Light regime influence

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Light regime influence

Variation in the daily light cycle, for example, acts through endocrine and neurobiological mechanisms to control several downstream physiological and behavioral processes. Interruptions in normal circadian light cycles and the resulting disruption of normal melatonin rhythms cause widespread disruptive effects involving multiple body systems, the results of which can have serious medical consequences for individuals, as well as large-scale ecological implications for populations. With the invention of electrical lights about a century ago, the temporal organization of the environment has been drastically altered for many species, including humans. The increasing prevalence of exposure to light at night has significant social, ecological, behavioral, and health consequences that are only now becoming apparent.

Endogenous biological clocks allow individuals to anticipate and adapt to the daily light-dark cycles in their environments to optimally time metabolism, physiology, and behavior each day. Aside from seasonal adjustments, there is marked circadian variation in physiological functions. In many species, including some birds, rodents, fish, and humans, for example, circulating concentrations of sex steroids and glucocorticoids vary with the light/dark cycle throughout the day, causing corresponding changes in reproductive activities and metabolic functions.