Male prairie voles that sleep around appear to have poorer spatial memories than those of a more monogamous bent, new research reveals. It is as yet unknown whether cheating voles claim to have forgotten the way home, but if so they can blame their genes.
Prairie voles (Microtus ochrogaster) have garnered interest thanks to the fact that most form life-long, often monogamous, pair-bonds, while a minority of males are highly promiscuous. Their close relatives, meadow voles, however, are entirely promiscuous. Intriguing hormonal differences have been found between prairie voles that appear to determine their sexual behavior and may shed light on human sexuality.
During mating seasons bonded voles establish a home range, while promiscuous voles roam widely. However, although the majority of bonded males stick to their spouse and home, some cheat, establishing a pair bond, but fathering children with neighbors. Around a quarter of pups' genetics indicate they were conceived outside the pair bond.
Noting that the parts of the vole brain that reveal a difference in pertinent hormone receptors are also important in spatial memory, Dr. Steven Phelps of the University of Texas at Austin used radiotelemetry to track the vole's movements. He compared the brains of those whose movements ranged into other voles' territory with those that stayed home.
The single-partner voles have many receptors for the hormone vasopressin in their hippocampus and laterodorsal thalamas, consistent with better spatial memory. This vasopressin-receptor expression is controlled by the version of the avpr1a gene the vole has, Phelps reports in Science.
According to Phelps and his coauthors, it may be this bad memory that leads the voles to roam. "The relationship between spatial memory and sexual fidelity is not clear," Phelps and his coauthors write. However, they point to a theory that poor memory may interfere with males' capacity to remember where they strayed into others' territory and suffered an encounter with an enraged male defending his territory.
"This brain variation isn't just there by chance. It isn't random," Phelps said in a statement. "It's actually something that selection has kept around for a very long time. When it comes to social behavior, maybe there isn't a normal brain."
Being forgetful appears to work out about equal for the voles, which Phelps thinks is why both behaviors persist. Those who stray outside their territory sometimes get to father pups with other partners, but their mate equally often entertains gentlemen callers in their absence. This is in contrast to the males who failed to form a pair-bond at all, who Phelps found in a previous study fathered substantially fewer offspring than the ones that stayed home.
Phelps says his team are yet to confirm the connection by testing the voles' memories, rather than relying on their brain regions. "We're working on it," he told IFLScience, adding that "spatial memory is a plausible hypothesis," given that there is a strong relationship between sexual fidelity in the voles and their use of space, and the differences seen in relevant brain regions.