Around the word stress: its biological and evolutive implications

Stress is a general adaptive reaction crucial for survival and basically positive that involves the neuroendocrine and the immune systems. In all bilaterian metazoans, the molecular mediators of the stress response, i.e., corticotrophin-releasing hormone, corticotrophin, catecholamines and glucocorticoids, have been preserved during evolution, even if the increased complexity of animals have corresponded to a more articulated stress response that, following the eco-immunology perspective, we speculate to be hierarchically organized along three levels.