Pheomelanin, the sulfurated form of melanin pigment, is known to produce reactive oxygen species (ROS) and oxidative stress-mediated cytotoxicity. Previous studies have shown a conversion of the benzothiazine moiety of pheomelanin to the benzothiazole moiety under heat or energetic radiation exposure, but it is unknown whether endogenous conditions can also produce this structural change.

Competitive environments promote high testosterone levels, oxidative stress and, consequently, impair cellular homeostasis. The regulation of genes involved in the synthesis of the pigment pheomelanin in melanocytes seems to help to maintain homeostasis against environmental oxidative stress. Here, social interactions in some zebra finch Taeniopygia guttata males were experimentally increased by keeping them in groups of six birds during feather growth, while others were kept alone, to test...