The effect of diet on melanin pigmentation in animals

Abstract Melanin, including both eu‐ and pheomelanin forms, is the most common pigment type in animals and plays numerous adaptive roles. However, the effect of diet on melanin pigmentation is not well reviewed or synthesized. Understanding how diet influences melanin may lead to valuable insights such as explaining intraspecific variation or explaining when melanin‐based traits are plastic or condition dependent versus when they are prioritized or canalized. In order to assess the state of the literature and the current understanding of the effects of diet on melanin pigmentation we conducted a systematic literature search. We use the search results to highlight common patterns across animals. In particular we focus on three questions: Which dietary components can influence melanin? Which aspects of melanin‐based traits are influenced by diet? What factors can mediate the influence of diet on melanin? The effect of diet on melanin is complex and multifaceted. Diet itself can vary in a number of ways including diet quantity, protein content, fatty acid content and amount of metals and other micronutrients. We discuss the mechanisms by which these components influence melanin pigmentation. Diet can influence the size, darkness and colour of melanin‐based traits. Often, diet influences one of these aspects but not another, which may reflect the processes of melanin synthesis and distribution. Factors that mediate whether melanin pigmentation responds to dietary variation include the type of trait, life stage, sex and environmental stress. Methodology (e.g. degree of manipulation relative to natural conditions) can also influence results. These nuances should be considered when developing hypotheses about the effects of diet on melanin pigmentation. We conclude with important areas for future research, including the proximate mechanisms connecting diet and melanin, how diet affects internal melanin, how diet mediates costs of melanin pigmentation and how diet affects the evolution of melanin‐based traits. Overall, diet has important and complex effects on melanin and likely plays an important role in the ecology and evolution of melanin pigmentation. Read the free Plain Language Summary for this article on the Journal blog.