How a population of lizards was forever changed by 2017's extreme hurricane season

The extreme winds from last year's destructive hurricane season seems to have come with some unexpected consequences.

Hurricanes Irma and Maria — some of the most destructive in Caribbean history — may have forced rapid evolutionary change in a native population of small-bodied anole lizards (Anolis scriptus), researchers in the West Indies say.

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According to a new study about the lizards released in Nature this week, much of the surviving population of lizards after the hurricanes have larger toe pads, longer forelimbs, and shorter hind limbs than the average anole.

Still of lizard clinging to an experimental perch in hurricane-force winds. Wind speed meter is displaying in miles per hour. (Credit: Colin Donihue)

Those long forelimbs and toe pads would have allowed these anoles to cling to surfaces during gale-force winds brought by the hurricanes.

Effectively, this means that the hurricanes forced natural selection in real-time, the scientists suggest.

“Day in and day out, natural selection favors those lizards who can run around branches, find food, and find mates,” lead author of the study Colin Donihue said in an interview.

“It’s only in these atypical instances like hurricanes that we would be able to see a shift away from historical selection.”

With the frequency and intensity of hurricanes ramping up, species within affected ecosystems are being forced to adapt to extreme conditions.

It's even possible that certain adaptations might aid survival chances in one instance, and hurt them in another, Martha Muñoz, an evolutionary biologist not affiliated with the study, said.

"One trait can enable survivorship in a storm, like shorter hind limbs, but on a daily basis longer hind limbs will help these animals escape predation because it helps them run faster," Muñoz said.

But it would take an entirely different study to determine how this selection affects the future of the species, and findings like this are rare.

In fact, the data from Donihue and colleagues was due to a coincidence. They had just completed a survey of the lizard population immediately before the hurricanes swept through the island. After the hurricanes, they recognized that they had a unique opportunity, and decided to return.

The hurricanes key to their research, Irma and Maria, have gone down as two of the worst natural disasters to affect the Caribbean — where it's possible that almost 5,000 people have lost their lives. And a year later, some places affected, like Puerto Rico and Dominica, still don't have power.

See photos of Irma's aftermath:

The literature on the impact of extreme weather events on localized animal populations is a relatively scarce, but burgeoning field due to increased extreme weather.

A study published in 2017 found that a polar vortex that hit the Southeast in 2014 drove selection in a population of green anole lizard.

The researchers behind that study were able to survey the population of lizards before and after the weather event, and found that the surviving population of lizards had many of the genetic qualities in northern populations of the same species. For example, the surviving lizards had an abnormally high tolerance for cold weather in that region.

Aside from these two studies, there isn’t much known about how fast-acting extreme weather events change animal populations on a large scale.

But with extreme weather events becoming more and more common as human-caused climate change continues, it’s likely that the common agents of natural selection will shift toward those which influence survival during these catastrophes.

“The key to this study is understanding that natural selection is on-going and is constantly in the background,” Donihue said

The next step? Muñoz suggests going back to the island a year later and measuring the new generation of lizards to see if this natural selection has truly translated into evolution.

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