YOSEMITE NATIONAL PARK, Calif. - The mountain yellow-legged frog has survived for thousands of years in lakes and streams carved by glaciers, living up to nine months under snow and ice and then emerging to issue its raspy chorus across the Sierra Nevada range. But the frog's call is going silent as a mysterious fungus pushes it toward extinction. "It's very dramatic," said Yosemite biologist Lara Rachowicz. "One year, you visit a lake and the population will seem fine. The next year you go back, you see a lot of dead frogs scattered along the bottom of the pond. In...