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Carotenoid esterification: a key factor in the expression of carotenoid-based ornaments?

Carotenoid-based colorations are a paradigm among signals of quality in animals. Despite the great interest on carotenoid-based ornamental colorations, there are many aspects of carotenoid metabolism, transformation and deposition in teguments that remain unsolved. One of these understudied topics is the fact that, in contrast to metabolically inert tissues like feathers that accumulate only free forms of carotenoids, living tissues (skin, scales, beaks) accumulate esterified carotenoids, that is, carotenoids combined with fatty acids. However, most studies quantifying carotenoid levels in these tissues perform a saponification step that eliminates these free acids, thus preventing the separate quantification of free and esterified forms of each carotenoid present in the tissue. In a recent studied published in Physiological and Biochemical Zoology we analyze the free and esterified forms of the carotenoids pigmenting the beak, legs and eye rings of wild and captive red-legged partridges (Alectoris rufa). We found that 80% of carotenoids in these tissues are esterified, and for some ornaments the amount of carotenoid esters was a better predictor of ornament coloration than free or total carotenoids. The function of carotenoid esters is far from clear. We hypothesize that carotenoid esterification may contribute to pigment stability, thus contributing to color expression. It is also possible that carotenoid esters may play a significant role in carotenoid mobilization, taking part in the dynamism of the colour of these living tissues.

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  • Carotenoid(ester)-based ornaments in the head of a partridge
  • Typical cromatogram of the ornaments of red-legged partridges
  • The study species, the red-legged partridge (Alectoris rufa)