Ecosystems transformed through Evolution of Lizards

Saturday - July 1 2023, 08:51 UTC - 1 year ago

A study by the University of Rhode Island has shown that the evolutionary changes in lizards can result in significant impact on vegetation growth and spider populations on small islands in the Bahamas. This is one of the first times, the researchers say, that such dramatic evolution-to-environmental effects have been documented. The conclusion of the study has profound implications for restoration of habitats and preservation of animal populations.

While it’s well-established that environmental factors shape the evolution of species, a recent study illustrates a reciprocal relationship where the evolutionary adaptations of species, in turn, impact their environment.

The narrative of the peppered moths is a well-known example of evolution in action. During the Industrial Revolution in England, the pollution from coal smoke darkened the tree bark around the urban areas, rendering the white-bodied peppered moths highly visible to predators, which led to a rapid decline in their population. Simultaneously, the previously uncommon black-bodied moths flourished, becoming the dominant variety due to their ability to blend into the newly darkened environment.

This phenomenon is often cited as a classic illustration of how environmental alterations can drive the evolution of species. However, in recent times, researchers have started to explore the inverse scenario. Could it be possible that there is a reciprocal relationship where the evolution of a species influences and instigates changes in its ecosystem? .

Now, a new study by researchers at the University of Rhode Island shows some of the best evidence yet for that very phenomenon.

In research published in the Proceedings of the National Academy of Sciences, the researchers show that an evolutionary change in the length of lizards’ legs can have a significant impact on vegetation growth and spider populations on small islands in the Bahamas. This is one of the first times, the researchers say, that such dramatic evolution-to-environment effects have been documented in a natural setting.

"The idea here is that, in addition to the environment shaping the traits of organisms through evolution, those trait changes should feed back and drive changes in predator-prey relationships and other ecological interactions between species," said Jason Kolbe, a professor of biological sciences at the University of Rhode Island and one of the study’s senior authors. "And we really need to understand how those dynamics work so we can make predictions about how populations are going to persist, and what sort of ecological changes might result." .

For the last 20 years, Kolbe and his colleagues have been observing the evolutionary dynamics of anole lizard populations on a chain of tiny islands in the Bahamas. The chain is made up of around 40 islands ranging from a few dozen to a few hundred meters in the area—small enough that the researchers can keep close tabs on the lizards living there. And the islands are far enough apart that lizards can’t easily hop from one island to another, so distinct populations can be isolated from each other.

Previous research had shown that brown anoles adapt quickly to the characteristics of the surrounding vegetation. In habitats where the diameter of the brush and tree limbs is smaller, natural selection favors lizards with shorter legs, which enable individuals to move more quickly when escaping predators or chasing a snack. In contrast, lankier lizards tend to fare better where the tree and plant limbs are thicker. Researchers have shown that this limb-length trait can evolve quickly in the absence of predators and a somewhat favorable climate.

Armed with the knowledge of these background dynamics, the researchers went into the field to conduct a controlled experiment on the anole lizards. Working on a separate chain of three islands around the same size—ranging from 40m to 200m—the researchers found that the average leg length of lizards on each island (measured from the heel to the knee) was can be as much as one-and-a-half times longer than those on the other islands. After holding the size, shape and setting of the islands’ environments constant, this discrepancy suggests there may be more at play than just pure environmental factors.

To get to the root of the problem, the researchers compared vegetation plots on each of the islands. To their surprise, they found that the plots with lizards that had longer legs had more spider abundance and foliage density. Even more telling, the researchers reported that spider abundance and foliage density were both higher in plots where lizards were present at all, compared to those where lizards were absent. Together, these results, suggest that it’s not just environment, but also evolution that is driving differences among the islands.

The conclusion of the study has profound implications for restoration of habitats and preservation of animal populations. Understanding how evolutionary changes are reflected in the environment, and the underlying process through which species can alter the ecosystems they live in, is the first step to understanding how conservation projects can succeed. The findings also shed light on the symbiotic relationship between species and the environment. Being aware of this complex relationship can help us appreciate the immense interconnectedness of all life on Earth, and make better, more informed decisions when it comes to conservation efforts.