USF researchers find island snakes adapt venom

Scientists at the University of South Florida have discovered surprising new clues about how animals adapt to habitat loss by studying rattlesnake venom.

Their study, announced Wednesday morning, found that rattlesnakes on larger islands with more biodiversity produce venom with fewer and more focused toxins. The results challenge long-held evolutionary theories.

While the study occurred on remote islands off the California coast, the lead researcher’s work primarily focuses on coastal areas of Pinellas County and the eastern United States. Mark Magres, an assistant professor in the integrative biology department, noted the data will also help ensure antivenoms remain effective and affordable.

“Antivenom is only effective against the venoms used to produce it,” Magres said. “But you can change what venoms are used to produce it if you find a hole. So, that’s kind of what we’re looking for now.”

Magres and doctoral student Samuel Hirst began studying snake venom in May 2022. The overarching goal was to discern how rapid environmental changes – often caused by human activity – influence species evolution at a molecular level.

Hirst said 11 uninhabited islands in the Gulf of California provided a naturally fragmented environment. Hurricanes and overdevelopment play a similar role locally.

Venom plays a critical role in survival, hunting and reproduction, and provides a valuable tool for studying broader evolutionary trends. Hirst said he and most other scientists thought rattlesnakes on larger islands would develop more complex venom.

“We actually found an opposite pattern with that,” he added. “Less complex venom indicates to us that these species may not be as equipped to evolve.”

Doctoral student Samuel Hirst on a remote island in the Gulf of California. Photo: USF.

The findings could have a significant impact on conservation efforts. Magres said environmental experts frequently debate if it is better to preserve large swaths of land or “several smaller chunks of habitat.”

The common perception is that expansive wildlife refuges increase biodiversity. While true, Magres said the increased competition could harm a specific species.

He noted that island snakes, like those found around Pinellas County, typically become less aggressive as there are fewer predators. “Diamondback rattlesnakes on Caladesi Island – there’s nothing out there that scares them once they’re an adult,” Magres said.

“There is nothing out there that’s going to wrangle with a five, six-foot rattlesnake. But the venom is different, and that is important.”

While bites are rare, Pinellas County’s barrier islands receive millions of visitors annually. Antivenom is only effective against the venoms used in the manufacturing process.

Hirst is working with a colleague in Mexico to discern if current antivenoms are effective against evolved snake venom. They are also conducting tests to see if symptoms have changed.

Magres explained that pharmaceutical companies create a cocktail of antivenom from five common snake species. The time-consuming process is expensive, and the result is only stable for a short period, “before you need to toss it and use something else.”

He said antivenom administered locally would also work well in Arizona. However, it would lose efficacy against an island snake with unique venom.

“And, unfortunately, that’s really our only course of treatment when it comes to a snake bite,” Magres said.

Rattlesnake venom reflects what they eat and how they survive in the wild. Photo: USF.

Rattlesnakes are adept at floating and swimming, and storms often push them and other animals, like several new tortoises at Fort De Soto Park, to new island habitats. Magres said venomous snakes were prevalent on local barrier islands before Hurricanes Helene and Milton.

Now, on a “good day,” he will find two or three in the morning. “We actually haven’t had much sampling success since those hurricanes,” he said.

Magres also wonders if diamondback and tortoise populations will rebound as humans develop coastal habitats. “It’s easy to measure the ecological impacts of destroying the environment,” he said.

“It’s easy to go in and measure what species aren’t there anymore, but how does that affect their evolution 20, 30, 40 or 50 generations from now?” Magres continued. “That’s what’s important if we’re thinking about preventing extinction, and that’s something really difficult to measure.”

He and Hirst believe islands serve as proxies for fragmented environments. Magres said researchers will test their findings on other wildlife and begin to reach a consensus on how animals evolve amid habitat loss.

The National Geographic Society funded and supported their study. Magres said the islands were a five-hour boat ride from the nearest town and offered no shade, facilities or cell phone reception.

The researchers packed extensive equipment to capture venomous snakes and collect samples. “We got to go play Robinson Crusoe for several weeks a couple of times throughout the last several years,” Magres said of the fictional adventurer. “So, it was a lot of fun.”