Data from: Biosynthesis of long-chain omega-3 fatty acids in a generalist seabird

Docosahexaenoic acid (DHA), a long-chain omega-3 fatty acid (n3-LCPUFA),
is integral to vertebrates’ brains. Mammals require continuous DHA
replenishment to maintain cerebral function and structural integrity;
evidence points towards birds having similar requirements. Vertebrates
maintain their DHA levels by endogenously synthesizing DHA using
alpha-linolenic acid (ALA; omega-3 precursor) or by consuming preformed
DHA and other n3-LCPUFAs. Given n3-LCPUFAs’ abundance in marine organisms,
marine predators are presumed incapable of biosynthesizing n3-LCPUFAs;
this assumption remains seldom tested. Alarmingly, many marine predators,
including generalist seabirds, now forage on anthropogenic resources
deficient in n3-LCPUFAs. Whether they can offset such deficiency by
bioconverting ALA into DHA remains unknown. Here, we tested whether
ring-billed gulls (Larus delawarensis), a generalist seabird now thriving
in cities, can biosynthesize n3-LCPUFAs, including DHA, from ALA. We
brought into captivity 24 hatchlings from two breeding colonies, including
12 from an urban colony and 12 from a natural colony. Nine hatchlings from
each colony received an oral 13C-enriched ALA tracer to follow the
potential bioconversion of ALA into n3-LCPUFAs, in addition to being fed
490 μL of unlabelled ALA daily for three days. The control groups (N=3
urban hatchlings and 3 natural hatchlings) received a caloric equivalent
(free of omega-3s) in place of the ALA tracer and supplement. All chicks
received a diet deficient in all omega-3s throughout the 72 hours of
captivity. We analyzed their brains’ and livers’ fatty acid content and
established their 13C signatures for each omega-3 using compound-specific
isotope analysis. We found evidence of incomplete ALA bioconversion where,
compared to controls, experimental chicks from both colonies accumulated
more of all ALA derivates in their tissues except for DHA. We demonstrate
for the first time that a seabird shows some omega-3 bioconversion
abilities, albeit at levels insufficient to mitigate DHA deficiencies
associated with urban foraging and shifting marine ecosystems.