Relocation to avoid costs: a hypothesis on red carotenoid-based signals based on recent CYP2J19 gene expression data

El congreso tuvo lugar del 2 al 4 de febrero de 2022 en Vigo.Sexual and social selections drive the evolution of conspicuous colorations in many animal species. These traits would function as individual quality signals whether they transmit reliable information. In animal signaling theory, that reliability is guaranteed if those costs of trait production are too expensive for low-quality individuals or, alternatively, assured if the trait expression is inherently linked to individual quality and thus cannot be falsified (“index signals”). A new hypothesis proposes that colored ornaments produced by red keto-carotenoid pigments could act as unfalsifiable index signals similar to other classical examples where quality was ultimately linked to individual body size. These ketocarotenoid pigments are often obtained by enzymatic transformation of dietary yellow carotenoids. Recently, the first enzyme performing this transformation was described: CYP2J19. It belongs to the cytochrome p450 superfamily. It is presumably located in the inner mitochondrial membrane, therefore connecting color expression with cell respiration efficacy. Nevertheless, it is still unknown if the tissue where this cell mechanism acts affects signal honesty and evolution. CYP2J19 expression levels in different species and tissues are currently available. We review current data in avian species and propose that CYP2J19 activity could have evolved by being relocated from the hepatic tissue to the epidermis in those birds where the red color is expressed in non-feathered bare parts. Bare parts require continuous carotenoid mobilization to sustain color. We suggest that tissue-based relocation avoids production costs due to potential CYP2J19 interfering with vital liver functions. Implications for signal reliability in ornamental evolution are discussed