Immune systems and sickness behavior

Hormones help coordinate animals’ physiology and behavior to match their environment and maximize fitness. Among the most important processes influenced by endocrine hormones are the immunological and behavioral responses to infection. These behavioral changes are collectively termed sickness behaviors and include lethargy, anorexia, somnolence, and decreased libido. Sickness behaviors are widespread, but show considerable variation among individuals, populations, and species. In this article, we summarize this variation in vertebrates and discuss how interactions among the endocrine, nervous, and immune systems contribute to this diversity