Sticky Toes Unleash Life in Trees | Source

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Many lizards are phenomenal climbers. Their sharp, curved claws are ideal for clinging to tree trunks, rocks and other rough surfaces. However, in the precarious world of the treetops – filled with slippery leaves and unstable branches – three particular groups of lizards possess a remarkable evolutionary accessory: sticky pads on their fingers and toes.

Sticky pads evolved independently in geckos, skinks and Anolis lizards – producing tree acrobats specially adapted for life in the forest canopy. Scientists have long viewed sticky pads as a “key evolutionary innovation” that allows arboreal lizards to interact with the environment in ways that many lizards without pads cannot.

Miller (left) and Stroud

Yet some padless lizards have adopted the canopy lifestyle, an observation that has puzzled scientists for decades. Biologists Aryeh Miller and James Stroud of Washington University in St. Louis investigated whether lizards with pads had an evolutionary life advantage in trees over their non-padded counterparts.

They analyzed data from 2,600 species of lizards around the world and found that while hundreds of different types of lizards evolved independent of arboreal lifestyles, species that possessed sticky pads prevailed.

“Lizards with toes have a greater ecological advantage in the arboreal environment,” said Miller, a graduate student of the Evolution, Ecology and Population Biology program at the University of Washington and lead author of the study. “Toes are essentially a biological superpower allowing lizards to access new resources that lizards without toes cannot.”

“We have found that lizards with sticky legs dominate the arboreal environment. Once adapted to life in trees, they rarely go away, ”said Stroud, postdoctoral associate researcher in the arts and sciences, who is the lead author of the article. “Conversely, lizards without sticky pads frequently switch from life in trees to life on the ground. “

The study is published in Systematic Biology.

The evolution of toepad shapes the diversity of lizards

“Scientists have long questioned the role that the origin of key innovation plays in subsequent evolutionary diversification. Lizards are an excellent type of organism for such studies because of their exceptional species richness and the incredible extent of anatomical variation and habitat use, ”said Jonathan Losos, distinguished professor at William H. Danforth University and professor of biology in arts and sciences. as director of the Living Earth Collaborative at the University of Washington.

Using a recently published database of habitat use for almost all lizard species around the world, researchers were able to perform a comprehensive analysis of the evolution of toepads in the context of the use of the habitat of lizards – for the first time, the evolutionary relationships between which lizards live. trees and which have not become clear.

Lizards with sticky toes have a greater grip capacity. The tree canopy specialist, the American green anole (Anolis carolinensis), in the photo on the left, has enlarged pads, while the Ibiza wall lizard (Podarcis pityusensis), on the right, lacks such adhesive structures. (Photo courtesy of Day’s Edge Productions)

“Miller and Stroud have developed an elegant new approach to understanding this diversity and the role anatomical evolution plays in shaping the great diversity of lizard species. This work will be a model for researchers working on many types of plants, animals and microbes, ”Losos added.

Miller, who led the analysis, is the first to discover that species have evolved to specialized life in trees at least 100 times in thousands of lizards. In other words, it is easy scalable for a lizard to become an arboreal lizard.

What is difficult is to stay (pun intended!). The toes only evolve after the lizards have entered the trees, not before. And lizards without pads will leave trees at a high frequency – much higher than pad lizards.

“There are hundreds of lizards living in the trees, but over time many of these species end up leaving for life on the ground because, presumably, they interact with these stuffed lizards which have a greater advantage,” he said. Stroud said.

The next step in this research is to find out exactly what padded lizards can do that their padless parents can’t. Scientists can learn more by observing animals in their natural habitat.

“Analyzing evolutionary relationships can tell us a lot, but then we have to go into nature – to see what parts of the environment lizards use and why these evolutionary relationships exist,” Miller said.


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