Evolutionary Insights from Florida’s Wild Lizards Challenge Traditional Views of Natural Selection

New research has shed light on the dynamics of evolution by examining the survival patterns of lizards in their native Florida habitat. Contrary to conventional wisdom, the study has uncovered that natural selection, which typically maintains the average traits of a species, is far from a constant force. Instead, it has revealed that advantageous traits for survival fluctuate from year to year, even though the overall appearance of species remains relatively stable over time.

This long-term observation of lizards challenges the prevailing understanding of natural selection, suggesting that species can retain consistent appearances while still undergoing evolutionary processes.

The Traditional Explanation

Traditionally, biologists have attributed the stability of species over extended periods to natural selection favoring individuals with moderate characteristics. It is believed that individuals with more extreme features, such as longer limbs, are at a disadvantage, while those with moderate or average traits are more likely to survive and reproduce, passing on their common characteristics.

Redefining Evolutionary Relations

However, groundbreaking research conducted by scientists from Washington University in St. Louis and the Georgia Institute of Technology offers a more nuanced explanation of how evolution unfolds among species that coexist. By directly observing the long-term survival of lizards in their natural environment, the researchers have demonstrated that coexisting species occupy distinct “fitness peaks.” These peaks are best understood as part of a broader “fitness surface” or landscape that encompasses the entire community of species.

This study, led by James Stroud at Georgia Tech and published in the Proceedings of the National Academy of Sciences, introduces a novel perspective on how species interact and evolve over time, emphasizing how their differences contribute to their distinctiveness.

Testing Theories with Lizards

Jonathan Losos, a distinguished professor of biology at Washington University, explained their approach: “If species are well-suited to their environment, and the environment remains constant, we wouldn’t expect significant changes in the species. However, when scientists have examined natural selection in the wild, they have rarely found evidence of such stabilizing selection.”

To investigate further, Stroud and his team focused on an island in the Fairchild Tropical Botanical Garden near Miami, where four different species of anoles coexisted. They captured and tagged thousands of lizards, measuring their body proportions. Over a period of 2 ½ years, spanning two to three generations of lizards, they regularly recaptured the lizards.

New lizards that appeared were considered offspring of the island’s inhabitants. If a lizard disappeared from their records, it was assumed to have perished due to the presence of predatory fish in the surrounding lake, preventing escape. By tracking which lizards survived from one year to the next, the researchers could assess whether survival was linked to the measured traits, such as leg length.

Findings and Implications

The study of Florida lizards unveiled that the traditional stabilizing form of natural selection, which maintains a species’ average traits, was exceptionally rare. Natural selection exhibited substantial variation over time. In some years, lizards with longer legs thrived, while in other years, those with shorter legs had an advantage. At times, there was no discernible pattern at all.

Stroud summarized the most intriguing finding, stating, “The most fascinating result is that natural selection was extremely variable through time. We often saw that selection would completely flip in direction from one year to the next. However, when combined into a long-term pattern, all this variation effectively canceled itself out: species remained remarkably similar across the entire time period.”

Understanding how evolution operates at the community level remains a challenge. Long-term studies like this one are rare due to the extensive effort and time required. Nonetheless, this research underscores that evolution is an ongoing process, even when animals appear to remain unchanged in the long run.

For further details on this research, you can refer to the article titled “Fluctuating selection maintains distinct species phenotypes in an ecological community in the wild,” authored by James T. Stroud, Michael P. Moore, R. Brian Langerhans, and Jonathan B. Losos, published in the Proceedings of the National Academy of Sciences on October 9, 2023. (DOI: 10.1073/pnas.2222071120)

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More about Evolutionary Dynamics

• Proceedings of the National Academy of Sciences: The original research article titled “Fluctuating selection maintains distinct species phenotypes in an ecological community in the wild” by James T. Stroud, Michael P. Moore, R. Brian Langerhans, and Jonathan B. Losos.

• Washington University in St. Louis: The institution where the research was conducted, providing additional information about the study.

• Georgia Institute of Technology: The university that collaborated on the research, offering insights into their involvement in the study.

• Fairchild Tropical Botanical Garden: The location of the lizard study site near Miami, Florida, where the research on coexisting lizard species took place.