Abstract: Why do seals develop cataracts after living 40 years, rats after 2 years, and humans after 70 years, while whales do not develop cataracts even after 100 years of age? To address that question, lenses from pinnipeds—walrus, spotted seals, ringed seals, bearded seals, and a ribbon seal—were studied. The cholesterol and phospholipid content of the lenses were measured using 1H and 31P-NMR spectroscopy, respectively. Lens lipid structure was measured using FTIR spectroscopy. We found that in Phocidae, similar to various terrestrial species, lifespan is related to lens sphingolipid, and lens sphingolipid is related to lens membrane order and cholesterol. Shifting lens lipid composition toward increased levels of sphingolipids has been proposed as an adaptive evolutionary molecular mechanism to limit reactive oxygen species lens damage (oxi¬dative stress) and, thus, age-related cataract formation. Additional comparative studies of lens lipid composition of pinnipeds across taxa with various foraging and diving strategies are needed to further explore and test underlying assumptions for the observed divergent sphingolipid content between Phocidae and Odobenidae. While the causes of the lens compositional differences between Phocidae and Odobenidae remain undetermined, our study provides novel physiological data on lens lipid composition in marine mammals and largely complements lens lipid compositional findings in terrestrial and other aquatic species that demonstrate a linkage between lifespan, sphingolipids, and cataracts.
Key Words: pinnipeds, seals, walruses, cataract, lens, lifespan, lipids
Document: Article
DOI: https://doi.org/10.1578/AM.44.5.2018.506
Page Numbers: 506-518

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