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 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.
Highlights
To optimize their fitness, living organisms must acquire and allocate energy stores in a way that maximizes their survival and reproduction (Stearns, 1989)
To the best of our knowledge, this study provides the most comprehensive assessment of the lipidome in cetaceans
The predominance of triradylglycerols was almost exclusively driven by high content of triacylglycerols and is consistent with previous investigations conducted on several cetacean species including harbor porpoises (Phocoena phocoena; Tilbury et al, 1997), gray whales (Eschrichtius robustus; Krahn et al, 2001), white whales (Delphinapterus leucas; Krahn et al, 2004), striped dolphins (Stenella coeruleoalba; Kawai et al, 1988), killer whales (Krahn et al, 2004), fin whale (Balaenoptera physalus; Lockyer et al, 1984; Ruchonnet et al, 2006), sei whale (Balaenoptera borealis; Bottino, 1978), and humpback whales (Waugh et al, 2012)
Summary
To optimize their fitness, living organisms must acquire and allocate energy stores in a way that maximizes their survival and reproduction (Stearns, 1989). Investigating the lipid composition of blubber can provide key insights about the lifestyle of cetaceans including knowledge about dietary specialization, nutritional status, space-use strategy, physiological state, and reproductive stage (Aguilar & Borrell, 1990; Bernier-Graveline et al, 2021; Irvine et al, 2017; Mau, 2004.; Tang et al, 2018; Waugh et al, 2012; Linder et al, 2010; Ruchonnet et al, 2006). The objectives of this study were to document an extended lipidomic fingerprint in killer whales and humpback whales present in northern Norway during wintertime to better understand the determinants of lipid stores and uses in these cetaceans. To provide more information on potential dietary specialization in the killer whales, stable isotopes of nitrogen (δ15N) and carbon (δ13C) were determined in skin tissue of sampled individuals
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