What Can Rodents Tell Us About Why Humans Love? | Science | Smithsonian
(Joel Sartore / National Geographic Creative / Photo Illustration By Erik Washam, SI)

What Can Rodents Tell Us About Why Humans Love?

A relative of the mouse may hold the key to understanding why human beings are one of the few mammals that seek lifelong mates

Smithsonian Magazine | Subscribe

The pile of cotton and hamster bedding rises and falls steadily, as though the two prairie voles snuggled beneath are breathing in unison. In the wild, these “potato chips of the prairie” would be lucky to enjoy a few months of a partner’s company: Their snackable size makes them popular with weasels, hawks and snakes. But here in the breeding cages at Atlanta’s Yerkes National Primate Research Center, the voles can expect two or three years of blissful cohabitation, cranking out litters at the rate of one a month.

“Life is good,” says Larry Young, a Yerkes researcher who has been studying voles for nearly two decades. “They’ve got a mate. Nesting materials. No parasites. All the rabbit food they could want.”

Voles may look like animated pompoms with shining, watchful eyes to you and me, but Young and his colleagues see them as the key to understanding some of humankind’s most tender and mysterious impulses: why we care for our partners, coddle our children, even mourn our dead. The word “vole” is, after all, an anagram for “love.”

“My work is all centered around this central question: Why do we interact with others the way we do?” says Young. The answer, in his opinion, almost always comes down to neurochemistry, but it’s not an easy subject to study. Scientists can’t tamper much with the brains of humans or other living primates, and dead ones aren’t much use. Many molecular investigations of the mind have, for better or for worse, focused on the white laboratory mouse, but Young dismisses this animal model as “a bag of mutations.” After a century of inbreeding for medical research, it’s far too removed from nature.

The vole is closely related to the lemming and resembles a hamster. (Joel Sartore / National Geographic Creative)
Unlike 97 percent of mammals, voles are monogamous, forming bonds that last long after mating (often for life, albeit a short one). (Joel Sartore / National Geographic Creative)
A male prairie vole sticks by his female partner, spending more than 60 percent of his time in the nest with the pups. (Todd Ahern)
Larry Young has been studying voles for nearly two decades. Earlier work investigated how genes drive behavior in whiptail lizards. (Courtesy of Larry Young)
By studying voles, Larry Young has learned that just a handful of molecules orchestrates our social interactions. (Courtesy Larry Young)
Prairie voles typically nest in underground burrows. They clip grass on the surface to create a network of trails two inches wide and up to 80 feet long. (Yva Momatiuk And John Eastcott)
Prairie voles live in grassy habitats with dry soil. Abundant ground litter is a plus; the voles use it to hide their network of trails. (Yva Momatiuk and John Eastcott)

The vole, closely related to lemmings and resembling hamsters, is a much newer experimental subject: The first prairie voles engineered to possess genes from another species came on the scene only in 2009. (They glowed green because they were tagged with a fluorescent jellyfish protein meant to signal visually that the DNA transfer had worked.) In 2012, scientists first read out the DNA in the voles’ genetic instruction book, or genome. And although in some ways the rodent is a bucktoothed burrower like any other, sometimes considered a pest by gardeners, it displays social traits that we think of as deeply human.

Most notable, voles—unlike 97 percent of mammals—are monogamous, forming bonds that last long after mating (often for life, albeit a short one). “Male and female come together, male courts the female so that she goes into estrus, and they mate,” Young explains. “And then something happens in the time when they mate, and in the hours after that, so that those two animals have bonded and they want to stay together always.” Rather than abandoning subsequent babies to fate, the males stick around to raise them. The female clearly expects this follow-through, yanking her guy by the scruff of his neck if he’s not doing his part. And when a partner dies, voles experience something akin to grief.

Perhaps most exciting of all, from a scientific perspective, prairie voles have near-identical cousins called meadow voles that share none of their social proclivities. By comparing the faithful rodents with their promiscuous doppelgängers, Young and his colleagues hope to reveal the neural circuits behind the prairie vole’s monogamous tendencies. “The prairie voles crave social contact, and the meadow voles don’t,” Young says.

An “extraordinary gift to science,” is how Thomas Insel, head of the National Institute of Mental Health and a pioneer in vole studies, describes the critters. “The experiment has already been done by nature,” he says. “What are the results? What was modified genetically in the brain to get this difference in behavior?”

To find out, Young uses a staggeringly sophisticated set of biomolecular tools, from genetic sequencing to transcriptomics.
But could an animal as humble as the prairie vole, only lately recruited from America’s plains, really have secrets to share about human conundrums such as infidelity, and perhaps even social disorders like autism? Absolutely, says Young, who himself began life as a provincial creature, born “a mile down a dirt road” in the sand and pine country of Sylvester, Georgia. (He still keeps a cabin there, where he hazes citified graduate students via goat skinning and other practices.) He had never even heard of DNA until after high school. Part of his interest in vole behavior and brain structure seems to stem from curiosity about his own life path: marriage, divorce, remarriage, five children and an ongoing love affair with neuroscience that’s taken him far from his rural roots.

***

The prairie vole first caught science’s eye in the 1970s, when the mammalogist Lowell Getz launched a routine population study in the alfalfa fields and bluegrass pastures close to the University of Illinois at Urbana-Champaign, where he taught at the time. To take the edge off the subzero temperatures at night, he and other researchers sometimes kept Jack Daniel’s in the study shed along with the data sheets and other materials. The alcohol was for the researchers’ own consumption; taste tests since have shown that prairie voles like liquor, and diluted whiskey may in fact have been good vole bait.

Cracked corn worked well enough in the traps, but the scientists did notice something unusual. Prairie voles frequently showed up in pairs, often a male and a female. Sometimes, the scientists would snare the same duo again months afterward. These couples made up some 12 percent of adult prairie vole catches, compared with just 2 percent among other trapped voles. To find out what was up, Getz outfitted a dozen prairie vole pairs with miniature radio collars powered by hearing aid batteries. Tracking their movements through the dense grass, he discovered that 11 of the 12 “couples” cohabited more or less permanently in subterranean dens, a behavior almost unheard of among rodents. Both members of the 12th couple had other partners in separate love nests. Getz had apparently captured the two mid-tryst.

Astonished, he took his findings to Sue Carter, a colleague at the University of Illinois who was working on hamster endocrinology. Female hamsters routinely slaughter and eat their sexual partners. “That’s what I thought was normal,” Carter recalls. She was unprepared for the voles’ attachment to their partners, or what turned out to be long-lasting and passionate mating sessions (“We had to put them on time-lapse video. No one could sit there for 40 hours!”).

But what makes the attachment so strong? How exactly does a pair forge its bond? Carter and others eventually homed in on the chemical messenger oxytocin—also a hormone associated with the perception of social cues, childbirth and maternal bonding. When a female prairie vole received an oxytocin injection in her brain, she huddled with her partner more and formed stronger bonds. Another hormone, vasopressin, related to territoriality, has been found to promote pair-bonding in males.

Tags
About Abigail Tucker

A frequent contributor to Smithsonian, Abigail Tucker is writing a book about the house cat.

Read more from this author

Comment on this Story

comments powered by Disqus