Paul jackman/Nature

Even as home experiments go, Hopi Hoekstras one was peculiar: she built a giant plywood box in her garage in San Diego, California, filled it with more than a tonne of soil and then let a pet mouse dig away.

This thing was bursting at its seams and held together with duct tape, says the evolutionary biologist, now at Harvard University in Cambridge, Massachusetts. But it worked. It allowed her to study the genetics of burrowing behaviour in a controlled setting. Armed with plastic casts of the burrows and state-of-the-art sequencing, Hoekstras team discovered clusters of genes that partly explain why the oldfield mouse (Peromyscus polionotus) builds elaborate two-tunnel burrows, whereas its close relative, the deer mouse (Peromyscus maniculatus), goes for a simple hole in the ground1.

The findings highlight an underappreciated benefit of a genomics revolution that is moving at breakneck speed. Thanks to cheap and quick DNA sequencing, scientists interested in the genetics of behaviour need not limit themselves to a handful of favourite lab organisms. Instead, they can probe the genetic underpinnings of behaviours observed in the wild, and glean insights into how they evolved. In my mind, the link between genes and behaviour in natural populations and organisms is the next great frontier in biology, says Hoekstra.

Hopi Hoekstra talks about what mouse burrows can reveal about the genetics of complex behaviours.

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Oldfield mice are native to the southeastern United States, where they burrow in soils ranging from sandy beaches to silt-rich clays. Wherever they dig, their holes look much the same, with a long entrance tunnel and a second tunnel that stops short of the surface and allows them to escape predators. Such invariability hints that the trait is encoded in DNA, says Hoekstra.

To find out where, she and her Harvard colleagues Jesse Weber and Brant Peterson cross-bred oldfield mice with deer mice, whose burrows are shallow and lack escape routes. The offspring continued to build complex tunnels, suggesting that the oldfield burrowing genes were dominant (see The genetics of burrowing).

A second round of breeding between the first-generation crosses and deer mice revealed that genes linked to burrow length were distinct from those influencing the escape tunnel. Some offspring produced short tunnels with escape routes, whereas others produced long tunnels without them. DNA analysis revealed that three genetic regions are responsible for much of the variation in tunnel length, and a fourth affects escape-tunnel digging.

This paper is awesome, says Cornelia Bargmann, a neurogeneticist at Rockefeller University in New York, noting that it combines cutting-edge molecular-genetics tools with established cross-breeding techniques to study behaviours that have been observed for more than a century in the wild. In the past, geneticists interested in unravelling behaviour had to focus on lab animals for which mutant and transgenic strains and genetic data were available, she says. But there were always questions we knew would be more interesting in wild animals. Bargmann and her team studied various wild strains of Caenorhabditis elegans flatworms to identify genes and brain circuits involved in seeking out new sources of food2.

See the article here:
Behaviour genes unearthed

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