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SIU doctoral student researches fungus that sickens hibernating snakes

Man holding snake
Provided by Tim Crosby
/
SIU News
Adrian Macedo, a doctoral student at Southern Illinois University Carbondale, works with a northern cottomouth snake in the Cache River Basin this fall. Macedo is looking into Ophidiomyces ophiodiicola, a fungus that causes skin and tissue breakdown, leading to lesions typically on the head and face of snakes. Severely infected snakes often lose the ability to eat and end up dying, while others clear the infection after shedding their skins. Below, Adrian Macedo, a doctoral student at Southern Illinois University Carbondale, and his adviser, Robin Warne, associate professor in the School of Biological Sciences, work with a northern cottonmouth snake in the Cache River Basin this fall.

CARBONDALE, Ill. – Cold temperatures are the enemy of snakes – ectotherms that get their body heat from the environment. A Southern Illinois University Carbondale student, however, is trying to find out more about another deadly adversary awaiting them in the warmer crevices of the sandstone cliffs where they typically ride out the winter.

Adrian Macedo, a doctoral student from the small mountain community of Cobb in northern California, is looking into Ophidiomyces ophiodiicola, a fungus that causes skin and tissue breakdown, leading to lesions typically on the head and face of snakes. Severely infected snakes often lose the ability to eat and end up dying, while others clear the infection after shedding their skins.

Working in a well-known Southern Illinois watershed, Macedo hopes to find ways to mitigate the disease, thereby protecting the hearty regional snake population. Often misunderstood and even vilified, the animals play a significant role in the area’s ecosystem.

“Reptiles remain some of the longest-lived vertebrates on earth, with immune systems that have been shown to cure forms of cancer and venom that is vital in making anti-venom that can save lives,” he said. “Snakes make up a huge portion of the living biomass of the swamps where I’m working, and they serve a vital role in controlling populations of fish, mice and amphibians. Because they also live in both wetland and terrestrial habitats, they can serve as indicators of both aquatic and terrestrial environmental health.”

A growing concern

Researchers first described the disease in 2006 based on cases in New Hampshire, where it has been decimating the timber rattlesnake population. By 2008, snake fungal disease, or SFD, also was found in Southern Illinois, where it heavily impacted the already-threatened massasauga rattlesnake population.

No one knows how long the disease has actually been around. Recent advances in DNA technology, however, helped researchers discover that what people typically observed as “hibernation scars” on snakes emerging from their winter hiding places were really signs of a past fungal infection and the lesions its causes. Such technology also reveals what appears to be an increase in the disease’s prevalence.

“This might be because of thousands of snakes all coalescing in one area and spreading the disease among themselves,” Macedo said. “It could be a combination of many factors that are leading to this increased infection rate during hibernation periods.”

Shelter from the cold

In the northern latitudes, winter is particularly tough on ectotherms, which don’t have the ability to regulate their body temperatures metabolically and instead rely on behaviors – such as basking in the sun – maintain the ideal range. If they become too cold, snakes lose the ability to move fast and have a difficult time catching and even effectively digesting food.

In Southern Illinois, this means snakes begin heading for the hills – the limestone bluffs and formations prevalent in the area, which contain numerous caves and crevices – called hibernacula – where temperatures remain considerably more moderate through the cold months.

In response to this semiannual migration, for instance, wildlife officials twice a year shut down “Snake Road” in western Jackson County to protect migrating snakes. In the fall, the snakes leave the nearby swampy area, heading for the sandstone bluffs lying just across the road. Then in spring, officials close the road again as the snakes leave their shelter and crawl back into their warm-weather habitat.

“The biannual snake migrations in Southern Illinois are an incredible natural phenomenon,” Macedo said. “Cottonmouths migrate from the swamp and climb up the slope to the hibernacula. In the fall, when all the leaves are on the ground, you can actually hear them slithering up the hillside one after another.”

Despite finding shelter, cold temperatures reduce metabolism, making it more difficult for snakes to fight off infection. Along this line, many scientists have begun studying animals’ microbiomes – the commensal bacteria and fungi communities that live in the gut and skin that may provide protection against disease and assist in immune responses.

