Diet explains interpopulation variation of plasma carotenoids and skin pigmentation in nestling white storks

Carotenoids have a dietary origin in birds, but mechanisms by which they ar e absorbed in the gut, transported in the blood, metabolized at various sit es, and deposited in the integument remain poorly understood. Variation in both plasma carotenoid levels and external color may reflect different acce ss to dietary carotenoids or individual physiological differences in the up take and deposition of carotenoids. We compared total plasma carotenoid con centration in nestling white storks (Ciconia ciconia) from 11 Spanish colon ies in two consecutive years. The main food item in one of the colonies was the red swamp crayfish (Procambarus clarkii), a recently introduced specie s. Storks in the remaining colonies ate a variety of foods but no crayfish. Total plasma carotenoid levels in the colony where crayfish were consumed were about five times higher than in any other colony. These differences we re maintained after controlling for the significant interyear variability, as well as for sex, age, and body mass of birds. Skin pigmentation also dif fered, being intensely orange in storks that consumed crayfish but white (u npigmented) in the remaining individuals. With thin-layer chromatography (T LC) and electronic absorption spectroscopy, astaxanthin was confirmed as th e major carotenoid in crayfish as well as in the plasma, skin, and body fat of crayfish-eating storks, whereas lutein was the main carotenoid in plasm a samples from the other colonies. These results indicate that a newly avai lable carotenoid in the environment, astaxanthin, can be absorbed in large quantities from the gut and be transported in the blood before deposition i n different tissues.