Sticky toes unlock life in the trees

Date:
August 5, 2021
Source:
Washington University in St. Louis
Summary:
Biologists analyzed data from 2,600 lizard species worldwide and
discovered that, while hundreds of different types of lizards have
independently evolved arboreal lifestyles, species that possessed
sticky toepads prevailed.



FULL STORY ==========================================================================
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 tree tops -- filled with slippery leaves
and unstable branches -- three peculiar groups of lizards possess a
remarkable evolutionary accessory: sticky pads on their fingers and toes.


========================================================================== Sticky toepads have independently evolved in geckos, skinks and Anolis
lizards -- producing tree acrobats specially adapted to life in the
forest canopy.

Scientists have long considered sticky toepads an 'evolutionary key
innovation' that allow arboreal lizards to interact with the environment
in ways that many padless lizards cannot.

Yet, some lizards without toepads have adopted the canopy lifestyle, an observation that has puzzled scientists for decades. Biologists Aryeh
Miller and James Stroud at Washington University in St. Louis set out
to find if lizards with toepads had an evolutionary advantage for life
in the trees relative to their padless counterparts.

They analyzed data from 2,600 lizard species worldwide and discovered
that, while hundreds of different types of lizards have independently
evolved arboreal lifestyles, species that possessed sticky toepads
prevailed.

"Lizards with toepads have a greater ecological advantage in the arboreal environment," said Miller, a graduate student in the Evolution, Ecology,
and Population Biology program at Washington University and lead author on
the study. "Toepads are essentially a biological superpower for lizards to access new resources that lizards without toepads cannot." "We found that lizards with sticky feet dominate the arboreal environment. Once adapted
to life in the trees, they rarely leave," said Stroud, a postdoctoral
research associate in Arts & Sciences, who is the senior author on
the paper.

"Conversely, lizards without sticky toepads frequently transition away
from living in trees to living on the ground." The study is published
in Systematic Biology.



========================================================================== Toepad evolution shapes lizard diversity "Scientists have long wondered
about the role that the origin of key innovation plays in subsequent evolutionary diversification. Lizards are an excellent type of organism
for such studies due to their exceptional species richness and the
incredible extent of anatomical variation and habitat use," said Jonathan Losos, the William H. Danforth Distinguished University Professor and
professor of biology in Arts & Sciences and director of the Living Earth Collaborative at Washington University.

Using a recently published database of habitat use for nearly every
lizard species across the globe, the researchers were able to perform
a comprehensive analysis of toepad evolution in the context of lizard
habitat use -- for the first time, the evolutionary relationships between
which lizards live in trees and which do not became clear.

"Miller and Stroud have developed an elegant new approach to understand
this diversity and the role that anatomical evolution plays in shaping the great diversity of lizard kind. 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 find that species have
evolved for specialized life in trees at least 100 times in thousands
of lizards. In other words, it is evolutionarily easy for a lizard to
become a tree lizard.



========================================================================== What's difficult is sticking around (pun intended!). Toepads don't evolve
until after lizards get into the trees, not before. And padless lizards
will leave trees at a high frequency -- much higher than padbearing
lizards.

"There are hundreds of lizards living in the trees, but over evolutionary
time many of those species end up leaving for life on the ground because, presumably, they interact with these padded lizards that have a greater advantage," Stroud said.

The next step in this research is to find out exactly what padbearing
lizards can do that their padless relatives can't. Scientists can learn
about this by watching the animals in their natural habitat.

"Analyzing evolutionary relationships can tell us a lot, but next we
need to go out into nature -- to see what parts of the environment the
lizards use and why these evolutionary relationships exist," Miller said.

========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Marta
Wegorzewska. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Aryeh H Miller, James T Stroud. Novel Tests of the Key Innovation
Hypothesis: Adhesive Toepads in Arboreal Lizards. Systematic
Biology, 2021; DOI: 10.1093/sysbio/syab041 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210805104557.htm

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