Studies of General and Sexual Development in Voles (Microtus)

Three experiments were conducted to investigate how patterns of general and sexual development might be correlated with the formation of social and mating systems among four species of voles ( Microtus ) . Species included pine voles ( Microtus pinetorum ), prairie voles ( M. ochroqaster ), meadow voles ( M. pennsylvanicus ), and montane voles ( M. montanus ) . In Experiment 1, general and sexual development were monitored as voles were exposed to pheromones contained in the soiled bedding from family groups, adult males, or adult females. Few significant effects were found to be due to the treatment. Male pine voles exposed to family or male bedding were significantly heavier than those exposed to clean or female bedding. The uteri of female montane voles exposed to clean or male bedding were heavier than the uteri of those exposed to family or female bedding.

In Experiment 2, the olfactory preferences of voles were measured when they were exposed to male and female bedding on weeks 4, 7, and 10 after birth. Few preferences were shown for either bedding type by any of the species.

Female prairie voles and meadow voles revealed a significant preference for male versus female bedding. Both sexes of all species differed little in the total duration they remained near the female stimulus. Male meadow voles remained near the female stimulus significantly less than the males of the other species on week 10. Female montane voles remained near the male stimulus significantly longer on weeks 4 and 7 than did females of the other species.

In Experiment 3, the influence of the fathers' presence and absence was studied during the rearing of the breeding pairs' first two litters. Pine voles produced their second litter considerably earlier if the male had been present during the rearing of the first litter rather than being absent. Pine voles weaned heavier offspring in the second litter than in the first, when the male had been present for the rearing of the first litter. Montane voles produced litters that were male-biased in sex ratio across both litters, if the male had been present during the rearing of the first litter.

Results are discussed and interpreted from known differences in their contrasting social and mating systems.

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