Life expectancy as related to juvenile and adult onset caloric undernutrition and to the age at sexual maturity, will be examined in Japanese quail (Coturnix coturnix japonica), a species characterized by rapid growth, early maturity, high reproductive capabilities, and a relatively short life span. Comparisons will be made among parental and hybrid lines to provide subjects differing in body composition, and among individuals with delayed sexual maturity due to photoperiodic manipulation. Since an inhibitory photoperiod delays sexual maturity with only minimal effects on growth rate and body weight, this approach will allow the separation of direct effects of age at sexual maturity on longevity from residual effects of prepubertal undernutrition. Four hundred quail from each of three populations (two parental lines and hybrids) will be equally divided and subjected to photoperiods of either 24 or 7 hr. Each population-photoperiod subgroup will be subjected to either ad libitum or restricted feeding regimes. At maturity, the males will be sacrificed for body composition studies. The females from each treatment group will be further subdivided, placed on either ad libitum or restricted feeding, and retained until natural death. Each animal will then be autopsied and probable cause identified. Several traits, including body weight, food consumption, reproductive capabilities, body temperature, immune responses and plasma lipids will be periodically monitored throughout the life cycle. Comparisons will be made on both a physiological and chronological age basis. Such comparisons will allow more definitive conclusions concerning the relationships among body weight, body composition, lipid metabolism, the onset of sexual maturity and food intake in altering life expectancy.