What rattlesnake venom can teach us about evolution: New USF study

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TAMPA, Fla. (Embrgoed for publication until April 23, 2025) – Researchers at the University of South Florida are uncovering new clues about how animals evolve by studying rattlesnake venom — and what they’ve found could help us better protect wildlife in a world increasingly shaped by human activity.

In their latest study, published in Evolution, they found that some rattlesnakes are producing simpler venoms containing fewer and more focused toxin families than complex venoms -- a surprising discovery that challenges long-held ideas about how living alongside a variety of other species influences evolution.

Mark Margres, assistant professor in the department of integrative biology, and doctoral student Samuel Hirst explored 11 uninhabited islands in the Gulf of California – pitching tents along the beach and exploring with head lamps after the sunset and the islands cooled enough for the snakes to come out. With help from scientists in Mexico and California, the team collected venom from 83 rattlesnakes — some stretching up to four feet long — to study how the makeup of their venom reflects what they eat and how they survive in the wild.

“The Baja California islands are pristine and largely untouched by human activity, making them an extraordinary place to study evolutionary processes in isolation,” Hirst said. “We initially hypothesized that larger islands, which support greater biodiversity and prey diversity, would be associated with more complex venoms, which are better suited for more diverse prey. However, we found the opposite pattern.

This unexpected result suggests that factors such as competition or ecological specialization may be at play, opening exciting avenues for future research.”

The study found that on islands with more space and more competition, rattlesnake venom became more specialized. As animals adapt to reduce competition, rattlesnakes may evolve venom that’s finely tuned to specific prey. This challenges long-standing ideas about evolution and offers fresh insight into how species and their traits adapt in fragmented environments.

"Habitat fragmentation is like breaking apart a completed puzzle. A healthy, intact ecosystem is like a 1,000-piece puzzle where every piece is in place — you can clearly see the full picture,” Margres said. “But when you start fragmenting it, pieces go missing or get rearranged, and the image becomes distorted. That distortion represents the disruption of ecosystem function."

This research offers a rare, measurable example of the effects of rapid changes in biodiversity — the variety of all living things in a particular area, including animals, plants, insects and even microscopic organisms. These changes, often driven by human activity, can affect not just which species live in an area, but how their bodies work on a molecular level. Because venom plays a key role in survival, hunting and reproduction, it’s a valuable tool for studying broader evolutionary trends.

“This isn’t just about rattlesnakes -- it’s about understanding the fundamental ways life evolves when isolation and biodiversity start to shift,” said Margres, who also studies rattlesnakes on coastal islands in the eastern U.S., including Honeymoon and Caladesi in Tampa Bay.

The study has provided an extensive amount of data, allowing Margres and Hirst to continue their research and further explore how island systems can inform habitat fragmentation and its effects on genetic diversity. They’re also working to test how well current Mexican antivenoms neutralize the unique venoms found on these islands -- a necessary step toward making sure that if someone is bitten, local hospitals have the correct antivenom to treat them effectively.

“Right now, we don’t know how well existing antivenoms work against these island venoms — but our research is helping to change that,” Margres said.

This study was funded and supported by the National Geographic Society and done in collaboration with the support of Mexico’s Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT) and Comisión Nacional de Áreas Naturales Protegidas (CONANP), whose conservation efforts protect these ecologically significant islands.

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About the University of South Florida

The University of South Florida, a high-impact research university dedicated to student success and committed to community engagement, generates an annual economic impact of more than $6 billion. Across campuses in Tampa, St. Petersburg, Sarasota-Manatee and USF Health, USF serves approximately 50,000 students who represent nearly 150 different countries. U.S. News & World Report has ranked USF as one of the nation’s top 50 public universities for six consecutive years and, for the second straight year, as the best value university in Florida. In 2023, USF became the first public university in Florida in nearly 40 years to be invited to join the Association of American Universities, a group of the leading 3% of universities in the United States and Canada. With an all-time high of $738 million in research funding in 2024 and a ranking as a top 20 public university for producing new U.S. patents, USF is a leader in solving global problems and improving lives. USF is a member of the American Athletic Conference. Learn more at www.usf.edu.