How Geography Impacts Animal Evolution in Tropical Caribbean Lizards

Evolution isn't just influenced by other animals and cataclysmic events; it's also influenced by geography. Now, scientists have taken a closer look at a Caribbean lizard in order to find out a little bit more about how geography can impact the evolution of species.

In this case, the researchers focused on Bergmann's rule, which is the tendency for warm-blooded animal body size to increase in colder environments. This rule has long been controversial with debate over whether or not it applies to col-blooded animals, and how the rule applies within or among species.

In order to better understand how interspecific and intraspecific patterns of animal size change through space, the researchers created a unified model. More specifically, they focused on two groups of Anolis lizard, one located in Cuba and the other located in the Dominican Republic. The scientists found that the size of the lizards actually decreased with elevation on both islands. Yet the model itself indicated that different ecological and evolutionary processes were responsible on each island.

"Our results suggest that restricted analyses to either the intraspecific or interspecific levels can miss important patterns," said Martha Munoz, one of the researchers, in a news release. "Both must be considered. We believe our approach can help integrate a divided research program by focusing on how the combined effects of intra- and interspecific processes can enhance or erode trait-environment relationships at large biogeographic scales."

In fact, the researchers believe that the different geographies of Cuba and its neighbor Hispaniola may account for some of the varying patterns seen on each island. Hispaniola has climatic gradients that are far more extensive than on Cuba, for example. This greater extent also shows a greater potential for reduced dispersal of lizards and isolation by environment along tropical elevational gradients in Hispaniola.

"We found that the similar body size gradients in the lizards on both islands are constructed in very different ways," said Adam Algar, one of the researchers. "Even though lizards are smaller at high elevations on both islands, these body size patterns are underlain by very different processes. On Hispaniola, interspecific processes dominate, while on Cuba, intraspecific processes drive the pattern."

The findings are published in the journal The American Naturalist.