Manatee
Survival largely depends on how the animal regulates energy intake and expenditure when times get tough. Fortunately, these decisions can be deferred due to a powerful internal headquarters: the endocrine system. This complex system of glands secretes hormones that regulate the body, influencing an animal’s physiological responses in times of food shortages. Endocrine systems in marine mammals, such as the manatee, follow the basic organization and chemical characteristics of other mammals, but the manatee must deal with constant changes imposed by its environment. Melatonin is the hormone most commonly associated with photoperiodism in mammals. It is produced primarily by the pineal gland (epiphysis) located above the third ventricle of the brain. Daylight suppresses the production of melatonin, which regulates the activity of the hypothalamus, pituitary, and, indirectly, the gonads and thyroid. Unfortunately, the hormone and its activity have received relatively little attention in the manatee. The thyroid hormones do exhibit some important dynamics during the course of the development and life history of the manatee. Marine mammals, such as the manatee, are well known for their ability to seasonally manage energy stores, enabling them to fast during migration or breeding. The hormonal modulation of energy consumption by tissues can allow for fat deposition, even when the energy intake is low, or mobilization of fat to sustain accelerated growth while feeding.