Photoperiodic Control of Reproduction in Male Hispid Cotton Rats, Sigmodon Hispidus
The hispid cotton rat, Sigmodon hispidus, has been shown to have a seasonal reproductive cycle and may use photoperiod to regulate this cycle. Male Sigmodon were placed in differing photoperiods, and serum prolactin, testicular size, testicular mass and spermatogenic activity were measured as parameters of reproductive status. In the first experiment, animals judged to be in a reproductively inactive state were caught in the fall of the year, and placed in long photoperiod (14L: 10D) to see if they would initiate a return to a reproductively state. Another group of animals were kept at ambient photoperiod as controls. Both groups showed an increase in all parameters over the course of an eight week treatment. The long photoperiod groups showed a 152% increase in testis size, while controls showed only a 90% increase. In a second experiment, a group of Sigmodon were captured during the third week of January. All were judged to be in a reproductively inactive state. These animals were placed in short photoperiod (9L :15D). Sigmodon were expected to naturally return to reproductive competence at this time of year. Five animals were killed each week along with a group of five animals that had been caught in the wild. No significant differences were found between these two groups of animals. Both showed increases in testicular size, testicular mass and spermatogenic activity, but a decrease in serum prolactin over the course of the experiment.
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