Climate change is often framed as “global warming,” a continual increase in the Earth’s surface temperature, but additional effects include extreme weather events. These events, such as cold spells, tropical storms, and heat waves, disrupt local weather patterns, making winter seasons colder and summer seasons warmer than average. This could potentially pose many challenges for wild animal populations. In particular, tropical lizard species were initially thought to be at high risk due to these weather fluctuations, especially the cold winters. Lizards, like other reptile species, are unable to regulate their own body temperature, which changes with air temperature. When the air temperature becomes too cold, lizards become immobilized. They often lose their grip on trees and fall stunned to the ground, making them vulnerable to predators.
However, new research has revealed a lower temperature tolerance than previously thought across all lizard species in Miami, Florida. Dr. James Stroud and his colleagues collected lizard specimens of various species from around the Miami area. The lizards’ cold temperature tolerance was tested using a thermometer and an ice cooler. The lizards were placed in the ice and their temperature was continually measured until they entered their characteristic stunned state of muscle immobilization. Across all tested species, the lizards could withstand temperatures 1 to 4 ℃ colder than previously thought before becoming immobilized. On average, the different lizards species were able to withstand a temperature of around 5.5 ℃.
This shift in thermal threshold is theorized to be a product of natural selection driven by climate change. Lizards that are able to withstand colder temperatures are less at risk from predation and are consequently more likely to pass on their genes to the next generation. This research highlights the adaptation of animal species to their changing climate and suggests that many species may be more resilient than was previously understood.
Dr. James Stroud is a postdoctoral research associate at Washington University in St. Louis studying climate change and conservation biology with a focus on tropical climates.