BREEDING PERFORMANCE IN CAPTIVITY OF MEADOW VOLES (MICROTUS-PENNSYLVANICUS) FROM DECLINE-PHASE AND INCREASE-PHASE POPULATIONS

A major enigma in understanding microtine cycles is the failure of decline-phase animals to increase. We compared the performance of wild-caught meadow voles and their progeny from Pinawa, Manitoba, collected from a decline year (1985) with that of animals from an increase year (1986) by breeding them in the laboratory in Pinawa (animals from both years) and in the field and laboratory in Toronto (only F1 and F2 animals from 1985). Overall only 35% of the 1985 females or their progeny bred in the laboratory in Pinawa compared with 100% of the 1986 females. The interval between pairing with a male and birth of litters was 2 - 7 months for the 1985 females compared with 3 - 4 weeks for the 1986 females. The poor breeding performance of 1985 females occurred only in the laboratory; in small field enclosures in Toronto all F1 and F2 females conceived and had litters within 3 - 4 weeks. In contrast, 1985 males readily sired litters either with 1986 females in the laboratory or with Toronto females in the field. We conclude that the prior experience of decline-phase females had long-term detrimental consequences for the performance of the first two generations under laboratory conditions.