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Venomous wide-bodied rattlesnakes on several serpent-infested Mexican islands have provided biologists from Florida with surprising new evidence about the evolution of animals.
A team from the University of South Florida joined scientists from Mexico on three separate camping expeditions to 11 uninhabited islands in the Gulf of California, a region known as the world’s biggest rattlesnake nest.
Upon capturing dozens of the snakes in cooler temperatures after sunset and extracting and analyzing their venom, they made an unexpected discovery. Rather than developing more complex toxins for a wide variety of potential prey, as the researchers assumed, the rattlesnakes were instead producing simpler venoms containing fewer and more focused venoms.
The findings indicate that, over time, the snakes were finely tuning their venom for more specific prey. The revelation challenges longstanding ideas about evolution and offers fresh insight into how species adapt naturally in habitats fragmented by geography, human activity or natural disasters.
“This isn’t just about rattlesnakes, it’s about understanding the fundamental ways life evolves when isolation and biodiversity start to shift,” said Mark Margres, assistant professor at USF’s department of integrative biology.
“We expected that snakes in areas with more biodiversity would have more complex venoms because they’re eating more of that available diversity. Studying a trait that can rapidly evolve and reflect the biodiversity of that habitat patch is really powerful.
“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. 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.”
Samuel Hirst, a USF doctoral student who helped organize the expeditions with the National Geographic Society, conservation partners in Mexico, and the Mexican government, said the islands were a perfect habitat for the study.
“The Baja California islands are pristine and largely untouched by human activity, making them an extraordinary place to study evolutionary processes in isolation,” he said.
“We initially hypothesized that the larger islands would be associated with more complex venoms, 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.”
Margres added that rattlesnake venom had been shown to evolve rapidly.
“Evolution typically requires many generations, and all of these changes, the most severe human impacts, are happening right now,” he said.
“We don’t want to wait 20, 100, 1,000 years from now to understand the evolutionary consequences.”
The USF research was published this week in Evolution, part of the Oxford University Press’s academic research platform.
In all, the team captured and released 83 rattlesnakes, the largest 4ft in length, belonging to four separate species, speckled, red diamond, Baja California and south-western speckled. The snakes were stimulated to bite on special sample collection cups and the venoms dried and analyzed.
Margres said that the next steps in his team’s research would be to look at the snake’s blood.
“Our next question is whether we see the same thing at the genetic level,” he said.
“When we catch these rattlesnakes we measure them, we see what sex they are, we collect a venom sample, but we also collect a blood sample.
“Unlike mammals, reptiles have nucleated blood cells and that means they have a ton of DNA. We’ll look at the genomes of each of these individual snakes and see if genetic diversity shows similar patterns.
“In conservation biology we want to maintain or increase genetic variation for endangered species, because things like inbreeding can have really dire consequences, so we want to see things like island area, do they also predict genetic diversity, not just venom diversity?”
