When it comes to relationships, does absence makes the heart grow fonder, or just forgetful? The latter may be true for prairie voles, and this absentmindedness could be inherited, according to a new study.
These mouselike rodents found in central North America are typically monogamous, but even faithful voles are known to sometimes stray. A new study peered at male voles on the genetic level, finding that one gene in particular plays an important role in deciding whether a vole will wander or stay close to home, and that this wandering may be linked to spatial memory.
Unlike most mammals, prairie voles bond for life (which is pretty short — only one to two years.) Once they've paired off, the males establish territories that they fiercely defend against trespassers. [Animal Sex: 7 Tales of Naughty Acts in the Wild]
Researchers observed that some males kept close by their mates, but others were inclined to venture farther from their nests, in spite of the risk of attack from rival males. These roaming voles were also more likely to mate outside their pair, the scientists found. Both behaviors have their advantages — males that stay home are safer, but males that roam increase their chances of siring more offspring.
To investigate what might lead some males to stray, the scientists zeroed in on a gene called avpr1a, already known for its associations with both sexual fidelity and spatial memory, and a receptor — a protein molecule that receives signals and converts them to trigger responses — known as V1aR, in memory structures.
They found that this gene and receptor behaved very differently between individuals. Variations in activity in the brain's memory regions could indicate whether a male vole was likely to wander, and might be related to the animals' ability to remember details of their social environments, according to the study's co-author Steve Phelps, director of the Center for Brain, Behavior and Evolution at the University of Texas at Austin.
"We knew species differ in how they express this gene," Phelps told Live Science, "And we knew there was variation within a species." Still, the researchers weren't prepared for the expression to vary so greatly from individual to individual, he said.
Phelps first glimpsed the potential for variation in prairie vole brains as a postdoctoral researcher, when he looked at their brains and observed how the genes were firing, and how widely that differed between individuals. "We were shocked at how diverse they were," he said. "There were some areas that they always had expression in, and there were others that varied as much between individuals as you'd expect to see between species."
Phelps noted that the variations were especially dramatic in the network of brain regions corresponding to memory — and to spatial memory, in particular.
"Then we were faced with all this diversity, and it raised interesting questions," Phelps said. "Why are these brains so variable? Is this kind of variation normal? And that's what set us off on this topic. Just trying to make sense of the diversity and figure out if it was there for a reason."
According to the study, individual differences in the voles' memory regions manifested in behavior — how much they intruded on other males' territory or how close they stayed to their own mate.
The next step, Phelps added, is to further explore the relationship between memory and fidelity in the prairie voles. "We know this brain region that predicts fidelity is critical to memory, but we don't know exactly how those two are related," he said. And the bigger picture, he added, will require examining how this gene works, the extent of variation in gene expression in the brain, and its relationship to social behavior.
"My intuition is that there will be a lot of genes related to social behavior that are variable, and that this variation has been maintained by natural selection," Phelps said. "It kind of challenges what it means for behavior — or for the brain — to be normal."
The findings were published online yesterday (Dec. 10) in the journal Science.