Conversion efficiency of alpha linolenic acid to omega-3 highly unsaturated fatty acids in aerial insectivore chicks

Food availability and quality are both critical for growing young animals. In nature, swallows (Tachycineta bicolor) and other aerial insectivores feed on both aquatic insects, which are rich in omega-3 highly unsaturated fatty acids (HUFA) and terrestrial insects, which contain considerably lower amounts of omega-3 HUFA. Carnivorous mammals and fishes must obtain omega-3 HUFA from diet, as they have lost the capacity to convert the precursor omega-3 ALA into omega-3 HUFA. Thus, the relative value of aquatic versus terrestrial insects depends not only on the fatty acid composition of the prey, but also upon the capacity of consumers to convert ALA into omega-3 HUFA. We used a combination of stable-isotope-labeled fatty acid tracers to ask if, and how efficiently, Tree Swallows can deposit newly synthesized omega-3 HUFA into tissue. Our data show for the first time that Tree Swallows can convert ALA into omega-3 HUFA deposited in liver and skeletal muscle. However, high Tree Swallow demand for omega-3 HUFA combined with low ALA availability in natural terrestrial foods may strain their modest conversion ability. This suggests that while Tree Swallows can synthesize omega-3 HUFA de novo, omega-3 HUFA are ecologically essential nutrients in natural systems. Our findings thus provide mechanistic support for our previous findings and the importance of omega-3 HUFA -rich aquatic insects for Tree Swallows and most likely other aerial insectivores with similar niches.