A lethal disease has been causing large die-offs of little brown bats; it has been found in bats hibernating in 16 States and 4 Canadian provinces. Researchers have now identified the fungus Geomyces destructans as the primary cause of white-nose syndrome. Tests have demonstrated that the fungus can be spread by contact in shared hibernation spots.
Though the fungus is widespread in Europe it does not cause die-offs, possibly because the bats in Europe have been previously exposed, and the current population is made up of the descendants of those that survived. This is the type of classic selection factor result that has been described in past posts addressing evolution driven by a variety of environmental selection factors.
The report on the cause of the disease can be found at http://www.nature.com/nature/journal/v480/n7377/full/nature10590.html.