Jul 26, 2018

Hurricanes force lizards to get a tighter grip on things

An anole lizard clings to a perch during simulated high winds. Credit: Colin Donihue and Nature Video.

Small-bodied anole lizards (Anolis scriptus) do not run and hide from oncoming hurricanes like one might think. Instead they cling to tree branches for survival, their bodies transforming into sails, anchored in place thanks to toe pads.

Why this matters: A new study published in the scientific journal Nature this week found that hurricanes can accelerate natural selection, favoring anole lizards that have larger toeholds and shorter rear legs. It also may help solve an enduring mystery about these commonly found lizards.

What they did: The possible selection of traits that allow these lizards to survive hurricanes was discovered serendipitously, when a team of researchers happened to be studying the species at the same time that Hurricanes Irma and Maria struck their habitat in the Turks and Caicos islands in 2017.

  • Colin Donihue, a postdoctoral researcher at Harvard University, and his colleagues had just finished a survey of anole lizards before the storms struck. They then returned to the islands 6 weeks after Hurricane Irma hit, and 3 weeks after Maria, to look at the differences between storm survivors and those that did not make it.
“We really didn’t know what to expect as we headed back to the Turks and Caicos."
— Colin Donihue, lead author of the new study.
  • The research team found that the surviving population had larger toe pads, longer forelimbs and shorter hind limbs on average than the lizards surveyed before the storms.
  • "The fact that we saw the same pattern on both Pine Cay and Water Cay is one of the big reasons we think this pattern wasn’t a fluke," Donihue said via email, referring to two islands in the Turks and Caicos. "The repeatability of the patterns was one of the linchpins of our argument for natural selection."
  • The researchers also carried out a crude experiment involving a leaf blower, some lizards, material resembling a branch or perch and netting.

By filming the lizards' behavior while being knocked around by strong winds, Donihue and his colleagues were able to see just how well the lizards were able to stay on branches despite the high winds.

“The lizards didn’t jump off the perch. They would hold on tight.”
— Donihue

What they found: As the winds increased, the scientists found that the lizards tucked their forelimbs close to their body, but jutted out their hind limbs at a 90-degree angle. Those hind limbs caught winds like a sail, and if they caught too much wind, the lizard would pop off the perch, and land harmlessly in the net in the experimental setting.

  • Hurricanes, Donihue said, can accelerate the process of natural section. He plans on another Turks and Caicos visit to see if the lizards' offspring resemble the hurricane survivors or the pre-storm lizards. He thinks they'll more closely resemble the pre-storm population, since short hind legs are not helpful for the lizards' mobility on the island.
  • “There are other consistent selective forces acting on these lizards,” Donihue said, adding that hurricanes would have to hit with a greater frequency to have a more lasting influence on the lizards' traits.

The intrigue: Interestingly, the new study may help shed light on a longstanding mystery of why anole lizards on these islands differ in their characteristics from anole species in South America and other areas.

“There’s been this long mystery about why the island lizards have such big overgrown toe pads relative to the lizards that live on the mainland. This study might point us toward an explanation.”
— Donihue

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