"Grasshopper mice have no respect for prairie dog territories," Jones said. "They're nasty little beasties, and when they eat the carcass of a prairie dog that's died of plague, the fleas climb aboard the mice. The mice then schlep the fleas around to different territories, connecting family groups that otherwise wouldn't be in contact."
The idea that plague could be facilitated by grasshopper mice was first proposed by Salkeld and co-author Paul Stapp of California State University-Fullerton. However, other researchers have been skeptical of the mouse hypothesis.
"A number of people familiar with prairie dogs say there is no way that the grasshopper mouse is causing this, because they only trap a few mice a year," Jones said. "So we decided to write a computer model to determine if the number of mice being trapped is consistent with driving these plague epizootics."
For the PNAS study, Salkeld obtained field data from the Pawnee National Grasslands in Colorado. Co-author Marcel Salath, now at Pennsylvania State University, created a computer model that simulates plague dynamics in a large prairie dog town.
The results of the simulation revealed that plague is endemic among prairie dogs.
"Even without grasshopper mice, plague kills one or two prairie dog families at a time, but it moves very slowly and is extremely hard to detect," Jones said.
As long as the disease is confined to isolated family groups, the town can survive. But once the density of susceptible prairie dog families and grasshopper mice crosses a critical threshold, plague can sweep through and wipe out virtually the entire town, he said.
"Plague sort of smolders in the prair
|Contact: Mark Shwartz|