An Interesting Natural Experiment in Disease Resistance Is Underway — Will Hibernating Bats Evolve the Ability to Resist White-Nose Syndrome?

© 2011 Peter Free

 

23 February 2011

 

 

First, what is white-nose syndrome?

 

For about 4 years, hibernating bats have been dying in “unprecedented” numbers in the eastern United States, while hibernating.  Some colonies have lost 90 to 100 percent of their inhabitants, apparently due to a fungal infection commonly called “white-nose syndrome.”  The syndrome is caused by the fungus, Geomyces destructans.

 

 

Why care?

 

Bats eat a prodigious amount of insects, which (among other things) helps agriculture.  They also pollinate plants and distribute seeds.

 

 

But reports about the threat of brown bat extinction from white-nose syndrome may be hype

 

Given the alarmist nature of the media, there are some reports that hibernating bat extinction could occur.  Some of these articles cite the fact that an estimated “million” have died.  But, without knowing the size and geographic distribution of bat species under attack, it seems silly to be talking about extinction, just yet.

 

The U.S. Geological Survey takes a more balanced approach to its reporting:

 

The USGS [U.S. Geological Survey] National Wildlife Health Center, working with many partners, continues to play a primary role in WNS [white-nose syndrome] research. Studies conducted at the Center were crucial to the identification and naming of the fungus, and to the development of histopathologic criteria for characterizing infection by G. destructans.

 

DNA from G. destructans has recently been identified on three new Myotis species (M. grisescens, M. velifer, and M. austroriparius) in Missouri, Oklahoma and Virginia, respectively, as well as on female little brown bats arriving at maternity colonies in Delaware.

 

Unusual mortality has not been reported associated with the apparent westward expansion of the fungus, and it remains to be seen if WNS will develop and manifest similarly in warmer climate zones.

 

Current estimates of bat population declines since the emergence of WNS are as high as 97% in some areas.

 

© 2011, National Wildlife Health Center, White-Nose Syndrome (WNS), U.S. Geological Survey (18 February 2011) (paragraph split)

 

Obviously, high mortality in some areas is not the same as high species-wide mortality.

 

 

The interesting twist — culling bat populations of sick ones probably will not help

 

The natural experiment is disease resistance is underway because a mathematical model (probably appropriately, given human experience with pandemics) predicts that removing diseased bats is not going to slow the white-nose epidemic down.

 

WNS [white-nose syndrome] has caused massive mortality of bats that hibernate. Efforts to control the disease have been ineffective.

 

The culling of bats in hibernacula has been proposed as a way to break the transmission cycle or slow the spread of WNS.

 

We formulated a disease model to examine the efficacy of culling to abate WNS in bat populations. We based the model dynamics on disease transmission in maternity roosts, swarms, and hibernacula, which are the arenas of contact among bats.

 

Our simulations indicated culling will not control WNS in bats primarily because contact rates are high among colonial bats, contact occurs in multiple arenas, and periodic movement between arenas occurs. In general, culling is ineffective in the control of animal diseases in the wild.

 

© 2011 Thomas G. Hallam and Gary F. McCracken, Management of the Panzootic White-Nose Syndrome through Culling of Bats, Conservation Biology 25(1): 189-194, doi:  10.1111/j.1523-1739.2010.01603.x (February 2011) (paragraph split)

 

 

So we will get to see how Geomyces destructans and bat species co-evolve

 

Not fun for the bats.  But knowledge-enhancing for humans.