White-nose Syndrome Changes Social Behavior in Bats

Virtually every mammalogist is aware of White-nose syndrome (WNS), an emerging infectious disease that targets hibernating bats. It is caused by Geomyces destructans, an introduced fungus in the family Myxotrichaceae. The fungus reached North America in the early 2006 at a cave in Schoharie County, NY (Figure 1).

WNSMAP05-03-12_300dpi
Figure 1. A US Fish and Wildlife Service map of the WNS occurrence in the Eastern United States and Canada. (From USFW Service)

G. destructans causes severe mortality in common bat species that hibernate in caves. The fungus causes WNS, which is characterized by lesions on flight membranes and by disruption in the torpor patterns. The later causes bats to become active prematurely during the winter months when food is unavailable – resulting in dehydration or starvation.

In a recent report in the journal
Biology Letters, researchers reveal the impact of WNS on bat communities over the past 5 years (Langwig et al., 2012). Prior to the introduction of this devastating disease, all species of hibernating bats had stable of increasing populations. In the years following the outbreak populations of most hibernating bats declined significantly (The US Fish and Wildlife Service estimates that over 5.5 million bats have died from WNS). Langwig and colleagues show that population growth rates are in decline and are unrelated to colony size.

One of the most interesting findings was that populations of the little brown myotis eventually stabilized within 4 years of WNS detection, albeit at much lower population size (Figure 2). The main reason for stabilization of little brown myotis populations is changes in social behavior.

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Figure 2. Boxplots of population trends for little brown myotis in the 5 years (x axis) post-WNS detection. This species population growth rates have increased significantly with years since WNS detection. (From Langwig et al., 2012)


Prior to WNS, little brown myotis hibernated almost exclusively in large clustered colonies. After WNS detection, a significantly greater percentage (44.5%) of bats roosted individually –17 times the number that roosted individually prior to WNS (Figure 3). This implies that little brown myotis reduced clustering behavior and thereby diminish WNS infection.

roost
Figure 3. Clustering behavior of little brown and Indiana myotis in hibernacula before (open symbols) and after (filled symbols) WNS detection. (From Langwig et al., 2012)

These findings highlight the role of behavior in reducing the impacts of pathogens in social species and may help provide a framework for managing extinction risk from this fungal disease.


References

Langwig, Kate E. (2012-07-02)
Sociality, density-dependence and microclimates determine the persistence of populations suffering from a novel fungal disease, white-nose syndrome. Ecology Letters, 1-n/a. DOI: 10.1111/j.1461-0248.2012.01829.x