Promiscuous male voles can be turned into paragons of monogamous virtue simply by increasing the expression of a single gene. This finding challenges the assumption of many evolutionary biologists that complex social behaviors evolve through several small steps.
The origin of long-lasting relationships in many species seems to be a receptor for the hormone vasopressin, the so-called V1a receptor (V1aR). Species with high levels of V1aR in the ventral forebrain tend to be monogamous, whereas species with low levels are more likely to have a swinging lifestyle. This pattern is true for two species of vole, the monogamous prairie vole (Microtus ochrogaster) and its promiscuous cousin, the meadow vole (M. pennsylvanicus).
The wayward ways of the meadow vole can be changed simply by increasing expression of V1aR in the brain, according to research published 17 June in Nature. Social neurobiologist Lawrence Young of Emory University in Atlanta, Georgia, and his colleagues injected a virus carrying the V1aR gene into the brains of meadow voles to boost levels of V1aR. The researchers put the males in a cage with a female for 24 hours, then added a second female. Normally, meadow voles show no allegiance to their old partner and hook up with the newcomer. But the treated voles preferred to cuddle with the familiar female.
This finding has important consequences for our understanding of the evolution of social behavior, says Gene Robinson, a neuroscientist at the University of Illinois, Urbana-Champaign. Most researchers assume that evolutionary change comes about through incremental changes to many genes. This research, by contrast, suggests that rapid evolution of a complex social behavior like pair bonding can occur by changing the expression of just one gene, he says. "This is the strongest and most direct demonstration of this phenomenon yet."
At present, it is not clear whether a similar mechanism could be involved in human bonding, says Young. However, some people with autism have a mutation in a stretch of DNA that regulates expression of the V1aR gene, which could explain why they find it difficult to form close relationships with others, note Young and his co-authors.
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