Cities serve as testbeds for evolutionary change

Abstract

Urban living can pressure flora and fauna to adapt in intriguing ways. Biologists are starting to take advantage of this convenient laboratory of evolution . Every student of evolution knows the story of the peppered moth. The species comes in two colors: one a peppered white, the other black. During Britain’s industrial revolution, hungry birds spotted the lighter morph in soot-coated forests surrounding cities. Meanwhile, the rarer and better camouflaged darker morph avoided becoming lunch and carried the darker gene variant to a higher frequency in the population. When pollution cleared, the lighter morph again became more common. Although the methodology of the original peppered moth research came into question in the late 1990s (1), subsequent research confirmed its findings (2). Researchers are studying white clover in cities across the globe to learn more about how urbanization shapes evolutionary change. Image credit: Marc Johnson (University of Toronto Mississauga, Mississauga, Canada). Yet despite this classic case of natural selection under urban conditions, so iconic that the peppered moth adorns the logo of the Society for the Study of Evolution, biologists have mainly chosen to study evolution in places with less human disturbance. “Most people didn’t think that cities were really interesting biologically, that they were kind of anti-life,” says evolutionary ecologist Marc Johnson, who directs the Centre for Urban Environments at the University of Toronto Mississauga. That mindset is changing as Johnson and others use cities as powerful testbeds for evolutionary mechanisms. Because species often live both within and beyond city borders, researchers can directly compare populations to pinpoint whether and how these mechanisms respond to the urban environment. They can also compare the same species’ responses across different cities. “That’s why a lot of people are getting excited about this,” says Johnson. “They like the idea of these replicated …