“But very little is known about snake microbiomes, and nothing is known about how they are affected during hibernation,” Macedo said. “Since snakes stop eating during hibernation in dark, cool crevices underground, snake microbiome communities are likely greatly reduced during hibernation, and this may in turn affect the snake’s susceptibility to disease.”

A unique setting

Macedo’s research centers on the snakes’ immune function, their microbiomes and presence of SFD during the entire hibernation window – before, during and after hibernation. Working in the Cache River Basin, which ranges from Anna, Illinois, to the confluence of the Ohio and Mississippi Rivers in Southern Illinois, Macedo is examining how hibernation affects snake physiology and consequently their immune function, microbiomes and how they handle disease.

“The Cache River Basin contains the largest northernmost bald cypress-tupelo swamp in North America,” Macedo said. “It’s like the Florida/Louisiana bayou of the Midwest.”

Of the original 21 million acres of bottomland swamps from Southern Illinois to coastal Louisiana, however, only 20% remain. What’s left are remnant patches of swamp scattered about, including the Cache River Basin at the intersection of four physiographic provinces. The unique setting contributes to diverse habitats, plant and animal life.

Macedo specifically is working in a portion of the coastal plain ecoregion, which is designated as the world’s 36th highest biodiversity hotspot. The area provides critical habitat making up 91% of Illinois’ remaining forested swamp and is used by 75% of all native amphibian and reptile species in Illinois.

Working with his adviser, Robin Warne, associate professor in the School of Biological Sciences, Macedo began collecting data this fall during the migration. He hopes to complete the study in two years and is aiming for a career as a research professor.

Working in the field

Cache River snakes include venomous northern cottonmouth, copperheads, and timber rattlesnakes as well as numerous nonvenomous reptiles such as North American racers, common water snakes, plain-bellied water snakes and gray rat snakes.

Macedo works with all of the ones he encounters, capturing and swabbing their skin and cloaca, a common chamber through which the snake passes feces, urine and reproductive products, to obtain samples for microbiome analysis and to test for SFD. He also takes a small blood sample from the tail using a needle and syringe.

“Lastly, I look for signs of disease, note the sex of the snake, and measure its length and weight,” he said. “Then I release it where it was found, and all equipment is sanitized before I catch the next one.”

Although he encounters a variety of species, the northern cottonmouth is the most frequent visitor in the study area, and it comes with some challenges. While not aggressive, it does not flee from humans and instead flattens its body and vibrates its tail before typically rearing its head and opening its mouth to expose its white, “cotton” interior.

The danger is real: The snake comes equipped with a potent cytotoxic venom that destroys tissue and causes severe pain, swelling and ecchymosis (a type of bruise). Deaths are rare, but bites can leave scars and on occasion lead to amputation.

To avoid such nasty outcomes, Macedo uses specialized tongs or snake hooks to hold the animals, and snake tubes to contain them during study.

“The work is potentially dangerous and requires specialized training and constant awareness,” he said. “With cottonmouths, I fit the open end of the tube over its head, then using the tongs or snake hook, I nudge it until it gets about halfway up the tube. Once in that position, the snake can be safely held at the base of the tube ensuring it cannot back out or turn around in the tube.”

Lab work follows

The labors of the field come to fruition in the laboratory, where Macedo applies various scientific techniques aimed at uncovering the physiological forces at work.

Using his collected blood samples, Macedo checks the white cell count to obtain a baseline of the specimen’s immune capacity. He then spins the sample to separate the red blood cells from the plasma, using the latter for further immunology tests.

Macedo then extracts DNA from the skin and cloaca swabs, quantifying how much of the SFD-causing fungus is present. The DNA samples further show which bacteria and fungus families are present in each specimen, which allows him to analyze the group diversity and microbiome communities.

“SIU has allowed me to pursue research that is often overlooked as well as develop skills I plan to use in the future to better understand the lives of these animals and assist in their conservation,” he said.

Note to editors: Adrian Macedo’s last name is pronounced “Mah Say Doh.”

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