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Researcher settles decades-old evolutionary biology question by examining Caribbean lizards

October 31, 2017

Martha Munoz holds a lizard
Martha Muñoz, an assistant professor of biological sciences in the College of Science, catches a male large-headed anole (Anolis cybotes) in the coastal town of Los Patos, Dominican Republic. Photo by Dr. M. del Rosario Castañeda.

Evolution can be both stimulated and halted by an animal’s behavior, it just depends which trait you’re talking about, according to a groundbreaking study led by a Virginia Tech researcher.

The study, published Oct. 25 in the journal American Naturalist, shows behavior can be both a brake and a motor for evolution in a manner where slowing evolution in one trait actually requires accelerating evolution in another, according to Martha Muñoz, a new assistant professor of biological sciences in the College of Science and an affiliate of Virginia Tech’s Global Change Center.

Understanding this delicate stop-and-go dance can help scientists predict how animals will adapt to global change, such as climate change and habitat degradation.

In the case of the anole lizard of the Dominican Republic, thermoregulation — or the ability to control one’s own body temperature — is crucial to survival.

Although it is located in the tropics, the Dominican Republic has lots of mountainous habitat and high elevations that challenge animals like lizards, which cannot regulate their temperature internally, the way that birds and mammals (including people) do.

When the lizards migrated from warm, low elevations to cool, high elevations, body temperature regulation required the lizard to take up a new microhabitat, dwelling on boulders and sheltering in crevices, rather than formerly preferred tree limbs, which were too chilly at higher elevations.

This switch to boulders allowed the lizard to remain quite warm — just as warm, in fact, as its counterparts in the balmy lowlands — despite the much colder habitat.

In a key twist, the lizard also evolved traits important for rock dwelling, such as a flatter skull and shorter legs for skittering into crevices at the first sign of a predator. In other words, the same behavioral switch to boulders that halted physiological evolution also promoted morphological evolution.

In the context of global climate change, these findings suggest that the effects of rising temperatures won’t be limited to directly impacting organisms’ physiology — because of their behavior, it could indirectly impact other features, like their morphology, as well. Such predictions, however, would not have been likely without this new understanding of the multidimensional ways in which behavior impacts evolution.

“Our observation settles a decades-long scientific question about whether behavioral inertia — the ability for behavior to function as a brake for evolution — can occur at the same time as behavioral drive — the ability for behavior to function as a motor for evolution,” said Muñoz, who is also affiliated with the Fralin Life Science Institute.  “This is a question that first presented itself in the 1940s, and we think we’ve finally come to a conclusion with this paper.”

“This study is a great example of the subtle way that organism and environment interact in evolution — it’s not a one-way relationship, it’s a far more interactive dance,” said Michael Kearney, an associate professor in the School of BioSciences at the University of Melbourne who served as an associate editor for the manuscript.

“Dr. Muñoz’s findings significantly advance our fundamental knowledge of evolutionary processes, and also have broad implications for understanding how animals are responding to rapid environmental changes caused by humans,” said William Hopkins, director of the Global Change Center.  “We are thrilled that Dr. Muñoz has joined the Virginia Tech community.”

The project was part of Muñoz’s doctoral work in the Department of Organismic and Evolutionary Biology at Harvard University, which she completed in 2014.  The co-author on the paper was Jonathan B. Losos, a professor in the in thew same department at Harvard University.

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