Hair Color, Molt, and Testis Size in Male Short-Tailed Weasels Treated with Melatonin

The study investigated the effects of melatonin on male short-tailed weasels by implanting it in beeswax. Treated weasels, which were either brown or transitioning to brown, molted, developed a new white coat, and became reproductively inactive. In contrast, control weasels retained or developed a brown coat and had enlarged testes. Additionally, treated weasels with pituitary autografts grew brown hair after plucking. The findings suggested that melatonin from the pineal gland triggered changes in the central nervous system and endocrine system, leading to molting, the growth of white winter fur, and reproductive quiescence.