No evidence that carotenoid pigments boost either immune or antioxidant defenses in a songbird

TLDR

Dietary carotenoids have been proposed to boost immune and antioxidant functions in vertebrates, yet many studies fail to support this. The study compared yellow canaries with high carotenoid levels to white recessive canaries with low carotenoid levels under oxidative and pathogen challenges. Across multiple physiological measures, no differences were found between the two groups, challenging the assumption that carotenoids directly support physiological function in birds and suggesting they may play little to no direct role.

Abstract

Dietary carotenoids have been proposed to boost immune system and antioxidant functions in vertebrate animals, but studies aimed at testing these physiological functions of carotenoids have often failed to find support. Here we subject yellow canaries (Serinus canaria), which possess high levels of carotenoids in their tissue, and white recessive canaries, which possess a knockdown mutation that results in very low levels of tissue carotenoids, to oxidative and pathogen challenges. Across diverse measures of physiological performance, we detect no differences between carotenoid-rich yellow and carotenoid-deficient white canaries. These results add further challenge to the assumption that carotenoids are directly involved in supporting physiological function in vertebrate animals. While some dietary carotenoids provide indirect benefits as retinoid precursors, our observations suggest that carotenoids themselves may play little to no direct role in key physiological processes in birds.