Female familiarity influences odor preferences and plasma estradiol levels in the meadow vole, Microtus pennsylvanicus.

To determine whether neighbor familiarity can affect reproduction, we studied the relationship between familiarity, odor preference, and plasma estradiol levels in the meadow vole, Microtus pennsylvanicus. Bedding was switched between pairs of female meadow voles for 2 wk to allow them to develop olfactory familiarity. When familiarization was complete animals were reexposed, after 24 h of no exposure to conspecific odors, to either the bedding of the familiar female or to the bedding of a new, unfamiliar female. Voles exposed to the bedding of unfamiliar females experienced a dramatic reversal in odor preference and failed to orient towards male odors. This behavioral change was accompanied by a significant decrease in plasma estradiol levels. These changes suggest that exposure to unfamiliar conspecifics may result in reproductive inhibition. Excessive contact between unfamiliar females in the field may be indicative of environmental conditions unfavorable to breeding.