Two thousand miles east of the coast of Argentina, Gough Island rises out of the Atlantic Ocean in an awesome display of ancient volcanic activity. A green carpet of windswept mosses and grasses covers 35 square miles of jagged peaks and steeply sloping valleys. Waterfalls spill out of craggy cliffs and fall hundreds of feet to the sea, which runs uninterrupted for another 1,700 miles before crashing into the tip of South Africa. It is one of the most remote places on our planet.
Four miles west of the University of Wisconsin– Madison campus, the Charmany Instructional Facility is a low-slung labyrinth of concrete hallways lined by bright fluorescent lights and permeated with a smell that is equal parts animal and antiseptic. Part of the UW School of Veterinary Medicine, Charmany is nearly half a world away from Gough Island (pronounced “Goff ”). Yet the two locations share a common trait— they both are home to the largest mice on Earth.
In terms of body size and weight, Gough Island mice are twice the size of their mainland cousins, notes Bret Payseur, a geneticist with a joint appointment in CALS and the School of Medicine and Public Health. “The amazing thing about them being twice the size is that they’ve only been on the island a couple of hundred years,” he says. The island’s early rodent settlers were a more moderate-sized strain of Mus musculus, house mice stowaways in the holds of sealing ships from Western Europe. But somewhere along the line, Gough Island mice outgrew that ancestry—doubling in size over the course of only a few hundred generations. “That’s incredibly rapid evolutionary change,” Payseur says. “It’s some of the most rapid that I know about.”
In the canon of origin stories, however, this tale reads more like a mystery. How did the Gough Island mice get so big so quickly? It could be that a genetic mutation proved so advantageous that huge mice became the norm. Or maybe conditions on the island favored preexisting genetic traits that had lain dormant until the mice became castaways. For the time being, however, the Gough mouse story is transcribed only in A’s, T’s, C’s and G’s—the nucleic acids that write genetic code. Payseur hopes to translate that text. What he finds could not only shed light on evolution in action. It could also help illuminate the genetic mechanisms underlying human metabolic diseases like obesity and diabetes.
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