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Hurricanes have warped how lizards evolve, and still throw in a twist
When a hurricane is blowing away everything in sight, your instincts are going to tell you to hold on –if you’re a lizard.
Lizards have to keep a deathgrip on something if they don’t want to literally get carried away. The survivors are usually the ones whose toes can keep them stuck to a tree branch or something else until the wind dies down. After studying different species of anole lizards that live on the tropical mainland and the Caribbean islands, scientists from Washington University in St. Louis found that the island lizards have evolved larger toepads to get a grip in the face of killer winds. Evolution is clearly something that doesn’t always start with “millions of years ago”.
“Extreme climate events can act as agents of natural selection,” said WUSTL biology postdoc Colin Donohue, in a study recently published in PNAS. “Lizards hit by Hurricanes Irma and Maria in 2017 passed on their large, strong-gripping toepads to the next generation of lizards.”
A previous study by Donohue had found that lizards with longer legs (even if that is more glamorous by human standards) were less likely to survive a hurricane ripping through the islands than their shorter-legged counterparts with larger toe pads. Suspecting that frequent hurricanes in the tropics can affect lizard morphology, he and his team were able to prove that hurricanes in Turks & Caicos had influenced the evolution of the brown anole. Surviving lizards kept passing on their superior toe pads to upgrade the next generation.
Hurricanes are definitely more common in the tropics, but they never happened frequently enough in the past for scientists to actually believe lizards would evolve to survive them. The assumption was that the effects of hurricanes just didn’t last long enough to influence natural selection, which favors animals better equipped to survive in a certain situation. Those who make it are more likely to breed and pass on the genes that kept them alive. That one anole species was just the beginning, because even distantly related species of anoles exhibited this change.
Even more impressive is that a change has been noticed in only 70 years, since Donohue’s team looked into NOAA data and hundreds of anole toepad measurements going back to the 1950s. Anole populations in areas hit by hurricanes more often usually had larger toe pads. Anole toes grip similarly to those of geckoes. Toe pad size and claw size in anoles are closely related, meaning that they must have evolved together—and it makes sense. These parts of an anole’s morphology are already related to where that particular species or population of a species might live. Throw in a hurricane, and guess what is going to determine who lives and who dies.
“Given this short-term effect of hurricanes, we then asked whether populations and species that more frequently experienced hurricanes have larger toepads,” Donohue said, adding that “toepad area positively correlates with hurricane activity for both 12 island populations of Anolis sagrei and 188 Anolis species throughout the Neotropics.”
Will anole topeads keep evolving? That remains unknown. When hurricanes aren’t ravaging their habitats, lizards still have to be good at, you know, being lizards. Besides climbing and gripping, they also need to be able to catch food, attract a mate and flee predators. Evolution is a trade-off between what makes the anoles weather a storm and what keeps them alive when the forecast isn’t so grim. Donohue believes it is possible that such weather related morphological changes occur in other tropical flora and fauna, especially with the rise of precipitation caused by climate change.
While it is unlikely we’ll be seeing lizards with disproportionately enormous clown feet any time soon, when a hurricane hits, they aren’t just going to hang loose.