Prairie vole partners split up if one drinks more than the other

Prairie voles mate for life, but the bond is likely to break down if one partner drinks more alcohol than the other

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Heavy drinkers and abstainers don’t make the best couples. In humans, one partner that drinks more than the other is thought to be a recipe for a breakup. The same appears to be true for prairie voles, one of the only other mammals known to form long-term monogamous relationships.

The finding suggests the link between alcohol consumption and relationship failure may have a biological basis, say the researchers.

“There is an increase in divorce in couples in which there is discordant drinking,” says Andrey Ryabinin at Oregon Health and Science University. Money is thought to play a role, but nobody knows the precise causes because a randomised study in people would be unethical. “You can’t tell people to start drinking,” he says.

To explore the question in animals, Ryabinin and his colleague Andre Walcott turned to prairie voles: the only rodents known to form lasting, monogamous relationships. “They maintain the same pair bond for their entire lives,” says Ryabinin. Unlike other rodents, both partners take care of offspring. And rather than leaving the nest as soon as they reach adolescence, the young stay and look after their younger siblings.

Prairie voles are also the only rodents known to willingly drink alcohol. While mice and rats avoid the stuff, prairie voles prefer it to water, says Ryabinin.

Ryabinin has previously shown that alcohol consumption affects prairie vole relationships. When given a choice between their partner and a new female, male voles that drank more alcohol were more likely to go and mate with the new female than those that abstained. Alcohol seemed to have the opposite effect in females – those that drank more alcohol more strongly preferred their original partner.

Now Ryabinin and Walcott have tried to recreate human relationships, by testing the effects of alcohol consumption once two prairie voles have formed a bond. Each pair of voles were supplied with either only water or both alcohol and water. In a third group, only the males had a choice of alcohol or water.

The pair let the animals mate, then kept them together for one week, monitoring their alcohol consumption. They then separated the male and female with a wire mesh, while still allowing them to smell each other and interact.

When the prairie voles were given a choice between their partner and a new one, male voles tended to maintain a strong bond with their partner if both had drunk similar amounts of alcohol. But if only the male had been drinking, he was much more likely to mate with a stranger.

Ryabinin is presenting his results this month at the annual meeting of the Society for Neuroscience in Washington, DC.

The finding mimics what has been observed in humans, says Ryabinin. But it also suggests that there might be a biological reason for such relationship breakdowns. “We still need to take the human factors into account,” he says. “But now we have identified that biology plays a role, and can study that.”

The study is “fascinating”, says Zoe Donaldson at the University of Colorado, Boulder. But she says it doesn’t necessarily show that discordant drinking leads to broken relationships. It could be that some voles had weaker bonds to begin with, and that influenced how much alcohol they drank

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