Eco-Immunology: Role of Melatonin in Avian Immune Defense

Avian immunology is a fascinating and growing field. Ecologists are now taking an interest in measuring immune-competence and determining its importance as a heritable trait for the survival of the wild species. Seasonally breeding animals encounter different environmental challenges throughout the year. In order to survive in specific environments these animals have developed various strategies that help them to find food, protect themselves from the tough environments, and also reproduce accordingly. Indeed, wild birds are continually challenged with different natural stressors such as shortage of food (during winter and rainy season), lack of water during summer, predator pressure in social system, sudden change in weather, season-bound diseases, infection (like avian influenza), etc. Only a few ecological studies have analyzed the stress and general immunity in wild birds that might have a link with the anti-stress hormone melatonin. Therefore, approaches improving our understanding of the stress-induced immune depression and their interrelationship in birds are most desirable. Unfortunately, our knowledge of the immune system has advanced at a much faster pace for mammals while immunology of wild birds received less attention. The purpose of this review is to bring together the current knowledge on the biological effects of melatonin on avian immune defense with special emphasis on new immerging area of neuro-immuno-endocrinology i.e., eco-immunology.