Early age of vaginal opening in common voles (Microtus arvalis)

Female common voles, Microtus arvalis, are able to mate immediately after vaginal opening. Under laboratory conditions, I determined age at vaginal opening in females born to laboratory-raised and wild-caught mothers maintained under three different light regimes: 12L:12D, 14L:10D and 16L:8D. Out of the 465 females examined, only 7 females did not exhibit vaginal opening by 25 days of age. In the remaining 458 females, the age at vaginal opening was unimodally significant but small, with longer photoperiods slightly retarding development of this trait.