Meadow voles, Microtus pennsylvanicus, display a memory for the what, when, and where of a same-sex dyadic interaction

Background/Question/Methods

The ability to recall details of previous events may give an individual a fitness advantage over conspecifics that cannot. In species that compete for resources such as territories, remembering when and where a neighbor was previously encountered may allow an individual to exploit weaker conspecifics or to avoid stronger competitors. During the breeding season, female meadow voles, Microtus pennsylvanicus, are territorial and display agonistic behaviors against female conspecifics. We used a two-phase experiment to test the hypothesis that female meadow voles can use details of an encounter with another female in one location to later navigate nearby areas. In the encounter phase, 36 pairs of subjects were placed into one isolated quadrant of a Y-maze and were allowed to interact for two minutes; 34 control subjects were placed in alone. Paired females were scored as either winners or losers of the dyadic encounter, with winners displaying 100% more agonistic acts against their opponent. The test phase took place after a retention interval of one hour, one day or one week. Single subjects were returned to the empty arena, allowed to explore the entire apparatus for 15 minutes; we recorded the amount of time spent in each quadrant of the maze.

Results/Conclusions

The amount of time that subjects spent in the separate quadrants of the maze depended on whether they won or lost the dyadic encounter and the retention interval between the exposure and test phases. After retention intervals of one hour and one week, subjects that were classified as winners, subjects classified as losers, and controls spent similar amounts of in each of the quadrants (p > 0.5). However, after a retention interval of 24 hours, differences existed in the amount of time that winners, losers and controls spent in the quadrants of the arena (p < 0.01). After 24 hours, winners spent significantly more time in the quadrant were the encounter took place, while losers spent significantly more time in the quadrant furthest away (both comparisons p < 0.05); control voles showed no quadrant preferences (p > 0.05). The results suggest that female meadow voles can remember specific details of the what, when and where of a single event, which is influenced by its emotional valence. This duration of memory may be associated with the stability of territories among female meadow voles.