Reduced seed dispersal potential in dandelions isolated within urban historical sites

Historical sites preserved within cities often serve as refuges for local biodiversity. However, these sites are surrounded by buildings and roads, creating sharp contrasts in habitat suitability between them and the surrounding urban matrix. Under such conditions, reduced dispersal potential may be favoured if remaining within the site enhances fitness. We tested this hypothesis in the self-incompatible dandelion, Taraxacum platycarpum (Asteraceae). We compared the morphological traits affecting seed-dispersal potential between populations inhabiting historical sites (castles and shrines) in a major metropolitan area and those inhabiting open sites in rural areas. Pappus volume, which is positively associated with dispersal potential, was significantly smaller in historical-site than in open-site populations. In contrast, achene volume, which is less directly related to dispersal potential, did not differ between site types. Moreover, populations in historical sites tended to exhibit a lower genetic diversity than those in open sites did. These results suggest that seed dispersal traits in dandelions have diminished in urban historical sites, potentially leading to reduced genetic diversity as an evolutionary consequence. Together, our findings illustrate how extreme habitat isolation within cities can shape dispersal evolution and emphasize the importance of incorporating evolutionary processes into the conservation of plant populations in these environments.