CASE STUDY: “No Bats in the Belfry: The Origin of White-Nose Syndrome in Little Brown Bats”
by Dechaine and Johnson
Part I – The Basic Question
Imagine going out for a brisk winter snowshoe and suddenly stumbling upon hundreds of bat carcasses littering the forest floor. Unfortunately, this unsettling sight has become all too common in the United States (Figure 1). White-nose syndrome (WNS), first discovered in 2006, has now spread to 20 states and has led to the deaths of over 5.5 million bats (as of January 2012). WNS is a disease caused by the fungus, Pseudogymnoascus destructans. Bats infected with WNS develop white fuzz on their noses (Figure 2, next page) and often exhibit unnatural behavior, such as flying outside during the winter when they should be hibernating.
WNS affects at least six different bat species in the United States and quickly decimates bat populations (colony mortality is commonly greater than 90%). Scientists have predicted that if deaths continue at the current rate, several bat species will become locally extinct within 20 years. Bats provide natural pest control by eating harmful insects, such as crop pests and disease carrying insect species, and losing bat populations would have devastating consequences for the U.S. economy.
Researchers have sprung into action to study how bats become infected with and transmit P. destructans, but a key component of this research is determining where the fungus came from in the first place. Some have suggested that it is an invasive species from a different country while others think it is a North American fungal species that has recently become better able to cause disease. In this case study, we examine the origin of P. destructans causing WNS in North America.
Some Other Important Observations
• WNS was first documented at four cave sites in New York State in 2006.
• The fungus can be spread among bats by direct contact or spores can be transferred between caves by humans (on clothing) or other animals.
• European strains of the fungus occur in low levels across Europe but have led to few bat deaths there.
• Bats with WNS frequently awake during hibernation, causing them to use important fat reserves, leading to death.
Figure 1. Many bats dead in winter from white-nose syndrome.
Answer the following questions.
What is a hypothesis?
A hypothesis is an educated guess during a project or an experiment.
2. What is a null hypothesis?
A null hypothesis is a type of hypothesis that proposes that no significance exists in a set of given observations.It is is a hypothesis which someone tries to disprove, reject or nullify an observation or idea.
3. What is the basic question of this study and why is it interesting?
The basic question of this study is ” is the European strain causing the WNS attacks on the North American bats”. It is interesting because if the european strain is killing the birds in North America then why isn’t it having the same effect on the European birds.
4. What specific testable hypotheses can you develop to explain the observations and answer the basic question of this study? Write at least two alternative hypotheses.
1. the european strain of WNS is the same as the North American strain of WNS
2. the european strain of WNs is different from the North American strain
5. What predictions about the effects of European strains of P. destructans on North American bats can you make if your hypotheses are correct? Write at least one prediction for each of your hypotheses.
If my first hypothesis is right then the European strain of WNS is killing more North American bats because of environmental or climatic factors. If my second hypothesis is right then the bats in North American are dying more than the European bats because the two funguses are completely different.
Figure 2. White fuzz on the muzzle of a little brown bat indicating infection by the disease.
Part II – The Hypothesis
As discussed in Part I, researchers had preliminary data suggesting that the pathogen causing WNS is an invasive fungal species (P. destructans) brought to North America from Europe. They had also observed that P. destructans occurs on European bats but rarely causes their death.
Preliminary research also suggested that one reason that bats have been dying from WNS is that the disorder arouses them from hibernation, causing the bats to waste fat reserves flying during the winter when food is not readily available.
These observations led researchers to speculate that European P. destructans will affect North American bat hibernation at least as severely as does North American P. destructans (Warnecke et al. 2012).
6. Explicitly state the researchers’ null (H0) and alternative hypotheses (HA) for this study.
Null Hypothesis is that the European strain will affect the North American bat hibernation at least as severely as does North American strain.
Alternative Hypothesis is that the disorder arouses the bats from hibernation causing them to waste fat reserves during the winter when food is not readily available which eventually causes them to die.
7. Describe an experiment you could use to differentiate between these hypotheses (H0 and HA).
a group of healthy bats could be separated into groups of trials where one group is injected with the european strain and the other is injected with the north american straian and the last group will be the control group under the same conditions.
Part III – Experiments and Observations
In 2010, Lisa Warnecke and colleagues (2012) isolated P. destructans fungal spores from Europe and North America. They collected 54 male little brown bats (Myotis lucifugus) from the wild and divided these bats equally into three treatment groups.
• Group 1 was inoculated with the North American P. destructans spores (NAGd treatment).
• Group 2 was inoculated with the European P. destructans spores (EUGd treatment).
• Group 3 was inoculated using the inoculation serum with no spores (Control treatment).
All three groups were put into separate dark chambers that simulated the environmental conditions of a cave. All bats began hibernating within the first week of the study.
The researchers used infrared cameras to examine the bats’ hibernation over four consecutive intervals of 26 days each. They then used the cameras to determine the total number of times a bat was aroused from hibernation during each interval.
8. Use the graph below to predict what the results will look like if the null hypothesis is supported. The total arousal counts in the control treatment at each interval is graphed for you (open bars). Justifiy your predictions.
9. Use the graph below to predict what the results will look like if the null hypothesis is rejected. The total arousal counts in the control treatment at each interval is graphed for you (open bars). Justify your predictions.
Part IV – Results
Figure 3 (below) shows the real data from the study. There is no data for interval 4 bats that were exposed to the European P. destructans (gray bar) because all of the bats in that group died.
10. How do your predictions compare with the experimental results? Be specific.
My predictions was relatively close with the experimental results. In the first interval my predictions were 30 arousal counts for the North American strain and on the second interval my predictions were the same as the experimental results. On the third interval my predictions were that the European strain will be around 120 but in the experimental results it was 110 and for the fourth interval i predicted that the control will be 40 arousal counts but it was around 22 in the experimental results.
11. Do the results support or reject the null hypothesis?
The results supports the null hypothesis
12. If the European P. destructans is causing WNS in North America, how come European bats aren’t dying from the same disease?
This could be because of an environmental or climatic factor which might be present in North America and not in Europe.
U.S. Fish and Wildlife Service. 2012. White-Nose Syndrome. Available at: http://whitenosesyndrome.org/. Last accessed December 20, 2013.
Warnecke, L., et al. 2012. Inoculation of bats with European Geomyces destructans supports the novel pathogen hypothesis for the origin of white-nose syndrome. PNAS Online Early Edition: http://www.pnas.org/cgi/ doi/10.1073/pnas.1200374109. Last accessed December 20, 2013.