Meeting Abstract
Carotenoid-based signaling is thought to be a classic example of honest signaling, in that acquiring and metabolizing carotenoids likely imposes costs and individuals expressing the most carotenoid rich signals are therefore predicted to be in the best condition. Yet the proximate mechanisms of carotenoid production remain poorly resolved, which limits our understanding of the evolutionary constraints and physiological costs associated with this widespread signaling modality. The red-backed fairywren (Malurus melanocephalus) provides a useful context in which to examine mechanisms underlying expression of carotenoid-based ornamentation: male red-backed fairywrens exhibit flexible reproductive phenotypes, where older individuals have high circulating testosterone and breed in red/black plumage and younger individuals have low circulating testosterone and breed in female-like brown plumage. To better understand the mechanisms that regulate signal expression, we asked if circulating carotenoid levels and gene expression of a carotenoid ketolase gene (CYP2J19) differ as a function of sex and male phenotype, and if testosterone may be regulating this expression. As predicted, red/black males had higher concentrations of circulating carotenoids in their plasma than either brown males and females. In addition, we experimentally manipulated testosterone levels in brown males, and found a relationship between testosterone and the expression of CYP2J19 in the liver. This work highlights the complex ways in which carotenoids may be used to signal quality, and how hormones, gene expression, and circulating carotenoids may underlie the production of carotenoid-based ornamentation.
