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. 2020 Sep;16(9):20200511.
doi: 10.1098/rsbl.2020.0511. Epub 2020 Sep 30.

Multivariate phenotypic divergence along an urbanization gradient

James S Santangelo  1   2   3 , L Ruth Rivkin  1   2   3 , Carole Advenard  4 , Ken A Thompson  5
Affiliations

Multivariate phenotypic divergence along an urbanization gradient

James S Santangelo et al. Biol Lett. 2020 Sep.

Abstract

Evidence suggests that natural populations can evolve to better tolerate the novel environmental conditions associated with urban areas. Studies of adaptive divergence in urban areas often examine one or a few traits at a time from populations residing only at the most extreme urban and nonurban habitats. Thus, whether urbanization drives divergence in many traits simultaneously in a manner that varies with the degree of urbanization remains unclear. To address this gap, we generated seed families of white clover (Trifolium repens) collected from 27 populations along an urbanization gradient in Toronto, Canada, grew them in a common garden, and measured 14 phenotypic traits. Families from urban sites had evolved later phenology and germination, larger flowers, thinner stolons, reduced cyanogenesis, greater biomass and greater seed set. Pollinator observations revealed near-complete turnover of pollinator morphological groups along the urbanization gradient, which may explain some of the observed divergences in floral traits and phenology. Our results suggest that adaptation to urban environments involves multiple traits.

Keywords: Trifolium repens; cline; rapid evolution; urban evolution.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1.
Figure 1.
(a) Locations of the 27 populations from which we collected plants (orange points). Points are scaled by human population density (from [26]) within 1 km2. The city centre (yellow star, Yonge-Dundas Square, lat.: 43.6561°, long.: −79.3803°) and common garden location (green square, lat.: 43.5494°, long.: −79.6625°) are also shown. Inset: photograph of the common garden. (b) Plot of clinemax scores against distance to the urban centre (km).
Figure 2.
Figure 2.
(a) Mean number of visits per inflorescence against the distance of the population from the urban centre (solid black line). We also show a locally estimated scatterplot smoothing (i.e., LOESS) fit for bumblebees (red dashed), honeybees (yellow dotted), and sweat bees (blue dot–dashed) separately to illustrate the change in visitation rate by different pollinator taxa (see electronic supplementary material, figure S10 for plot with linear fits). (b) Number of seeds per flower among field-collected infructescences (grey-filled circles, dashed line) and common garden plants (white triangles, dotted line) from these same populations. The thick black line shows the decrease in the number of seeds per flower with increasing distance from the urban centre.
See this image and copyright information in PMC

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