UTM students explore parallel evolution, write chapter for new urban biology book

Some plants grow larger in the city, but others don’t reach the same heights as their rural counterparts when they take root in an urban environment, says James Santangelo, a PhD student in the Department of Ecology and Evolutionary Biology at U of T Mississauga.

“We don't really know why. There's no one-size-fits-all solution to living in the city, if you're a plant.”

A student in Marc Johnson’s EvoEco lab at UTM, Santangelo collaborated with his colleagues in the lab to produce Urban environments as a framework to study parallel evolution. He was the lead author for the book chapter written with Lindsay Miles, Sophie Breitbart, David Murray-Stoker, Ruth Rivkin, Marc Johnson, and Rob Ness. It’s part of Urban Evolutionary Biology, a first-of-its-kind publication from Oxford University Press that maps out this relatively new approach to studying how cities can shape species.

White clover is one plant that grows larger in urban environments, but that isn’t the only difference between city clover and its rural counterpart.

“Some clover plants produce hydrogen cyanide, and others don't. This evolved as a plant defense – it deters insects from feeding on clover. In cities, clover produces hydrogen cyanide less frequently,” says Santangelo.

“Our hypothesis was that this occurred because there are fewer insects or small mammals eating the clover, and not as much benefit to producing hydrogen cyanide. We have yet to rule that out, but there are also temperature effects. Cities tend to be hotter, and that melts snow in the winter. When there's no snow, plants aren't buffered from cold air temperatures. The lower ground temperatures could be causing the reduction in hydrogen cyanide. We're still trying to figure out what the driving force is, and whether this is the same across all cities.”

The new book chapter explores this idea of parallel evolution – whether the same types of evolutionary changes will be present in different urban environments. Cities can have more in common with each other than with surrounding habitat, but also retain many distinct differences in climate, density, pollution and other factors, so they provide an opportunity to identify the specific forces that are driving evolutionary change.

“We wanted to provide a glimpse in to how often species are responding in similar ways in cities, and whether they are responding to the same environmental cues,” says Santangelo.

“For example, is temperature or pollution driving a change? If species are not responding in similar ways, what is driving the differences that we are seeing?”

Changes in plant life can have a cascading effect within the food chain. Their disappearance can also impact the animals that consume them. Recognizing the forces that are shaping change can help inform conservation decisions.