Making the best of a difficult year
With a group of other students here at Ohio Wesleyan University, I had successfully written a grant to research the common wall lizard (Podarcis muralis) in the south of France for the summer of 2020. Like so many plans that year, this trip was canceled. While the streets of Cincinnati aren’t quite as scenic as the Pyrenees Mountains, we made the best of the situation. The wall lizards themselves offered a great model of adaptability to new environments!
Invading the city
In order to understand why certain organisms are better invaders than others, we must first understand how organisms interact with and change in response to their new environment. We studied the common wall lizard (Podarcis muralis) in an effort to understand three main questions: (1) How does morphology change over time within a population living in a novel environment, (2) How do these morphological shifts influence sprint performance, and (3) How does sprint performance change in a variety of conditions? These are important questions to ask because the answers not only provide insight into why invaders are successful, but as the world is becoming more urbanized, it is increasingly necessary to understand how species respond to urban environments.
The common wall lizard is abundant and widespread throughout southern Europe but has invaded several places including England, Germany, and several locations in North America, including Cincinnati, Ohio, USA. The common wall lizard was introduced into Cincinnati in the early 1950s when a young boy released several into a yard following a vacation to Northern Italy. In the present day, they have exploded in population and are extremely abundant in Cincinnati and the surrounding areas. To investigate how morphology has changed over time, we used museum specimens collected in the 1980s (courtesy of the Cincinnati Museum Center), 30 years after introduction, and compared them with present-day lizards, 70 years after introduction.
Testing performance
To test the effect of morphology, substrate, and running condition on sprint performance, we built a racetrack that could be modified to test a full-factorial design of substrate type (cork bark, artificial grass, and sandpaper), incline level (level or 30º incline), and obstacle condition (presence or absence). We chose the substrates because they represent materials that the wall lizards would come into contact with in nature: cork imitating wood, artificial grass representing real grass and foliage, and sandpaper mimicking artificial terrain, such as pavement and walls. The incline level was chosen because it approximates the level of incline found in their natural habitat. We chose to add obstacles because they allowed us to test for maneuverability, which is ecologically relevant because, in nature, it is necessary for these animals to maneuver around obstacles for prey capture and territory defense.
Contemporary lizards display morphological shifts unrelated to sprint performance
We found that morphology has shifted dramatically when comparing lizards caught in the 1980s to the present day. Contemporary lizards display reduced relative head, hind foot, and front limb length, as well as decreased relative pelvic girdle width. In contrast, contemporary lizards have relatively wider shoulder girdles. Interestingly, we found that body size didn’t change over time. This means that these lizards have developed smaller body dimensions, apart from the shoulder girdle, but didn’t change their overall body size.
We also found no relationship between the aspects of morphology that shifted over time and sprint performance on any of the conditions tested. This lack of relationship is very interesting because it suggests that other factors are influencing the observed shifts of morphology. For instance, these morphological shifts could be useful to help better squeeze into rock crevices. Furthermore, these changes might not be related to performance at all. These lizards are also invasive and were founded by a population, possibly as little as three reproducing individuals. These observed morphological shifts could be a result of low genetic diversity and subsequent genetic drift.
Lizards run faster uphill?
Surprisingly, we also found that lizards run faster on a 30º incline as opposed to a flat track. This is a novel result because most organisms display decreased performance up an incline. Along with this, we found that, when running up an incline with obstacles, the obstacles slowed them down more than when running on a level track with obstacles.
We think that running up an incline causes a shift in body posture, such that the lizards are running in a more bipedal position. This new position allows them to push off the ground more with their stronger back legs, enhancing their speed. However, this position comes at a cost. Increased bipedalism means that the lizards can’t use their front limbs to steer as effectively, leading to a greater decrease in speed when having to maneuver around obstacles up an incline. We hope to explore this question more with future studies.
What’s next?
Despite the challenges of 2020, I was still able to participate in great research with wonderful people. I was able to present my research at incredible conferences like the annual meeting of the Society of Integrative and Comparative Biology (SICB) and share it with incredible people (you can see a recording of my talk here). I was also able to publish my work in an academic journal, a first for me (see https://doi.org/10.1093/biolinnean/blab076).
We are continuing to work with the Podarcis system in Cincinnati this summer. Currently, I am working with another student to investigate the relationship between claw micromorphology and clinging and climbing performance in various conditions.
Overall, this experience has been a great opportunity to learn and develop as a scientist and I am very excited to keep working and see what the future holds!
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