Amid the bustle of downtown Portland, Chris Moore walked very slowly. A hand lens hung from a lanyard around his neck, and his eyes tilted searchingly toward the ground. Somewhere near the Portland Museum of Art, a familiar flash of white caught his attention. Crouching, he comes face-to-flower with the plant he’s been looking for—Trifolium repens, or the white clover.
The species abounds among the concrete of Maine’s largest city, just as it does in hundreds of other cities all around the world.
Moore, assistant professor of biology, was collecting data for the largest study on evolutionary biology ever conducted. He eventually gathered clover samples in parks and other public spaces along a 20-mile transect stretching from urban Portland to rural Cumberland, then tested the plants for hydrogen cyanide, or HCN, a compound some plant species use to deter hungry herbivores. His findings joined those of 288 other contributing authors, reporting data from 160 cities worldwide.
“The key objective was to look at how cities affect evolution,” Moore said reflecting on the clover study, which recently made the cover of the prestigious journal Science, coincidentally, on St. Patrick’s Day.
Previous research has documented how the creation of urban environments has altered species behavior and evolution, from bird calls to moth camouflage. No studies, however, have endeavored to explore the relationship between evolution and urbanization on such a global scale.
The report reveals that HCN production in white clover varies along a gradient from urban centers to surrounding rural areas, with lower levels in city populations, and levels that increase moving outward into less-developed landscapes. This pattern is called parallel evolution, and it means that a clover in downtown Portland might share more with a clover from London than with one on a farm just a few miles away. Moore attributes this variation to the relative scarcity of herbivores inside cities as opposed to outside of them, which is ultimately a product of urbanization.
“The biggest implication of this work was to show definitively, incontrovertibly, that human development has an effect on evolution,” Moore said.
He hopes this study will help societies realize their capacity for altering evolutionary trajectories and corresponding ecological interactions on a global scale. Further, he wants this research to inspire greater care in the choices cities make, because development can change life in ways previously unrecognized, or among species hiding in plain sight.
White clover, as it happens, tends to proliferate more than hide. The species is ubiquitous in yards, farmlands, forests, parks, and sidewalk cracks all over the world. “It’s pretty charismatic,” Moore said. “It’s definitely familiar.”
Chances are you would at least recognize the plant. It’s verdant, with a thin smear of pale green on each of its three—sometimes four—leaves, and a stout white inflorescence, consisting of 20 to 50 minuscule flowers, rising above its iconic shamrock shape.
Reflecting on opportunities for further research following this study, Moore said, “We have a lot left to learn about urban ecology and evolution, and we are only beginning to scratch the surface. As urban centers grow and new urban areas are created, we must understand how populations and species respond to more fully understand and weigh the consequences of our decisions. But also,” he continued, “since urbanization is relatively new compared to the time over which evolution ordinarily occurs, urban areas are ripe for asking questions about how quickly evolution can occur.”
Several follow-up studies have already been proposed, supported by the Global Urban Evolution Project, or GLUE—a growing network of scientists from around the world, brought together by the lead authors of this report, whose aim is to elucidate further trends in white clover evolution as driven by urbanization. In addition to GLUE, Moore points to social media as an up-and-coming way for both researchers and students to enlist, and become, participants in studies of this magnitude.
“Science Twitter is a pretty big, pretty good community,” Moore said. “I think harnessing the world through social media is one benefit of having it. It’s really hard to do a global study, even just being in different parts of the world—plants flower at different times, depending upon where in the world they are, depending on precipitation, and depending upon all of these other factors, like, it’s a really intractable problem. So, to be able to mobilize a mass, that’s a pretty big hurdle that this group was able to overcome.”
Moore, a first-generation college student, studied biology as an undergraduate at California State Polytechnic University, Pomona, before working for a year as an industry microbiologist. He then landed a fieldwork position studying post-fire ecology in the middle of the Mojave Desert. “I was looking at how the animals and the plants responded to a severe fire … what species arrived first, and how the community of plants and animals changed over time,” Moore said. Specifically, he explored how rodents disperse seeds, and in doing so, revegetate scorched areas.
For the young biologist, this experience spurred a lifelong fascination with species interactions, which remain central to his studies today.
Having come to Colby in the fall of 2017 because of his passion for population modeling, and his desire to balance science and education, Moore says that “teaching really has informed my research, in the sense that anytime you have to try to explain something to a different mind, it enhances the way you think.” The expansive nature of the classroom has enabled Moore to critique traditional views of species interactions, break down narratives of competition, and allow collaborative concepts like symbiosis and mutualism—both critical at this time of ecological collapse—to come to the forefront.
Collaboration among researchers, Moore said, is critical at this time in our world as well.
“I think this kind of large-scale, collaborative science has enormous potential to transform the future,” he says. “To be able to run experiments globally will not only help us better understand the phenomena that we study, but should eventually lead to a more representative, cooperative approach to science that we desperately need. As you can imagine, most environmental work is done in the U.S. and Europe, which greatly biases our understanding of natural phenomena. It’s no different than clinical or psychological biases that misinformed our understanding of health for so long because experiments were over-represented by college-aged white males. In any event, I’m excited to see what the future holds now that this precedent has been set; hopefully it will serve as a model for other environmental biologists to follow for large-scale studies in the future.”
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