Fat stores in birds: an overlooked sink for carotenoid pigments?

Abstract

Summary 1.Carotenoids are responsible for the most striking colours in birds, but also play an important role as enhancers of the immune system. Consequently, a trade-off between the ornamental and health functions of carotenoids in birds has been proposed. 2. Although it is well known that birds can store carotenoids in different organs and tissues, including the fat stores, until now all field studies of the regulation of carotenoid stores have focused on plasma carotenoids. 3. Carotenoids in the fat of 44 wild Greylag Geese ( Anser anser L.) wintering in southwestern Spain were identified and quantified. In addition, the relationships between carotenoids and the size of the fat stores, as well as the sex and age of the geese, were analysed. 4. The major carotenoid in goose fat was lutein. This and related carotenoids are also the most prevalent pigments in bird plasma and secondary sexual characters. We also detected β -cryptoxanthin, β -carotene, neochrome and neoxanthin. Total carotenoid concentration was negatively correlated with the size of the fat stores. Males had higher concentrations of carotenoids than females. 5. A possible explanation for these patterns is that male birds tend to have higher plasma carotenoids than females, a difference that could be transposed to fat if carotenoids diffused passively from the blood into adipose tissues. Carotenoids, however, may tend to remain in the fat stores. If this were true, fat would not be a reservoir of carotenoids, but a sink where a significant amount of these pigments would be sequestered, being no longer available for other functions.

Carotenoid-based bill and eye ring coloration as honest signals of condition: an experimental test in the red-legged partridge (Alectoris rufa)

“…However, although at the time of postrestriction sampling all food-deprived birds were ingesting 50% of their daily food intake (and hence 50% of carotenoids), their circulating levels of blood carotenoids decreased only by 15% with respect to prerestriction values. One possible explanation is that food-deprived birds partially compensated the reduction of carotenoids ingested by actively releasing them from body stores such as fat or liver (Negro et al 2001a). Alternatively, carotenoids stored in body fat may have been released passively to the bloodstream when fat was mobilized as a result of the decrease in food intake.…”

“…Alternatively, carotenoids stored in body fat may have been released passively to the bloodstream when fat was mobilized as a result of the decrease in food intake. However, to date, it is unknown whether carotenoids stored in fat can be selectively mobilized when they are required by the bird (Negro et al 2001a). Another possibility to explain the smaller than expected decrease in plasma carotenoid levels of food-deprived birds is that foodrestricted birds compensated their lower carotenoid intake by increasing their absorption efficiency.…”

Testosterone increases bioavailability of carotenoids: Insights into the honesty of sexual signaling

“…Second, the anabolic effects of testosterone could increase the production of reactive oxygen species and hence a requirement for antioxidants. As a result, carotenoids may be liberated from major body stores such as the liver and fat (29,30) into circulation. A third possibility is that testosterone increases the absorption efficiency of ingested carotenoids (e.g., changing the activities of digestive enzymes or levels of lipoproteins), resulting also in elevated plasma levels.…”

Carotenoid Coloration in Greenfinches Is Individually Consistent Irrespective of Foraging Ability

“…On the other hand, several experiments have also convincingly shown that expression of carotenoid ornaments depends on parasitic infections (reviewed in Hill 2002Hill , 2006Hõrak et al 2004), immune system activation (e.g., Blount et al 2003;Faivre et al 2003;McGraw and Ardia 2003), or individual nutritional state (Hill 2000;McGraw et al 2005). Other studies have also shown that birds kept on a uniform diet do not converge on the same plasma carotenoid levels (e.g., Bortolotti et al 1996;Negro et al 2001).…”