Bat populations in Colorado may be headed for decline that could cause ecological disruption across the state.
Two bats discovered in Boulder County in late February 2024 were confirmed to have white-nose syndrome, a deadly fungal disease. Other bats in Larimer County also tested positive for white-nose syndrome earlier this spring.
The first North American bats with white fungus on their faces, ears and wings were discovered in 2006 in hibernating caves near Albany, New York. The fungus causes bats to lose nutrients and moisture through their skin and wake up early from hibernation in search of food and water.
The disease spread rapidly westward, reaching Washington state in 2015 and California four years later. It was confirmed in Montana and New Mexico in 2021. Evidence of the fungus was first reported in Colorado in the summer of 2022.
I am a bat biologist and most of my research has focused on the genetics of Myotis bats. Knowing which bat populations are genetically unique and where they are found will help researchers understand how white-nose syndrome will affect them and how it moves between geographic areas.
What is white nose syndrome?
White nose syndrome is the result of an infection with a fungus, Pseudogymnoascus destructans.
Most fungi thrive in warm, humid conditions, but Pseudogymnoascus destructans is a “cold-loving” fungus. This trait makes it well adapted to growing in bats when their body temperature drops during hibernation and their immune system is suppressed.
Bats infected with Pseudogymnoascus destructans lose nutrients and fat reserves critical to surviving winter hibernation as the fungus grows in their skin. One of the first signs of white-nose syndrome is when bats wake up early from hibernation in search of food. The fungus also affects other metabolic factors, such as electrolyte levels.
After the discovery of Pseudogymnoascus destructans in North America, scientists searched for the fungus around the world and found it in European and Asian caves, where they believe it is native. Bats in those areas do not appear to be negatively affected by the fungus, probably because they evolved with the fungus and developed some immunity.
Pseudogymnoascus destructans was probably brought to the United States by travelers who explored caves in Europe and returned with contaminated equipment.
Myotis species could decline in Cace
Among the species most affected by white-nose syndrome are members of the diverse group of Myotis bats that I study. Most North American Myotis bats are found in western states, including Colorado.
Sixteen of the 45 bat species in North America are Myotis bats. Of those 16, 11 live in western North America alone and seven live in Colorado.
All of those Myotis bats could face massive population declines if exposed to white-nose syndrome.
Some North American bat species have lost more than 90% of their population to white-nose syndrome since 2006, including two found in Colorado:
Little brown bats, Myotis lucifugus, which are being considered by the U.S. Fish and Wildlife Service for listing as endangered, but are not yet listed.
Tricolor bats, Perimyotis subflavus, which are proposed as endangered, a status that indicates that the species is in danger of extinction and is awaiting a final determination to be on the endangered species list.
Colorado Tests for White Nose Syndrome
Colorado Parks and Wildlife has been testing for Pseudogymnoascus destructans since 2019.
In summer 2022, 25 bats were tested at Bent’s Old Fort National Historic Site in Otero County. Only one, a Yuma bat (Myotis yumanensis), tested positive for the fungus, although it showed no signs of illness.
A year later, in July 2023, a second Yuma bat at Bent’s Old Fort had signs of the fungus on its wings and was euthanized by the National Park Service. It was the first bat in Colorado confirmed with the disease.
A long-eared bat in Illinois is sampled for white-nose syndrome. Steve Taylor/University of Illinois/US Fish and Wildlife, CC BY
Prevent further spread
Since the disease is highly infectious in eastern bats, finding even a Colorado bat with white-nose syndrome raises alarm bells. But biologists know little about the population structure, hibernation sites, and hibernation behaviors of most western Myotis species. This is a major barrier to understanding the potential impact of white-nose syndrome on Colorado bats.
Researchers believe that western Myotis bats may hibernate in smaller sites, unlike many eastern bats that hibernate in large mines and dams. This behavior could mitigate the impact of the disease in the West, as groups that hibernate together may be smaller, limiting opportunities for the disease to spread.
Researchers also lack information on the genetic structure of western Myotis bat populations, which is a critically important aspect of management and conservation strategies.
Genetic research I published with a group of colleagues shows strong evidence that biologists are underestimating the number of Western Myotis species due to a phenomenon called “cryptic” or hidden species. This research suggests that there are Myotis bats that are similar in size and shape but genetically different. Since most species are identified by morphological characteristics, it is likely that the number of species recognized by science is too low.
For example, little brown bats are currently considered a single species, although research has found five independent lineages within this species.
The cryptic species most affected by white-nose syndrome in the East is Myotis lucifugus lucifugus.
Two of these cryptic species – M. l. lucifugus and M. l. carissima: Lives along the Front Range in Wyoming and Colorado, so contact between bats and the spread of the disease is possible there.
Researchers administer white-nose syndrome vaccine to a bat during a field trial. Public domain
What’s next for bats in Colorado?
Denver Museum of Nature and Science biologist John Demboski and I are partnering to analyze genetic samples from across Colorado. We will analyze tissues from diseased bats in Boulder and Larimer counties along with a large genetic data set of Myotis bats from across the state.
The results of our DNA analyzes will help predict how white-nose syndrome may spread among Colorado bat populations and where to direct efforts to protect them. Specifically, the results will clarify where the two cryptic species are found in the state and, therefore, where disease transmission might be occurring.
Some promising developments:
The US Geological Survey recently developed a vaccine against white nose syndrome and is currently evaluating its effectiveness. However, its promise is currently limited because use of the vaccine requires capturing all bats and giving them an oral dose of the drug, a nearly impossible task for free-ranging and nocturnal animal populations.
Some preliminary studies on eastern populations of little brown bats suggest that they may be developing resistance to the fungus. A small number survive.
Even if bats recover, rebuilding populations will take a long time. Most female bats produce only one offspring per year throughout their lifespan, which can range from 10 to more than 30 years. And most bat populations face other threats to their survival, such as habitat destruction, threats to prey populations, and persecution.
Tanya Dewey is an associate professor of biology at Colorado State University. This article is republished from The Conversation under a Creative Commons license. Read the original article.
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