Faithful voles have hidden infidelities.

Prairie voles, the standard model for mammalian-monogamy studies, actually get around more than most scientists had expected.

Vole mating intrigues researchers because the various species of the hamster-size rodents show lifestyles ranging from nuclear families to single-mom-and-deadbeat-dad situations. Comparing species gives scientists a window on the biological basis of social bonds. Prairie vole moms and dads share home ranges and pup care, and earlier studies provided evidence of only low rates of extra-pair encounters. There's even been talk of a monogamy gene behind the prairie voles' fidelity (SN: 7/9/05, p. 30).

Now, Alex Ophir of the University of Florida in Gainesville and his colleagues report results of a new approach. When they combined radio tracking and DNA testing, they revealed moderately high amounts of sexual infidelity among the voles.

In eight outdoor enclosures, each housing 12 prairie voles, Ophir and his colleagues monitored radio-collar signals to determine which voles shared a home range. The researchers also used DNA samples to test paternity in the 27 litters that came from the females of those pairings.

The genetic tests indicated that only one mother carried a litter fathered partly by one male and partly by another. With these data alone, Ophir might have concluded that only one female had mated outside her pair bond. However, the home range data further indicated that five of the other litters were sired entirely by a male other than the one living with the mom.

Ophir's Florida colleague Steven Phelps suggests that the so-called monogamy gene "might have been more aptly called the social-bonding gene."--S.M.