THE EFFECTS OF PHOTOPERIOD AND FOOD-INTAKE ON REPRODUCTIVE DEVELOPMENT IN MALE DEER MICE (PEROMYSCUS-MANICULATUS)

Seasonal breeding is a tactic that has evolved in rodents that limits reproduction to specific times of the year to increase reproductive su ccess. In order to time breeding accurately, many animals respond to c hanges in daily photoperiod. Short day lengths inhibit breeding in man y nontropical rodent species. Restricted food availability can also in hibit reproductive function among some individuals in these so-called ''photoperiodic'' populations. Rodents born at the end of the breeding season typically delay sexual maturation until the following spring. Prepubertal rodents exposed to day lengths that are <12 h light/day wi ll not undergo puberty for 4-7 months in the laboratory. Food restrict ion can also affect the timing of puberty onset. Reproductive function of food-restricted juvenile mice may remain inhibited until food avai lability improves. Alternatively, reproductive function of food-restri cted juvenile mice might eventually develop despite restricted food in take. This study examined the effects of chronic food restriction and photoperiod on reproductive development in male deer mice (Peromyscus maniculatus bairdii). Short-day mice fed ad lib delayed gonadal develo pment for 5-7 months, but eventually achieved reproductive maturity. T he reproductive function of short-day mice fed ad lib was indistinguis hable from long-day control animals when assessed at week 32. Long-day food-restricted mice exhibited an intermediate level of gonadal devel opment and function, Short-day food-restricted deer mice also inhibite d reproductive growth, but failed to demonstrate reproductive maturity by week 32 of the study. Taken together, these results suggest that r etardation of reproductive development by food restriction is only sup erficially similar to the delay in reproductive maturation imposed by short day exposure. It does not appear that male deer mice escape from the inhibitory effects of food restriction to attain sexual developme nt. (C) 1997 Elsevier Science Inc.