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 pla sma estradiol levels in the meadow vole, Microtus pennsylvanicus. Bedd ing was switched between pairs of female meadow voles for 2 wk to allo w them to develop olfactory familiarity. When familiarization was comp lete 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 unfamilia r females experienced a dramatic reversal in odor preference and faile d to orient towards male odors. This behavioral change was accompanied by a significant decrease in plasma estradiol levels. These changes s uggest that exposure to unfamiliar conspecifics may result in reproduc tive inhibition. Excessive contact between unfamiliar females in the f ield may be indicative of environmental conditions unfavorable to bree ding.