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

The city and forest bird flock together in a common garden: genetic and environmental effects drive urban phenotypic divergence

Urban phenotypic divergences are documented across diverse taxa, but the underlying genetic and environmental drivers behind these phenotypic changes are unknown in most wild urban systems. We conduct a common garden (CG) experiment using great tit (Parus major) eggs collected along an urbanization gradient to: (1) determine whether documented morphological, physiological, and behavioral shifts in wild urban great tits are maintained in birds from urban and forest origins reared in a CG (N = 73) and (2) evaluate how different sources of genetic, early maternal investment, and later environmental variation contributed to trait variation in the experiment. In line with the phenotypic divergence in the wild, CG birds from urban origins had faster breath rates (i.e., higher stress response) and were smaller than birds from forest origins, while wild differences in aggression and exploration were not maintained in the experiment. Differences between individuals (genetic and environmentally induced) explained the most trait variation, while variation among foster nests and captive social groups was limited. Our results provide trait-specific evidence of evolution in an urban species where genetic change likely underlies urban differences in morphology and stress physiology but that urban behavioral divergences are more strongly driven by plasticity.

The flower does not open in the city: evolution of plant reproductive traits of Portulaca oleracea in urban populations

BACKGROUND AND AIMS

The impact of urbanization on plant evolution, particularly the evolution of reproductive traits, remains largely unknown. In this study, we aimed to investigate the consequences of urbanization on the reproductive traits of Portulaca oleracea in the Kantō region of Japan. Portulaca oleracea has a unique cleistogamous reproductive system, which consists of genetically determined chasmogamous (open, CH) and cleistogamous (closed, CL) plants.

METHODS

We collected seeds of P. oleracea from ten populations in rural areas and ten populations in urban areas. In a common garden experiment, we recorded the type of flowers (CH or CL), reproductive phenology and seed production.

KEY RESULTS

All individuals produced either CH or CL flowers, allowing us to classify them as either CH or CL plants. We observed a significant difference in the prevalence of CH and CL plants between rural and urban populations: the number of CH plants was generally low and was particularly low among urban individuals. Compared to CH plants, CL plants showed earlier phenology and produced heavier seeds, which is consistent with stress avoidance in response to heat and drought stress conditions in urban areas.

CONCLUSIONS

Our findings suggest that urbanization may drive an evolutionary change in the cleistogamous reproductive system of P. oleracea. CL plants with earlier phenology and larger seeds might be better adapted to urban environments, where they are subjected to harsh heat and drought stress.

Allopolyploidy enhances survival advantages for urban environments in the native plant genus Commelina

BACKGROUND AND AIMS

Urbanization-induced environmental changes affect the geographical distribution of natural plant species. This study focused on how polyploidization, a dynamic genome change, influences the survival and distribution of Commelina communis (Cc) and its subspecies C. communis f. ciliata (Ccfc), which have variable chromosome numbers (e.g. Cc, 2n = 88 for Cc; Ccfc, 2n = 46 for Ccfc). The aim was to investigate polyploidization effects on natural plant distribution in urban environments.

METHODS

The geographical distribution across urban-rural gradients was investigated at a total of 218 sites in Japan. Stomata size and density were measured and compared between Cc and Ccfc. Flow cytometry determined genome size and polyploidy. Chromosome karyotyping was performed using the genomic in situ hybridization (GISH) method.

KEY RESULTS

Urban areas were exclusively dominated by Cc, while Cc and Ccfc coexisted in rural areas. Cc had larger and fewer stomata and a genome size more than twice that of Ccfc. GISH results indicated that Cc possesses Ccfc and another unknown genome, suggesting allopolyploidy.

CONCLUSIONS

Our results show that the ploidy difference affects the geographical distribution, stomata traits and genome size between two distinct taxa in the genus Commelina, C. communis as a neo-tetraploid and C. communis f. ciliata, the diploid. Cc is an allopolyploid and is therefore not only polyploidy but also has an additional genome that provides new sets of genes and alleles, contributing to Cc having enhanced survival potentials in urban environments compared with Ccfc. This is the first investigation to clarify the distribution difference related to urban environments, the difference in stomata traits and genome size, and to study chromosome composition in Commelina species.

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

Urban development greatly alters the natural and semi-natural habitats of native plants. Urbanisation results in a range of diverse habitats including remnant agricultural lands, urban parks, and roadside habitats. This habitat diversity often promotes trait divergence within urban areas. However, the mechanisms by which diverse urban habitats influence the population genetic structure of individual plant species remain poorly understood. We investigated the effects of urbanisation on genetic diversity and structure within 24 Commelina communis populations across diverse habitat types (rural agricultural land, urban agricultural land, urban park land, and urban roadsides) within the Kyoto-Osaka-Kobe megacity in Japan. We conducted multiplexed inter-simple sequence repeat genotyping to compare genetic diversity among populations in different habitats. We also examined the correlation between Nei's genetic distance and geographic and environmental distances and performed principal coordinate analysis (PCoA) to evaluate genetic differentiation among urban habitats. There were no significant differences in genetic diversity indices between urban and rural populations and among urban habitat types. Although we detected no isolation-by-distance structure in population pairs of the same habitat type and in those of different habitats, the difference in surrounding landscape facilitated genetic differentiation not only between urban and rural habitats but also between different urban habitats. PCoA revealed no clear genetic differentiation among rural and urban habitat populations. Our findings indicate that the establishment of diverse habitat types through urbanisation has no and little impact on genetic diversity and structure, respectively, in C. communis, likely due to its high selfing rate and ability to adapt to urban conditions.