Geographic variation in Peromyscus leucopus: short-day induced reproductive regression and spontaneous recrudescence

In order to determine if intraspecific differences exist in the photoperiodic control of the reproductive cycle of white-footed mice (peromyscus leucopus), 34 male and 60 female mice from either Connecticut (CT), Virginia (VA), or Georgia (GA) laboratory stocks were exposed to either a long (16L:8D) or short (9L:15D) photoperiod for up to 27 weeks. Reproductive status (testis length or the presence of a perforate vagina) of these mice was assessed every 1 to 2 weeks. After this time, the males were killed and testis length, testes weight, and seminal vesicle weight determined. Testis length in mice from CT and VA began to decrease after Week 5 of short-day exposure and reached a minimum at Week 13; this effect was less pronounced in the VA mice. Little change occurred in the GA short-day mice and in the three groups exposed to long photoperiods. Spontaneous gonadal recrudescence began after Week 17 in CT males and Week 15 in VA males, but was not yet complete at the end of Week 27. Similar results were obtained with the females. These results show that genetic differences exist in both the degree and duration of reproductive quiescence in this species.