Abstract: We live in an increasingly urban world. In the past 200 years, urbanization has changed the environment in a way which now affects ecological and evolutionary processes. This in turn has led to flora and fauna to experience both phenotypic and genetic changes in response to urban environments. This newly created field of urban-eco evolutionary biology now tries to answer questions surrounding how organisms change in response to urbanization. One these questions include the role which urban environmental heterogeneity plays in the development of phenotypic traits. Urban environments have traditionally been classified on single environmental variables such as impervious surfaces. Relying solely on these classifications may overlook important environmental heterogeneity found within urban environments such as pollution and socio-economic factors. By using the invasive, annual plant Centaurea melitensis as a model organism, we wanted to test how classifying urban environments using a dynamic urban framework can be applied when measuring phenotypic differences across an urban gradient in California. We predicted that this dynamic classification framework will explain differences in phenotypic traits in C. melitensis better than traditional urban classification.
To classify urbanization, Census tracts across California were classified into different urban types through a hierarchical cluster analysis. This analysis created seven different urban type based spatially acquired data found within each census tract containing variables for land cover, climate, pollution, and socio-economics. Seeds from sixteen populations of C. melitensis across multiple urban types in California were collected from and grown in greenhouse conditions. Greenhouse grown individuals had several life history traits measured for both growth and reproduction including the number of leaves produced, number of flower heads, specific leaf area, and total above ground biomass.
Preliminary results show that conventional urban classification shows no difference between urban and natural populations of C. meltiensis for both reproductive and growth life history traits. However, significant differences for the number of leaves and flowerheads were observed across the different urban types. This suggests that this framework was able to capture traits within C. melitensis which correspond to specific urban variables.
Future directions for this study include running a second greenhouse study with more populations across the state of California. Additionally, a genome-wide association study (GWAS) and genome environmental association (GEA) will be performed to complement these phenotypic measurements. The results of this study highlights the importance of more dynamic environmental classification for researchers interested in studying urban environments.
