AP Behold, the moral rodent

LOVE, of course, is what makes the world go round, but what makes love go round? To aesthetes, such a question is imponderable. To scientists, it is not only ponderable but increasingly open to scrutiny—the more so now that Zoe Donaldson and her colleagues at Emory University in Atlanta, Georgia, have succeeded in creating a new kind of transgenic prairie vole. For, unlikely as it might seem, these tiny rodents could be the key to understanding bonding, trust and even decision-making in humans.

For those unfamiliar with the delightful prairie vole, it is a small rodent found in the grasslands of central North America. What makes it unusual among mammals is that it is both sociable and monogamous. Prairie voles groom each other, nest with one another, collaborate to guard their territory and are affectionate and attentive parents who form, for the most part, devoted couples. Their close relatives the meadow voles, by contrast, prefer a solitary, promiscuous existence.

It turns out that these large behavioural differences between the two species are caused by small genetic ones. To be precise, they have been linked to a hormone called vasopressin and the protein molecule that acts as its receptor. Prairie voles have many vasopressin receptors in the reward centres of their brains. It seems as though these are wired up in a way that causes the animal to take pleasure from monogamy. In people, by contrast, certain variations of the vasopressin receptor have been linked with rocky marriages, and overenthusiastic journalists have dubbed it the “divorce gene”.

Being able to create genetic variants of prairie voles to order would therefore be helpful to research. And that, as they describe in the December issue of Biology of Reproduction, is what Dr Donaldson and her team have done. Using viruses as carriers, they have introduced novel genetic material into embryonic prairie-vole cells, and then grown each modified cell into a complete animal.

In this case, to prove the point, the gene they introduced was for green fluorescent protein—a molecule derived from jellyfish. This molecule, as its name suggests, glows bright green when exposed to light of a suitable frequency. The resulting glowing prairie voles were evidence that the embryos had indeed been altered, and that the alteration had been transmitted to every cell in the vole's body, including its sex cells. The offspring of such voles will therefore carry the change as well.

Having proved the principle, Dr Donaldson—or anybody else who wishes to—will now be able to make voles that do more than just glow in the dark. Biologists will thus be able to test theories about how behaviour is governed by the vole's various genes. This, in turn, should help explain complex social interactions seen in both rodents and people.

In some cases the monogamous rodents will, no doubt, become promiscuous. Certainly, the reverse can happen. One study has already shown that it is possible to inject a viral vector for the vasopressin receptor into the brains of the fickle meadow voles and make them better partners and parents. It may be some time before such interventions are available for human males, but women can always live in hope.