Evolution 2018: Selection on Thermal Plasticity in City Lizards

Cities were hot at this year’s Evolution meeting because they provide valuable petri dishes for asking myriad evolutionary questions. For example, cityscapes tend to create and retain heat–the so-called urban heat island effect–resulting in significantly elevated temperatures in urban areas relative to nearby undeveloped landscapes. Hot cities thus provide scientists an opportunity for asking questions about how plants and animals adapt to tolerate high temperatures. These questions are especially relevant as the built landscape continues to creep into less-developed surroundings and the globe as a whole experiences year after year of record temperatures.

Dr. Shane Campbell-Staton and colleagues used steep thermal differences between cities and nearby forests in four municipalities in Puerto Rico to determine whether, and to what extent, lizards may have adapted to warmer temperatures in the city. First, they found that operative temperature does change: lizards in cities use warmer perches and they operate at higher body temperatures than their forest counterparts. When brought back to the lab, however, those city lizards did not continue to function better at higher temperatures than their forest counterparts.

So what might be underlying this thermal plasticity?

Campbell-Staton and his collaborators then brought lizards back to the U.S., bred them, and raised the offspring in common conditions. Surprisingly, they found that the differences they observed in the wild populations disappeared in the next generation, an indication that this thermal ability is a plastic response to the thermal environment.

This thermal plasticity observation generated another question: Is thermal plasticity the target of natural selection in urban heat islands? To investigate this, Campbell-Staton isolated and analyzed transcriptomes of skeletal muscles in lizards from the hot city and cool(er) forests. Indeed, after the lizards were subjected to controlled heat treatments in the lab, they found a suite of candidate genes that were expressed at different levels between the populations. More genomic wizardry is planned for the very near future.

The work is ongoing and a very exciting paper is coming together. Keep your eyes peeled because it will certainly make a splash. Additionally, if you’re interested in this kind of work, Campbell-Staton has just started a lab at UCLA and is actively recruiting new lab members. Shoot him an email here.