Metabolism of Dietary Cetoleic Acid (22:1n‐11) in Mink (Mustela vison) and Gray Seals (Halichoerus grypus) Studied Using Radiolabeled Fatty Acids

Abstract

Cetoleic acid (22:1n-11) is a good indicator of diet in marine predators and has proven to be an important fatty acid (FA) when using adipose tissue FA composition to study diet in marine mammals and seabirds. Feeding studies have shown that 22:1 isomers are predictably underrepresented in adipose tissue relative to diet, implying that metabolism within the predator strongly influences the relationship between the level of these FAs in diet and adipose tissue. Fully understanding such metabolic processes for individual FAs is important for the quantitative estimation of predator diets. We employed a dual-label radioisotope tracer technique to investigate the potential modification of 22:1n-11 and its recovery in the blubber of gray seals (Halichoerus grypus) and in the adipose tissue and liver of mink (Mustela vison), a smaller model carnivore also accustomed to fish-based diets. In both seals and mink, (3)H radioactivity was found in the chain-shortened products of 22:1n-11, with 18:1 being the dominant product. We also found (3)H radioactivity in saturated FAs. The distribution patterns of (3)H radioactivity across the FAs isolated from seal blubber and mink subcutaneous adipose tissue were comparable, indicating that mink are a good model for the investigation of lipid metabolism in marine carnivores.

Age-related differences in skeletal muscle lipid profiles of Weddell seals: clues to developmental changes

“…The isomers of 22:1 were under-represented in the blubber of adults (present study, N3, 1.62±0.05%) and from the blubber of lactating females (1.77%) (Wheatley et al, 2008), indicating this MUFA may be conserved in juvenile muscle. Cooper et al reported similar findings in the gray seal (Halichoerus grypus) and suggested that the discrepancy between diet and blubber is a reflection of 22:1 efficient peroxisomal chain-shortening systems (22:1 to MUFAs) and de novo synthesis (22:1 to SFAs) (Cooper et al, 2006). While pups had significantly lower IMTG 22:1 values, these values correspond with published milk 22:1 values (Wheatley et al, 2008).…”

Evaluating quantitative fatty acid signature analysis (QFASA) using harbour seals Phoca vitulina richardsi in captive feeding studies

“…Calibrations from juvenile harbour seals were more reliable than CCs from grey seal pups, irrespective of the FA subset employed. Further testing with calibrations generated from alternate prey and under different intrinsic conditions, as well as estimating CCs via radiolabelled FA (Cooper et al 2006), should continue. Using the newly developed Reduced FA subset provided diet estimates with the fewest false positives overall and using different FA subsets affected reported diet composition.…”

Tracing aquatic food webs using fatty acids: from qualitative indicators to quantitative determination

“…A more important process however, especially in mammals, may be peroxisomal chain-shortening of some long-chain monounsaturated FA. Thus, some ingested 20:1 and especially 22:1 isomers are likely shortened primarily to their 18-carbon isomers (Norseth and Christophersen 1978 ;Osmundsen et al 1979 ;Cooper et al 2005Cooper et al , 2006, r esulting in somewhat reduced and increased deposition of these FA relative to diet, respectively.…”

“…Whether this could ever be realized remains to be established, but almost certainly could not be accomplished using FA and QFASA alone. Additional tools for better understanding trophic transfer of FA in general and the performance of QFASA in particular could make use of advanced and targeted techniques, such as using radio or stable isotope-labeled FA to trace pathways from diet to deposition (Budge et al 2004 ;Cooper et al 2006) . These types of methods should provide even better insight at all trophic levels but are fairly cost-intensive.…”