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

Abstract

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 lipidomic 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 bioinformatic tool (LION/web), we showed contrasting fingerprint 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 triacylglycerol 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 sphingolipid 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 in δ 15 N and δ 13 C 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.

Applications of lipidomics in marine organisms: progress, challenges and future perspectives

“…These studies performed the first comprehensive characterization of the lipid profile of the plasma, 166,167 heart, 168 and adipose tissue (i.e., blubber). 169 Lipidomics can be applied as a diagnostic tool to screen the metabolic and physiological conditions of marine mammals. Understanding lipidome fluctuations between health and sick organisms contributes to uncovering metabolism alterations, helping in the identification of sick animals.…”

“…A comparative lipidomic study using the blubber of two whale species (Orcinus orca and Megaptera novaeangliae) suggested that differences in the blubber lipidomic fingerprints were triggered by their contrasted This journal is © The Royal Society of Chemistry 2022 life-history strategies, but lipidomic similarities were also found due to their phylogenetic association. 169 Additionally, the authors combined lipidomic and isotopic ratio analyses to identify intraspecific dietary specializations in the killer whale (Orcinus orca) population. The results clustered the killer whales into two different groups according to their diets.…”

“…Food specialization showed that lipid-enriched individuals fed mainly on herrings and seals, while lipid-depleted individuals just fed on herring. 169 In the evolutionary history of mammals, the development of cetaceans represents one of the most striking adaptations to habitat change, and the efficient use of lipids is a feature that contributed to this adaptive success. 170 Therefore, comparative studies between marine and terrestrial mammals are essential to understand their evolution.…”

“…Food specialization showed that lipid-enriched individuals fed mainly on herrings and seals, while lipid-depleted individuals just fed on herring. 169…”

Climate change and cetacean health: impacts and future directions

“…lipid profile) and blood parameters related to metabolism [135]. As such, lipidomics shows great promise to assess the change in energy body reserves and thus body condition in free-ranging cetaceans [99,133,140,141]. Other omics approaches such as proteomics and metabolomics are also emerging as novel methods to increase our understanding of cetacean metabolism [137,[142][143][144][145].…”