Food availability and photoperiod affect reproductive development and maintenance in the marsh rice rat ( Oryzomys palustris)

Abstract

To examine whether photoperiod and food availability interact to influence reproductive development (Experiment 1), we exposed juvenile male and female rice rats to 16L:8D or 14L:10D and to ad lib, 80% of ad lib, or 60% of ad lib food intake from 3 to 8 weeks of age and recorded body and reproductive organ masses. Absolute paired testis masses were similar in ad lib and 80% of ad lib groups but significantly different than the 60% of ad lib group in both photoperiods. Relative paired testis masses were significantly different in the 80% and 60% of ad lib groups on 16L:8D only. Absolute seminal vesicle masses (SVM) were directly dependent upon the level of food restriction in both photoperiods, but relative SVMs were different only in the 60% of ad lib group. Terminal body masses were also directly dependent upon the level of food restriction and were greater on 16L:8D than on 14L:10D at most levels of food availability. In juvenile females, absolute uterine mass was only affected in the 60% of ad lib group on 14L:10D, while absolute paired ovary masses were affected on both photoperiods in the 60% of ad lib groups only. There was no effect of photoperiod or food on relative uterine and paired ovary masses. Terminal body mass was affected by food intake in both photoperiods. Lastly, in adult males (Experiment 2), photoperiod and food restriction affected reproductive function. Within a photoperiod, there was no effect of food restriction (75% of ad lib) on the testes, seminal vesicles, or testosterone levels in animals housed on 16L:8D, but terminal body mass was significantly reduced. On 12L:12D, however, food restriction significantly decreased testes and SVMs relative to ad lib-fed controls. Testosterone levels were reduced regardless of food availability. There was no effect of food restriction on terminal body mass. These results suggest that multiple potential environmental cues can be utilized to affect gonadal status in both juvenile and adult marsh rice rats.