a novel bioinformatics tool (LION/web), we showed
contrasting fingerprints composition between species. The higher content
of triradylglycerols in humpback whales is necessary to fuel their
upcoming half a year fasting and energy-demanding migration between
feeding and breeding grounds. In adipocytes, we assume that the intense
feeding rate of humpback whales prior to migration translates into an
important accumulation of triacylglycerols content in lipid droplets.
Upstream, the endoplasmic reticulum is operating at full capacity to
supply acute lipid storage, consistent with the reported enrichment of
glycerophosphocholines in humpback whales, major components of the
endoplasmic reticulum. There was also an enrichment of membrane components
which translates into higher sphingolipids content in the lipidome of
killer whales, potentially as a structural adaptation for their higher
hydrodynamic performance. Finally, the presence of both lipid-enriched and
lipid-depleted individuals within the killer whale population in Norway
suggests dietary-specialization, consistent with significant differences
of δ15N and δ13C isotopic ratios in skin between the two groups, with
higher values and a wider niche for the lipid-enriched individuals.
Results suggest the lipid-depleted killer whales were herring-specialists,
while the lipid-enriched individuals might feed on both herrings and
seals.