An urban-rural spotlight: evolution at small spatial scales among urban and rural populations of common ragweed

  • Adam Kostanecki (Creator)
  • Amanda J Gorton (Creator)
  • David Moeller (Creator)



Urbanization produces similar environmental changes across cities relative to their neighboring rural environments. However, there may be high environmental heterogeneity across an urban-rural gradient. Previous research in Minneapolis, MN, USA, found mixed evidence that urban and rural plant populations of common ragweed have locally adapted, and that urban populations exhibit greater among-population divergence in ecologically-important traits. To investigate whether there are parallel patterns of urban-rural trait divergence across different urban areas, we examined trait variation across an urban-rural gradient in a second city, St. Louis, MO, USA. We used growth chamber and greenhouse common environments to investigate variation in six traits within and among 16 populations of common ragweed (eight from each urban and rural area). Urban and rural plants diverged significantly in three of five traits, with rural plants having lower percent germination, greater height and lower leaf dissection index. We also found greater variance in plant height among urban compared to rural populations, potentially driven by heterogeneity in human management practices on urban populations. Patterns of urban-rural trait divergence (e.g. in flowering time) differ substantially from those found previously in the reciprocal transplant experiment in Minneapolis, contradicting the hypothesis of parallel evolution across different metropolitan areas. The results of this study suggest that there is considerable population variation in ecologically-important traits, but that urban populations do not consistently differ from neighboring rural populations.

These files include data from our germination and greenhouse experiments. For the germination experiment, we recorded days to germination as well as germinants per cell, which were used to calculate percent germination. For the greenhouse experiment, we measured several phenological (initiation of reproduction, male flowering time, female flowering time) and morphological traits (height and leaf dissection). We selected these traits as they are known to be ecologically important, vary within and among populations of A. artemisiifolia, and that trait variation has a genetic basis. Initiation of reproduction was scored as the date on which a reproductive bud at the apical meristem first appeared. Male flowering time was scored as the number of days from transplanting to first observed open anther. Female flowering time was scored as the number of days from transplanting to the first visible stigma. Plant height was measured during week 7, 9, 11, and 13. After seven weeks, the third fully expanded leaf of each plant was collected to measure leaf dissection index. Leaf area and perimeter were calculated using ImageJ, and leaf dissection index was calculated by dividing leaf perimeter by twice the square root of the product of leaf area and π, or the formula: DI = Perimeter / (2√Area x π).

Funding information
Sponsorship: EEB Research Award (University of Minnesota); University of Minnesota Undergraduate Research Opportunities Program; NSF PGRP grant #1856744
Date made available2021
PublisherData Repository for the University of Minnesota
Date of data productionJun 18 2018 - Feb 9 2019

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