Meeting Abstract
The immunocompetence handicap hypothesis posits that ornamental traits are honest signals of parasite resistance because ornament production is dependent on high levels of steroid hormones that depress immune responsiveness. This hypothesis was proposed with little understanding of hormonal regulation of the immune system or of the mechanisms that could connect ornamentation to immunocompetence. I review a growing biomedical literature that identifies the mitochondrion as the primary site of action for steroid and thyroid hormones and that ties mitochondrial bioenergetics to innate immunity and to the overall immune response. Mitochondria are the source for both ATP and free radical production, and they also serve as core mediators of innate immunity. Thus, under the influence of hormones, mitochondria coordinate tight functional integration of host defense and metabolic processes. Dysfunction of cellular respiration leads to reduced production of ATP and increased oxidative stress via the release of free radicals. Oxidative stress and reduced energy production, in turn, negatively affect ornament production while inhibiting innate immune responsiveness. A fundamental link between cellular respiration and both ornamentation and innate immunity explains the commonly observed associations between ornamentation, oxidative state, and disease and reveals the true information content of ornaments.
