Trait variation along an urban–rural gradient in Asian dayflower: the contribution of phenotypic plasticity and genetic divergence

Abstract

Environmental changes associated with urbanisation can exert pressure that facilitates both adaptations and plastic responses in plants. Field surveys or common garden experiments (CGE) alone cannot differentiate between the observed phenotypic traits resulting from plastic responses versus evolutionary adaptations to urban environments. We conducted a field survey of habitat environmental factors and four vegetative traits in 12 Commelina communis populations along an urban–rural gradient in the Osaka‐Kobe megacity area. We collected seedlings from six of the 12 populations, transplanted them into a greenhouse, and measured six vegetative traits. We investigated correlations between pairs of measured traits in both the field survey and CGE. Plant height and leaf area increased significantly in increasingly developed land areas (DLA) in the field survey, whereas no such variations were found in the CGE, suggesting that the observed phenotypic variation was due to a plastic response to urban eutrophication. Leaf number and specific leaf area (SLA) significantly decreased with increasing DLA in the CGE, suggesting the adaptation of these traits to urban environments. Positive correlations between plant height and leaf area were only observed in urban populations in both the field survey and CGE, indicating the evolution of this trait correlation in urban environments. It has been suggested that urban environments promote both plastic response and genetic divergence of a set of traits in native plants. Our findings suggest that low leaf number, SLA, and positive plant height–leaf area correlations have evolved. In addition, larger plant size is achieved via phenotypic plasticity in urban environments.

Habitat diversification associated with urban development has a little effect on genetic structure in the annual native plant Commelina communis in an East Asian megacity

“…There is limited information on phenotypic trait differentiation along urban–rural gradients available for C. communis (Taichi & Ushimaru, 2024 ; Ushimaru et al., 2014 ). To understand the relationship between genetic and phenotypic trait adaptation in this species, we propose conducting trait measurements in common garden and reciprocal transplant experiments (e.g., Gorton et al., 2018 ) to determine whether diverse urban habitat populations are forced to adapt to local environments or can survive in a range of urban habitats.…”

Allopolyploidy enhances survival advantages for urban environments in the native plant genusCommelina

“…The distribution results suggested that polyploids distribute larger and have a higher tolerance to urban environmental stresses. In urban Cc habitats, compared to rural habitats, there are higher levels of soil pH, drought, shaded, and pollinator-limited conditions (Ushimaru et al ., 2014; Taichi and Ushimaru, 2024; Taichi et al ., unpublished data). However, it is still unclear why polyploidy enables Cc to be more adaptive to such conditions compared to Ccfc with lower ploidy.…”