Anole lizards evolved to coexist in various thermal niches

Over 180 anole lizard (Anolis spp.) species of unique shapes and variegated colors live side by side on tree trunks, branches and grasses in the Caribbean, but there’s more to their evolutionary history than meets the eye. These island lizards became physiologically differentiated according to temperature, a team of biologists concluded, which permits them to inhabit distinct niches and boost diversity in their communities.

The species’ body shapes are known to differ based on the different types of perches they use, said Alex Gunderson, first author on the study published in Proceedings of the Royal Society B. “They also occupy different microclimates based on whether it’s shaded or sunny,” he said. “They may have physiologically adapted to different temperatures. Physiological differences allow these species to partition space at a fine scale and allow communities to have more species occupy different microclimates a couple meters apart.”

The species are found throughout the Greater Antilles — Puerto Rico, Jamaica, Cuba and Hispaniola. Gunderson, a biology professor at Tulane University, and his colleagues studied 300 animals from 16 anole species in Puerto Rico and Jamaica from 2011 to 2012. They assessed each lizard’s capacity to deal with heat by subjecting them to rising temperatures, turning them over and identifying the threshold at which they no longer exhibited the coordination to get back on their feet. The biologists also evaluated the lizards’ ability to sprint as the heat increased by observing how quickly they could scurry across a ramp and extrapolating the temperature at which they’d go the fastest.

Researchers found that species in warmer microclimates have higher heat tolerances and higher optimal temperatures for sprinting. “It suggests there’s a lot of physiological evolution in this group,” Gunderson said. “It seems thermal adaptation does facilitate niche partitioning. It allows more species to occupy a space than there would be if they didn’t adapt physiologically to different microclimates. It’s a mechanism that can promote high biodiversity in a particular place.”

Although an abundance of research has investigated rapid diversification — known as adaptive radiation — in terms of morphology in these species and others, physiological evolution hasn’t been given much attention, he said.

“If you don’t know what mechanisms allow species to cooccur, you’re not going to be maintaining biodiversity,” he said. “Where you have physiological divergence, managing for microclimate heterogeneity can facilitate that.”

Gunderson and his fellow biologists plan to probe into how genetic variations enabled the lizard species’ physiological differentiation for separate thermal environments. They’re also predicting habitat suitability for these species to see where they may intersect or move apart as the climate changes. Because physiological adaptation doesn’t occur as swiftly as morphological adaptation, the scientists fear some anoles may not be able to keep up with intensifying temperatures.

“As things warm, microclimates that allow species to cooccur are going to change, and that’s going to change the dynamic of how species interact and how many can occur in a place,” Gunderson said.

Header Image: Endemic to Puerto Rico, a yellow-chinned anole perches in the shade by the ground. ©Manuel Leal