Evolution 2019: The Effect of Urbanization on White Clover (Trifolium repens) in Los Angeles

When it comes to current studies on urban plant evolution, The Global Urban Evolution Project (GLUE Project) is by far the most robust in terms of replication at a global scale. This worldwide collaboration spans every continent except Antarctica and includes hundreds of contributing researchers. The GLUE Project aims to answer two main questions: 1) are cities driving parallel evolution in plants at a global scale and 2) what selective pressures play a role in whether or not plants adapt to city life?

To find answers, contributors to the GLUE Project examine populations of white clover (Trifolium repens) along urbanization gradients around the world. They test plants for the presence or absence of the defense compound hydrogen cyanide. Plants that produce hydrogen cyanide may be better protected from herbivory, but they are also more susceptible to freezing temperatures.

Cities have higher air temperatures than adjacent rural areas (known as urban heat island effect), but can actually experience colder ground temperatures in winter. Systematic snow removal in cities leaves the ground bare – and colder – compared to rural areas that remain blanketed/protected by snow. Colder ground conditions in cities might select for white clover plants that can tolerate the increased chill. Indeed, parallel clines of white clover with decreased hydrogen cyanide production were identified in New York City and Toronto (Thompson et. al. 2016).

Nicholas Poulos (California State University Northridge; Yoder Lab) is a contributor to the GLUE Project. He surveyed white clover plants along a 40-km gradient from the center of downtown Los Angeles and tested for the presence of hydrogen cyanide. Los Angeles is located near the ocean in a warm climate, unlike that of NYC and Toronto. We may expect that with the lack of snow cover, the cline may not be as strong. Cities like these provide great opportunities to test the strength of clines because they are so different from where the original cline data came from.

At the meeting, James Santangelo gave us a deeper look at the global project and left us with the teaser that the results are pretty fascinating, but we will have to wait for the next GLUE Project update to find out about global trends. The GLUE Project is on-going and data is still coming in from around the world thanks to the efforts of contributors like Nicholas Poulos.

Read more about white clover and urban adaptation:

K.A. Thompson, M. Renaudin, M.T.J. Johnson, Urbanization drives the evolution of parallel clines in plant populations. Proc. R. Soc. B 283, 20162180 (2016)

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Rebecca Panko

PhD Candidate - Bunker Lab at Rutgers University and NJIT

Rebecca Panko is a Post Doctoral Research Associate in the Josephs Lab at the Department of Plant Biology at Michigan State University. She is broadly interested in urban evolution and ecology, and studies plant evolution in urban environments. In her post doc work, she aims to quantify the relative contributions phenotypic plasticity, local adaptation, and epigenetics in shaping urban populations of the cosmopolitan weed, shepherd's purse (Capsella bursa-pastoris). She received her PhD at the Federated Department of Biological Sciences at Rutgers University - Newark and the New Jersey Institute of Technology, where she was advised by Daniel E. Bunker. Her dissertation work examined local adaptation of shepherd's purse in the New York Metropolitan area.

Latest posts by Rebecca Panko (see all)

• Evolution 2019: The Effect of Urbanization on White Clover (Trifolium repens) in Los Angeles - July 2, 2019
• Evolution 2019: Population Structure, Genetic Diversity, and Genotypic Specificity in Flowering Time of Boston Area Dandelions (Taraxacum sp.) - July 1, 2019