Forgetful male voles more likely to wander from mate

Poor memory could lead monogamous male prairie voles to stray, a new study suggests.

Male prairie voles with low levels of a molecule in the part of the brain related to spatial memory wandered more and encountered more females (and thus potential mates) than other males, researchers report December 11 in Science. The molecule, a receptor that sits on the surface of brain cells and changes cell activity when bound to the hormone vasopressin, has previously been associated with social behavior in voles and seems to play a part in male vole forgetfulness. Low levels of the receptor, called V1aR, may spur the male vole to be more promiscuous, say scientists, who also linked lower levels of V1aR to a certain version of the gene for the receptor.

Prairie voles are among the less than 5 percent of animals that live a monogamous lifestyle. But a “faithful” monogamous relationship for male voles means nesting with one female and protecting her, while still stepping out on occasion. 

Evolutionary neurobiologist Steve Phelps and colleagues tracked prairie voles (Microtus ochrogaster) in the field. Male voles that had larger home ranges left their nests more often and met up more with different females. Those with smaller ranges stuck closer to home and left their female partners less often.

“This is a story about evolutionary fitness within an environment and having alternate strategies,” says Larry Young, a neuroscientist at Emory University in Atlanta who was not involved with the study.

The voles’ promiscuous behavior in the wild could be linked to their poor spatial memory, which could make it hard for male voles to remember where their nests are and the location of fights with other males, the researchers think. In the lab, the vole’s field behaviors were linked to the differing levels of the V1aR hormone receptor in brain areas involved in spatial memory. The team measured V1aR abundance and found that males with decreased V1aR were also the ones that wandered more and had more female encounters. Males with higher levels of V1aR, and apparently a better memory, were homebodies and didn’t cross paths with as many females.   

Different versions of the avpr1a gene influenced the distribution and abundance of the V1aR receptor, the researchers show. In the brain area important for memory, how many V1aR receptors are produced “alters space use and sexual fidelity of males,” concludes Phelps, of the University of Texas at Austin.

The number of V1aR receptors in a male vole helps determine which evolutionary strategy male voles follow — one in which males meet many potential mates, but spend less time guarding their partner, or one in which males meet fewer females but keep things monogamous at home. There’s a trade-off to each behavior, says coauthor Alexander Ophir, a behavioral neuroscientist at Cornell University. “Those that try to cheat also get cheated on.”

Wandering males with poor memory might meet more females, and have the chance to mate with more partners, than males that stick close to the nest. But while the memory-deficient males are out, they leave their nests open to visits by other males and risk being cuckolded.