Lizard groups that frequently experience hurricanes evolve larger toepads than those that don’t, according to a new study.
That makes sense and had rather been assumed, but a definitive link has not been possible because hurricanes happen so infrequently that some scientists suspected their impact would be erased by natural selection favouring normal conditions.
Now researchers from Washington University in St. Louis, US, think they have the evidence after studying 12 island populations of Anolis sagrei lizards in the Caribbean and, separately, 188 Anolis species with ranges from Florida to Brazil.
And the effect is much broader than anyone anticipated, they report in a paper in the journal Proceedings of the National Academy of Science.
It is observable at the population level, at the species level and across a broad region of neotropics including the Caribbean, Central America and much of South America.
“We poked and prodded the data every which way to try to find if there were any holes in it and I’m convinced that it’s robust,” says co-author Jonathan Losos.
It’s a tricky thing to try to prove because it’s not possible to go back and actually see how the incidence of hurricanes has affected toepad size.
Instead, lead researcher Colin Donihue and colleagues looked at many different lizard populations with different histories, substituting a comparison across space for a comparison over time.
To quantify exposure to hurricanes, Alex Kowaleski from Penn State College used data from the National Oceanic and Atmospheric Administration on historical hurricane paths, primarily tapping the Atlantic Basin Hurricane Database (HURDAT 2) archive.
“Correcting for things like differences in body size, we found that island populations that had been hit by hurricanes more [frequently] had larger toepads,” Donihue says.
“Hurricanes seem to be having some sort of additive effect on the evolution of these lizards… the more hurricanes you have, the larger toepads you have, on average.”
But hurricanes are the only factor in play, the researchers note.
“Toepads might be a key trait for helping lizards hold on tight to the vegetation during storms, but there’s probably a trade-off between the traits that make you really good at surviving a hurricane and the traits that make you really good at being a lizard day in, day out,” says Donihue.
“Most of the selective pressure is to just be good at being a lizard: to go catch food, find a mate and avoid predators.
“These hurricane events are very infrequent and unpredictable, so we expect that there are other selective pressures that are acting on toepads. In other words, over time, these toepads are not going to turn into big snowshoes, or something like that. There’s a balance.”
And there may be a bigger story. “My best guess is that this isn’t just a lizard thing,” says Donihue. “For any other species affected by hurricanes where survival is non-random, you would predict this same kind of pattern occurring.”
Nick Carne is the editor of Cosmos Online and editorial manager for The Royal Institution of Australia.
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