Ecology of timekeeping: feeding times effect clock-controlled behavior, metabolism and reproduction in diurnal vertebrates

To most, if not all, species, the food availability shows both daily and seasonal fluctuations in its timing, quality, and abundance. Hence, coupled with the appetite (urge to eat), it results in species-specific foraging (eating or feeding) patterns, an ecological determinant of almost all the aspects of behavior and physiology in animals. The feeding times control mutually inclusive physiological events by affecting metabolic homeostasis (a direct effect) and/ or by their synchronization effects on the underlying circadian rhythms (an indirect effect). Experiments have shown that food intake at an inappropriate time of the day (i.e., at a wrong time relative to the internal circadian clock) negatively affects the circadian homeostasis and consequently the behavior, metabolism and reproduction in animals. The food availability times as a conditioning environment influence epigenetics, evidenced by chromatin activation/ silencing at genome levels in several species. Here, we review briefly the experimental evidence largely from birds and mammals to provide insights into when and how daily feeding times affect the clock-controlled behavior, metabolism and reproductive fitness in diurnal species.