Hi Dr Dennis,, melatonin is an important substance found in pineal gland of many vetebrates and mammals apart from humans. It has important role in maintaining sleep awake cycle, controlling blood pressure and in seasonal reproduction. In cats and dogs it has some important functions like...

Improves immune function

Antioxidative property

Protects skin

Opposes the side of corticosteroids

Reduces the side effects of cancer chemotherapy and radiotherapy

Thanks...

Everywhere down to fish although I would suggest that even in single cell organisms it lurking and does something try running a blast search against ameobas and such like it should pick it up what it does is interesting but should be there

Mammals, insects etc