Nearly six years after the discovery of a catastrophic fungal infection that's decimating bat populations in the U.S. and Canada, scientists have concluded that the disease is primarily transmitted by highly social bats. But just because scientists have a better handle on how bats spread the disease doesn't mean there's good news. If anything, the discovery is leading scientists to conclude that white-nose syndrome will likely result in the outright extinction of certain bat populations.
A single disease usually can't wipe out an entire species. Because virtually every organism exhibits a wide array of variation (random mutations) in its populations, there's always a good chance that some members will survive a blight and pass on those characteristics to surviving members. Even if the disease afflicts 99% of a population, there's still a good chance that the species can eventually survive.
But not in all cases, it turns out. Some diseases, it would appear, are so nasty and so thorough in their infestation that certain populations run the risk of being wiped out completely.
Take Colony Collapse Disorder, for example. Early last month we reported on how the Deformed Wing Virus (DWV) is affecting honey bee populations by piggybacking on mites. DWV works in such a way that, once it hits a colony, it infects 100% of the bees; the entire hive consequently collapses. And as it spreads from colony to colony, entire geographic regions completely lose their ability to host honey bee populations.
And now it appears that bats may be in for similar kinds of trouble. A recent study from the University of California, Santa Cruz (UCSC) has discovered that the spread of white-nose syndrome depends on how social the bats are, during periods of hibernation. According to ecologists Kate Langwig of Boston University, and Marm Kilpatrick of the University of California, Santa Cruz, some bats like to sleep in large clusters, while others sleep alone. It's those bats who sleep in clusters that are primarily responsible for transmitting the disease.
White-nose syndrome works by growing on the exposed skin of hibernating bats, which disrupts hibernation and causes unusual behavior, loss of fat reserves, and eventually death. The disease is unbelievably virulent, causing the deaths of upwards of 95% of bats in certain populations.
The study, which is published in the current issue of the journal Ecology Letters, analyzed population trends in six bat species in the northeast United States. The researchers concluded that, based on the hibernating behaviours of different bat species, some bats were almost certain to meet extinction. Others, on the other hand, are showing signs of population stabilization — an indication that their social behaviors are in check. But they also discovered that some bat populations are changing their behaviors (likely through selectional processes) and exhibiting more individuals who have become solitary — and as a result, are better at staving off the disease.
But other species aren't so lucky. Certain populations like the northern long-eared bat and the Indiana bat have disappeared completely. The researchers wory that these two species are doomed.
The researchers will continue to study bat populations, and consider microclimates as a potential factor in the spread of the disease.
Top image via MicrobeWorld. Inset images via Ryan von Linden, New York State Department of Environmental Conservation and Al Hicks, New York State Department of Environmental Conservation.