Wednesday, October 10, 2018

On the Getting of Big Feet, Long Forelimbs and Short Forelimbs

Image result for male anole lizard
Environmental & Science Education
Biological Diversity
Edward Hessler

Perhaps you have seen a film of lizards hanging on for dear life in what appear gale force winds.

It is quite likely that the film is of experiments undertaken by Colin Donihue, a post-doctoral student at Harvard who studies male anole lizards (Anolis scriptus) living on two small islands SE of the Bahamas. Just after returning home, hurricanes Irma and Maria battered the two islands. A few weeks later, Donihue and his colleagues returned interested to learn whether his research critters had survived.

They had. This led Donihue to take advantage of an opportunity. He did a before-and-after survey. As noted in the Nature editorial for July 25, 2018, The researchers hadn’t marked the lizards, so they couldn’t identify and track the fate of individuals. But they found clear trends of natural selection in action. In general, anoles found after the storms had bigger toepads, longer forelimbs and shorter hindlimbs than did lizards collected before the storm.

And these observations led Donihue's team to do an experiment for which they needed a perch, some lizards, a leaf blower and a way to measure the windspeed at which the critters were knocked off. No lizards were harmed in the conduct of this experiment. When blown off the perch they fell into padding.

The takeaway? The research hypothesis was supported by the evidence."Natural selection interfered with the way in which these traits were spread across the population." Anoles with smaller toepads, longer hindlimbs and shorter forelimbs were less able to hang-on while those with bigger toepads, shorter hindlimbs and longer forelimbs were more able to hang-on.

This is how the abstract of the paper puts it.  Our serendipitous study, which to our knowledge is the first to use an immediately before and after comparison to investigate selection caused by hurricanes, demonstrates that hurricanes can induce phenotypic* change in a population and strongly implicates natural selection as the cause. In the decades ahead, as extreme climate events are predicted to become more intense and prevalent, our understanding of evolutionary dynamics needs to incorporate the effects of these potentially severe selective episodes.

More information may be found in the Nature editorial puts this work into an evolutionary perspective, provides a link to the original paper (behind a paywall). In addition, National Geographic has some footage of the lizards in their natural habitat and their behavior in artificial storm conditions.

*These are observable traits or characteristics such as size, color, shape, etc.

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