Male prairie voles that roam widely looking for mates have poorer spatial memory than their faithful male counterparts, who better recall locations of rough encounters with other males and thus stay closer to home, a new study shows. The study suggests that promiscuity some prairie voles exhibit may be related to gene expression that's heritable. North American prairie voles are most often monogamous, forming couples and raising their young together. Yet, not unlike humans, "cheating" happens, with males who venture outside of their home range facing an interesting tradeoff: while they are more likely to mate with a female and potentially pass on their genes, they are also at an increased risk of encountering aggressive males defending their mates. To explore the effects of promiscuity on the genetic level, Mariam Okhovat and colleagues took a closer look at the expression of avpr1a, a gene that predicts sexual fidelity in males and that's well known to play a role in a spatial-memory circuitry. Lower expression of the related receptor V1aR in certain brain regions is associated with a poor memory for locations of aggressive interactions with other males, a result that could lead to wandering (and contact with non-pair females). By contrast, abundance of V1aR is linked to a better spatial memory for past aggressive encounters, and less wandering. The researchers ran a number of experiments, identifying four single nucleotide polymorphisms (SNPs) that influence expression of avpr1a and found differences in levels of methylation in various parts of the avpr1a gene that were linked to sexual behavior. These methylation sites, which enhance gene expression, are heritable and show distinct patterns among different populations. Due to genetic differences between lab and wild populations, the authors suggest that high population densities favor genetic variants resulting in lower V1aR expression, poorer spatial memory, and more expansive home ranges to increase the males' chances of mating, while low population densities favor the opposite. A Perspective by Gene Robinson delves into these findings in greater detail.