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.
Figure 3: Lizard phylogenetic tree.Groups of related species that includea common ancestor and all the descendants (living and extinct) of thatancestor are referred to as clades. In this illustration, horizontal blacklines connect clades on different islands. The island clades wereestablished either by overwater dispersal or by ancient geologicalconnections among islands. Colored lines represent the four islands. Forease of presentation, the Jamaican clade (J) and Puerto Rican clades (P1,P2, and P3) are shown separately. They fit into the phylogeny at thepositions marked. The data show that in general, species on each islandare more closely related to each other than to species on other islands,with few exceptions. For example, some species of lizards on Puerto Ricoare more closely related to species on Hispaniola than to other species onPuerto Rico; this suggests that on rare occasions some lizard populationsmigrated from one island to another, perhaps carried there by hurricanes.(Image reproduced with permission from Losos, B.J., and Ricklefs, R.E.Adaptation and diversification on islands. 2009. Nature 457:834.)6. Reviewing the Dataa. How was relatedness determined in the phylogenetic tree shownin figure 3? (0.5)
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b. What conclusion can you draw about the evolution of theAnolislizards based on Figure 3? (1)
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