This from Nature:
Lim’s team paired male prairie and meadow voles with a sexually receptive female of the right species. Each pair was allowed a day to get to know each other, then the males were given a fidelity test.
Each vole was allowed to wander freely between his tethered partner and a tethered stranger. Prairie voles and genetically modified meadow voles huddled close to their partner; untreated meadow voles preferred to spend time alone.
Earlier work has shown that boosting vasopressin receptor levels speeds up pair bond formation in monogamous voles. The new research shows that a similar technique can turn a promiscuous species of vole into a faithful one.