We often see the results of evolution, but not the process directly. Now, scientists have been treated to front row seats of evolution unfolding in real time, as two similar lizard species encounter each other for the first time and quickly adapt to fill different roles.
Researchers at Georgia Tech were conducting a study of Cuban brown anoles (Anolis sagrei) at Fairchild Tropical Botanic Garden in Florida when suddenly, a new species appeared on the scene: the Puerto Rican crested anole (Anolis cristatellus).
Although the two lizard species look very similar, they’re actually separated by more than 40 million years of evolution, living on different Caribbean islands. However, they do fill almost the same ecological niche in their environments, living in the same kinds of habitats and eating the same foods. The researchers recognized the opportunity this presented.
“When two similar species compete for the same resources, like food and territory, they often evolve differences that allow them to coexist,” said James Stroud, lead author of the study. "Most of what we know about how animals change in response to this process comes from studying patterns that evolved long ago. This was a rare opportunity where we could watch evolution as it happened.”
Over the next few years, the team observed physical and behavioral changes in both species as they learned to live together. These were compared with other lizards living in single-species environments.
The crested anoles spent more of their time living in trees, and were found to perch higher up on average than the brown anoles. The latter lizards, meanwhile, adapted to spend more time on the ground.
Most interesting of all, the brown anoles evolved new physical traits to support their new ground-dwelling lifestyle. They were found to start growing longer legs, which helps them run faster and boosts their survival rates.
“We found that brown anoles with longer legs had higher survival after crested anoles showed up,” said Stroud. “This matches perfectly with the physical differences we see in populations where these species have been living together for many generations.”
It’s an intriguing study that adds to a growing body of direct evidence of evolution in action. Another study charted the changes in isolated populations of geckos in Brazil after the building of a dam, finding that over the course of 15 years island geckos grew bigger heads than mainland geckos. Other research found that protected waters make fish evolve to be less mobile with each generation, since adventurous fish are more likely to get caught. Swallows have been found to evolve shorter wings to avoid becoming roadkill, and frogs in the Chernobyl exclusion zone are turning black to protect against radiation damage.
The lizards in Florida could help scientists better understand the pressures that human activity imposes on evolution, and predicting how species will respond.
The research was published in the journal Nature Communications.
Source: Georgia Tech
