Developing a biochemical index to track physiological adaptations of cetaceans to environmental changes

Abstract

In order to track the physiological adaptation of minke whales (Balaenoptera acutorostrata) to environmental changes, we investigated a new biochemical approach, called compound-specific isotope ratio, because the carbon isotopic ratio of individual fatty acids could be changed via the modification of compounds for physiological requirements. Preliminary results showed that carbon isotope ratios of some fatty acids varied vertically throughout the blubber layers. In particular, the isotope ratios of 16:1(n-7) became lighter from the outermost layer to the innermost layer, whereas the isotope ratio of 18:1(n-7) was heavier in the innermost layer than in the outermost layer. 16:1(n-7) was transformed via the desaturation of longer carbons (>16 carbon fatty acids) but 18:1(n-7) was transformed via the elongation of shorter carbons (<18 carbon fatty acids). However, among PUFAs, the isotope ratios of 20:5(n-3) and 22:6(n-3), generally used as dietary indicators, didn’t show any significant changes. It confirms that long-chain PUFAs can’t be synthesized in cetaceans. We could infer that only specific fatty acids (i.e. MUFAs) were modified and transformed in the blubber for physiological needs (i.e. insulation, buoyancy and streamlining). These approaches may provide a history of physiological adaptation of cetaceans experiencing any environmental changes during their life span.of individual fatty acids could be changed via the modification of compounds for physiological requirements. Preliminary results showed that carbon isotope ratios of some fatty acids varied vertically throughout the blubber layers. In particular, the isotope ratios of 16:1(n-7) became lighter from the outermost layer to the innermost layer, whereas the isotope ratio of 18:1(n-7) was heavier in the innermost layer than in the outermost layer. 16:1(n-7) was transformed via the desaturation of longer carbons (>16 carbon fatty acids) but 18:1(n-7) was transformed via the elongation of shorter carbo