Meeting Abstract
For many animals, testosterone (T) activates ornamentation in males. However, our mechanistic understanding of the relationship between T and ornamentation is limited in two main ways: 1) T does not impact all tissue types in the same manner, and 2) sex-specific coloring is likely mediated by polygenetic interactions, rather than simple genetic variation. As a consequence, transcriptional differences—and how hormones may regulate them—are critical to understanding the link between genotype and phenotype. In this study, we investigate the role of testosterone in mediating gene expression across tissues associated with a sexual signal in wild Red-Backed Fairywrens (Malurus melanocephalus). In this species, males exhibit flexible reproductive phenotypes: some individuals have high circulating T and breed in red/black plumage, and others have low circulating T and breed in female-like brown plumage. Previous work has shown that females prefer mating with red/black males over brown males, and redder males have higher reproductive success, suggesting the red back is an important sexual signal. To assess how the endocrine system impacts gene regulation and red plumage production, we experimentally manipulated T levels in males and sequenced the transcriptome of both the liver and feather, two important tissues for red carotenoid coloration. We identified genes involved in generating variation in plumage color by comparing the transcriptome of control brown males, T-implanted brown males, and naturally red/black males. We found that testosterone regulates the expression of CYP2J19 in the liver, which is essential for carotenoid metabolism, while also mediating carotenoid transport into feathers. To our knowledge, this is the first study to demonstrate a causal link between testosterone and carotenoid metabolism in a wild population.
