Is It or Isn’t It (Just Another Mouse)?

Why science alone will not settle the West’s endangered species dilemmas

  • Preble's meadow jumping mouse

    Federal Highway Administration
  • Rob Roy Ramey, during his tenure at the Denver Museum of Nature and Science

    James Glader
  • Preble's mouse specimens at the Denver Museum of Natural History

    James Glader
  • Mouse Range

    Diane Sylvain
  • Urban sprawl on Colorado's Front Range, in Preble's meadow jumping mouse habitat

    Jacob Smith and Lighthawk
  • Preble's mouse skull at the Denver Museum of Natural History

    James Glader

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Like Ramey, King examined snippets of DNA from various populations of Preble’s and four neighboring jumping mouse subspecies. But where Ramey tested a few individuals from many different populations, King looked at DNA from many individuals from a smaller number of populations. Each approach has its dangers. Collect DNA from too few individuals from a given population, and you may not detect the true patterns of variation within that group. Collecting many samples from each population solves this problem, but unless you sample every population, you still may miss differences that exist in these groups. Ideally, the two sampling methods would be combined, but in the real world, funding and time constraints can make this impossible.

King tested two regions of mitochondrial DNA and 21 regions of nuclear DNA from each individual. Unlike Ramey, King saw clear distinctions between the Preble’s mouse and the other four subspecies. In a peer-reviewed report sent to the Fish and Wildlife Service in January 2006, King argued that the variations suggested that the Preble’s mouse had mutated and diverged from other meadow jumping mice.

King pointed out that Krutzsch split the Preble’s mouse from other subspecies based not only on its physical features, but also on its geographic isolation. A gap of 60 miles or more separates the Preble’s mouse from the nearest Bear Lodge mouse populations, and King says that the differences that have evolved in the Preble’s DNA show that it has been isolated from other subspecies for thousands of years.

To King, the implications were clear: The Preble’s mouse was headed down its own, unique evolutionary path. "The data are unequivocal," he said.

Two studies. Two opposing conclusions. While it might smell of dirty politics, such conflicts are not unheard of in taxonomy. The problem arises because scientists can’t agree on a definition of species, let alone subspecies, says Susan Haig, a geneticist at the U.S. Geological Survey’s Forest and Rangeland Ecosystem Science Center in Corvallis, Ore. Taxonomists have spent entire meetings, even whole careers, debating species concepts without ever reaching an agreement. "It’s not like scientists are space cadets," Haig says. "It’s the fact that technology changes, our view of the world changes, we learn more."

At issue are questions like: How unique must a population be to warrant status as a subspecies? Is geographic isolation enough, or should genetic differences or physical traits like size or pelt color be required too? Which traits should carry the most weight? How much intermixing can go on between subspecies without jeopardizing their status? Science has yet to reach a consensus on these issues, says Haig. "Someone puts out a definition, and people pick it apart and refine it, and then other people pick it apart and keep refining it."

The debate that once took place at obscure conferences has spilled into the public arena, because under the Endangered Species Act, subspecies receive as much protection as full species. In fact, 20 percent of all the wildlife species protected by the act are actually subspecies. Deciding where to draw the lines between subspecies is critical, but the Fish and Wildlife Service’s guidelines are open to interpretation.

In the case of the mouse, Ramey chose one definition and King chose another. Stakeholders on both sides of the debate claimed the science lay in their court. And to some extent, both sides were right.

The debate roiled for nearly three years, with neither side giving an inch. "King has what I consider a very, very low bar," said Ramey. He argued that the genetic differences King found between Preble’s and the Bear Lodge mouse were not biologically meaningful, because they were found in "neutral markers," which don’t encode genes. "Most people would call this junk DNA," Ramey said, adding that he’d found similar levels of genetic variation between populations of bighorn sheep on opposite sides of Interstate 40 in California. "The sheep are literally staring across the highway at each other," he said.

But King’s backers argued that Ramey failed to gather enough data to test his criteria, which they called unduly strict. "The King study literally quadrupled the amount of genetic data and found clear separations between all five subspecies," said Sylvia Fallon, a conservation genetics fellow at the Natural Resources Defense Council in Washington, D.C. "Ramey and King aren’t arguing over where to draw the line. Ramey’s study failed to find any lines to draw because he didn’t have enough information."

Ramey’s critics also questioned his interpretation of his results. "Ramey set a very, very high bar," said Wayne Spencer, a biologist at the Conservation Biology Institute in San Diego, who, at the request of the Fish and Wildlife Service, reviewed both papers. "The genetic tests (Ramey) used don’t even show differences between valid species, like between polar bears versus grizzlies," he said.

King added fuel to the fire this June, when he submitted a paper for publication in the journal Molecular Ecology revealing that he tried, and failed, to replicate some of Ramey’s genetic data. In dispute are seven Bear Lodge mouse museum specimens that, in Ramey’s study, turned up mitochondrial DNA sequences also found in Preble’s mouse specimens. King’s work showed that none of these seven specimens contained the Preble’s sequences. What’s more, King turned up discrepancies in more than a dozen nuclear DNA sequences from Ramey’s museum specimens, which, King said, suggested a systematic error in Ramey’s methods.

Ramey said he was looking into the samples in question and will file a correction if his original data were wrong. But he argued that the dispute was not about whose dataset was most robust, but about how to interpret the data. "Tim can find these statistically different things between populations, but how biologically significant are they? If you look at species and subspecies through the end of a pipette you can lose the forest for the trees." In fact, neither Ramey nor King has ever seen a live Preble’s meadow jumping mouse.

Whose conclusions were correct? Both of them, said BYU’s Keith Crandall, who, with funding from Wyoming, combined and analyzed both datasets. Though Crandall came down on Ramey’s side, he acknowledged that King’s arguments had merit. "They both collected data relevant to the questions they posed and both addressed them in ways that they thought were reasonable and came to opposite conclusions," Crandall said. "How do you resolve that? You don’t. You argue until the cows come home."

But the Fish and Wildlife Service doesn’t have that kind of time. By law, the agency must respond to Wyoming’s petition to delist the Preble’s mouse by the first week of August. The agency needs an answer now. So with the clock ticking and the entire Front Range looking on, the agency contracted the Portland-based Sustainable Ecosystems Institute to convene a panel of scientists to weigh the scientific evidence.

The panel meets in early July, in a small conference room at Colorado State University in Fort Collins. A courtroom-like aura hangs in the room. The three panelists — Brian Arbogast of Humboldt State University, John Dumbacher from the California Academy of Sciences and Scott Steppan of Florida State University — sit behind a table at the front of the room. Given their distinct morphology (bald head), adaptations (identical Macintosh laptops) and behavior (a tendency to ask probing questions) the panelists themselves might qualify as a distinct subspecies under some definitions.

The audience includes scientists from several universities and the Fish and Wildlife Service, employees of a Colorado Springs utility, representatives from numerous environmental groups, a landowner who claims the Preble’s mouse has prevented him from developing his five-acre parcel on Monument Lake, and representatives from the offices of several politicians, including a well-coiffed woman who will type messages on her BlackBerry throughout much of the meeting.

The mouse itself is absent, but Craig Hansen, a flamboyant young biologist who has spent hours tagging and tracking the little creatures, passes around his newly bound master’s thesis like a new father with his firstborn’s baby book. "Just look at his feet — they’re huge!" Hansen exclaims, pointing at a photo. "These mice are so cool!"

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