Evolution: storm induced natural selection (Evolution)

by David Turell @, Thursday, July 26, 2018, 21:12 (612 days ago) @ David Turell

Studies of tree lizards after severe hurricanes shows how variation helps survival:


" biologists at Washington University in St. Louis have published a first-of-its-kind look at the physical characteristics of lizards that seem to make the difference between life and death in a hurricane,


"The team spent two days collecting just shy of 100 lizards on two separate islands, then measured their forelimbs, hindlimbs and core body lengths, and took pictures of their toe pads.

"The vital statistics of the survivors could be compared with the measurements of the general lizard population that had been collected before the storm.

"'The prediction was that if we saw any changes, they would be changes in the features that help lizards hold on -- they would be related to clinging ability," Donihue said. "For example, the sticky toe pads on their fingers and toes, maybe they would be larger."

"Comparing lizards collected before and after the storm, the researchers found that the survivor populations on both islands had larger toe pads on both their forelimbs and hindlimbs.

"The survivors had proportionately longer fore legs than the initial/pre-hurricane population, while the long bones in between their hips and knees on their back legs (their femurs) were shorter. The survivor population had smaller bodies, too. The observations were statistically significant and consistent at both island sites.


"The missing piece of the story is still a behavioral one. Researchers don't know what lizards actually do in the middle of a hurricane. Do they abandon their typical tree perches and go to the ground? Or do they try to seek cover in notches or crevices within the trees? Or do they just hang on?

"A pilot study exploring wind threshold provides some insight into this aspect of the lizard decision-making process.

"When the researchers exposed lizards from the survivor population to hurricane-force winds, the lizards almost uniformly swiveled around their perches to the side opposite from the wind source -- and just held on tight. As wind speeds increased, they lost hold with their hindlimbs first, and were left hanging by their forelimbs.

"It appears that lizards are built to cling, but because of their stance on the perch, their big hindlimbs make them vulnerable to getting pushed off by high winds. This could explain the pattern that survivor lizards have longer forelimbs and shorter hindlimbs after a hurricane, the researchers speculate."

Comment: This is just the result one would expect. We know populations vary and in this case the expected variation survived. A clear picture of the theory of variation and survival..

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