A blog fave of ours, Ontogeny, posts on the prairie vole which is best known to science, and its mates, for being monogamous — that is, until recently earning their scarlet letter. Why the no-good, cheating rats!   Via:: Nature:

‘Monogamous’ vole in love-rat shock

Randy rodent revels in raunchy romps. by Heidi Ledford

By traditionalist standards, prairie vole couples may enjoy the ideal relationship: the rodents form lifelong partnerships — a highly unusual practice in mammals. Males help raise the children; females help build the nest.  As for their sex life, let’s just say it far exceeds the efforts required for procreation. But the respectable public behaviour of North American prairie voles (Microtus ochrogaster ) may hide a bed-hopping double life. Paternity tests published last week indicate that the animals touted as paragons of monogamy frequently cheat on their partners. “Ironically”, the study’s authors conclude, “the dissociation of social and sexual fidelity leads us to suggest that prairie voles are even better models of human attachment than has been appreciated.” Studies on prairie voles have led scientists to look at the role of hormones such as vasopressin and oxytocin in strengthening human relationships. Revelations of infidelity in the creatures will not change the significance of that research, but may make the voles a little less popular among political agitators for sexual abstinence. (Eric Keroack, who headed a government family-planning committee in the United States, even used the monogamous voles as evidence to support his view that people who have extramarital sex damage their oxytocin signalling mechanisms.)