Induced components in the spontaneous ovulatory cycle of the Djungarian hamster ( Phodopus campbelli)

Although Djungarian hamsters, Phodopus campbelli, show regular, 4-day spontaneous estrous cycles when tested for behavioral receptivity, this study shows that over 50% of 624 virgin females paired with males show their first behavioral estrous on the third day after pairing. The observed pattern is compared against predictions of estrous synchrony and/or estrous cycle suppression models. They fail to explain the high incidence of mating on the third day, and are incompatible with our current understanding of the natural history of the species. An alternative hypothesis, that Djungarian hamsters fail to cycle in the absence of a male, but are rapidly induced into a succession of 4-day cycles by his presence, appears to explain both the pattern of matings and earlier observations that estrous cycles could not be monitored by vaginal smear or lavage, only by interactions with a male. These analyses, thus, conclude that Djungarian hamster females may require a signal from a male to initiate and maintain successive 4-day estrous cycles.