Podarcis muralis, or common wall lizards, were introduced to urban Cincinnati in the 1950’s, and the population has since exploded to hundreds of thousands of individuals in the city. These lizards are considered to be saxicolous, meaning that they spend most of their time on rocks or rock-like surfaces. They are specialized climbers, but unlike geckos and anoles, these lizards do not possess adhesive toepads. Instead, they rely on their sharp claws to interlock into the rough surfaces they climb on. Urbanization affects the surfaces that an animal interacts with and can also affect the temperature the animal experiences. How animals survive and thrive in urban environments has fascinated scientists as we continuously develop the natural world around us to accommodate humans. To better understand whether this population of lizards has experienced selective pressures to change their morphology, Princeton Vaughn and colleagues at Ohio Wesleyan University compared claw shape and clinging and climbing performance in common wall lizards. They aimed to understand if claw shape has changed in these lizards over time, and they also wanted to determine what factors may contribute to climbing and clinging performance.

The researchers collected adult male Podarcis muralis lizards in Cincinnati, OH. They measured the lizards’ clinging and climbing performance on various substrates (sandpaper, cork, and turf) and in different temperatures. Then they used powerful microscopes to compare the claw morphology of modern lizards to museum specimens from the 1980s.

(Above) Scanning electron microscopy image of a common wall lizard claw from Vaughn et al. (2023).

They discovered that claw shapes in modern common wall lizards is not different than lizards from ~40 years ago. This may mean that the lizards that were originally introduced to the area in the 1950s had already possessed claws that made climbing and clinging easy in their new environment. Alternatively, the original lizards may have experienced selective pressures against their claw shape in the first 30 years of living in Cincinnati, and by the time that the 1980s lizards were collected, claw shapes were already well adapted to city living. The researchers also found that clinging performance in modern common wall lizards was not affected by temperature, but instead was affected by their front limb lengths, with longer limbs allowing for better clinging. We see similar findings in other species of climbing lizards, too. Interestingly, climbing was affected by temperature, so lizards in warmer environments climbed faster than those that climbed in cooler temperatures. Longer claws also allow for faster climbing. There appeared to be a trade off between clinging and climbing performance in these lizards, where excellent climbers were worse at clinging and vice versa.

These results offer some amazing insights into how species may survive, and even thrive, in an increasingly urbanized world. Urbanization changes the environment that an animal lives in in several ways, but variation in body shape, claw shape, and behavior may allow for improved performance in these environments. Understanding the body shape and performance relationship can help us to predict how changes in environmental factors such as temperature and structural environment may affect a population. This knowledge can help researchers to understand how to protect at risk populations despite increasing human activity, or to understand how urbanization may cause changes in a population’s morphology.

Amanda M. Palecek-McClung is a PhD candidate at Clemson University. She studies functional morphology, biomechanics, and adhesion mechanisms in fish and other vertebrates. You can find more about her at ampalecek.weebly.com or contact her at apalece@g.clemson.edu.