Urbanization, the creation and spread of urban habitats, is increasing across the world. Species that live in these urban habitats are subject to many alterations in their environment, including changes in food, predators, noise, and light among others. One of the most well-known changes associated with cities is the “Urban Heat Island” effect, where city habitats are hotter than surrounding areas due to increases in pavement and other heat-absorbing materials. For lizards such as anoles, living in this hotter environment could be challenging, as increased heat could reduce time available for foraging for food or defending territories, or, in more serious cases, might even lead to death. Shane Campbell-Staton, a postdoctoral researcher at the University of Illinois and the University of Montana, decided to test if anoles were adapting to these hot urban environments, and, if so, what mechanisms were driving this adaptation.
Cities are hotter than the surrounding landscape.
Shane worked with crested anoles (Anolis cristatellus) from four different areas of Puerto Rico that had both urban and nearby natural environments. He and Kristin Winchell, his coauthor, verified that anoles in these urban habitats did indeed experience hotter conditions, and that, as a result, their body temperatures were also higher than anoles from nearby natural areas. In the lab, Shane found that these city anoles were capable of tolerating higher temperatures than their counterparts from natural areas as well. However, after 8 weeks in the lab, anoles from both types of habitats had similar temperature tolerances. Shane also raised offspring from these anoles under common conditions in the lab and found that these offspring had similar temperature tolerances (thermal limits), regardless of whether they came from urban or natural environments. These results show that anoles can have a plastic response to the thermal conditions in their environment, meaning that the differences Shane and Kristin saw in Puerto Rico are induced by an anole’s exposure to temperatures and are not completely determined by their genes.
Crested anoles (Anolis cristatellus) make use of many human-altered habitats. Photo by Andrew Battles.
Shane, however, continued to explore this question: he wanted to know if the ability, or plasticity, of an anole to alter its thermal tolerance in response to exposure to high urban temperatures was due to changes in its genetic structure. In essence, he wanted to know if anoles had evolved a higher responsiveness (or plasticity) in response to inhabiting hotter, city habitats. To get at this, Shane exposed anoles to both hot and normal temperatures in the lab and looked at their levels of gene expression. Using a transcriptomics approach, Shane could see which genes were activated differently when lizards were exposed to temperatures indicative of city and natural habitats. Shane observed differences in variation in the genes in use at these temperatures. He also found higher levels of differentiation between genes involved in thermal adaptation between lizards from city and natural environments. These exciting results show that living in hotter city environments has selected for lizards which are more able to respond to these hot temperatures when they experience them. Shane is continuing to dig deeper into these data to determine which specific genes may have been altered to understand the mechanisms by which lizards are able to alter their heat tolerances. We’re looking forward to seeing these results at a future conference!
On a side note, Shane will be setting up his own lab at UCLA this year, and he’ll be looking for talented graduate students interested in physiology, adaptation, and genomics. Don’t hesitate to look him up!