Like humans, prairie voles form monogamous pairs. And also like people, not all of these rodents are faithful. Around one-quarter of voles are sired by a parent outside of the pair. Scientists call these dalliances “extra pair fertilizations.”
New research suggests a genetic basis for this type of behavior: Males that tend to stray share certain genetic characteristics, says Steve Phelps, a researcher at the University of Texas. Specifically, males with a weaker spatial memory seem to be more likely to engage in an extra-pair mating, according to a study describing the finding, published December 10 in the journal Science.
Although the researchers can only speculate about why the two seem to be connected, they have a good guess as to what’s going on. Those males with a better spatial memory may be better at guarding their female mate, remembering exactly where they were when various social interactions took place and, critically, may be better at avoiding intrusion on another male’s territory, Phelps says.
To mate with another female, a male vole most leave its territory to find a receptive female vole, but that might also involve trespassing on another male’s home range, Phelps explains. If a male senses another is encroaching on its territory, it will chase it away and maybe even bite it if it gets the chance, he says. Those males with a good memory will remember the negative consequences of straying. But those with a weaker memory may forget where past encounters of this kind took place and are thus more likely to literally stray and come into contact with other females and mate with them.
Spatial memory is linked to the quantity and location of brain receptors for a hormone called vasopressin. The study found that those with more receptors for this hormone had better spatial memories. The difference in the amount of vasopressin receptors in the voles could be traced to a single different base pair of DNA in one of the animal’s genes. In other words, a tiny difference in the vole genome meant worse spatial memory, explains Larry Young, a researcher at Emory University who wasn’t involved in the study.
Young says it’s amazing how a single, seemingly tiny genetic difference could have wide-ranging effects, influencing “how faithful an animal is, and how good it is at protecting its partner, and how likely it’s going to be a wanderer.”